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
1004 AM CST Sat Dec 13 2025

Valid 131630Z - 141200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

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

...Southeast TX/Southwest LA...
Morning satellite loops confirm northward transport of low-level
moisture into parts of the southern Plains and lower MS Valley. 
This trend will continue this afternoon and evening as a shallow
surface cold front sags southward through the region.  Model
guidance suggests that weak but sufficient instability will develop
after dark from southeast TX into southwest LA to result in a few
pre-frontal thunderstorms.  Shear is weak, and limited CAPE will
preclude organized severe storms.  However, small hail is possible
in the strongest cores tonight.

...FL...
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.

..Hart/Dean.. 12/13/2025

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1111 AM CST Sat Dec 13 2025

Valid 141200Z - 151200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
A few storms are possible across South Florida and the Florida Keys,
as well as the western Gulf Coast tomorrow (Sunday).

...Synopsis...
A pronounced mid-level trough will eject into the Atlantic as
another upper trough approaches the Pacific Northwest tomorrow
(Sunday). Surface high pressure and an associated statically stable
airmass will overspread much of the CONUS east of the Rockies,
limiting thunderstorm development over most locales. The best chance
for any isolated thunderstorm development will be along a surface
cold front. At the start of the period (12Z Sunday), a few
thunderstorms may develop along the cold front across the western
Gulf Coast as the front encounters low-level moisture and moves
offshore. Later in the day, the cold front will encounter a
low-level moisture-driven, marginally unstable airmass across the
southern FL Peninsula/FL Keys, where isolated thunderstorms will
also be possible. 

Across the Pacific Northwest, cooler temperatures aloft (and
accompanying scant buoyancy) will impinge on the shoreline toward
the end of the period (06-12Z Monday morning). While a couple of
lightning flashes may occur during this time frame, the current
thinking is that the overall coverage of lightning will likely be
too sparse to warrant thunder probabilities at this time.

..Squitieri.. 12/13/2025

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1023 AM CST Sat Dec 13 2025

Valid 131700Z - 141200Z

...NO CRITICAL AREAS...

Today's fire weather forecast remains on-track. Please see the
previous discussion below for more information - including the
potential for brief/spotty elevated fire weather conditions across
the central/southern High Plains.

..Elliott.. 12/13/2025

.PREV DISCUSSION... /ISSUED 1124 PM CST Fri Dec 12 2025/

...Synopsis...
The upper trough in the northern Plains/Upper Midwest will amplify
today as it moves toward the Mid-Atlantic/Northeast. This will help
drive colder air into the Plains. Ahead of the colder air, a modest
surface low will develop and evolve southward within the central and
southern High Plains. There will be brief potential for dry/breezy
conditions that may approach elevated criteria locally. Given the
short duration of these conditions and the generally unreceptive
fuels, no highlights are warranted.

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