Login to AccuWeather.com Premium Login to AccuWeather.com Professional Login to AccuWeather.com RadarPlus AccuWeather.com

Welcome Guest ( Log In | Register )

5 Pages V  « < 3 4 5  
Reply to this topicStart new topic
> March 23-24 Plains Severe Weather, SPC Risk Level; Days 4-8 Possible: Forecasts and OBS
StL weatherjunki...
post Yesterday, 03:53 PM
Post #81




Rank: F5 Superstorm
***

Group: Founding Member
Posts: 6,146
Joined: 10-June 07
From: St. Louis, Missouri
Member No.: 6,288





3km NAM indicates higher CAPE potential with similarly impressive hodographs to the example I posted above extending from ~Houston to Shreveport to Southeast Arkansas

Houston, TX:

Attached Image


Shreveport, LA:

Attached Image


Southeast Arkansas:

Attached Image


--------------------
All model guidance is just that, guidance. It is the responsibility of the forecaster to take that information, make it better, and to appropriately communicate the forecast to the users.

Fervent supporter of the idea to make GFS output beyond hour 168 proprietary! Anyone wanting to post/share/tweet/etc GFS output beyond day 7 should have 1) a limited set of graphics available with the option to 2) contribute a nominal fee to get a full suite of products while improving future GFS output. #EURObusinessfor-the-win
Go to the top of the page
 
+Quote Post
StL weatherjunki...
post Yesterday, 03:56 PM
Post #82




Rank: F5 Superstorm
***

Group: Founding Member
Posts: 6,146
Joined: 10-June 07
From: St. Louis, Missouri
Member No.: 6,288





QUOTE(ClicheVortex2014 @ Mar 22 2017, 03:51 PM) *
I mean, to be fair, you guys are posting images of soundings and talking about guidance-based analogs.

You say you use the models for wind profiles, but you haven't mentioned anything about the VBV.

Valid point about the surface heating, but you also haven't mentioned anything about moisture return. I know SWH was talking about the potential for weak low-level moisture on the previous page... but other than that, there's been no talk of that when guidance is split heavily.

Because the sounding locations I am using don't indicate VBV

I'm looking in the pre-frontal region where models are struggling with cloud cover resulting in reduced values of practically every severe parameter.

With respect to moisture return, every model I have access to shows dew points greater than 60F (many solutions > 65F) on Friday afternoon. More than sufficient low level moisture for much higher CAPE values.


--------------------
All model guidance is just that, guidance. It is the responsibility of the forecaster to take that information, make it better, and to appropriately communicate the forecast to the users.

Fervent supporter of the idea to make GFS output beyond hour 168 proprietary! Anyone wanting to post/share/tweet/etc GFS output beyond day 7 should have 1) a limited set of graphics available with the option to 2) contribute a nominal fee to get a full suite of products while improving future GFS output. #EURObusinessfor-the-win
Go to the top of the page
 
+Quote Post
so_whats_happeni...
post Yesterday, 04:58 PM
Post #83




Rank: F5 Superstorm
***

Group: Member
Posts: 13,120
Joined: 23-March 08
From: Millersville, PA
Member No.: 14,460





QUOTE(StL weatherjunkie @ Mar 21 2017, 01:16 PM) *
I understand and agree that the 500 mb structure over the central US bears more resemblance to 2007 than 2011. However, the fact that both events were statistical matches to the current model solutions means we shouldn't rule out the possibility of strong/long-lived tornadoes.

As far as I can tell, the main missing ingredient in current model solutions for a more major severe outbreak is the magnitude of surface heating and resultant destabilization, especially for the 24th. At this time of year, a couple hours of direct solar heating goes a long way and there is no way the models have accurately resolved the location/magnitude of greatest destabilization.


Look I get that while it still may be in analogs but it does not mean that the pattern supports it. The biggest difference I see is the storm from 2011 at 500mb had stronger energy and winds, also a larger varying of winds from surface to aloft. At the surface SLP was rapidly deepening in 2011 when many models still continue to show this storm closes off rather quickly. This does not look like a real classic tornadic outbreak let alone historic.

QUOTE(ClicheVortex2014 @ Mar 22 2017, 03:01 PM) *
I'm really not understanding the hype over this event.

NAM is impressive. Kinda. The problem is that I feel it's overestimating the moisture content. Also, GFS and NAM both have VBV profiles... so that will mess with the potential.



GFS is probably underestimating the moisture, otherwise this profile is just ugly for severe potential.


Yea not really sure what the big deal was outside of sporadic tornado reports in CO, NE, and western KS region leading to a potential large squall line. Would not be surprised within a few kinks in the line you get some tornadic warned cells but this is not what you should look for if that is what you want.

QUOTE(StL weatherjunkie @ Mar 22 2017, 03:14 PM) *
I think you are looking in the wrong place, probably along and just ahead of the cold front?

As I mentioned in a post earlier this morning the environment well ahead of the front is what worries me. For example, this sounding taken from the 12z NAM over the Mississippi River at hour 60 shows a textbook supercell hodograph (no VBV). Add another 1000 J/kg of CAPE to this sounding and it becomes instantly hype-worthy.

As I've mentioned on multiple occasions this season has plenty of moisture (CAPE) to work with and favorable dynamics such that it already has an observed propensity to produce severe thunderstorms and tornadoes. I don't see any good reasons not to be hyped.


If that is what you consider a textbook hodo that seems pretty funny. While you have the curve its not defined and winds become virtually the same through a large layer. Nice rise from surface to what looks like 700mb after this winds tend to get locked as the system cuts off from flow which does not allow stronger winds to become injected into the system and allow the stronger surface to aloft difference. Not rather strong veering showing up either to add to the rotation.

I know models tend to struggle on the realistic aspect of storm development but not to the point of not forecasting what would be a major tornado outbreak from what is currently being seen.


--------------------
Tylor Cartter

B.S. in Meteorology
Millersville University


Weather Observer:
KMDT: Harrisburg International Airport
KBWI: Baltimore/ Washington International Airport

Stratosphere Discussion:
2016/2017


AccuWeather Forum MidAtl/NE Snowfall Forecasting Champion Winter 2017
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Yesterday, 05:00 PM
Post #84




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





QUOTE(StL weatherjunkie @ Mar 22 2017, 04:56 PM) *
Because the sounding locations I am using don't indicate VBV

I'm looking in the pre-frontal region where models are struggling with cloud cover resulting in reduced values of practically every severe parameter.

With respect to moisture return, every model I have access to shows dew points greater than 60F (many solutions > 65F) on Friday afternoon. More than sufficient low level moisture for much higher CAPE values.

2 rebuttals:

1) the sounding you posted earlier of the 12km NAM is well ahead of the squall where there's no convection. If you skip 3 hours ahead, you'll see the squall is in the vicinity of the sounding and a VBV profile exists.

This is the sounding you posted earlier... or close to it. It's in extreme SE AR, near the MS border. The squall is quite far away, so the sounding at the time is irrelevant as there's nothing going on. Even if there's some discrete action ahead of the line that's not picked up on, that CAPE is quite marginal.




3 hours later... squall is now in the vicinity of the area. Look how the profile has changed. Yes, CAPE increased... but there's definitely a VBV profile just ahead of the squall. If you click on soundings up and down the squall, you'll see the same wind profile.




2) I disagree regarding the dew points. Not even 12km NAM has dew points >65F across 90% of the threat area. There's just a small strip down in Texas ahead of the dryline that has it... and there's a strong VBV that's rooted just above 3km AGL. It's mostly 60-65 dew points.

Furthermore, NAM is notorious for overestimating the dew points. And I trust you know better than to hang on to NAM and especially 3km NAM.

Now, I will say... if you're talking about moderate risk potential, I wouldn't be using NAM. I'd definitely be using Euro. Euro's pretty nasty... but it's slower than NAM and GFS so I guess we'll just have to wait and see who wins. But I'd say Euro holds the greatest potential.

This post has been edited by ClicheVortex2014: Yesterday, 05:01 PM


--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Yesterday, 05:06 PM
Post #85




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





SHV SREF



LZK SREF



--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
so_whats_happeni...
post Yesterday, 05:07 PM
Post #86




Rank: F5 Superstorm
***

Group: Member
Posts: 13,120
Joined: 23-March 08
From: Millersville, PA
Member No.: 14,460





QUOTE(StL weatherjunkie @ Mar 22 2017, 04:53 PM) *
3km NAM indicates higher CAPE potential with similarly impressive hodographs to the example I posted above extending from ~Houston to Shreveport to Southeast Arkansas

Houston, TX:

Attached Image


Shreveport, LA:

Attached Image


Southeast Arkansas:

Attached Image


Looks like tall skinny cape. If I am not mistaken the hodo reads out in MPH?? just getting an idea because many outlets change that.

Temp profile looks at the unstable atmosphere condition level. Just not seeing that extra umphh needed to really make this a defining feature. Again isolated reports not out of the question because you can nice microscale conditions that setup, but at the synoptic level im just not seeing it.


--------------------
Tylor Cartter

B.S. in Meteorology
Millersville University


Weather Observer:
KMDT: Harrisburg International Airport
KBWI: Baltimore/ Washington International Airport

Stratosphere Discussion:
2016/2017


AccuWeather Forum MidAtl/NE Snowfall Forecasting Champion Winter 2017
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Yesterday, 06:35 PM
Post #87




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





JAN thinks there won't be much prefrontal activity. Knife in the heart of the event if there actually is a VBV profile associated with and just in front of the advancing squall. Still wouldn't be able to rule out tornadoes with the squall, but it'd be more isolated.

QUOTE
Thursday night through Wednesday,

The weather will continue to be quiet as we end the work week, but
the prospect for severe weather still exists for late Friday
night into Saturday, and another potential severe weather event
will need to be monitored as we go into early next week.

Low level moisture will be on the increase Friday into Friday
evening as upper/surface ridging shift to the east out ahead of a
deepening upper low/trough in the plains, and isolated showers
will be possible in what should be a strongly capped airmass.
The upper trough will begin to push into the west Friday night
and move across the area Saturday with significant height falls.
It looks like an organized line of storms will move into the west
during the late evening hours Friday night, and push eastward
during the overnight hours, but the strong cap will help to limit
any prefrontal discrete storm activity. The best combination of
moisture, instability and shear will be north of the Natchez Trace
Corridor. Depending on what occurs Friday night into Saturday
morning, thunderstorms may develop once again in the east Saturday
afternoon. Given this event is still a few days away, will
continue to highlight the entire area in the HWO and will add
more emphasis on timing soon as confidence increases. Moisture
will linger across the area on Sunday with a continued chance for
showers, mainly in the east.


This post has been edited by ClicheVortex2014: Yesterday, 06:36 PM


--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Yesterday, 06:37 PM
Post #88




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





In the interest of objectivity, or at least for posterity... 3km NAM is pretty nasty.





Not sure about that storm mode or the longevity of the supercells... but nothing's set in stone.

This post has been edited by ClicheVortex2014: Yesterday, 06:39 PM


--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
StL weatherjunki...
post Yesterday, 07:26 PM
Post #89




Rank: F5 Superstorm
***

Group: Founding Member
Posts: 6,146
Joined: 10-June 07
From: St. Louis, Missouri
Member No.: 6,288





QUOTE(so_whats_happening @ Mar 22 2017, 05:58 PM) *
Look I get that while it still may be in analogs but it does not mean that the pattern supports it. The biggest difference I see is the storm from 2011 at 500mb had stronger energy and winds, also a larger varying of winds from surface to aloft. At the surface SLP was rapidly deepening in 2011 when many models still continue to show this storm closes off rather quickly. This does not look like a real classic tornadic outbreak let alone historic.
Yea not really sure what the big deal was outside of sporadic tornado reports in CO, NE, and western KS region leading to a potential large squall line. Would not be surprised within a few kinks in the line you get some tornadic warned cells but this is not what you should look for if that is what you want.
If that is what you consider a textbook hodo that seems pretty funny. While you have the curve its not defined and winds become virtually the same through a large layer. Nice rise from surface to what looks like 700mb after this winds tend to get locked as the system cuts off from flow which does not allow stronger winds to become injected into the system and allow the stronger surface to aloft difference. Not rather strong veering showing up either to add to the rotation.

I know models tend to struggle on the realistic aspect of storm development but not to the point of not forecasting what would be a major tornado outbreak from what is currently being seen.

I appreciate that you are using solid synoptic analysis to counter my argument, but my point remains the same. From a statistical perspective April 15, 2011 was the second best match to the 00z GFS solution at hour 72. Therefore, out of every single day between January 1979 (I think this is the begin date) and present April 15, 2011 was the second best match; this is an indisputable fact that should not be ignored simply because the #1 match looks like a better fit (from a statistical perspective, it better!).

Just like any model guidance, trends in analog guidance are very telling. The fact that the number of analogs with significant and long-track tornadoes has increased as well as the April 15, 2011 analog moving from #15 at day 5 to #2 at day 3 strongly indicates that model solutions are trending towards more volatile solutions.

Moving onto the textbook hodograph comment, I am really at a loss for words. Yeah there is a layer between 2km and 5km that has steady southwesterly winds at 50 knots, but that doesn't make it less textbook. Case and point shown below.

First google images result for "textbook supercell hodograph":
Attached Image

Zoomed in hodograph from my previous comment:
Attached Image

This post has been edited by StL weatherjunkie: Yesterday, 07:27 PM


--------------------
All model guidance is just that, guidance. It is the responsibility of the forecaster to take that information, make it better, and to appropriately communicate the forecast to the users.

Fervent supporter of the idea to make GFS output beyond hour 168 proprietary! Anyone wanting to post/share/tweet/etc GFS output beyond day 7 should have 1) a limited set of graphics available with the option to 2) contribute a nominal fee to get a full suite of products while improving future GFS output. #EURObusinessfor-the-win
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Yesterday, 07:35 PM
Post #90




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





Again... the hodograph is veering like that only 50+ miles ahead of the squall where there's no convection. But if you look at the hodographs immediately ahead of the squall, you'll see there's a much uglier VBV hodograph

This post has been edited by ClicheVortex2014: Yesterday, 07:36 PM


--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
StL weatherjunki...
post Yesterday, 07:47 PM
Post #91




Rank: F5 Superstorm
***

Group: Founding Member
Posts: 6,146
Joined: 10-June 07
From: St. Louis, Missouri
Member No.: 6,288





QUOTE(ClicheVortex2014 @ Mar 22 2017, 06:00 PM) *
2 rebuttals:

1) the sounding you posted earlier of the 12km NAM is well ahead of the squall where there's no convection. If you skip 3 hours ahead, you'll see the squall is in the vicinity of the sounding and a VBV profile exists.

This is the sounding you posted earlier... or close to it. It's in extreme SE AR, near the MS border. The squall is quite far away, so the sounding at the time is irrelevant as there's nothing going on. Even if there's some discrete action ahead of the line that's not picked up on, that CAPE is quite marginal.

3 hours later... squall is now in the vicinity of the area. Look how the profile has changed. Yes, CAPE increased... but there's definitely a VBV profile just ahead of the squall. If you click on soundings up and down the squall, you'll see the same wind profile.

2) I disagree regarding the dew points. Not even 12km NAM has dew points >65F across 90% of the threat area. There's just a small strip down in Texas ahead of the dryline that has it... and there's a strong VBV that's rooted just above 3km AGL. It's mostly 60-65 dew points.

Furthermore, NAM is notorious for overestimating the dew points. And I trust you know better than to hang on to NAM and especially 3km NAM.

Now, I will say... if you're talking about moderate risk potential, I wouldn't be using NAM. I'd definitely be using Euro. Euro's pretty nasty... but it's slower than NAM and GFS so I guess we'll just have to wait and see who wins. But I'd say Euro holds the greatest potential.

Taking an excerpt from the day 3 SPC discussion that directly addresses some of your points
QUOTE
Wind damage will be possible along the leading edge of this convective
line with the greatest potential in the Arklatex during the evening
as the MCS gains access to higher quality moisture where surface
dewpoints may reach the mid 60s F
. In addition, forecast soundings
across the Arklatex Friday evening show low-level shear profiles
sufficient for tornadoes. Supercells that develop in the line or
ahead of the line could be accompanied by a tornado threat.
Isolated
large hail may also occur with cells that rotate. An isolated wind
damage and hail threat will be possible in much of the overnight
period as the line of storms approaches the Mississippi River.


The SPC is talking about mid-60s dew points and the potential for supercells ahead of the front.

The situation you are describing with CAPE, shear, location of the squall lines etc. in the NAM solution is a self fulfilling prophecy.

From Wikipedia: "A self-fulfilling prophecy is a prediction that directly or indirectly causes itself to become true, by the very terms of the prophecy itself, due to positive feedback between belief and behavior."

In this case the NAM is the prophecy and your belief in the NAM is resulting in positive feedback between what the NAM is showing and what you anticipate will occur. Just because that solution doesn't show convection where the better wind profiles are doesn't mean that convection can't occur where the wind profiles are better. This is especially important in this situation where convective inhibition is actually equal to 0 in two of the 3km NAM soundings above, a well-aimed sneeze could initiate convection with a cap that weak and LCL/LFC heights so low.

I'm only using the NAM because I have easy access to everything I want to see. An argument in support of the 3km NAM is that because of the higher resolution it resolves cloud patterns better (including convection) and therefore likely has a more realistic representation of surface heating potential. I stress potential as it is on the upper end of guidance, but before I break my record I want to reiterate that this is a season where favoring the upper end of guidance is a good bet given the season's propensity to produce.


--------------------
All model guidance is just that, guidance. It is the responsibility of the forecaster to take that information, make it better, and to appropriately communicate the forecast to the users.

Fervent supporter of the idea to make GFS output beyond hour 168 proprietary! Anyone wanting to post/share/tweet/etc GFS output beyond day 7 should have 1) a limited set of graphics available with the option to 2) contribute a nominal fee to get a full suite of products while improving future GFS output. #EURObusinessfor-the-win
Go to the top of the page
 
+Quote Post
StL weatherjunki...
post Yesterday, 07:51 PM
Post #92




Rank: F5 Superstorm
***

Group: Founding Member
Posts: 6,146
Joined: 10-June 07
From: St. Louis, Missouri
Member No.: 6,288





QUOTE(ClicheVortex2014 @ Mar 22 2017, 08:35 PM) *
Again... the hodograph is veering like that only 50+ miles ahead of the squall where there's no convection. But if you look at the hodographs immediately ahead of the squall, you'll see there's a much uglier VBV hodograph

Just because there's no convection at a given location in a particular model solution doesn't mean convection can't occur in that location.

In the soundings above the cap is 0 and both LCL and LFC heights are very low such that a well placed hill or valley would provide sufficient vertical motion for initiation.


--------------------
All model guidance is just that, guidance. It is the responsibility of the forecaster to take that information, make it better, and to appropriately communicate the forecast to the users.

Fervent supporter of the idea to make GFS output beyond hour 168 proprietary! Anyone wanting to post/share/tweet/etc GFS output beyond day 7 should have 1) a limited set of graphics available with the option to 2) contribute a nominal fee to get a full suite of products while improving future GFS output. #EURObusinessfor-the-win
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Yesterday, 07:57 PM
Post #93




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





I'm not just talking about the NAM in your "self-fulfilling prophecy" theory about me, GFS has it too. Both models have that signature.

You're just looking at the warm sector, posting how the hodograph is perfect for supercells, and assuming that discrete cells are popping ahead of the squall. That's not something you can assume, and even on day 1, that's still not something you can assume will happen. Those are very hard to predict. So yes, any cells that pop ahead of the line would be tornadic supercells. However, how can we know that this'll happen at this point when we have such model discrepencies? Especially regarding the Euro vs. NAM.

Regarding your use of 3km NAM... obviously it has better skill with clouds. However, I know from personal use (and I assume you know too) that it tends to greatly overestimate CAPE. Especially almost 60 hours out! That's like relying on the solution presented by the hour 84 NAM.

This post has been edited by ClicheVortex2014: Yesterday, 07:58 PM


--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
ingyball
post Yesterday, 08:21 PM
Post #94




Rank: Tornado
**

Group: Member
Posts: 194
Joined: 22-January 16
From: Columbus Ohio
Member No.: 30,830





Hmm, I don't know as much as a lot of you yet, but from my experience most of the models(except for maybe the RAP and HRRR) don't do well at all with small scale features like Outflow boundaries. If the MCS ends up producing one that races out ahead into an area of weak capping, sufficient shear, and enough energy and moisture, that's all you need for some pretty big storms to form ahead of the main line.
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Yesterday, 08:38 PM
Post #95




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





QUOTE(ingyball @ Mar 22 2017, 09:21 PM) *
Hmm, I don't know as much as a lot of you yet, but from my experience most of the models(except for maybe the RAP and HRRR) don't do well at all with small scale features like Outflow boundaries. If the MCS ends up producing one that races out ahead into an area of weak capping, sufficient shear, and enough energy and moisture, that's all you need for some pretty big storms to form ahead of the main line.

You're right. However, the challenge is whether or not there'll be sufficient capping where the outflow boundary tries to force convection.

Another thing is that the outflow boundary typically doesn't head very far out ahead of the squall (otherwise it'll choke the instability available and the squall will die). So any cells that it pops will not be very far from the line. In most, if not all cases, there are 2 characteristics of OFB cells ahead of a line:

1) it has more of a northerly motion than the squall due to being located in the warm sector.
2) its motion is slower than the squall

Since these 2 conditions typically occur together, they're not usually long-lived cells. What can happen is the threat for significant severe for a short time if the conditions are right enough for the cell to explode in intensity because there's only a small window of opportunity for it to live.

The major events like the Super Tuesday outbreak with cells ahead of the squall weren't forced by an outflow boundary but rather they just popped ahead of the squall... hundreds and hundreds of miles ahead of the squall and outflow boundary.

An event like 10/26/10 is an example of how a forecast of warm sector supercells can bust.
An event like 11/10/02 is an example of how a warm sector supercells can occur despite the forecast (see IN/OH)

This post has been edited by ClicheVortex2014: Yesterday, 08:49 PM


--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
StL weatherjunki...
post Yesterday, 09:02 PM
Post #96




Rank: F5 Superstorm
***

Group: Founding Member
Posts: 6,146
Joined: 10-June 07
From: St. Louis, Missouri
Member No.: 6,288





QUOTE(ClicheVortex2014 @ Mar 22 2017, 08:57 PM) *
I'm not just talking about the NAM in your "self-fulfilling prophecy" theory about me, GFS has it too. Both models have that signature.

You're just looking at the warm sector, posting how the hodograph is perfect for supercells, and assuming that discrete cells are popping ahead of the squall. That's not something you can assume, and even on day 1, that's still not something you can assume will happen. Those are very hard to predict. So yes, any cells that pop ahead of the line would be tornadic supercells. However, how can we know that this'll happen at this point when we have such model discrepencies? Especially regarding the Euro vs. NAM.

Regarding your use of 3km NAM... obviously it has better skill with clouds. However, I know from personal use (and I assume you know too) that it tends to greatly overestimate CAPE. Especially almost 60 hours out! That's like relying on the solution presented by the hour 84 NAM.

Okay so the GFS can join the party, it's even worse in this situation. I know you understand that CAPE is the critical factor in this situation such that any localized area of surface heating will result in higher CAPE. Even if it's not direct sunshine, temperatures will rise throughout the day as long as it isn't raining. I think we can agree that won't be the case across the warm sector where a strong warm air advection regime. Naturally, strong WAA off the Gulf (with above normal SSTs) will also help to boost both temperatures and moisture, well ahead of the very well advertised linear feature.

Our disagreement is solely centered around the probability of pre-frontal convection occurring.

When the warm sector is uncapped with LCL/LFC values of 300-500 meters, I don't think it is unreasonable to assume that convection will initiate at some point ahead of that line wherever surface heating is maximized. It may not be southeast Arkansas, but I'm favoring someplace in the MS river basin primarily due to topography (shown below, acts as a wind tunnel to enhance WAA) and the dual-nature of the moisture plume shown on all model guidance (one from Cuba and the dominant plume from the western GoM).

Attached Image


The Feb 28 tornado outbreak was largely caused by prefrontal convection due to localized/differential heating within a similar prefrontal band of enhanced surface moisture emanating out of the Caribbean. It's probable that topographic funneling influenced initiation with the Feb 28 event as well.

Attached Image


So yeah, I'm clearly biased towards a solution (with model support) that favors a more substantial tornado potential due to higher CAPE values (irrespective of model bias). Maybe it will bite me, but the climatology of this season is a high-end season already (due to recent ENSO transition to Nina [even though it's over], warm GoM SSTAs, and topography). So I have climatology, analogs, low LCL/LFC/topography, GoM SSTAs, and a bit of convection allowing operational guidance in my favor and perhaps the EURO as well (really am not sure). You can have the 12k NAM and GFS solutions laugh.gif

This post has been edited by StL weatherjunkie: Yesterday, 09:04 PM


--------------------
All model guidance is just that, guidance. It is the responsibility of the forecaster to take that information, make it better, and to appropriately communicate the forecast to the users.

Fervent supporter of the idea to make GFS output beyond hour 168 proprietary! Anyone wanting to post/share/tweet/etc GFS output beyond day 7 should have 1) a limited set of graphics available with the option to 2) contribute a nominal fee to get a full suite of products while improving future GFS output. #EURObusinessfor-the-win
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Yesterday, 11:44 PM
Post #97




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





CIPS is honing in on the Texas Panhandle as the highest relative threat area today. 5 of the analogs have significant severe weather there.





% of 15 analogs with 1 tornado


% of 15 analogs with 1 significant tornado


This post has been edited by ClicheVortex2014: Yesterday, 11:54 PM


--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Today, 12:48 AM
Post #98




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





Potential for discrete supercells in the north half, south half mostly linear


QUOTE
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1234 AM CDT Thu Mar 23 2017

Valid 231200Z - 241200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING ACROSS CENTRAL AND SOUTHERN PORTIONS OF THE
HIGH PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS
SURROUNDING AREAS OF THE CENTRAL AND SOUTHERN PLAINS INTO THE MIDDLE
MISSOURI VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TODAY ACROSS
PARTS OF SOUTHERN FLORIDA...

...SUMMARY...
Strong thunderstorms are expected from parts of the central and
southern Plains into the mid Missouri Valley late this afternoon
into tonight, accompanied by potential for severe hail and damaging
surface gusts. Thunderstorms with a risk for severe wind and hail
are also possible across parts of southern Florida.

...Synopsis...
Much of the nation will remain under the influence of split
westerlies emanating from the mid-latitude Pacific. Within this
regime, one prominent northern stream trough is forecast to continue
to progress away from the Atlantic Seaboard. As it does, models
suggest remnant southern stream troughing will linger over the
Bahamas/parts of southern Florida and the Caribbean, while short
wave ridging builds to its northwest (across the Southeast), ahead
of a more significant southern stream short wave trough forecast to
progress east of the southern Great Basin/lower Colorado Valley,
through the southern Rockies/High Plains by 12z Friday.

In association with this latter feature, models generally indicate
that significant surface cyclogenesis will initiate across parts of
northeastern Colorado during the day today, before redeveloping
southeastward into western Kansas tonight, in closer proximity to a
lower/mid tropospheric cyclone developing within the larger-scale
trough as it crosses the southern Rockies. This should be
accompanied by considerable strengthening of southerly low-level
flow through portions of the Plains into Mississippi Valley,
particularly by tonight, when speeds around the 850 mb level are
expected to reach 50-70 kt across much of the southern into central
Plains.

Despite the favorable evolving large-scale flow, a substantive
return flow of moisture from the Gulf of Mexico appears unlikely
during this period due to recent drying across much of the Gulf
region. This probably will limit the extent of the convective
potential today and tonight. However, steep mid-level lapse rates
associated with a plume of elevated mixed-layer air emerging from
the southern Rockies/Mexican Plateau region may contribute to
sufficient destabilization to support at least some risk for severe
storm activity across the central and southern Plains into the mid
Missouri Valley. A remnant plume of elevated mixed-layer air, which
has advected considerably south and east of the Plains, may also
contribute to some severe weather potential across parts of southern
Florida.

...Central and southern Plains into mid Missouri Valley...
The lack of substantive deep return flow of moisture, coupled with
downward mixing of dry lower/mid tropospheric air, will be
problematic with regard to severe thunderstorm potential today.
Guidance continues to suggest that the most substantive
boundary-layer moistening may be confined to a narrow corridor along
the lee surface trough across parts of western Kansas (perhaps as
far south as parts of the Texas/Oklahoma Panhandle region) into
southwestern Nebraska by the 21-23Z time frame this afternoon. Even
this may be characterized by surface dew points only on the order of
55-60F. However, beneath steep mid-level lapse rates, this may be
sufficient for a corridor of mixed-layer CAPE up to around 1000
J/kg, as a 50-70 kt southwesterly mid-level jet streak noses across
the region.

While the primary upper impulse may still be lagging near or to the
west of the Rockies, the environment along/east of the sharpening
dryline probably will be conducive to discrete supercell
development. Some risk for at least weak/brief tornadoes may exist
with initial development, but severe hail may be the most prominent
risk with this activity as it develops northeastward/eastward
through early evening.

As the main impulse/developing mid-level circulation emerges from
the intermountain region this evening, storms with severe hail
potential may become focused within an area of strengthening
low-level warm advection across north central and northeastern
Nebraska. Additional storm development may become focused on the
leading edge of stronger lower/mid-tropospheric cooling, from parts
of western Kansas into the Texas South Plains. In the presence of
intensifying environmental wind fields, potentially damaging wind
gusts seem likely to be the primary threat with an evolving squall
line. This could continue into the overnight hours, eastward toward
the lower Plains, but it remains unclear at this time if instability
will remain sufficient to support vigorous convection east of
western Kansas/Oklahoma and northwest Texas.


--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Today, 12:57 AM
Post #99




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453







QUOTE
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1252 AM CDT Thu Mar 23 2017

Valid 241200Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN PLAINS...ARKLATEX...AND LOWER MISSISSIPPI VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN/CENTRAL PLAINS...OZARKS...AND LOWER TO MID MISSISSIPPI
VALLEY...

...SUMMARY...
Wind damage, isolated large hail, and a tornado threat is forecast
Friday and Friday night across parts of the southern and central
Plains, Arklatex, and lower to mid Mississippi Valley.

...Synopsis...
An upper trough/low with an embedded and cyclonically curved 80-100
kt upper jet will move eastward across the southern and central
Plains Friday and into the Arklatex and lower/mid MS Valley by early
Saturday morning. At the surface, a low should move from western KS
to central/eastern KS and northern OK by Friday evening while slowly
weakening. A composite dryline/cold front extending southward from
this low will advance eastward across much of the southern Plains
and into the Arklatex/lower MS Valley through the period.

...Southern and Central Plains/Arklatex/Lower to Mid MS Valley...
Convection that will likely form during the Day 1/Thursday period
across the southern and central High Plains may still be ongoing
Friday morning across parts of central OK into north/central TX
along a pre-frontal trough/outflow boundary. Latest model guidance
is generally consistent in showing gradual intensification and an
increase in coverage of thunderstorms associated with this
pre-frontal trough/boundary across eastern OK/east TX into western
AR/LA and perhaps southwestern MO from mid-morning through early
afternoon. If this convection occurs, it would hamper diurnal
destabilization across the warm sector, likely limiting the
development of any more than weak instability downstream.
Regardless, an increasing severe threat will probably be realized
across the lower MS Valley and Arklatex Friday afternoon/evening as
convection likely organizes into a squall line with strong
large-scale ascent associated with the upper trough/low
overspreading this region. The prospect for a somewhat higher wind
damage/large hail threat may exist across the Arklatex, where
greater low-level moisture should reside. A tornado threat may also
exist with any supercells within or ahead of the line across the
Arklatex and towards the MS River as a southerly/southwesterly 40-50
kt low-level jet develops across this region early Friday evening.
Low-level shear will be more than sufficient to support a tornado
threat, but instability is forecast to remain weak, and convective
mode (mainly linear) may not be overly favorable.

A second round of convection along the eastward-moving front/dryline
appears highly uncertain, as early day thunderstorms will likely
overturn much of the pre-frontal warm sector. Perhaps a slightly
higher chance for initiation along the front/dryline may be realized
across eastern KS into western MO Friday afternoon/evening, where
the likelihood for early day thunderstorms is less probable. If
convection were to form in this region, then all severe hazards
appear possible, as effective shear will be strong and steep
mid-level lapse rates will at least partially compensate for more
limited low-level moisture compared to locations farther south.
Regardless of the exact details regarding the convective evolution
through the day, a strong to damaging wind risk should continue
through much of the overnight hours across the lower MS Valley as
the squall line moves eastward.


--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post
ClicheVortex2014
post Today, 01:33 AM
Post #100




Rank: F5 Superstorm
***

Group: Member
Posts: 18,769
Joined: 21-April 14
From: Athens, Ohio
Member No.: 29,453





HRRR is picking out Nebraska as the highest potential.







--------------------
Meteorology undergrad at Ohio University

Historic weather events in the Ohio Valley:
- The 1974 Super Outbreak (read more)
- The 2012 "Super" Derecho
- The Great Blizzard of 1978
- ILN Severe Weather Climatology

2017 Weather for Cincinnati

Days >90: 0 (Last: 9/8/16)
Marginal risks: 3 (Last: 3/20/17)
Slight risks: 0 (Last: 9/10/16)
Enhanced risks: 3 (Last: 3/1/17)
Moderate risks: 0 (Last: 6/22/16)
High risks: 0 (Last: 11/17/13)

Realtime Weather on Campus: http://www.phy.ohiou.edu/~scalia/state_street/upload.png
Go to the top of the page
 
+Quote Post

5 Pages V  « < 3 4 5
Reply to this topicStart new topic
10 User(s) are reading this topic (10 Guests and 0 Anonymous Users)
0 Members:

 

RSS Lo-Fi Version Time is now: 23rd March 2017 - 09:17 AM