SPC AC 111959

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0259 PM CDT Wed May 11 2022

   Valid 112000Z - 121200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN SD
   ACROSS CENTRAL MN INTO WEST-CENTRAL WI...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   SOUTHERN HIGH PLAINS...

   ...SUMMARY...
   Severe thunderstorms are expected this afternoon/evening over the
   north-central states.  Very large hail, wind, and a threat for
   tornadoes is expected.  Additionally, widely scattered severe
   thunderstorms are anticipated across the southern High Plains.
   Wind/hail are the primary threats.

   ..Discussion...
   Only change this outlook update is to reduce probabilities over
   parts of eastern NE and IA to the latitudinal south of the MCV over
   the mid MO Valley.  Otherwise, the forecast remains unchanged.

   ..Smith.. 05/11/2022

   .PREV DISCUSSION... /ISSUED 1126 AM CDT Wed May 11 2022/

   ...Synopsis...
   Expansive upper ridging currently extended from eastern Mexico
   through the Upper Great Lakes is expected to amplify throughout the
   day today. This amplification will occur as a shortwave trough
   embedded within the western CONUS mean troughing moves eastward
   towards the central Rockies and a large cyclone retrogrades
   westward/southwestward off the Atlantic Coast. 

   Despite the presence of these large-scale features, the severe
   weather potential will be driven primarily by low-level and/or
   mesoscale features today, most prominently the convectively induced
   vorticity maximum moving northeastward out of KS. Severe
   thunderstorm development is anticipated as this vorticity maximum
   moves into the Mid MO Valley and Upper Midwest this afternoon and
   evening. Severe thunderstorms are also possible this afternoon and
   evening across the southern High Plains along the dryline and over
   the northern High Plains later this evening and overnight.

   ...Mid MO Valley into the Upper Midwest...
   A reservoir of 70 dewpoints is already in place from northeast
   KS/southeast NE across southern IA and into southern WI. Mid 60s
   dewpoints exist just north of this region. As the warm front lifts
   northward, expectation is for this low-level moisture to
   correspondingly advect northward/northwestward throughout the day.
   By the early afternoon, upper 60s dewpoints are expected to cover
   into southern MN and much of WI, with 70s dewpoints over eastern NE
   and much of IA. 

   Steep mid-level lapse rates (sampled well by the 12Z OAX sounding)
   coupled with this abundant low-level moisture will result in a very
   unstable air mass downstream of the mesoscale convective vortex
   currently over KS. Strong heating will remove any convective
   inhibition and the expectation is for thunderstorm initiation across
   eastern NE early this afternoon as the leading edge of the MCV. An
   initially discrete mode is probable, with shear profiles supportive
   of supercells, even though some mid-level southeasterly flow around
   the MCV (as noted on the UEX VAD) does cast some uncertainty towards
   overall storm structure. Even so, strong buoyancy will support
   intense updrafts capable of large to very large hail and strong
   water loaded downbursts. Low-level flow is also sufficient for
   tornadogenesis, particularly if the southeasterly mid-level flow
   around the MCV turns more southerly with time. Upscale growth also
   appears probable after the initially discrete mode, with the
   orientation of the line perpendicular to the vertical shear vector.
   This results in the potential for some significant wind gusts over
   MN.

   ...Southern High Plains...
   Thunderstorms are expected to develop along the dryline this
   afternoon as the air mass destabilizes amid strong heating and
   modest low-level moisture. Mid to upper level flow will be rather
   modest, but enough directional shear should exist for some updraft
   organization. Higher dewpoints and buoyancy will exist across
   southern portions of the region, contributing to higher potential
   for all severe hazards, particularly very large hail.

   ...Southeast MT/Eastern WY into the Northern Plains...
   Large-scale ascent will increase this evening and overnight across
   the region, as the strong shortwave trough pivots out of the Great
   Basin and approaches. At the same time, associated mid-level
   moistening will help promote elevated thunderstorm development
   across southeast MT and eastern WY. Though buoyancy will be meager
   (MUCAPE generally 300-800 J/kg), favorable deep shear
   (effective-shear magnitudes around 50-65 kt) will favor supercell
   potential, with large hail as the primary threat.

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