030
FXUS63 KLOT 231112
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
512 AM CST TUE DEC 23 2025
KEY MESSAGES
- TODAY WILL FEATURE HIGHS IN THE UPPER 40S TO LOWER 50S AMIDST
UPPER-LEVEL CLOUDS AND LIGHT (~10 MPH) NORTHWEST WINDS.
- WEDNESDAY AND THURSDAY/CHRISTMAS DAY WILL BE MARRED IN LOW
CLOUDS WITH NEARLY STEADY TEMPERATURES IN THE UPPER 30S
(NORTH) TO LOWER 40S (SOUTH).
- A PERIOD OF DRIZZLE IS LIKELY (>60% CHANCE) WEDNESDAY
AFTERNOON THROUGH EARLY THURSDAY MORNING.
- A PERIOD OF COLDER WEATHER MAY MATERIALIZE LATE WEEKEND INTO
EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 233 AM CST TUE DEC 23 2025
THROUGH THURSDAY/CHRISTMAS DAY:
EARLY MORNING WATER VAPOR IMAGERY FROM GOES-16 AND GOES-17
DEPICT SEVERAL UPPER-LEVEL SHORTWAVES COLLECTING INTO A LARGER,
AGGREGATE TROUGH ACROSS THE EASTERN PACIFIC OCEAN. IMPLIED
EXPANSIVE MID-LEVEL WARM AIR ADVECTION DOWNSTREAM OF THE
DEVELOPING LONGWAVE TROUGH IS LEADING TO GRADUALLY STRENGTHENING UPPER-
LEVEL RIDGING ACROSS THE CENTRAL UNITED STATES. THE GREAT LAKES
ARE LOCATED MORE OR LESS BENEATH THE MIDDLE OF THE DEVELOPING
LONGWAVE RIDGE, AND WITHIN A BROAD, EAST TO WEST-ORIENTED LOW-
LEVEL BAROCLINIC ZONE. A WEAK SURFACE LOW PRESSURE SYSTEM
(ANALYZED NEAR 1012MB) IS MOVING ACROSS LAKE SUPERIOR ON THE
NORTHERN FLANK OF A SURFACE PRESSURE TROUGH EXTENDING
SOUTHWESTWARD THROUGH THE UPPER MISSISSIPPI RIVER VALLEY AND
INTO THE SOUTHERN PLAINS. THE SOMEWHAT BAGGY LOW-LEVEL PRESSURE
GRADIENT IS RESULTING IN FAIRLY LIGHT SOUTHWESTERLY WINDS ACROSS
THE AREA (ONLY AROUND 5 TO LOCALLY 10 MPH). MEANWHILE, THICK
UPPER-LEVEL CLOUDS STREAMING DIRECTLY OVERHEAD ARE PREVENTING
TEMPERATURES FROM DROPPING MUCH EARLY THIS MORNING, WITH
READINGS HOLDING STEADY IN THE LOWER 30S TOWARD THE NORTH TO
AROUND 40 TOWARD THE SOUTH.
WHILE UPPER-LEVEL CLOUDS AT VARYING COVERAGE APPEAR POISED TO
CONTINUE STREAMING OVER THE REGION THROUGHOUT THE DAY, UPWARD
MIXING IN THE WAKE OF A WEAK FRONTAL BOUNDARY AND INTO A PLUME
OF UNSEASONABLY WARM 925 TO 850MB TEMPERATURES (AROUND +8C)
SHOULD LEAD TO AFTERNOON HIGHS IN THE UPPER 40S TO LOWER 50SF.
TONIGHT, A SURFACE HIGH PRESSURE SYSTEM WILL MOVE THROUGH THE
GREAT LAKES REGION LEADING TO NEARLY CALM WINDS AND AT LEAST
PARTIAL CLEARING OF SKIES. WITH SCANT LOW-LEVEL MOISTURE IN THE
REGION, CURRENTLY AM NOT EXPECTING ANY DEVELOPMENT OF FOG
OUTSIDE OF PERHAPS ISOLATED INSTANCES OF SHALLOW FOG IN RIVER
VALLEYS SHOULD CLEARING OF UPPER-LEVEL CLOUDS BE MORE AGGRESSIVE
THAN CURRENTLY EXPECTED. OVERNIGHT LOWS SHOULD FALL INTO THE
UPPER 20S TO LOWER 30S.
ON WEDNESDAY, UPPER-LEVEL CLOUDS WILL THICKEN AS THE UPPER-
LEVEL JET STREAM INTENSIFIES OVERHEAD. AT LEAST SOME WARMING OF
AIR TEMPERATURES SHOULD TAKE PLACE THROUGHOUT THE MORNING,
THOUGH READINGS LOOK LIKE THEY'LL GET STUCK IN THE UPPER 30S
NEAR THE WISCONSIN STATE LINE TO LOWER 40S SOUTH OF I-80 AS
CLOUDS CONTINUE TO THICKEN AND COLUMN-WIDE ADVECTION STALLS.
DURING THE AFTERNOON HOURS, A LOW-AMPLITUDE UPPER-LEVEL WAVE
PROPAGATING THROUGH THE MEAN LONG-WAVE TROUGH ACROSS THE CENTRAL
UNITED STATES WILL MOVE OVER THE GREAT LAKES, LEADING TO A
RAPID INCREASE IN LOW-LEVEL STRATUS. ENSEMBLE GUIDANCE REMAINS
IN REMARKABLY STRONG AGREEMENT THAT THE APPROACHING WAVE WILL
INDUCE AREAS OF DRIZZLE AND RAIN SHOWERS THROUGH THE EARLY
MORNING HOURS OF THURSDAY. WILL CONTINUE TO MANUALLY INCREASE
POPS BEYOND THE NBM FOR THIS PERIOD, WITH EPS GUIDANCE SHOWING A
NEAR CERTAIN (>90%) CHANCE FOR MEASURABLE PRECIP. WITH THICK
CLOUDS AND WEAK NEAR-SURFACE WINDS (NO ADVECTION), OVERNIGHT
LOWS LOOKS LIKE THEY'LL BE PRETTY SIMILAR TO WEDNESDAY AFTERNOON
HIGHS.
COVERAGE OF SHOWERS AND DRIZZLE SHOULD TAPER BY DAYBREAK
THURSDAY/CHRISTMAS DAY, THOUGH CONTINUED LIGHT WINDS AND LOW-
LEVEL MOISTURE TRAPPED BENEATH THE STRONG LOW-LEVEL INVERSION
MAY SUPPORT THE DEVELOPMENT OF AREAS OF FOG. WITH TIME, WINDS
WILL ADOPT A NORTH TO NORTHEASTERLY COMPONENT AS A STRONG HIGH
PRESSURE SYSTEM TRAVERSES THROUGH SOUTHERN CANADA, ERODING ANY
LINGERING FOG. A CONTINUATION OF THICK CLOUD COVER AND THE
INTRODUCTION OF WEAK LOW-LEVEL COLD AIR ADVECTION SUGGESTS THAT
TEMPERATURES WILL BE FAIRLY STAGNANT ON CHRISTMAS DAY WITH
READINGS NEAR THE UPPER 30S (NORTH) TO LOWER 40S (SOUTH). IT
WILL BE INTERESTING TO SEE BY HOW MUCH TEMPERATURES VARY ACROSS
A 36 HOUR PERIOD FROM WEDNESDAY AFTERNOON THROUGH THURSDAY NIGHT
(IT MAY ONLY BE A FEW DEGREES).
BORCHARDT
CHRISTMAS NIGHT THROUGH NEXT TUESDAY:
MODEST MID-LEVEL RIDGING WILL BE IN THE PROCESS OF GETTING
SHOVED EASTWARD BY A PAIR OF PACIFIC SHORTWAVE TROUGHS (ONE
TRAVERSING ACROSS SOUTHERN CANADA AND THE NORTHERN GREAT LAKES
AND THE OTHER EJECTING OUT OF THE CENTRAL PLAINS) THURSDAY
EVENING. AT THE SURFACE THE BAROCLINIC ZONE WILL STILL BE
RESIDING IN CENTRAL IL, BUT WILL BEGIN TO LIFT NORTHWARD AS THE
PLAINS SHORTWAVE AND ITS ASSOCIATED SURFACE LOW MOVES INTO THE
MISSISSIPPI VALLEY AND SOUTHERN GREAT LAKES. AS THIS OCCURS A
BAND OF LIGHT RAIN AND DRIZZLE IS EXPECTED TO DEVELOP ALONG THE
SURGING WARM FRONT THURSDAY NIGHT AND TRANSITION INTO A MORE
BONAFIDE BAND OF RAIN ON FRIDAY AS MORE ROBUST MOISTURE ARRIVES.
WHILE RAINFALL AMOUNTS DO NOT LOOK TO BE OVERLY IMPRESSIVE
(AROUND 0.10-0.15 INCHES) LOCALLY, FORECAST SOUNDINGS DO SHOW
SOME VERY STEEP MID-LEVEL LAPSE RATES TO BE PRESENT WHICH COULD
YIELD LOCALLY HIGHER AMOUNTS ACROSS PORTIONS OF NORTHEAST IL AND
NORTHWEST IN IN ADDITION TO PERHAPS A RUMBLE OR TWO OF THUNDER.
THAT SAID, GIVEN THAT DEW POINTS DURING THIS PERIOD LOOK TO
ONLY BE IN THE MID-40S TO LOWER 50S IT APPEARS THAT THE
ATMOSPHERE MAY NOT BE FULLY BUOYANT ENOUGH TO WARRANT HIGH
CONFIDENCE IN THUNDER OCCURRING AND THUS HAVE FOREGONE A FORMAL
MENTION AT THIS TIME.
AS FOR TEMPERATURES ON FRIDAY, THE SURGING WARM FRONT DOES LOOK
TO ALLOW TEMPERATURES TO WARM INTO THE MID-40S TO LOWER 50S
(POSSIBLY MIDDLE 50S CLOSER TO CENTRAL IL). HOWEVER, WITH THE
AFOREMENTIONED ONGOING RAIN AND CLOUD COVER THERE IS STILL THE
POTENTIAL FOR TEMPERATURES TO VERIFY A DEGREE OR TWO COOLER THAN
FORECAST ESPECIALLY FOR AREAS NORTH OF I-80.
HEADING INTO SATURDAY, ANOTHER BOUGHT OF MID-LEVEL RIDGING IS
FORECAST TO PIVOT OVER NORTHERN IL AND NORTHWEST IN WHICH SHOULD
ALLOW THE RAIN TO CONCLUDE FRIDAY NIGHT. THOUGH, FORECAST
SOUNDINGS DO SHOW SOME LOW-LEVEL MOISTURE HANGING AROUND SO
MOSTLY TO COMPLETELY CLOUDY SKIES ARE EXPECTED. COUPLE THESE
CLOUDS WITH THE FACT THAT THE AFOREMENTIONED BAROCLINIC ZONE
WILL STILL BE HOVERING NEAR THE I-80 CORRIDOR AND WE ARE LOOKING
AT ANOTHER MILD DAY ON SATURDAY WITH HIGHS IN THE MID-40S TO
LOWER 50S ONCE AGAIN, BUT WITH THE BAROCLINIC ZONE FORECAST TO
BE A BIT FURTHER NORTH THAN FRIDAY SEEMS OUR SOUTHERN COUNTIES
COULD MAKE A RUN AT THE UPPER 50S IF CLOUDS ARE THIN ENOUGH.
WHILE WE ENJOY A BRIEF BREAK IN THE WET WEATHER, THE LONGWAVE
TROUGH THAT HAS BEEN PARKED OVER THE PACIFIC NORTHWEST THE PAST
SEVERAL DAYS IS FORECAST TO FINALLY BREAK LOOSE AND EJECT
EASTWARD ON SATURDAY. AS IT DOES SO IT IS EXPECTED TO PHASE WITH
A DEEPENING SHORTWAVE TROUGH OVER THE CANADIAN PRAIRIE
PROVINCES AND NORTHERN PLAINS WHICH IN TURN WILL ALLOW A SURFACE
LOW TO DEVELOP OVER ONTARIO. ATTACHED TO THIS LOW IS EXPECTED
TO BE A COLD FRONT THAT LOOKS TO BE DRAPED ACROSS THE UPPER
MIDWEST TO CENTRAL PLAINS SATURDAY AFTERNOON. THE COLD FRONT
WILL THEN BEGIN TO RACE EASTWARD THROUGH OUR AREA AND THE REST
OF THE GREAT LAKES SATURDAY NIGHT INTO SUNDAY. TYPICALLY A COLD
FRONT OF THIS MAGNITUDE WOULD YIELD AND PERIOD OF RAIN SHOWERS
ALONG THE FRONT BUT SINCE GUIDANCE IN THIS CASE IS INDICATING A
SECONDARY SURFACE LOW DEVELOPING ON THE TAIL END OF THE FRONT IN
MO AND LIFT ACROSS IL AND IN DURING THIS PERIOD; IT APPEARS
THAT OUR AREA COULD GET SPLIT BY THESE FEATURES AND THUS GET
AWAY WITH VERY LITTLE PRECIPITATION. DESPITE THE RATHER DECENT
SIGNAL IN GUIDANCE (BOTH DETERMINISTIC AND ENSEMBLE) FOR THIS
EVOLUTION THERE IS STILL SOME UNCERTAINTY AS TO WHERE EXACTLY
THE SECONDARY LOW WILL TRACK AND IF NORTHERN IL AND NORTHWEST IN
WILL ACTUALLY GET DRY SLOTTED. THEREFORE, HAVE OPTED TO
MAINTAIN THE 15-20% POPS OFFERED BY THE NBM SATURDAY NIGHT INTO
SUNDAY AT THIS TIME, BUT WILL KEEP AN EYE ON TRENDS IN CASE
HIGHER POPS ARE NEEDED IN THE FUTURE.
IN THE WAKE OF THE COLD FRONT, TEMPERATURES ARE FORECAST TO
TANK WITH LOWS SATURDAY NIGHT IN THE 20S WHERE THEY LOOK TO
RESIDE THROUGH THE DAY ON SUNDAY. ADDITIONALLY, THE STRONG COLD
ADVECTION AND TIGHT PRESSURE GRADIENT GENERATED BY THE SUB 1000
MB LOW IN THE NORTHERN GREAT LAKES WILL LEAD TO BLUSTERY
NORTHWEST WINDS GUSTING IN EXCESS OF 25-35 MPH ON SUNDAY INTO
THE DAY ON MONDAY. WITH OVERNIGHT LOWS SUNDAY NIGHT FORECAST TO
DIP NEAR THE LOWER TEENS TO SINGLE DIGITS THERE LOOKS TO BE A
PERIOD OF SUB-ZERO WIND CHILLS TO START OFF NEXT WEEK. AS FOR
PRECIPITATION, MOST OF THE ACCUMULATING PRECIPITATION SHOULD
CONCLUDE AS THE FRONT MOVES THROUGH BUT LINGERING MOISTURE AND
-18 TO -22 C 850MB TEMPERATURES DOES LOOK TO SUPPORT A PERIOD OF
FLURRIES AND/OR LIGHT SNOW SHOWERS ON SUNDAY.
BEYOND MONDAY THE FORECAST BECOMES MUCH MORE UNCERTAIN AS
GUIDANCE STRUGGLES ON WHAT TO DO IN THE WAKE OF THE DEPARTING
UPPER TROUGH. SOME GUIDANCE SHOWS ANOTHER PERIOD OF RIDGING
DEVELOPING TOWARDS THE MIDDLE OF NEXT WEEK WHICH IN TURN WOULD
MODERATE TEMPERATURES BEFORE ANOTHER POTENT STORM SYSTEM DIVES
INTO THE GREAT LAKES ON OR SHORTLY AFTER THE NEW YEAR. HOWEVER,
OTHERS SHOW THE NEXT STORM SYSTEM ARRIVING MUCH SOONER (POSSIBLY
AS EARLY AS WEDNESDAY) WHICH IN TURN WOULD KEEP THE COLD
TEMPERATURES AROUND THROUGH NEXT WEEK. WHILE THIS PERIOD DOES GO
JUST BEYOND THE CURRENT 7-DAY PERIOD IT WILL BE GETTING INTO IT
OVER THE NEXT COUPLE OF DAYS AND THUS WE COULD ONCE AGAIN SEE A
VARYING FORECAST UNTIL THE AFOREMENTIONED SCENARIOS CONVERGE.
SO FOR ANYONE LOOKING AHEAD FOR THEIR NEW YEARS PLANS SHOULD
KEEP A CLOSE ON THE FORECAST GOING FORWARD.
YACK
AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 512 AM CST TUE DEC 23 2025
NO MAJOR FORECAST CONCERNS ARE EXPECTED FOR THIS TAF PERIOD AS
HIGH PRESSURE WILL BE BUILDING INTO THE AREA. THEREFORE, EXPECT
SCT TO BKN VFR CIRRUS CLOUDS TO LINGER OVERHEAD TODAY BEFORE
THEY SCATTER OUT THIS EVENING AND OVERNIGHT. WINDS WILL
GRADUALLY BECOME MORE WEST-NORTHWEST LATER TODAY AND THEN BECOME
EAST-SOUTHEAST OVERNIGHT INTO WEDNESDAY MORNING. THOUGH SPEEDS
WILL REMAIN IN THE 5-10 KT RANGE THROUGH THE FORECAST PERIOD.
THAT SAID, THERE IS A LOW CHANCE (<15%) FOR SOME PATCHY FOG TO
DEVELOP LATE TONIGHT INTO WEDNESDAY MORNING. WHILE MOST GUIDANCE
DOES SHOW SOME MVFR VISIBILITIES MATERIALIZING OVERNIGHT,
FORECAST SOUNDINGS SHOW THAT THE SURFACE MAY NOT FULLY SATURATE.
COUPLE THIS WITH THE 10-15 KT WINDS JUST ABOVE THE SURFACE AND
DRIER AIR ALOFT IT SEEMS AS IF ANY FOG THAT DOES ATTEMPT TO FORM
MAY GET CHEWED UP BY DRY AIR ENTRAINMENT. SO WITH THE FOG
COVERAGE BEING LOW CONFIDENCE HAVE OPTED TO FOREGO IT IN THE
TAFS AT THIS TIME.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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