SPC AC 271256

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0756 AM CDT Sat Apr 27 2024

   Valid 271300Z - 281200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT
   FOR OK...NORTH TX...SOUTHEAST KS AND EXTREME SOUTHWEST MO...

   ...SUMMARY...
   Severe thunderstorms are likely today and tonight across the
   southern and central Plains into the lower to mid Missouri Valley.
   The most numerous/intense storms are expected from north Texas into
   Oklahoma and southeast Kansas, where strong tornadoes, very large
   hail of 2-3 inches in diameter and damaging winds of 60-70 mph are
   all possible.

   ...A regional severe-weather outbreak is expected from north TX
   across OK into KS with strong tornadoes, very large hail and
   damaging winds all part of a long-duration threat...

   ...OK/KS/north TX through tonight...
   A pronounced midlevel trough over the Four Corners will move
   eastward today and then begin to eject northeastward tonight over
   the central/southern High Plains.  This synoptic pattern will
   maintain a lee cyclone in southeast CO and a dryline arcing
   southeastward and then southward close to the western OK border. 
   Farther north, a stalling baroclinic zone will move slowly northward
   into northern KS today and central IA by this evening.
   A broad, unstable warm sector with boundary-layer dewpoints of 65-70
   F will support multiple rounds of severe/tornadic storms through the
   period, both along the synoptic boundaries and in parts of the open
   warm sector for OK/KS.

   The initial severe/tornado threat has already begun near Caprock
   from Lubbock to Childress as an embedded jet streak (evident as the
   fast-moving cloud streak over west TX) begins to interact with the
   northwest edge of the richer low-level moisture.  Despite the
   unusually early start, there will be the potential for embedded
   supercells capable of all hazards as the storms overspread
   western/northern OK into southern KS through midday.  An outflow
   boundary and/or differential heating corridor is likely in the
   immediate wake of these morning storms from southern KS into north
   central and southwest OK.  Additional thunderstorm development is
   likely by early-mid afternoon along this zone and the dryline to the
   south into TX, and storms will spread generally northeastward toward
   southern/central OK and southeast KS.  A moist boundary layer,
   MLCAPE of 2500-3500 J/kg and lengthening/enlarging hodographs with
   time (as a mass response to the approaching shortwave trough) will
   become more favorable for tornadic supercells, including the
   potential for long-track EF2-EF3+ tornadoes.  The significant
   tornado threat will be greatest if semi-discrete supercells can be
   maintained well into the afternoon/evening.  Very large hail up to 3
   inches in diameter can also be expected with the more intense
   supercells.

   The storm evolution has the potential to be a bit messy with
   multiple training/conjoined supercells, posing a relatively
   long-duration and repeat threat to areas within the training storm
   corridors across the central third of OK.  Damaging winds will
   become more probable with storm clustering, and there will likely be
   upscale growth into a larger QLCS this evening into tonight as the
   primary shortwave trough approaches from the west.  The potential
   for tornadoes with embedded circulation will continue into the
   overnight hours, along with damaging winds.

   ...East central CO/far western KS this afternoon/evening...
   Near the lee cyclone and a stalled front, thunderstorm development
   is expected by early afternoon in a small cluster/arc across east
   central CO.  Despite boundary-layer dewpoints only in the 40s, cold
   midlevel temperatures and steep lapse rates will contribute to
   surface-based CAPE up to 1000 J/kg.  Relatively large, curved
   hodographs will favor supercells capable of producing a few
   tornadoes and large hail, as well as damaging gusts once any upscale
   growth into a line segment occurs.

   ...Northern IL/southeast WI/Lower MI this afternoon/evening...
   A midlevel trough and associated surface cyclone will move
   northeastward today from the upper MS Valley to the upper Great
   Lakes.  The stronger forcing for ascent has already moved northeast
   of the surface warm sector, so storm development in this corridor
   will likely be later this afternoon/evening in association with
   low-level ascent along the stalling front across WI/lower MI.  A
   band of storms is expected along the front, and other convection
   could eventually spread into northern IL from eastern IA.  Forecast
   profiles along and south of the front show sufficient hodograph
   length/deep-layer shear for organized line segments and some
   embedded supercells capable of producing damaging gusts and possibly
   a tornado or two.  Isolated large hail will also be possible, given
   some potential for embedded supercells within the northeast extent
   of the 7-8 C/km midlevel lapse rates.

   ..Thompson/Hart.. 04/27/2024

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z