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> March 23-24 Plains Severe Weather, SPC Risk Level; Days 4-8 Possible: Forecasts and OBS
StL weatherjunki...
post Today, 03:53 PM
Post #81




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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


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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.

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StL weatherjunki...
post Today, 03:56 PM
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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
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so_whats_happeni...
post Today, 04:58 PM
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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.


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ClicheVortex2014
post Today, 05:00 PM
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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: Today, 05:01 PM


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