Mesoscale Discussion 2258
NWS Storm Prediction Center Norman OK
0943 AM CST Sat Dec 13 2025

Areas affected...far southeast IA...central IL...amd west-central IN

Concerning...Heavy snow 

Valid 131543Z - 131945Z

SUMMARY...A band of moderate to heavy snow with bursts of rates
around 1 inch per hour expected through around 20Z.

DISCUSSION...The latest mosaic radar data and surface observations
depict a swath of moderate to locally heavy snow spreading eastward
across eastern IA, central IL, and western IN. As strengthening DCVA
preceding an embedded midlevel perturbation (evident in water-vapor
imagery) continues spreading eastward into IL over the next couple
hours, an uptick in the coverage of heavy snowfall rates can be
expected. This increase should generally focus in an east/west
corridor extending from southeast IA across central IL into
west-central IN through around 20Z -- when the aforementioned lift
overspreads a cold, deeply saturated profile with a favorable
isothermal layer below 700 mb for aggregation. Snowfall rates of
around 1 inch per hour are expected beneath the core of the heaviest
banding, with bursts of locally higher rates possible.

..Weinman.. 12/13/2025

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...IWX...IND...LOT...ILX...DVN...

LAT...LON   39398761 39728927 40099058 40519152 40969185 41349183
            41669154 41669096 41338964 40968807 40738664 40418605
            39778602 39338653 39398761 

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0640 AM CST Sat Dec 13 2025

Valid 131300Z - 141200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected today or tonight.

...Discussion...
Large-scale trough amplification will occur over the Midwest/East
through tonight, with expanding surface high pressure across the
Plains and Midwest in the wake of a cold front progressing
south-southeastward toward the Lower Mississippi Valley and Gulf
Coast by late tonight and early Sunday. Preceding the front, weak
warm/moist advection should allow for northeastward-expanding
thunderstorm development across southeast Texas and Louisiana today,
with potential persisting until the frontal passage tonight. 

A low-latitude disturbance crossing the Gulf and a northward
moisture flux ahead of it will contribute to thunderstorm potential
across the Florida Keys/Florida Straits today, and also across the
southern Florida Peninsula tonight. Severe thunderstorms are
unlikely with these scenarios.

..Guyer/Lyons.. 12/13/2025