SPC AC 250057

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0757 PM CDT Sun Oct 24 2021

   Valid 250100Z - 251200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF CENTRAL AND SOUTHERN ILLINOIS INTO CENTRAL AND EASTERN MISSOURI
   AND NORTHERN ARKANSAS...

   ...SUMMARY...
   Scattered severe thunderstorms with damaging wind gusts, large hail
   and a couple of strong tornadoes are likely from parts of the Ozarks
   into the middle Mississippi Valley the remainder of this evening
   into tonight. Isolated damaging gusts and a tornado or two will also
   be possible along the Oregon/Washington coast.

   ...Synopsis...
   A well-defined mid-level trough is progressing eastward toward the
   central MS Valley, and is coupled with a surface low, centered over
   northeastern MO, which is poised to move into the OH Valley
   overnight. A cold front trails the surface low across central MO
   into eastern OK/north-central TX, while a warm front ahead of the
   low gradually lifts northeastward eastern MO into central IL/IN.
   Widespread 70-80F temperatures, coupled with 60-65 F dewpoints and
   overspread by 6+ C/km mid-level lapse rates are contributing to
   adequate buoyancy for continued scattered strong to severe storms
   across the MO Valley into the central MS Valley this evening into
   tonight. 

   Along the Pacific Northwest Coast, a potent mid-level trough
   continues to amplify across the region. Strong kinematic flow fields
   are in place, with 30-50 kts of 925-850 mb flow overlapped by 70-100
   kt flow at 500 mb. Though scant, buoyancy may become adequate enough
   to support a very isolated severe threat along the WA/OR coastline
   with any deep-moist convection that can become established. 

   ...MO Valley into the Mid-MS Valley through tonight...
   Scattered strong to occasionally severe storms (some showing
   transient supercellular structures) are ongoing along and ahead of
   the cold front across central MO into eastern OK and northern TX, as
   well as with a secondary confluence band across eastern MO into
   northern AR. Around 1500 J/kg MLCAPE exists ahead of the cold
   front/south of the warm front, within the LLJ axis from southwest IL
   into AR, where 200-400 m2/s2 effective SRH is present. As such, any
   supercell or embedded rotating line segment that can become
   sustained may pose a tornado/damaging wind threat this evening
   through tonight.

   Strong to occasionally severe line segments have also been
   traversing the warm front across central/northern IL. Though these
   storms will cross the LLJ axis this evening into tonight, the more
   buoyant surface-based airmass has struggled to reach this convection
   thus far. Nonetheless, given the highly sheared, at least marginally
   buoyant environment, a couple damaging gusts and perhaps a tornado
   or two cannot be ruled out through tonight.

   ...OR/WA Coastline...
   While surface temperatures along the WA/OR coastline are barely
   reaching 60F (with dewpoints struggling to exceed the mid 40s F),
   6-7 C/km mid-level lapse rates are overspreading the coastline,
   supporting patchy areas of marginal buoyancy. The aforementioned
   strong kinematic fields will support 50+ kts of effective bulk
   shear/200 m2/s2 effective SRH. As such, a damaging gust and or
   perhaps a brief tornado may accompany any sustained updraft that can
   develop tonight.

   ..Squitieri.. 10/25/2021

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