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.

   ..Edwards/Broyles.. 05/07/2024

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