Severe WX April 22-24th, 2020 Severe Weather Threat (3 Viewers)


Kory

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What would you say is lacking to keep these storms from developing beyond wall cloud status?
Pretty weak and veered LLJ combined with a pretty stable airmass immediately behind that rain mass. This is one of those instances where really backed surface winds (SE/SSE) are bringing in stable and cooler air from behind that rain shield in S AL.
 

Tyler Penland

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Quite a few SVR warnings along that boundary south of bham.


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Peter Griffin

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Aren't all the models pretty much suspect at this point not just the NAM? Greatly reduced flights and therefore less atmospheric data points seem to be wreaking havoc on most models lately.

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Matt Grantham

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Aren't all the models pretty much suspect at this point not just the NAM? Greatly reduced flights and therefore less atmospheric data points seem to be wreaking havoc on most models lately.

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It was almost certain that morning storms would cause disruption. However, many models are notorious for underestimating the impact on the thermal fields and wind fields. The advertised recovery almost always comes up short of projections. This is why I felt safe downplaying the tornado threat.
 

WesL

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Meanwhile south of Tallahasee multiple tornado warnings continue.

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It was almost certain that morning storms would cause disruption. However, many models are notorious for underestimating the impact on the thermal fields and wind fields. The advertised recovery almost always comes up short of projections. This is why I felt safe downplaying the tornado threat.
hey matt, glad see you on the forum... you think the mid south memphis area will get in on the severe action before the before the plains start see most the action later... the storm track as been pretty far south which is unual for this late april, gues negative nao helping that
 

WesL

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Video of a waterspout near Panama City Beach. Slight language warning with the video.


Additional view of the waterspout coming onshore -
 

Bevo

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Rinse, wash, repeat--after 2 days (day and a half?), the threat returns to east Texas/ArkLaTex...and Florida.

SPC Day 1 8 AM outlook
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Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0753 AM CDT Fri Apr 24 2020

Valid 241300Z - 251200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN THE ARKLATEX
VICINITY...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER CENTRAL
FLORIDA...

...SUMMARY...
The greatest severe-storm potential today into tonight will shift
from eastern parts of Oklahoma and Texas toward the lower
Mississippi Valley.

...Synopsis...
In mid/upper levels, broadly cyclonic flow will cover most of the
CONUS between the Rockies and Appalachians through the period. An
embedded, initially low-amplitude perturbation is apparent in
moisture-channel imagery over CO, with smaller vorticity maxima
southeastward across the south-central High Plains. These features
should phase into a more-coherent, strengthening shortwave trough,
today, reaching south-central KS, central OK and north-central TX
around 00Z. By 12Z, this perturbation should reach the Mid-South
region.

At the surface, 11Z analysis showed a cold front extending from a
low over the Chesapeake Bay southwestward across western SC, the Fl
Panhandle and the north-central Gulf. This boundary was loosely
linked to a warm-frontogenetic zone over east and north TX, and in
turn, to another low near CDS. The latter low will move eastward
across OK today then over the Ozarks region tonight. A trailing
cold front, initially over the TX South Plains region and eastern
NM, will strengthen and move southeastward/eastward across west TX
and central OK through the day, reaching eastern OK and northeast/
central TX by 00Z. By 12Z, the cold front should extend from the
low across southern AR, northwestern LA and south-central TX. The
warm-frontal zone should shift northward diffusely across eastern OK
and AR, ahead of the more-robust moisture return of a partly
modified Gulf air mass.

...Eastern TX/OK, LA to Ozarks/Mid-South regions ---
Scattered thunderstorms are expected to develop this afternoon near
the surface low, an inverted trough/weak frontal zone extending
poleward of the low, and the cold front. The greatest severe
potential at first will be large hail, with a few tornadoes possible
(especially southward into more-favorable moisture). Damaging gusts
should become more common with time into the evening as activity
shifts eastward.

The greatest potential for rich low-level moisture return should be
from southeastern OK and the Arklatex southward, beneath favorable
deep shear. Meanwhile, mass response to the low and midlevel
perturbation will be strongest in the area of marginal but adequate
low-level theta-e will weaken southward toward the Gulf. Associated
low-level convergence becomes more uncertain south of northeast/
east-central TX. As such, the most favorable buoyancy/shear
parameter space for sustained and potentially tornadic supercells
should be across northeast TX, southeastern OK, and adjoining parts
of southwestern AR and northwestern LA. By contrast, favorable
MLCAPE and shear for supercells -- including those capable of very
large/damaging hail -- will be over a more north/south-elongated
swath of the region, before potential upscale merger/growth
transitions the threat toward wind-dominant modes. The severe
threat is expected to diminish gradually overnight as the convection
moves into a more-stable air mass, somewhat outpacing the geometry
of its supportive return-flow plume.

...FL Peninsula...
An ongoing, quasi-linear complex of strong/sporadically severe
thunderstorms -- with embedded LEWP/bow features and mesovortices
locally concentrating the severe threat -- should shift
southeastward across central FL today. Damaging gusts are that main
concern, though a tornado cannot be ruled out. See the remainder of
tornado watch 144 and related mesoscale discussions for the
near-term threat.

The convective band and associated boundary have been progressing
faster and further south/east than suggested by CAMs and most
synoptic guidance. However, the activity is decelerating with
southward extent and becoming somewhat more zonal in alignment, more
parallel to flow aloft, with additional convection expected to train
across the region from the Gulf. Rich low-level moisture, with
surface dew points commonly in the 70s F, will combine with diurnal
heating of the upstream air mass across south-central and southern
FL to boost MLCAPE into the 1500-2500 J/kg range, especially near
the coasts. Meanwhile, stronger vertical mixing inland may stem the
diurnal increase in MLCAPE, but also, should steepen boundary-layer
lapse rates in support of strong-severe gusts.

Favorable deep shear will continue through at least midday, with
45-55-kt effective-shear magnitudes expected. However, a slow
decrease in hodograph size with time in forecast soundings --
related to veering near-surface winds and reduction of flow near 850
mb -- indicates continued general lessening of tornado threat and
low-level convergence from early/mid-afternoon into the evening.
However, at least isolated/marginal severe potential may persist
into tonight with convection along the composite outflow boundary,
where lift will remain maximized.

..Edwards/Broyles.. 04/24/2020
 

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