SPC AC 152135

   Day 1 Convective Outlook AMEND 1
   NWS Storm Prediction Center Norman OK
   0435 PM CDT Sun May 15 2022

   Valid 152130Z - 161200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN
   OKLAHOMA INTO WESTERN ARKANSAS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM OKLAHOMA TO
   INDIANA AND FROM NORTHEAST OREGON INTO IDAHO...

   AMENDED TO UPDATE LINES

   ...SUMMARY...
   Scattered to numerous severe storms with swaths of wind damage, very
   large hail, and a couple brief tornadoes remain possible through
   evening from easern Oklahoma into Arkansas. Other isolated severe
   storms will be possible later this afternoon across the interior
   Pacific Northwest.

   A primary cluster of storms continues to develop south across AR,
   with damaging winds and hail likely. Other cells with hail persist
   north of the outflow across southeast KS. Probabilities have been
   reduced in the wake of this activity across MO.

   Elsewhere, storms are forming along the front in IL, with a plume of
   instability to the east. Other cells may rejuvenate across southeast
   MO where outflow is enhanced. See mesoscale discussion 769.

   To the west, heating continues over OK, with a reservoir of strong
   instability across eastern OK.  Midday soundings as well as
   objective analysis indicate MLCAPE in excess of 3000 J/kg with steep
   lapse rates aloft. This will clearly favor vigorous convection
   developing along the outflow boundary and ahead of the dryline now
   into central OK. It is unclear whether storms will affect the OKC
   area given the drying, but an unstable air mass remains with hot
   temperatures and a boundary approaching from the north. As such,
   will maintain a conditional Slight here.

   ..Jewell.. 05/15/2022

   .PREV DISCUSSION... /ISSUED 1124 AM CDT Sun May 15 2022/

   ...Ozark Plateau to the Lower OH/MS/Red River Valleys...
   Several clusters are ongoing across eastern KS and western MO, with
   the leading cluster in west-central to southwest MO having a
   reported history of sporadic wind and hail. With pronounced
   boundary-layer heating occurring downstream, further intensification
   is expected to the east-southeast as an MCV shifts towards the
   confluence of the MS/OH rivers. Damaging winds and a brief tornado
   or two will be the primary hazard in this regime.

   Farther south and southwest, low 70s surface dew points beneath the
   eastern plume of a stout elevated mixed layer over OK/TX, should
   yield a very unstable air mass with MLCAPE of 3000-4000 J/kg by
   mid-afternoon. Both warm-advection driven activity south of the MCV
   track, as well as regenerative development along and behind the
   trailing outflow will support supercells embedded within emerging
   south-southeast tracking clusters. Most guidance has become better
   aligned in suggesting multiple bowing segments within the broader
   northwest flow regime across eastern OK/western AR towards the Lower
   Red River Valley mainly during the late afternoon and early evening.
   Overall setup should support scattered swaths of golfball to
   baseball size hail in semi-discrete supercells, and 60-80 mph
   damaging winds within embedded bows. Some form of the MCSs should
   make it as far east as the Lower OH Valley and as far south as the
   Lower MS Valley and Ark-La-Tex, though the damaging wind threat will
   be diminishing later this evening.

   ...Interior Pacific Northwest/northern Rockies...
   A compact shortwave trough now off the OR/WA coast will move
   northeast into southern British Columbia by evening. Heating of
   boundary-layer dewpoints from the upper 40s to lower 50s and
   increasing ascent with the approaching shortwave trough/front will
   support scattered thunderstorm development this afternoon across
   northeast OR. Though buoyancy will be weak with MLCAPE of 500-750
   J/kg, strengthening wind profiles/deep-layer shear will support the
   potential for organized convection, including a few supercells
   and/or short line segments with an attendant threat for large hail,
   damaging winds, and perhaps a tornado. Convection should eventually
   weaken in the ID Panhandle vicinity later this evening. 

   ...Mid-Atlantic/Northeast...
   A diffuse surface trough should remain anchored from central NY
   southward in the lee of the Appalachians. This should help focus
   scattered thunderstorm development this afternoon, and a few of the
   storms could produce strong outflow winds and minor damage, along
   with marginally severe hail in an environment characterized by weak
   vertical shear and modest buoyancy with MLCAPE of 500-1500 J/kg.

   ...Eastern FL Peninsula...
   Downstream of a low-amplitude upper trough in the eastern Gulf,
   adequate vertical deep-layer shear will exist for a threat of
   marginally severe hail and localized damaging winds amid isolated to
   scattered thunderstorms this afternoon.

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