342
FXUS63 KLOT 151204
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
604 AM CST THU JAN 15 2026
KEY MESSAGES
- AN INTENSE LAKE EFFECT SNOW BAND WILL RETROGRADE WEST AND MAKE
A VERY CLOSE PASS AT NORTHEASTERN PORTER COUNTY THIS MORNING.
WILL BE EXTENDING THE WINTER STORM WARNING UNTIL 12 PM TO
ACCOUNT FOR POTENTIAL 2-3" HOUR RATES AFFECTING NORTHEAST
PORTER UNTIL MID TO LATE MORNING BEFORE THE BAND SHIFTS EAST.
- ACCUMULATING SNOW IS EXPECTED TONIGHT, LIKELY RESULTING IN
HAZARDOUS TRAVEL CONDITIONS.
- THURSDAY NIGHT SYSTEM WILL BE JUST ONE OF MANY CLIPPER-LIKE
SYSTEMS RIDING THE NORTHWEST FLOW ACROSS THE REGION BRINGING
OCCASIONAL CHANCES FOR SNOW, EACH FOLLOWED BY VERY COLD AND
WINDY CONDITIONS. BITTERLY COLD CONDITIONS ARE POSSIBLE SUNDAY
NIGHT THROUGH EARLY TUESDAY.
DISCUSSION
ISSUED AT 358 AM CST THU JAN 15 2026
THROUGH FRIDAY:
PORTER COUNTY LAKE EFFECT SNOW THIS MORNING:
THE LAKE EFFECT SNOW OVERNIGHT HAS BEEN A STREAM OF MULTI-
CELLULAR/MULT-BANDED LIGHT TO OCCASIONALLY MODERATE SNOW. WE'RE
CLOSELY MONITORING THE ANTICIPATED WESTWARD PROGRESSION OF THE
INTENSE BAND THAT HAS BEEN IMPACTING SOUTHWEST LOWER MICHIGAN
AND INTERIOR NORTHERN INDIANA. THE HRRR AND RAP (AND 00Z WRF-ARW
LAST NIGHT HAVE DEPICTED THE MOST AGGRESSIVELY FAR WEST SHIFT OF
THE INTENSE BAND. THESE MODELS HAVE BEEN A GENERALLY BETTER
OBSERVATIONAL MATCH FOR WINDS ACROSS WESTERN LOWER MICHIGAN, VS.
FARTHER EAST GUIDANCE SUCH AS THE NAM AND NAMNEST. IT APPEARS
THE CLEARING AND COLDER CONDITIONS FROM MUSKEGON TO BENTON
HARBOR HAVE BEEN KEY IN TERMS OF AIDING A WESTWARD SHIFT IN THE
LAKE INDUCED CONVERGENCE AXIS.
WITH THE ABOVE BEING SAID, THERE HAS BEEN A RECENT SLIGHT RUN TO
RUN SHIFT BACK A BIT EAST WITH THE DEPICTION OF THE BAND ON THE
HRRR (TO A LESSER EXTENT WITH THE RAP). THIS WILL BE ESSENTIALLY
A NOWCAST SITUATION WITH RESPECT TO INTENSE SNOWFALL RATES (UP
TO 2-3"/HOUR) AND HIGHER END (DANGEROUS) TRAVEL IMPACTS REACHING
INTO NORTHEASTERN PORTER COUNTY OR STAYING JUST EAST OF THE
PORTER-LAPORTE LINE. WITH THE SLOWER WESTWARD PROGRESS OF THE
BAND TO THIS POINT AND HEAVIEST SNOW NOT OCCURRING UNTIL AFTER 6
AM THEN FINALLY SHIFTING EAST 10-11 AM, OPTED TO PROACTIVELY
EXTEND THE WINTER STORM WARNING TO NOON TODAY. SHOULD THE
HEAVIER SNOW FAIL TO PUSH INTO NORTHEASTERN PORTER, WE'LL BE
ABLE TO CANCEL THE WARNING EARLY. ANTICIPATE SIGNIFICANT
VARIABILITY OVER SHORT DISTANCES COMMON IN LAKE EFFECT SNOW.
CASTRO
THIS AFTERNOON THROUGH FRIDAY:
FOCUS DURING THE REMAINDER OF THE SHORT TERM FORECAST PERIOD IS
ON THE POTENTIAL FOR ACCUMULATING SNOW TONIGHT INTO EARLY
FRIDAY, IN ASSOCIATION WITH A DIGGING SHORT- WAVE CURRENTLY
CROSS THE CANADIAN ROCKIES. STRONG LOW- LEVEL WARM ADVECTION AND
ASSOCIATED ISENTROPIC ASCENT DEVELOPS INTO THE REGION THIS
AFTERNOON AHEAD OF THE APPROACHING WAVE. INCREASING
ASCENT/COOLING LEADS TO MID-LEVEL SATURATION DEVELOPING ACROSS
FAR NORTH/NORTHWEST IL PRIOR TO SUNSET, AND WHILE DRY LOW-LEVELS
WILL TAKE A LITTLE LONGER TO MOISTEN, LIGHT SNOW OR FLURRIES
MAY DEVELOP AS EARLY AS 4-5 PM. STRONGEST FORCING AND DEEP
SATURATION APPEARS FOCUSED ON THE EVENING HOURS, WITH A FEW HOUR
PERIOD OF ACCUMULATING SNOW THROUGH MIDNIGHT OR SO (A LITTLE
LATER FARTHER EAST INTO NORTHWEST IN). NOTED IN RECENT GUIDANCE
HOWEVER, IS A TREND TOWARD MID-LEVEL DRYING AND EVEN POTENTIALLY
THE LOSS OF ICE NUCLEI BEHIND THE WARM ADVECTION WING FOR A
TIME AFTER MIDNIGHT TO VARYING DEGREES BETWEEN VARIOUS MODELS.
THIS WOULD APPEAR TO LIMIT THE DURATION OF BETTER SNOW
ACCUMULATION TO THE EVENING HOURS WITH A TRANSITION TO POOR
QUALITY/LOWER SLRS OVERNIGHT, OR IN SOME GUIDANCE EVEN
POTENTIALLY A CHANGE OVER TO FREEZING DRIZZLE FOR A TIME.
NEEDLESS TO SAY THIS LOWERS CONFIDENCE IN SNOW AMOUNTS
(GENERALLY AROUND AN INCH MOST AREAS WITH CURRENT GUIDANCE).
HAVE NOT INCLUDED ANY FREEZING DRIZZLE MENTION AT THIS TIME WITH
INCONSISTENCIES IN GUIDANCE, BUT THIS WILL NEED TO BE ASSESSED
FURTHER TODAY WITH NEW MODEL DATA.
MOISTURE DEPTH DOES INCREASE FRIDAY MORNING AS THE MAIN VORT
ROTATES OVERHEAD, THOUGH THERE REMAINS SPREAD IN GUIDANCE EVEN
AT 30 HOURS OUT IN JUST LONG IT PERSISTS. CONTINUED COOLING OF
THE COLUMN AND STEEPENING OF LAPSE RATES DOES LOOK TO SUPPORT A
PERIOD OF SNOW OR SNOW SHOWERS DURING THE DAY FRIDAY WITH SOME
ADDITIONAL ACCUMULATION POTENTIAL ESPECIALLY DURING THE MORNING,
AFTER WHICH THE MID-LEVEL VORT AXIS MOVES EAST.
TEMPERATURES WILL REMAIN BELOW AVERAGE TODAY IN THE WAKE OF
WEDNESDAY'S COLD FRONT, GENERALLY IN THE MID-20S BY THIS
AFTERNOON. TEMPERATURES SHOULD SLOWLY RISE TONIGHT AFTER A BRIEF
EVENING DIP AS BREEZY SOUTH-SOUTHWEST WINDS DEVELOP. FRIDAY
LOOKS TO BE THE MILDEST OF THE NEXT SEVERAL DAYS, WITH HIGHS
WARMING ABOVE FREEZING IN THE MID-30S.
RATZER
FRIDAY NIGHT THROUGH WEDNESDAY:
IN THE WAKE OF THE NEXT ARCTIC FRONT PASSAGE FRIDAY EVENING,
SNOW SHOWERS AND/OR FLURRIES WILL BE POSSIBLE REALLY AT ANY
TIME THROUGH SATURDAY EVENING AS THE COLUMN IS PROGGED TO BE
FIRMLY WITHIN THE DGZ. THIS LOOKS LIKE A "LEAKY STRATUS" SETUP,
WITH PASSING SHORT-WAVE IMPULSES INVIGORATING SNOW SHOWER
ACTIVITY, BUT ALSO LENDING LOWER PREDICTABILITY TO WHERE AND
WHEN ACCUMULATIONS MAY CAUSE SOME TRAVEL IMPACTS (CONSIDERING
THE WELL BELOW FREEZING TEMPS). TEMPERATURES MAY END UP
FLATLINING AT BEST ON SATURDAY WITH BLUSTERY WESTERLY WINDS
KEEPING WIND CHILLS IN THE -5 TO +5 RANGE.
SIGNS ARE POINTING TO A SHORT BREAK OVERNIGHT SATURDAY NIGHT
INTO SUNDAY WITH BREEZY SOUTHWESTERLY "WARM" ADVECTION IN
ADVANCE OF THE NEXT ARCTIC FRONT CROSSING THE AREA SUNDAY
EVENING AND NIGHT. THIS COULD HAVE SNOW SHOWERS OR FLURRIES
AHEAD OF AND IN THE WAKE OF THE ARCTIC FRONT LATE IN THE DAY
INTO THE EVENING. STRONG NORTHWEST WINDS LATER SUNDAY NIGHT
INTO MONDAY COULD RESULT IN PATCHY BLOWING SNOW IN OPEN AREAS
(DEPENDENT UPON SUFFICIENT SNOW COVER).
ENSEMBLE SUPPORT INCREASED IN THE 00Z CYCLE FOR A DUMP OF
BITTERLY COLD AIR FOLLOWING THE SUNDAY NIGHT ARCTIC FRO-PA. COLD
WEATHER HEADLINES ARE A DISTINCT POSSIBILITY SUNDAY NIGHT-MONDAY
AM THROUGH MONDAY NIGHT/EARLY TUESDAY PRIOR TO THE NEXT BRIEF
MODERATION IN TEMPS MIDWEEK NEXT WEEK.
CASTRO
AVIATION /12Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 604 AM CST THU JAN 15 2026
MAIN CONCERN:
- PERIODS OF ACCUMULATING SNOW THIS EVENING INTO FRIDAY MORNING
ADDING UP TO AROUND 1", ACCOMPANIED BY MVFR TO OCCASIONAL IFR
FLIGHT CATEGORIES. HIGHEST CONFIDENCE TIMEFRAME IS LATE
EVENING-EARLY OVERNIGHT.
FLYING CONDITIONS WILL BE MUCH QUIETER DURING THE DAYTIME HOURS
TODAY. MVFR CIGS AND INTERMITTENT FLURRIES FROM ORD AND MDW TO
GYY SHOULD FINALLY CLEAR OUT THIS MORNING, WITH GUSTY
NORTHWESTERLY WINDS ALSO EASING.
WINDS WILL BECOME SOUTHWESTERLY THIS AFTERNOON IN ADVANCE OF THE
NEXT SYSTEM AS MID-LEVEL CLOUDS THICKEN. CONFIDENCE HAS
DECREASED IN DRY AIR BEING SUFFICIENTLY ERODED TO ENABLE SNOW TO
REACH THE GROUND IN THE LATE AFTERNOON AND EARLY EVENING. OPTED
TO HOLD ONTO TEMPO MENTION FOR 5-6SM FLURRIES. ACCUMULATIONS ARE
NOT EXPECTED WITH THE INITIAL SNOW.
THERE IS SOME UNCERTAINTY FOR THE EXACT ONSET TIME OF
ACCUMULATING SNOW THIS EVENING (02-04Z IN THE TAFS). AFTER
ONSET, EXPECT A 2-3 HOUR PERIOD WHERE IFR VSBY SNOW IS PROBABLE.
FOLLOWING A LULL, ANOTHER DISTURBANCE MOVING OVER THE AREA IN
THE PRE-DAWN THROUGH JUST AFTER SUNRISE FRIDAY TIMEFRAME COULD
PRODUCE A SHORT BURST OF IFR VSBY SNOW (1-3 HOURS), COVERED WITH
A PROB30 FOR NOW IN THE TAFS. SOUTHWEST WINDS WILL GUST UP TO
20-25 KT AT TIMES LATE THIS EVENING THROUGH FRIDAY MORNING.
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...WINTER STORM WARNING UNTIL NOON CST TODAY FOR INZ002.
WINTER WEATHER ADVISORY UNTIL 9 AM CST THIS MORNING FOR INZ011.
LM...SMALL CRAFT ADVISORY UNTIL 3 PM CST THIS AFTERNOON FOR
WINTHROP HARBOR IL TO GARY IN.
SMALL CRAFT ADVISORY UNTIL 6 PM CST THIS EVENING FOR GARY TO
BURNS HARBOR IN-BURNS HARBOR TO MICHIGAN CITY IN.
VISIT US AT WEATHER.GOV/CHICAGO
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