Friday 9/27/2019 Day 1 Enhanced

A place to discuss upcoming severe weather setups. Unless otherwise noted, all posts of weather graphics are for informational purposes only, by non-meteorologists. All posted weather models should be taken with a grain of salt. Please refer to your local news or radio and other official sources for up-to-date weather information.
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thunderchaser83
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Posts: 19
Joined: Wed Sep 25, 2019 1:41 am

Friday 9/27/2019 Day 1 Enhanced

Post by thunderchaser83 » Thu Sep 26, 2019 4:04 pm

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SPC AC 260540

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1240 AM CDT Thu Sep 26 2019

Valid 271200Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
CENTRAL PLAINS TO THE MID MISSISSIPPI VALLEY...

...SUMMARY...
Thunderstorms associated with wind damage, large hail and an
isolated tornado threat will be possible Friday afternoon and
evening from the central Plains to the mid Mississippi Valley.

...Southern and Central Plains/Lower Missouri and Mid Mississippi
Valleys...
West-southwesterly mid-level flow will be in place on Friday from
the Great Plains into the Great Lakes region. At the surface, a cold
front will advance southeastward across the central Plains, lower
Missouri Valley and mid Mississippi Valley. Ahead of the front,
surface dewpoints are forecast to be in the upper 60s F which should
result in moderate instability by midday. As surface heating takes
place and low-level convergences increases along the front,
thunderstorm development will be likely along the majority of the
front from eastern Kansas to northern Illinois.

NAM and GFS forecast soundings along the front for 00Z/Saturday have
MLCAPE values generally from 2,000 to 4,000 J/kg with 35 to 40 kt of
0-6 km shear. This should support supercell development with cells
that remain discrete. However, strong low-level convergence and
mid-level flow parallel to the front should result in mostly linear
development as the event progresses. Supercells early in the event
or rotating cells embedded along the line should have an isolated
tornado and large hail threat. Wind damage will also be possible
especially as a squall line organizes near the front during the
early to mid evening.

...MAXIMUM RISK BY HAZARD...
Tornado: 5% - Slight
Wind: 15% - Slight
Hail: 15% - Slight

..Broyles.. 09/26/2019
Last edited by thunderchaser83 on Fri Sep 27, 2019 7:05 pm, edited 1 time in total.
Reason: Updated Outlook Day and Category.

thunderchaser83
Site Admin
Posts: 19
Joined: Wed Sep 25, 2019 1:41 am

Re: Friday 9/27/2019 Day 2 Slight

Post by thunderchaser83 » Fri Sep 27, 2019 5:55 pm

Day 1 Probabilities and outlook discussion.
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SPC AC 271630

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Fri Sep 27 2019

Valid 271630Z - 281200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IA/IL/MO BORDER
AREA...

...SUMMARY...
Scattered to numerous severe thunderstorms are possible, including a
few tornadoes, mainly during the late afternoon and evening from
northern Illinois to eastern Kansas.

...KS to Lower MI...
Elevated convection is ongoing within a low-level warm advection
regime across the Mid-MO Valley and northern IL. Robust
boundary-layer heating is underway in the wake of this morning
activity beneath an elevated mixed layer that is attempting to
advect northeast from the central Great Plains/Lower MO Valley. In
conjunction with surface dew points increasing into the upper 60s to
lower 70s surface dew points, a strongly unstable air mass with
MLCAPE of 2500-3500 J/kg should develop ahead of a
southwest-northeast cold front from eastern KS to the IA/IL/MO
border area.

Despite near-neutral mid-level height tendency, guidance is fairly
consistent with the presence of a mid-level speed max developing
across northeast KS this afternoon and reaching the IA/IL border
area this evening. While the bulk of initial convective development
may be atop a more stable boundary-layer from central IA to southern
WI, sufficient convergence should exist for storm development along
the front and into the warm sector from its intersection with the
differential heating boundary in northern IL to the dryline
intersection in south-central KS. The greatest convective coverage
should reside near the IA/IL/MO border region with more scattered
coverage back into eastern KS.

Low to deep-layer wind profiles will favor potential for several
supercells during the early evening which will probably consolidate
into multiple organized clusters through late evening. Large hail
will be the most probable hazard with scattered severe wind gusts
expected as well. Given rich boundary-layer moisture and an enlarged
low-level hodograph, certainly a tornado risk will exist with any
supercells just ahead of the front. 12Z HREF guidance and related
CAMs are indicative of higher-end tornado coverage. However, with
cyclolysis expected, the overall synoptic pattern should be a
limiting factor. Still, given the potential for at least a few
tornadoes, will double-upgrade from less than 2 percent to a 5
percent area with this outlook.

...Southeast NM and west TX...
A low-amplitude shortwave trough near the AZ/Sonora border should
approach the TX Panhandle. Scattered storms should develop this
evening into the overnight. Modest buoyancy, the bulk of which
should remain below the strong speed shear from the mid to upper
levels, will probably marginalize the overall severe hail and wind
risk.

..Grams/Smith.. 09/27/2019

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