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> April 12-14 Plains/MW/OV Severe Weather, SPC Risk Level; Day 1 Moderate Risk: Forecasts and OBS
WeatherMonger
post Apr 7 2018, 03:56 PM
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SPC mentioning the possibility/probability of severe weather during this time period. Delineation possible in subsequent outlooks. Will add regions if/when necessary.

QUOTE
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0332 AM CDT Sat Apr 07 2018

Valid 101200Z - 151200Z

...DISCUSSION...
Through the middle of the upcoming week, persistent northwesterly
flow aloft over the central US will generally maintain broad surface
high pressure east of the Rockies, precluding substantive inland
destabilization. A few storms may develop across northern Florida on
D4/Tuesday, but unimpressive lapse rates and modest low/mid-level
wind fields should preclude widespread organized severe weather.

By mid-week, a western US ridge is forecast to flatten, and
increasing westerly flow across the Rockies will yield a deepening
lee trough. The resultant surface pressure gradient will enhance
return flow across the southern/central Plains during the latter
half of the week. Meanwhile, medium-range guidance indicates an
energetic trough and strong west/southwesterly mid-level jet maximum
will approach the Plains late D6/Thu into D7/Fri. As it does so,
strengthening southwesterly flow is forecast to spread steepening
mid-level lapse rates across much of the region.

While severe weather seems possible, if not probable, to occur
across parts of the Plains/Mississippi Valley by D7/Fri,
considerable spatial uncertainty remains, owing to several factors:

1) Notable timing/amplitude differences amongst model guidance with
regards to the main trough and associated closed cyclone that is
forecast to develop over the north-central US.
2) The potential for a relatively narrow warm/moist sector ahead of
a dry line -- the placement of which is difficult to determine at
this forecast range due to the timing/amplitude differences noted
above.
3) The possibility that only modest moisture return renders
convective inhibition too great for more organized open warm sector
development, reducing the areal coverage of potential severe
weather.

Considering these concerns, predictability too low is maintained for
D6/Thu-D8/Sat. Nonetheless, severe probabilities may be introduced
in upcoming forecast cycles.

..Picca.. 04/07/2018


This post has been edited by WeatherMonger: Apr 13 2018, 04:14 PM
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WeatherMonger
post Apr 7 2018, 05:11 PM
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WeatherMonger
post Apr 8 2018, 07:59 AM
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Day 6 delineated and OV added to title.


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QUOTE
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Sun Apr 08 2018

Valid 111200Z - 161200Z

...DISCUSSION...
The primary feature of interest during the extended period will be a
deep/amplified mid-level trough that will reach the central US by
D6/Fri. As it does so, strengthening west/southwesterly flow aloft
will transport steep lapse rates over much of the southern/central
Plains. Meanwhile, a robust low-level mass response will feature a
narrow corridor of enhanced poleward theta-e transport, generally
from eastern Texas to the lower Missouri Valley. As a dry line and
cold front accelerate east across the region, low/mid-level ascent
is forecast to strengthen sufficiently to overcome convective
inhibition and promote thunderstorms from eastern Texas to parts of
the Midwest through Friday night.

While medium-range guidance continues to exhibit run-to-run
variability with regards to the amplitude/timing of the trough, most
deterministic/ensemble guidance suggest strong/severe thunderstorms
will be most likely from eastern Texas to the Ozarks and Mid-South
Friday afternoon through the overnight. Within this corridor,
vigorous low/mid-level wind fields should overlap adequate
surface-based buoyancy, such that all severe hazards may be possible
with maturing convection. Therefore, a 15-percent probability has
been introduced with this forecast cycle. Further refinements of
this area (with some potential for a northward expansion) will
likely be needed in future updates.

The trough will advance further east through D7/Sat-D8/Sun, with
pockets of strong/severe convection potentially persisting across
areas from the Ohio Valley south to the Gulf Coast. Despite this
potential, uncertainties regarding availability of adequate
instability, the eastward evolution of the trough, and subsequent
timing/placement of stronger convection remain too high to introduce
probabilities beyond D6/Fri.


This post has been edited by WeatherMonger: Apr 8 2018, 08:01 AM
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cincysnow
post Apr 8 2018, 09:22 AM
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QUOTE(WeatherMonger @ Apr 8 2018, 08:59 AM) *
Day 6 delineated and OV added to title.


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Nice to see you posting again
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ClicheVortex2014
post Apr 8 2018, 03:07 PM
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GFS is full of 'meh'. Euro's not bad. Strong low, and an extra low along the OK/AR border adds to the potential down there.





--------------------
Meteorology undergrad at Ohio University (weather on campus)

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

2018 Weather for Cincinnati

Days >90: 18 (Last: 7/14/18) (Highest: 96)
Days <0: 5 (Last 1/6/18) (Lowest: -7)
Marginal risks: 19 (Last: 7/10/18)
Slight risks: 6 (Last: 6/26/18)
Enhanced risks: 0 (Last: 11/5/17)
Moderate risks: 1 (Last: 4/3/18)
High risks: 0 (Last: 11/17/13)
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ClicheVortex2014
post Apr 8 2018, 07:12 PM
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FWIW... MJO is expected to enter phase 2 around April 12. Models disagree on magnitude of the wave though.



Nice central trough to kick off phase 2.


--------------------
Meteorology undergrad at Ohio University (weather on campus)

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

2018 Weather for Cincinnati

Days >90: 18 (Last: 7/14/18) (Highest: 96)
Days <0: 5 (Last 1/6/18) (Lowest: -7)
Marginal risks: 19 (Last: 7/10/18)
Slight risks: 6 (Last: 6/26/18)
Enhanced risks: 0 (Last: 11/5/17)
Moderate risks: 1 (Last: 4/3/18)
High risks: 0 (Last: 11/17/13)
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ClicheVortex2014
post Apr 8 2018, 11:36 PM
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A problem I'm seeing on soundings is VBV. Only place this isn't a big issue is near the warm front.





--------------------
Meteorology undergrad at Ohio University (weather on campus)

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

2018 Weather for Cincinnati

Days >90: 18 (Last: 7/14/18) (Highest: 96)
Days <0: 5 (Last 1/6/18) (Lowest: -7)
Marginal risks: 19 (Last: 7/10/18)
Slight risks: 6 (Last: 6/26/18)
Enhanced risks: 0 (Last: 11/5/17)
Moderate risks: 1 (Last: 4/3/18)
High risks: 0 (Last: 11/17/13)
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WeatherMonger
post Apr 9 2018, 05:35 AM
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QUOTE
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0339 AM CDT Mon Apr 09 2018

Valid 121200Z - 171200Z

...DISCUSSION...
The main focus of the extended period continues to be the impressive
amplification of a mid/upper trough over the central US late this
week into the weekend. Along the base of the trough, an approximate
100-kt west/southwesterly 500-mb jet will overspread the
southern/central Plains on D5/Fri, transporting a broad area of
relatively steep lapse rates across the region. Concurrently, a
deepening low over the central US will encourage a narrow corridor
of enhanced poleward moisture return (generally characterized by
surface dew points in the 60s) from eastern Texas to the lower
Missouri Valley. Attendant to this low, a dry line and cold front
will accelerate eastward from the Plains towards the Mississippi
Valley through Friday night, promoting thunderstorm activity from
the western Gulf Coast to the Midwest.

While still exhibiting diversity in the timing of the eastward
evolution of the trough, medium-range guidance continues to
highlight areas from eastern Texas to the Mid-South for the highest
probability of severe weather late Friday into the overnight. Here,
deterministic/ensemble guidance indicates robust wind fields will
overlap adequate surface-based buoyancy for the development of
severe thunderstorms. Considering the magnitude of forcing for
ascent and the forecast meridional nature of deep-layer flow,
upscale growth into larger convective complexes appears probable.
Such evolution should enhance the ability of severe convection to
spread east overnight; therefore, the ongoing 15-percent area has
been expanded slightly towards the Mississippi Valley.

Farther north towards the lower Missouri and mid Mississippi
Valleys, guidance also indicates a possibility for severe
convection. However, a narrowing moist/warm sector towards the
primary surface low yields greater uncertainty with the spatial
placement of such convection during the afternoon/evening. In turn,
15-percent probabilities have not been expanded northward with this
cycle, but could be in later updates.

Beyond D5/Fri, timing of the eastward progression of the trough and
associated convection remains quite uncertain. Furthermore,
lessening buoyancy with eastward extent suggests stronger convection
will likely remain focused near the corridor of greatest deep
ascent, magnifying concerns regarding temporal uncertainty.
Subsequently, predictability too low is maintained through the
remainder of the extended period.

..Picca.. 04/09/2018
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ClicheVortex2014
post Apr 9 2018, 02:55 PM
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Still not that impressed with the setup.The flow is pretty meridional, and at least the GFS is still showing signs of VBV all across the regiion.





--------------------
Meteorology undergrad at Ohio University (weather on campus)

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

2018 Weather for Cincinnati

Days >90: 18 (Last: 7/14/18) (Highest: 96)
Days <0: 5 (Last 1/6/18) (Lowest: -7)
Marginal risks: 19 (Last: 7/10/18)
Slight risks: 6 (Last: 6/26/18)
Enhanced risks: 0 (Last: 11/5/17)
Moderate risks: 1 (Last: 4/3/18)
High risks: 0 (Last: 11/17/13)
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ClicheVortex2014
post Apr 9 2018, 05:26 PM
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I can see a greater tornado threat up near the low and warm front in Iowa in the late morning/early afternoon hours. You have much more veering and a weaker VBV signature. There's a cap which is strong enough to inhibit activity but weak enough that it could be broken. The combination of these 2 might support at least brief semi-discrete or discrete activity... especially if VBV goes away.



--------------------
Meteorology undergrad at Ohio University (weather on campus)

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

2018 Weather for Cincinnati

Days >90: 18 (Last: 7/14/18) (Highest: 96)
Days <0: 5 (Last 1/6/18) (Lowest: -7)
Marginal risks: 19 (Last: 7/10/18)
Slight risks: 6 (Last: 6/26/18)
Enhanced risks: 0 (Last: 11/5/17)
Moderate risks: 1 (Last: 4/3/18)
High risks: 0 (Last: 11/17/13)
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ClicheVortex2014
post Apr 9 2018, 11:32 PM
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VBV everywhere.

Sounding in east Texas... VBV and dry temp profile


Sounding in Iowa... everything looks good but there's obvious VBV. Frustrating.


--------------------
Meteorology undergrad at Ohio University (weather on campus)

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

2018 Weather for Cincinnati

Days >90: 18 (Last: 7/14/18) (Highest: 96)
Days <0: 5 (Last 1/6/18) (Lowest: -7)
Marginal risks: 19 (Last: 7/10/18)
Slight risks: 6 (Last: 6/26/18)
Enhanced risks: 0 (Last: 11/5/17)
Moderate risks: 1 (Last: 4/3/18)
High risks: 0 (Last: 11/17/13)
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WeatherMonger
post Apr 10 2018, 06:51 AM
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QUOTE
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0348 AM CDT Tue Apr 10 2018

Valid 131200Z - 181200Z

...DISCUSSION...
Medium-range models continue to highlight continued deepening of the
upper low/trough as it moves eastward across the Plains Day 4
(Friday), though differences between the GFS and ECMWF are evident
-- particularly with respect to the surface frontal advance across
Kansas/Texas/Oklahoma.

At this time, the much faster GFS appears to be the outlier (in
accordance with its typical bias), as the Canadian and UKMET runs
also suggest slower frontal progression more similar to that
depicted by the ECMWF. Given the uncertainties, it remains
difficult to confidently narrow down the envelope of highest severe
potential, but will make minor adjustments to the prior outlook
northward (into central Missouri) and westward (toward the DFW
Metroplex).

Otherwise, an area centered over the Arklatex appears to be at risk
for severe storms, as boundary-layer moistening/strengthening
southerly flow spread beneath increasing mid-level winds yield an
amply sheared/unstable warm sector. Along with risk for hail,
locally damaging winds and potential for a couple of tornadoes will
be possible during the afternoon and evening.

By Day 5/Saturday, uncertainties highlighted for Day 4 become
increasingly apparent. This -- combined with the likelihood for
widespread/ongoing convection Saturday morning -- precludes
confident assessment of severe potential into the
Mississippi/Ohio/Tennessee Valleys and central Gulf Coast area.

Predictability concerns linger through the remainder of the medium
range, as this system shifts into the eastern U.S. and the next
upper trough shifts into/across the western half of the country.

..Goss.. 04/10/2018
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StL weatherjunki...
post Apr 10 2018, 01:18 PM
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I agree that the wind profiles on the 12th are not particularly inspiring and are more conducive to another afternoon hail and evening/overnight wind threat similar to April 3.

I'm curious about the potential for isolated severe storms along the potent west-east warm front, especially as moisture deepens on the 13/14th. Supercells popping along west-east oriented warm fronts at this time of year are arguably more threatening than what is currently being advertised along the cold front.

Additionally, I'm not convinced the entire warm sector will stay capped on the 13/14th, particularly in areas where lots of rain has fallen in the past month or two (OHV). Seems to me like models may have too much cloudiness across the warm sector, which is artificially limiting heating/instability.


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

We live in a day and age where the quantity of model guidance is overwhelming, particularly within 24 hours of an event. We must remind ourselves that all models are wrong, but some are more useful than others.
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WeatherMonger
post Apr 10 2018, 01:25 PM
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ClicheVortex2014
post Apr 10 2018, 01:37 PM
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Good ol' Reed talking about hour 84 NAM and neglecting the detrimental VBV. Classic.


--------------------
Meteorology undergrad at Ohio University (weather on campus)

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

2018 Weather for Cincinnati

Days >90: 18 (Last: 7/14/18) (Highest: 96)
Days <0: 5 (Last 1/6/18) (Lowest: -7)
Marginal risks: 19 (Last: 7/10/18)
Slight risks: 6 (Last: 6/26/18)
Enhanced risks: 0 (Last: 11/5/17)
Moderate risks: 1 (Last: 4/3/18)
High risks: 0 (Last: 11/17/13)
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MichelleOH
post Apr 10 2018, 05:27 PM
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They are mentioning this system on the local news, but I don't see much here from you guys for Ohio. Am I missing something?
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ClicheVortex2014
post Apr 10 2018, 05:49 PM
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QUOTE(MichelleOH @ Apr 10 2018, 06:27 PM) *
They are mentioning this system on the local news, but I don't see much here from you guys for Ohio. Am I missing something?

Probably will get some thunderstorms from this system. There's a renewed threat for strong storms in Indiana and maybe western Ohio on Saturday but I see it being mostly a damaging wind threat. The winds are southwesterly essentially through the entire atmosphere so there won't be much vertical spin in the atmosphere. In fact, the only time the winds turn with height is with the backing about 6km above ground which makes the tornado threat even lower.

So I'd imagine a low-topped squall will be the most likely thing to happen with strong to maybe marginally severe winds.

This post has been edited by ClicheVortex2014: Apr 10 2018, 05:52 PM


--------------------
Meteorology undergrad at Ohio University (weather on campus)

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

2018 Weather for Cincinnati

Days >90: 18 (Last: 7/14/18) (Highest: 96)
Days <0: 5 (Last 1/6/18) (Lowest: -7)
Marginal risks: 19 (Last: 7/10/18)
Slight risks: 6 (Last: 6/26/18)
Enhanced risks: 0 (Last: 11/5/17)
Moderate risks: 1 (Last: 4/3/18)
High risks: 0 (Last: 11/17/13)
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MichelleOH
post Apr 10 2018, 05:53 PM
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Thanks....I've got an outdoor thing for Saturday afternoon. I'll keep watching closely. Looks like they better move to an indoor venue.
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WeatherMonger
post Apr 10 2018, 06:42 PM
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I just wanted a Spring thread for the region, everything has been Winter or flood laugh.gif
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ClicheVortex2014
post Apr 10 2018, 06:51 PM
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QUOTE(WeatherMonger @ Apr 10 2018, 07:42 PM) *
I just wanted a Spring thread for the region, everything has been Winter or flood laugh.gif

It's certainly deserving of a thread... I was gonna make the thread but you beat me to it. This is certainly one of those cases where the severe threat is greatest in the Plains... then we have to deal with the beloved debris clouds.

The warmth will certainly be welcomed though. This weekend is one of the biggest party weekends here (yet another weekend tradition that OU has distanced themselves from)... supposed to be sunny and in the upper 70's on Friday and partly cloudy and in low-mid 70's on Saturday. With all of the cold weather recently, this warmup is perfectly timed.


--------------------
Meteorology undergrad at Ohio University (weather on campus)

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

2018 Weather for Cincinnati

Days >90: 18 (Last: 7/14/18) (Highest: 96)
Days <0: 5 (Last 1/6/18) (Lowest: -7)
Marginal risks: 19 (Last: 7/10/18)
Slight risks: 6 (Last: 6/26/18)
Enhanced risks: 0 (Last: 11/5/17)
Moderate risks: 1 (Last: 4/3/18)
High risks: 0 (Last: 11/17/13)
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