SPC AC 271709

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1209 PM CDT Tue Apr 27 2021

   Valid 281200Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   THE SOUTHERN PLAINS...

   ...SUMMARY...
   Severe thunderstorms are possible from across parts of Oklahoma
   southward into the Texas Hill Country on Wednesday. Large hail,
   damaging gusts and a few tornadoes will be possible with these
   storms. Isolated strong storms also are possible across parts of the
   middle Mississippi Valley to western New York.

   ...Synopsis...

   A southern stream upper shortwave trough moving across northern
   Mexico and the southern Rockies into the adjacent High Plains will
   phase with a deepening northern stream upper shortwave trough over
   the upper/mid-MS Valley on Wednesday. This will result in band of
   enhanced southwesterly flow from the southern Plains into the
   Midwest and lower Great Lakes vicinity. At the surface, a broad warm
   sector will be in place ahead of a cold front shifting southeast
   across the mid-MS/lower-OH Valley, and a dryline extending southward
   near the OK/TX border into western TX. Mid/upper 60s dewpoints will
   exist from the southern Plains into the mid-MS/lower OH Valley with
   more modest dewpoints in the upper 50s to low 60s further
   east/northeast toward western PA/NY. Some areas may see a few rounds
   of thunderstorms (some strong), but a more focus severe threat is
   expected to develop across parts of the southern Plains during the
   afternoon/evening.

   ...Southern Plains...

   Clusters of thunderstorms are likely to be ongoing Wednesday morning
   from parts of MO into OK and possibly TX. This activity should
   develop northeastward through the morning and allow for some airmass
   recovery across southwest OK into northwest TX. Forecast guidance
   continues to vary with regards to the exact position and strength of
   a surface low in the vicinity of northwest TX. Nevertheless, the low
   and dryline/cold front should serve as a focus for afternoon
   thunderstorm development. Midlevel lapse rates will be modest, but
   sufficient and rich boundary layer moisture will further contribute
   to MLCAPE around 1500-2000 J/kg amid supercell wind profiles. Large
   hail and damaging winds will therefore be possible with this
   activity. Furthermore, backed low level winds in the vicinity of the
   triple point will result in a local maximum in tornado potential.

   Further south, stronger heating is expected along the dryline across
   western TX. Convection is expected to develop in a deeply-mixed
   boundary layer over the higher terrain of Mexico and shift eastward
   across the Rio Grande into the Texas Hill Country during the
   afternoon/evening. Elongated hodographs appear favorable for
   supercells capable of producing very large hail (some greater than
   2.5 inches in diameter). Additionally temperature-dewpoint spreads
   of around 20-25 degrees and somewhat higher-based convection could
   promote stronger downdrafts and damaging winds also appear likely.

   ...Southeast MO/Lower OH Valley...

   Forecast guidance continues to be uncertain regarding severe
   potential across this area. Morning convection will likely have some
   influence over how much destabilization occurs across parts of
   southern MO. Furthermore, poor midlevel lapse rates will hinder
   greater instability and storm organization. Nevertheless, 30-40 kt
   midlevel southwesterly flow will exist over the region, with at
   least some backed southerly winds ahead of the front and weak
   instability. Some guidance suggests some forward-propagating
   clusters could develop and result in some locally strong wind gust
   potential. However, deep layer flow mostly parallel to the cold
   front also could result in storms becoming undercut by outflows or
   the front itself. Nevertheless, a narrow corridor of conditional
   severe potential may exist from parts of southeast MO/far northwest
   AR into western KY where strong gusts and perhaps a tornado could
   occur.

   ...OH into western NY...

   Strong west/southwesterly flow will overspread modest boundary layer
   moisture amid midlevel lapse rates around 7 C/km. Ample surface
   heating will result in steepening low level lapse rates by early
   afternoon as thunderstorms develop. Moderate shear and MLCAPE values
   around 1000-1500 J/kg should support a few strong cells capable of
   strong gusts and perhaps some hail.

   ..Leitman.. 04/27/2021

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z