243
FXUS63 KLOT 122356
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
556 PM CST MON JAN 12 2026
KEY MESSAGES
- AFTER UNSEASONABLY MILD TEMPERATURES TUESDAY/TUESDAY NIGHT,
EXPECT A RETURN TO GENERALLY MUCH COLDER TEMPERATURES
WEDNESDAY THROUGH THE UPCOMING WEEKEND.
- CHANCE OF WIND WHIPPED SNOW SHOWERS/FLURRIES WED MORNING,
MAINLY EASTERN IL AND NORTHWEST INDIANA.
- ACCUMULATING LAKE EFFECT SNOW EXPECTED DOWNWIND OF LAKE
MICHIGAN LATE WEDNESDAY THROUGH THURSDAY MORNING, HIGHEST
CHANCES OVER NORTHEAST PORTER COUNTY AND POINTS EASTWARD.
- UNSETTLED WEATHER PATTERN WILL CONTINUE LATE IN THE WEEK AND
THROUGH THE UPCOMING WEEKEND WITH PERIODS OF GUSTY WINDS AND
OCCASIONAL CHANCES FOR LIGHT SNOW/FLURRIES.
DISCUSSION
ISSUED AT 246 PM CST MON JAN 12 2026
UPPER TROUGH WILL BEGIN DIGGING INTO THE WESTERN/UPPER GREAT
LAKES LATE TONIGHT INTO TUESDAY. LEAD SHORTWAVE TROUGH IS
PROGGED TO MOVE ACROSS THE WESTERN GREAT LAKES LATE TONIGHT INTO
TUESDAY MORNING, RESULTING IN AN INCREASE IN MOSTLY MID-HIGH
LEVEL CLOUDINESS. CERTAINLY CAN'T RULE OUT A FEW SPRINKLES,
MAINLY NORTH OF I-88 LATE TONIGHT INTO EARLY WEDNESDAY MORNING,
BUT GIVEN THE DRY LOW LEVELS OPTED TO KEEP GRIDS DRY.
STRONG SFC LOW ASSOCIATED WITH THIS APPROACHING TROUGH WILL
DEEPEN TO <990MB AS IT TRACKS TO JUST NORTH OF LAKE SUPERIOR BY
MIDDAY TUESDAY. STRONG PRESSURE GRADIENT ASSOCIATED WITH THIS
LOW WILL RESULT IN STRONG AND GUSTY SOUTHWESTERLY WINDS AND
ASSOCIATED WARM AIR ADVECTION TUESDAY. IN THE WAKE OF THE EARLY
MORNING SHORTWAVE, THERE COULD BE SOME BREAKS IN THE
CLOUDINESS/SUNSHINE BY LATE MORNING INTO THE AFTERNOON.
GFS/ECMWF/NAM ARE ALL RUNNING A BIT COOL WITH 2M TEMPS, LIKELY A
RESULT OF THESE MODELS INITIALIZING A BIT OF SNOW COVER STILL.
YOU CAN ACTUALLY SEE THE GRADIENT IN TEMPS TOMORROW LINING UP
WITH WHERE THE MODEL THINKS THERE IS A TRACE TO A HALF INCH OF
SNOW ON THE GROUND. GIVEN THERE IS NO SNOW COVER, FELT
COMFORTABLE GOING WARMER THAN MOST AVAILABLE GUIDANCE FOR HIGH
TEMPS TUESDAY (UPPER 40S-LOWER 50S). IT'S PLAUSIBLE IF WE GET
MORE SUNSHINE THAT TEMPS COULD BE A BIT WARMER. SOUTHWEST WINDS
WILL EASE, BUT LIKELY REMAIN ELEVATED ENOUGH TO KEEP TEMPS
UNSEASONABLY MILD TUESDAY NIGHT, LIKELY NOT FALLING BELOW
FREEZING MOST OF THE NIGHT.
THAT ALL WILL CHANGE ABRUPTLY VERY LATE TUES NIGHT OVER FAR
NORTHERN IL AND ACROSS THE REMAINDER OF THE CWA WEDNESDAY
MORNING AS A STRONG COLD FRONT RIPS THROUGH THE AREA. WHILE LOW
LEVEL LAPSE RATES WILL STEEPEN SUBSTANTIALLY BEHIND THE FRONT,
MOST GUIDANCE SUGGESTS THE CONVECTIVELY UNSTABLE LAYER WILL
REMAIN RATHER SHALLOW, CAPPED OFF A SHARP FRONT INVERSION,
GREATLY LIMITING THE DEPTH OF ANY COLD AIR STRATOCUMULUS AND THE
RESULTANT SNOW SHOWER THREAT. THE ECMWF IS THE LONE MODEL WITH
ANY MEASURABLE QPF AND EVEN FORECAST SOUNDINGS FROM THE ECMWF
AREN'T VERY IMPRESSIVE WITH SHALLOW CONVECTIVE CLOUD DEPTHS THAT
EVENTUALLY COOL SUFFICIENTLY TO CONTAIN ICE NUCLEI. NBM POPS
HAVE TRENDED DOWNWARD AND BARRING ANY SHIFTS IN MODEL GUIDANCE,
WOULD EXPECT THIS TREND TO CONTINUE WITH IT LOOKING MORE LIKE
SNOW FLURRIES AT BEST WEDNESDAY MORNING.
ATTENTION WILL TURN TO THE LAKE EFFECT POTENTIAL INTO THE
INDIANA SNOW BELT REGION LATER WEDNESDAY AND ESPECIALLY
WEDNESDAY NIGHT INTO EARLY THURSDAY MORNING. FAIRLY IMPRESSIVE
LAKE EFFECT PARAMETERS WITH TOP OF THE SYNOPTIC FRONTAL
INVERSION UP TO AROUND 7-8KFT WITH CONVECTIVE CLOUD LAYER WELL
WITHIN THE DGZ. BY WEDNESDAY EVENING, LES SHOULD ORGANIZE INTO A
A STRONG SINGLE BAND WITH THE MILLION DOLLAR QUESTION BEING
WHERE WILL THAT BAND SET UP. SYNOPTIC FLOW WOULD TEND TO FAVOR
LAPORTE COUNTY, BUT IT LOOKS CLOSE FOR ESPECIALLY NORTHEAST
PORTER COUNTY. BEFORE THE MORE INTENSE SINGLE BAND DEVELOPS WED
EVENING, WILL LIKELY SEE LAKE EFFECT SNOW SHOWERS INTO NORTHERN
PORTER COUNTY WITH SOME ACCUMULATIONS. IF MODELS WERE TO TREND A
BIT MORE VEERED WITH THE FLOW, THEN THAT WOULD POTENTIALLY OPEN
THE DOOR TO THE INTENSE SINGLE BAND AND MORE INTENSE SNOWFALL
RATES GETTING INTO NORTHEAST PORTER COUNTY FOR A TIME WEDNESDAY
EVENING. THE MOST LIKELY SCENARIO IS THE HEAVIER SNOWFALL RATES
AND TOTALS WILL END UP JUST EAST OF PORTER COUNTY, SO NO WINTER
STORM WATCH ISSUED AT THIS TIME. WILL BE SOMETHING FOR LATER
SHIFTS TO TAKE ANOTHER LOOK AT.
LONG WAVE TROUGH WILL BECOME ESTABLISHED OVER EASTERN NORTH
AMERICA THROUGH AT LEAST EARLY NEXT WEEK. MEDIUM RANGE MODELS
ARE IN GOOD AGREEMENT ON MULTIPLE STRONG SHORTWAVE TROUGHS
DIGGING DOWN THE SOUTHWESTERN FLANKS OF THE MEAN LONG WAVE
TROUGH IN QUICK SUCCESSION THROUGH THE WEEKEND. MODELS ARE IN
FAIRLY GOOD AGREEMENT ON A SHORTWAVE RACING ACROSS THE UPPER
MIDWEST THURSDAY NIGHT INTO FRIDAY, POTENTIALLY BRINGING A QUICK
HITTING SHOT OF WAA DRIVEN SNOW TO THE AREA THUR NIGHT-FRI
MORNING. THAT WOULD BE FOLLOWED BY A REINFORCING SHOT OF COLD
AIR. BEYOND THAT WAVE, THERE IS SIGNIFICANT SPREAD IN THE MODELS
AND THEIR RESPECTIVE ENSEMBLES IN TIMING ADDITIONAL, POTENTIALLY
POTENT, SHORTWAVES OVER THE WEEKEND INTO EARLY NEXT WEEK. THE
TIMING DIFFERENCES RESULT IN A LOW CONFIDENCE FORECAST WITH
RESPECT TO EXACT TEMPS AND SNOW SHOWER CHANCES. GIVEN THE LOW
CONFIDENCE, NO CHANGES WERE MADE TO NBM. IT IS WORTH NOTING
THAT THERE WILL BE SOME MODEST MODERATION IN TEMPS IN THE WAA
REGIME IN ADVANCE OF THESE INDIVIDUAL WAVES AND MORE
SIGNIFICANTLY THE POTENTIAL FOR BLAST(S) OF BITTERLY COLD AIR IN
THEIR WAKE. PERIODIC BOUTS OF SNOW SHOWERS/FLURRIES AND STRONG
WINDS ARE LIKELY OVER THE WEEKEND INTO EARLY NEXT WEEK AS WELL,
BUT TIMING OF THE TEMPERATURE SWINGS, STRONG WINDS, AND SNOW
SHOWER CHANCES WILL LIKELY NEED TO BE FINE TUNED AS WE GET
CLOSER AND MODEL AGREEMENT INCREASES.
- IZZI
AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 555 PM CST MON JAN 12 2026
- GUSTY WSW WINDS ON TUE WITH OCCASIONAL GUSTS AROUND 30 KT.
- MVFR CIGS MAY DEVELOP TUE EVENING, BUT MORE LIKELY OVERNIGHT.
SW WINDS CONTINUE TO EASE EARLY THIS EVENING WITH GUSTS NEAR
AND UNDER 10 KT EXPECTED FOR MUCH OF THE NIGHT. INCREASING
GUSTINESS IS THEN EXPECTED BY THE PRE-DAWN HOURS AS THE LOW-
LEVEL FLOW STRENGTHENS OVERHEAD. DIURNAL MIXING SHOULD THEN
ALLOW GUSTS IN THE UPPER 20S TO AROUND 30 KT TO OCCUR DURING THE
DAYTIME HOURS TUESDAY WITH WINDS TRENDING MORE WSW AND THEN W.
THE STRONGER GUSTS EASE SOME TOWARD SUNSET BUT REMAIN BREEZY AS
THEY TURN MORE WNW TUESDAY EVENING.
HIGH CLOUDS WILL CONTINUE TO DRIFT SOUTHEAST OF THE AREA THIS
EVENING WITH MOSTLY CLEAR SKIES EXPECTED AT THE TERMINALS FOR
MUCH OF THE OVERNIGHT PERIOD. HIGH CLOUDS WILL THEN STREAM INTO
THE AREA TOWARD THE PRE-DAWN HOURS WITH VARYING CLOUD COVERAGE
(SCT-OVC) EXPECTED AT TIMES THROUGH THE REST OF THE DAYTIME
HOURS. SCT TO BKN LOWER-LEVEL (MVFR) CLOUDS MAY THEN BEGIN TO
DRIFT INTO NORTHERN ILLINOIS TUESDAY EVENING (AND MORE LIKELY
LATE EVENING AND OVERNIGHT). HAVE INTRODUCED A LINE FOR SCT025
BKN050 TO ACCOUNT FOR THIS FOR NOW, BUT IT IS POSSIBLE TEMPO OR
EVEN PREVAILING MVFR CIGS WILL BECOME WARRANTED WITH LATER
UPDATES IF CONFIDENCE INCREASES.
PETR
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 3 AM TO 6 PM CST TUESDAY FOR THE IL
AND IN NEARSHORE WATERS.
GALE WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY NIGHT
FOR THE IL AND IN NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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