From Dumas Walker@21:1/175 to All on Tue May 7 08:10:00 2024
ACUS01 KWNS 071250
SWODY1
SPC AC 071249
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 AM CDT Tue May 07 2024
Valid 071300Z - 081200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF INDIANA...OHIO AND NORTHERN/CENTRAL KENTUCKY...
...SUMMARY...
Scattered severe thunderstorms are expected across the Ohio Valley
today. A few tornadoes (some strong), large to very large hail, and severe/damaging winds all appear possible.
...Synopsis...
A mid/upper cyclone, now occluded at low levels, will meander over
the northern Great Plains and fill gradually through the period. As
that occurs, a shortwave trough in its southeastern quadrant over IA
will eject northward across MN and weaken. A trailing shortwave
trough -- apparent in moisture-channel imagery over portions of KS
-- should merge with the trailing portion of the IA perturbation
then pivot across northern MO, southern IA and the DBQ vicinity,
reaching northern IL and Lake Michigan by 00Z. That trough then
should turn eastward through a larger-scale ridge and cross Lower MI
overnight. South of those troughs, a broad fetch of southwest to west-southwest flow aloft -- with minor and mainly convectively
influenced perturbations -- should extend from the southern Plains
to the Ohio Valley.
At the surface, 11Z analysis depicted a surface low near MBG, with
occluded front southeastward to southern IA, becoming a cold front
across western MO, eastern/southern OK, to the TX Permian Basin and southeastern NM. A warm front was drawn across central IL and
southern IN, with secondary warm front/frontogenesis to its north
over central IN and southern OH. The western part of both warm
fronts should consolidate through the day, amid a broader plume of
warm advection over the Ohio Valley. By 00Z, the cold front should
reach central IN, southern IL, the eastern Ozarks, southeastern OK, north-central and central TX, with the TX part becoming stationary.
The front will move northward overnight and become diffuse, amidst a
broad fetch of southerly flow responding to surface cyclogenesis
shifting from southeastern KS to northern OK.
...Ohio Valley and vicinity...
A complex and multi-episode severe threat exists today over the
region. First, an ongoing band of strong/isolated severe
thunderstorms was apparent across portions of IL, southwestward over southeastern MO and northeastern AR. Though favorable moisture and
buoyancy exists in the foregoing warm sector (along and south of the
warm front), height falls aloft and deep-layer lift will be greatest
over the middle and northern parts, near and just south of the warm
front and mainly north of the Ohio Rover. What does not overtake
too much of the warm frontal zone and dissipate in the next few
hours may reintensify as it encounters diurnally destabilizing low
levels, related both to low-level theta-e advection and cloudiness-
restrained surface diabatic heating. At least isolated severe gusts
would be the main concern with any such convection, which should
diminish as it moves over/past eastern IN/western OH while
outrunning already marginally favorable inflow-layer buoyancy.
The more-substantial severe concern exists for thunderstorms forming
this afternoon along/ahead of the cold front, then impinging on a
corridor of favorable heating and warm/moist advection behind the
morning activity. Surface dewpoints should recover into the mid-
upper 60s F, beneath a plume of steepening midlevel lapse rates that
is part of a remnant, somewhat modified EML spreading over the area
of low-level destabilization. Superposition of these processes
should yield peak MLCAPE in the 2000-3000 J/kg range over the
"enhanced" area, narrowing and weakening northward into Lower MI.
Favorable wind profiles are forecast, with effective-shear
magnitudes in the 55-65-kt range and large-enough hodographs to
support 200-400 J/kg effective SRH. To the extent an supercells
that develop can remain relatively discrete, hodographs in the
lowest couple km appear favorable for tornadoes (some possibly
strong). Damaging, large to very large hail also is a concern with
any such supercells. Buoyancy should be even greater with
southwestward extent into steeper midlevel lapse rates and greater boundary-layer moisture of the Mid-South, and also southward over
the Tennessee Valley into AL, but with weaker overall forcing and/or
vertical shear otherwise, coverage and organization of strong-severe
convection are likely to be less.
...Arklatex to north-central and south-central TX...
Isolated severe thunderstorms are possible during mid/late
afternoon. Damaging gusts and large hail would be the main
concerns. The threat over the area is conditional -- more due to
weak lift than thermodynamic considerations. Surface dewpoints
commonly in the 70s F will underlie a deep troposphere and enough
middle-level lapse rates for MLCAPE in the 3500-4500 J/kg range.
Weak low-level winds will constrain hodograph size and boundary-
layer shear. However, enough mid/upper flow remains to support
around 45-55 kt effective-shear magnitudes, yielding a conditional
supercell environment. In the absence of meaningful large-scale
support, and with shallower overall lift near the front/dryline,
convective coverage over this region is more in question and likely
isolated. Additional convection may form overnight in a warm-
advection plume near and southeast of the front, across parts of the
Mid-South to Arklatex regions. Marginal hail and isolated damaging
gusts would be the main concerns.