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    Day 2 Outlook >
Jun 25, 2024 1300 UTC Day 1 Convective Outlook
Updated: Tue Jun 25 12:49:11 UTC 2024 (Print Version | 20240625 1300Z Day 1 shapefile | 20240625 1300Z Day 1 KML)
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 Forecast Discussion
   SPC AC 251249

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0749 AM CDT Tue Jun 25 2024

   Valid 251300Z - 261200Z


   Damaging wind gusts and large hail are possible across parts of the
   central/southern Great Plains and Midwest, late this afternoon and

   In mid/upper levels, an initially zonal pattern from the northern
   Rockies to the Great Lakes will amplify through the period.  This
   will occur as ridging builds over the northern Rockies ahead of a
   strong synoptic-scale trough that will move ashore in the Northwest
   day 2.  Downstream, a shortwave trough was evident in moisture-
   channel imagery aligned nearly west-east over the southern Canadian
   Prairie Provinces.  The middle/western parts of this trough should
   cross the international border around 00Z, then assume more
   meridional tilt overnight.  By 12Z, the trough should extend across
   portions of Lake Superior, northern WI, southern MN, and
   southeastern SD.  A separate, smaller and weaker perturbation -- now
   apparent over southeastern WY -- should move slowly east-
   southeastward across NE to the TOP/STJ vicinity by the end of the
   period.  Elsewhere, a 500-mb high should strengthen over NM, with an
   MCV from earlier Mexican convection moving northwestward across
   parts of southern/western AZ.

   At the surface, the 11Z analysis showed a low over southwestern WI,
   with warm front southeastward over southern Lake Michigan, then
   southward over western IN, and a cold front across central parts of
   IA/NE.  By 00Z, the cold front should extend from parts of Lower MI
   across central IA to a weak frontal-wave low over eastern NE, then
   southwestward over southwestern KS.  By 12Z, the front should move
   to southern parts of IL/IN, central MO, eastern KS, and southeastern
   CO, with weak low(s) over parts of the lower Missouri Valley region.

   ...Central/northern Plains to Midwest...
   Earlier separate complexes of convection have merged into a lengthy
   corridor of thunderstorms from parts of southern Lower MI across the
   warm front to northern IL.  See SPC Severe Thunderstorm Watch 456
   and related mesoscale discussions for near-term guidance on this
   activity, most of which generally should diminish into late morning
   as it moves into weaker magnitudes of both low-level theta-e and
   mid/upper support.  The trailing/western part may persist into
   midday or early afternoon, as diurnal destabilization and moist
   advection boost buoyancy across eastern parts of the outlook area. 
   The main concern should continue to be damaging gusts, with isolated
   large hail also possible mainly from any relatively discrete cells.

   Though mid/upper support should remain modest over the central
   Plains to mid Mississippi Valley today, with the Canadian shortwave
   trough still well north of the area, weak large-scale lift is
   possible ahead of the smaller WY perturbation as it approaches. 
   Meanwhile, the airmass near the front, and near the western part of
   the outflow boundary from the morning MCS activity, should attain
   strong heating and evapotranspiratively aided surface dewpoints in
   the upper 60s to low 70s F.  By mid/late afternoon, with steep
   midlevel lapse rates, a corridor of 3000-4500 J/kg MLCAPE should
   develop from parts of northern IL across IA and eastern NE, perhaps
   into southern SD.  Lift east and northeast of the surface low, in
   the frontal zone, should contribute further to relatively weak
   MLCINH and convective potential.

   From late afternoon into early evening, favorable parameters should
   be relatively maximized, amid 35-40 kt effective-shear magnitudes. 
   This will support organized multicells, a few supercells, and
   merging/clustering of convection into one or more southward to
   southeastward over the lower Missouri and mid Mississippi Valley
   regions.  With time and upscale organization this evening, an early
   mixed-mode/mixed-hazard threat should evolve toward damaging gusts. 
   Specific areas for development in the high-CAPE corridor still
   appear uncertain due to weak low-level flow and the subtlety of
   associated forcing.  The threat is far from uniform across the
   15%-severe probability area, but mesoscale uncertainties preclude
   finer-scale refinement at this time.  More-isolated post-frontal
   convection may pose a marginal hail/wind threat over parts of the
   Dakotas in post-frontal, but still sufficiently moist/unstable flow
   as well, beneath a strip of ascent aloft that precedes the northern

   ...Southern Plains...
   Ahead of the front, most likely along a surface trough from southern
   KS across northern/western OK to the TX Panhandle, isolated to
   widely scattered thunderstorms are possible late this afternoon
   through early evening.  Isolated severe gusts and hail will be
   possible.  Hot surface temperatures, a deeply well-mixed boundary
   layer, and still enough low-level moisture will remain to support
   uninhibited buoyancy, with MLCAPE in the 1000-2000 J/kg range. 
   Despite veering of winds with height, weak low/middle-level winds
   will dampen vertical shear, except for some strong upper/anvil-level
   flow aiding ventilation high aloft.  Being strongly tied to daytime
   heating, this activity should weaken and diminish considerably after
   about 03Z.

   ..Edwards/Mosier.. 06/25/2024



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