SPC AC 020559

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Wed May 02 2018

   Valid 021200Z - 031200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST
   KS INTO FAR NORTHWEST MO...

   ...SUMMARY...
   Severe thunderstorms are expected across parts of the southern and
   central Plains into the middle Mississippi Valley today and tonight.
    Swaths of damaging winds, large to very large hail, and a couple of
   tornadoes will be possible.  Isolated to scattered severe storms may
   also develop across parts of the Midwest, with hail and damaging
   winds the primary threat.

   ...Synopsis...
   Upper pattern at the beginning of the period will look much like it
   did on Tuesday with a deep upper trough extending from the Canadian
   Prairie provinces southwestward to an upper low center over the
   Lower CO River Valley and upper ridging over the Lower MS Valley.
   Upper trough is expected to be a bit more progressive Wednesday with
   a lead shortwave trough (and accompanying enhanced mid-level flow)
   ejected into the central Plains during the afternoon. 

   The surface pattern at the beginning of the period will feature a
   low over the Upper Great Lakes with a cold front extending
   southwestward to another low over central KS. Expectation throughout
   the day is for the central KS low to remain largely in place as the
   frontal zone remains stationary. Dryline extending southward from
   the low will sharpen as moisture return persists across the southern
   and central Plains. Forcing for ascent associated with the
   previously mentioned shortwave as well as convergence along the
   dryline provide the impetus for another day of strong to severe
   storms.

   ...Central KS northeastward into the Middle MS Valley...
   Another day of return flow is expected across the region with
   dewpoints likely reaching the mid 60s across central KS by this
   afternoon. This return flow will occur beneath a strong EML
   characterized by mid-level lapse rates at or above 7.5 deg C per km.
   Temperatures across central KS and vicinity are expected to reach
   the low to mid 80s which, when combined with favorable low-level
   moisture and steep mid-level lapse rates will result strong
   instability by the early afternoon. Despite the strong EML,
   convective initiation is possible as early as 18Z as a subtle
   shortwave trough moving through the central/southern High Plains
   begins to provide forcing for ascent. Most probable location for
   initial convective initiation is currently southwest KS and far
   eastern TX/OK Panhandles with initiation then expanding northward
   along the dryline to the triple-point. 

   Convective initiation will occur in a similar area as Tuesday (with
   perhaps slightly more southwestward extent) and the overall
   thermodynamic environment is comparable. However, subtle differences
   in the wind fields will exists with the low-level flow a bit weaker
   and more veered. Additionally, more favorable dewpoints and warmer
   temperatures will result in less convective inhibition. These
   factors as well as slightly stronger forcing for ascent will result
   in a more linear convective evolution, as opposed to the more
   discrete storms experienced Tuesday. Anticipated linear nature of
   the storms lends itself to a higher threat for damaging wind gusts,
   although large to very large hail and a few tornadoes are still
   possible, particularly with initial development and/or along the
   southern flank of the line. 

   Anticipated MCS will likely mature near northeast KS and vicinity
   with the potential for a few significant wind gusts in this area.
   Severe threat will continue farther downstream with the expectation
   that the northern portion of MCS tracks along the frontal zone from
   IA into southern WI and the southern portion moves through central
   MO. 

   ...Far Eastern TX Panhandle....Western OK...
   A more conditional severe threat exists across this region. Numerous
   factors, including the lack of stronger forcing for ascent, only
   weak convergence along the dryline, and slightly cooler temperatures
   than areas farther north (resulting from abundant high cloudiness),
   contribute to the expectation that the strong capping inversion will
   likely inhibit anything but isolated storm development. Given the
   favorable thermodynamics and anticipated discrete storm mode, any
   storm that does develop would have the potential to produce very
   large hail and perhaps a strong tornado.

   ...TX Big Bend northward into north-central TX...
   Afternoon development is possible with the warm, well-mixed
   environment in the TX Big Bend vicinity. Steep lapse rates and
   strong shear support the potential for very large hail with any
   afternoon storms. Additional thunderstorms are possible later into
   the evening as a subtle shortwave trough approach the region.
   Favorable thermodynamics and kinematics will persist, supporting the
   potential for additional severe thunderstorms. Hail would be the
   primary threat will this activity. Expectation is for theses storms
   to track northeastward into north-central TX overnight.

   ...Northeast CO...
   Post-frontal, upslope flow will provide the impetus for a few
   thunderstorms during the afternoon. Steep lapse rates will support
   the potential for hail with the strongest/most persistent updrafts.

   ..Mosier/Leitman/Bentley.. 05/02/2018

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