SPC AC 231956

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0256 PM CDT Tue Apr 23 2024

   Valid 232000Z - 241200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHWEST
   TEXAS...

   ...SUMMARY...
   Isolated severe thunderstorms capable of producing large hail
   (potentially 2+ inch diameter) and gusts to 65 mph will be possible
   this afternoon and evening across northwest Texas.

   ...20Z Update...
   Overall forecast outlined in the previous discussion (appended
   below) remains valid. As mentioned in recently issued MCD 506, a
   supercell or two should develop across a portion of western North
   Texas through late afternoon, with large hail of 1.5 to 2.5 inches
   in diameter and localized severe gusts of 60-70 mph possible. An
   isolated storm or two is also possible farther south in the Texas
   Trans Pecos vicinity. Marginally severe hail (i.e. around 1" in
   diameter) and damaging gusts are possible here as well.

   Farther north, isolated thunderstorms are still anticipated from
   northern IL into Lower MI ahead of an approaching shortwave trough
   and associated cold front. A few strong to severe storms are
   possible with small to marginally severe hail and damaging winds as
   the primary hazards (as mentioned in recently issued MCD 507).

   ...Early tomorrow morning from TX Panhandle into
   north-central/central OK...
   Elevated thunderstorms may develop from the northeast TX/eastern OK
   Panhandles into central/north-central OK within the warm-air
   advection regime along the northeastern edge of the returning
   low-level moisture. Steep mid-level lapse rates and favorable
   cloud-bearing layer shear could support an isolated instance or two
   of hail with initial development. However, severe coverage is
   currently expected to remain less than 5%, precluding the
   introduction of any outlook areas.

   ..Mosier.. 04/23/2024

   .PREV DISCUSSION... /ISSUED 1123 AM CDT Tue Apr 23 2024/

   ...Northwest TX...
   Visible satellite imagery and surface analysis this morning indicate
   the initial stage of moisture return is occurring across the
   southern Great Plains in the wake of a frontal intrusion into the
   Gulf a few days ago.  A mid-level ridge will increasingly become
   established across the central/southern Rockies and adjacent High
   Plains as a Great Lakes disturbance gradually becomes more displaced
   from the region.  An associated cold front will move southward
   across KS/OK before eventually stalling tonight across southeast OK
   and northwest TX.  Weak lee cyclogenesis will aid in maintaining a
   southerly low-level fetch across central into west TX as strong
   heating results in a sharpening dryline by late afternoon.  Isolated
   thunderstorm development will be most probable near the triple point
   20-22Z.  Steep lapse rates coupled with adequate moisture (1500-2000
   J/kg MLCAPE) and veering flow beneath moderate westerlies, will
   support an initial supercell mode.  Isolated very large hail of
   2-2.5 inches in diameter will be the main threat, along with a few
   55-65 mph gusts.

   ...Northern IL/southeast WI/Lower MI late this afternoon/evening...
   Have not changed the existing outlook for this region due primarily
   to consistency in model data and the forecast conceptual model not
   deviating.  Water-vapor imagery this morning shows a mid-level
   trough over the Upper Midwest and this will continue southeast into
   the central Great Lakes by mid evening.  An associated surface
   trough will likewise move southeastward, and this trough will be
   preceded by a band of rain with minimal buoyancy.  Behind the rain
   band, surface heating with steepening low-level lapse rates and
   cooling midlevel temperatures will support weak surface-based
   buoyancy just ahead of a secondary frontal surge.  Some low-topped
   convection will be possible late this afternoon through late evening
   from northern IL/southeast WI into Lower MI.  The stronger storms
   could yield a localized marginal hail/damaging wind threat.

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