SPC AC 201243

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0743 AM CDT Fri Sep 20 2024

   Valid 201300Z - 211200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTHWEST
   LOWER MICHIGAN INTO PARTS OF ILLINOIS...INDIANA...AND SOUTHEAST
   MISSOURI...AND OVER PARTS OF THE CENTRAL PLAINS...

   ...SUMMARY...
   Isolated strong to severe thunderstorms are possible during the late
   afternoon over parts of southwest Lower Michigan, Illinois, Indiana,
   and southeast Missouri. Isolated strong to severe storms are also
   possible across parts of the south-central Plains.

   ...Synopsis...
   Shortwave trough currently moving through WI and Upper MI will
   continue eastward through the Upper Great Lakes region today.
   Another shortwave trough will follow quickly in its wake,
   progressing across Alberta, Saskatchewan, and Manitoba, and adjacent
   portions of MT and the northern Plains this evening and overnight.
   Father south, a deep upper low with seasonably cold mid-level
   temperatures will move from southern CA into AZ. Progression of this
   low will dampen the northwestern periphery of the upper ridging
   centered over TX. 

   A surface low attendant to this WI/Upper MI shortwave trough is
   currently near the IA/WI/IL border intersection, with weak cold
   front extending southwestward from this low to another subtle
   surface low over the central OK/KS border. Surface troughing
   continues southwestward from this secondary low, but this portion of
   the boundary has taken on more warm-front-like characteristics over
   the past several hours (evidenced by the dewpoint increase of 3-4
   deg F over the past 3 hours across the eastern TX/OK Panhandle).
   Enhanced westerly/southwesterly flow aloft attendant to both the
   central Canada/MT shortwave trough and CA upper low will contribute
   to sharpening surface lee troughing throughout the day and into this
   evening.

   ...Central Plains...
   Low-level moisture is expected to advect northward/northwestward
   throughout the day as Thursday's cold front returns northward as a
   warm front. As a result, low to mid 60s dewpoints will likely be in
   place across south-central/southeast KS during the late afternoon.
   Dewpoints will likely be in upper 50s farther west in southwest KS,
   with notably drier conditions across the adjacent TX/OK Panhandles
   where downsloping southwesterly surface winds are likely. 

   Southwesterly flow aloft ahead of the approaching upper low will
   advect steep mid-level lapse rates northeastward through the
   southern High Plains into western portions of the central Plains.
   Modest buoyancy is anticipated during the late afternoon where these
   lapse rates overlay the more favorable low-level moisture across
   southern KS. Limited large-scale ascent and low-level confluence
   near the warm front is anticipated over this region as well, with
   isolated to widely scattered high-based thunderstorm anticipated.
   Vertical shear will be modest, but still strong enough for
   persist/organized storm structures, and the potential for some
   strong gusts with the more robust storms. Some isolated hail is also
   possible over south-central KS where buoyancy is maximized.  

   Low-level moisture will continue advection northward during the
   evening and overnight, with a strengthening low-level jet
   anticipated as well. Consequently, additional thunderstorm
   development is expected after 04Z over northeast KS and adjacent far
   southeast NE and northwest MO. Isolated hail is possible with the
   strongest storms.

   ...Southwestern Lower MI into IN, IL, and southeast MO...
   Upper 60s to low 70s dewpoints are expected from southwest Lower MI
   southwestward across western IN, southern IL, and southeast MO.
   Daytime heating of this moist low-level air mass will yield a
   moderately unstable and uncapped air mass ahead of the approaching
   front, and thunderstorm development is anticipated as the front
   interacts with this airmass. Moderate vertical shear will be in
   place, but poor lapse rates and notable mid-level dry air could make
   updraft maintenance difficult. As such, a more multicellular storm
   mode is anticipated. Highest storm coverage is expected over
   southwest Lower MI and western IN, with warm mid-level temperatures
   likely limiting coverage across southern IL and southeast MO.
   Locally strong gusts will be the primary severe risk, with isolated,
   marginally severe hail possible as well.

   ..Mosier/Broyles.. 09/20/2024

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

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