710
FXUS63 KLOT 200252
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
852 PM CST SUN JAN 19 2025
KEY MESSAGES
- DANGEROUSLY COLD WIND CHILLS NEAR/AROUND -20F IN SPOTS TONIGHT
INTO MONDAY AM AND THEN -20 TO -29F WIND CHILLS EXPECTED
MONDAY NIGHT THROUGH TUESDAY AM, ESPECIALLY NEAR/NORTH OF I-80
(LIGHTER WINDS SOUTH MAY LIMIT WIND CHILL MAGNITUDES).
- AFTER A COLD TUESDAY EVENING, TEMPERATURES WILL MODERATE BACK
CLOSER TO LATE JANUARY NORMS THE REST OF THE WEEK.
- INTERMITTENT FLURRIES ARE POSSIBLE AREAWIDE MONDAY AFTERNOON
AND EVENING, WITH SOME CHANCE FOR OCCASIONAL ACCUMULATING SNOW
AND TRAVEL IMPACTS IN THE WEDNESDAY-THURSDAY TIMEFRAME.
UPDATE
ISSUED AT 852 PM CST SUN JAN 19 2025
NO CHANGES MADE TO TONIGHT'S FORECAST. TEMPS, WINDS, WIND CHILLS
ARE LOOKING RIGHT ON TARGET WITH PREVIOUS FORECAST.
DID MAKE SOME ADJUSTMENTS TO THE TIMING OF THE FLURRIES FOR
TOMORROW AND TOMORROW NIGHT. SHORTWAVE TROUGH EVIDENT ON WATER
VAPOR IMAGERY OVER SOUTHERN MANITOBA WILL PIVOT AROUND THE
SOUTHWESTERN PERIPHERY OF THE BROADER LONG WAVE TROUGH OVER
EASTERN CANADA. THE SHORTWAVE TROUGH OF CONCERN SHOULD REACH
SOUTHERN MN BY MIDDAY MONDAY, THEN EXTEND FROM LAKE MICHIGAN
SOUTHWEST TO NORTHERN MO BY MID EVENING MONDAY AS THE MORE
COMPACT SHORTWAVE BEGINS TO DEFORM/SHEAR OUT.
DCVA IN ADVANCE OF THIS TROUGH WILL LIKELY BE ENOUGH TO WRING
SOME FLURRIES OR LIGHT SNOW OUT OF A THIN STRATUS/STRATOCUMULUS
DECK LATE MONDAY AFTERNOON AND MONDAY EVENING. IT APPEARS THE
FLURRIES/VERY LIGHT SNOW WILL PROBABLY HOLD OFF UNTIL SUNSET IN
CHICAGO, BUT REACH THE ROCKFORD AREA DURING THE AFTERNOON. IT
TAKES VERY LITTLE FOR FLURRIES/VERY LIGHT SNOW IN AN AIR MASS
THIS COLD AND FORCING LOOKS PRETTY WEAK, SO CONFIDENCE ON
PRECISE TIMING IS LOW.
NOT SEEING MUCH SUPPORT FOR FLURRIES/SNOW CHANCES IN GUIDANCE,
SO FLURRIES SHOULD PROBABLY COVER THE THREAT. SECONDARY COLD
FRONT WILL ACCOMPANY THE MID-UPPER LEVEL TROUGH. MOST LIKELY
SCENARIO IS BOUNDARY LAYER BEING TOO DRY FOR ANYTHING MORE THAN
FLURRIES, BUT WILL NEED TO KEEP AN EYE POTENTIAL FOR SOME
SLIGHTLY BEEFIER SNOW ALONG THE LOW LEVEL CONVERGENCE ASSOCIATED
WITH THE COLD FRONT. CLOUD TEMPS AT OR BELOW -20C SUGGESTS VERY
SMALL SNOW FLAKES, ALMOST PIXIE DUST LIKE, SO IT SEEMS UNLIKELY
THAT THERE'D BE ENOUGH SNOW TO COVER PAVEMENT, BUT SUBTLE WAVES
IN ARCTIC AIR MASSES CAN OVERPERFORM AT TIMES.
UPDATED GRIDS AND TEXT PRODUCT HAVE ALREADY BEEN SENT.
- IZZI
DISCUSSION
ISSUED AT 235 PM CST SUN JAN 19 2025
THROUGH TUESDAY MORNING:
A COLD WEATHER ADVISORY REMAINS IN EFFECT FOR THE AREA TONIGHT
THROUGH MONDAY MORNING, WITH DANGEROUS WIND CHILLS OF NEAR TO
LOCALLY BELOW 20 BELOW ZERO EXPECTED. WE SHOULD THEN EXPERIENCE
IMPROVING WIND CHILLS MONDAY AFTERNOON AS ACTUAL AIR
TEMPERATURES REBOUND BACK TO AROUND 10 ABOVE. ACCORDINGLY, THE
MIDDAY END TIME OF TONIGHT'S COLD ADVISORY LOOKS LARGELY ON
TRACK. THIS WILL, UNFORTUNATELY, NOT MARK THE END OF OUR
DANGEROUSLY COLD WEATHER, HOWEVER, AS CONDITIONS ARE SET TO GO
DOWNHILL IN A HURRY AGAIN MONDAY NIGHT AS THE MAIN PUSH OF THIS
TRUE ARCTIC AIRMASS SLIDES INTO THE AREA ON BLUSTERY WEST-
NORTHWEST WINDS MONDAY NIGHT INTO TUESDAY MORNING. DURING THIS
PERIOD, MODEL AND ENSEMBLE GUIDANCE CONTINUE TO BE IN GREAT
AGREEMENT WITH TEMPERATURES AT 850 MB BOTTOMING OUT AROUND -30C.
TYPICALLY SUCH AN AIRMASS IS CAPABLE OF PRODUCING BRUTALLY COLD
TEMPERATURES IN EXCESS OF 10 TO 20F DEGREES BELOW ZERO,
PARTICULARLY IF AN EXISTING SNOW PACK IS ON THE GROUND. SINCE WE
HAVE LOST MOST OF THE SNOW ACROSS THE AREA, THERE REMAINS SOME
UNCERTAINTY IN EXACTLY HOW FAR BELOW ZERO ACTUAL AIR
TEMPERATURES WILL GET MONDAY NIGHT INTO TUESDAY. ACCORDINGLY, I
DID NOT GO AS COLD AS SOME OF THE MOS GUIDANCE, WHICH GENERALLY
SUPPORT COLDER TEMPERATURES IN THE TEENS BELOW ZERO MONDAY
NIGHT. INSTEAD, WE OPTED TO KEEP THINGS MORE CONSISTENT WITH THE
GOING FORECAST, WHICH HAS LOWS PRIMARILY REMAINING IN THE
SIGNAL DIGITS BELOW ZERO.
INTERESTINGLY, EVEN WITH THIS MORE CONSERVATIVE APPROACH, THE
BLUSTERY WEST-NORTHWESTERLY WINDS OF 10 TO 15 MPH STILL SUPPORT
WIND CHILLS OF 20 TO 29 BELOW ZERO MONDAY NIGHT THROUGH AT LEAST
TUESDAY MORNING, PARTICULARLY TO THE NORTH OF I-80. WITH
CONFIDENCE CONTINUING TO INCREASE IN THIS AREA FOR ANOTHER
PERIOD OF DANGEROUSLY COLD CONDITIONS, WE OPTED TO GO AHEAD AND
ISSUE A SECOND COLD WEATHER ADVISORY. FOR NOW, WE HAVE ONLY
INCLUDED AREAS ALONG AND NORTH OF I-80 IN THIS SECOND ADVISORY,
WHICH GOES INTO EFFECT STARTING LATER MONDAY EVENING AND
PERSISTING THROUGH MIDDAY TUESDAY. AREAS SOUTH OF I-80 MAY
ULTIMATELY NEED TO BE ADDED TO THIS SECOND ADVISORY, BUT FOR NOW
I JUST WANTED TO HIT THE AREAS OF HIGHEST CONFIDENCE FOR SUB
-20F WINDCHILLS.
PRIMARILY WESTERLY FLOW ACROSS LAKE MICHIGAN WILL FAVOR MOST OF
THE LAKE EFFECT SNOW FALLING ALONG THE EASTERN SHORES OF THE
LAKE EAST OF OUR AREA. OUTSIDE OF THE LAKE EFFECT, THERE
CONTINUES TO BE CHANCE FOR A PERIOD OF INTERMITTENT FLURRIES,
PARTICULARLY MONDAY AFTERNOON AND EVENING AS PERSISTENT
SPROCKETS OF FAIRLY INTENSE DCVA MEANDER OVERHEAD. WE THUS
CONTINUE TO HIT THIS MENTION IN THE FORECAST. CLOUD COVER SHOULD
THEN BE ON THE DECREASE LATE MONDAY NIGHT ENDING THE FLURRIES
AND AIDING IN FALLING TEMPERATURES INTO EARLY TUESDAY MORNING.
KJB
TUESDAY AFTERNOON THROUGH SUNDAY:
THE CORE OF THE COLDEST AIR MASS WILL START TO LOSE ITS GRIP
TUESDAY AFTERNOON (925 MB TEMPS RISING TO THE LOWER TO MID -20S
CELSIUS). WITH FULL SUN AND THE LACK OF SNOW COVER, THIS SHOULD
ALLOW TEMPS TO RECOVER TO THE LOWER TO MID SINGLE DIGITS ABOVE
ZERO (WIND CHILLS TO ABOUT -9 TO -15), AND CAN ENVISION
LOCALIZED "WARM" SPOTS WITH HIGHS IN THE UPPER SINGLE DIGITS.
~1040 MB SURFACE HIGH PRESSURE WILL MAKE ITS CLOSEST APPROACH TO
OUR SOUTH TUESDAY EVENING (DOWNSTATE IL TO SOUTHERN/CENTRAL
IN). THE VERY DRY ARCTIC AIR MASS AND CLEAR SKIES IN THE EVENING
WILL BE CONDUCIVE TO THE BOUNDARY LAYER DECOUPLING AND TEMPS
FALLING BACK INTO THE SINGLE DIGITS BELOW ZERO OUTSIDE OF
CHICAGO. LIGHT WINDS WILL REDUCE THE WIND CHILL EFFECT,
ESPECIALLY WHERE WINDS GO CALM IN THE SOUTHERN HALF OR 1/3 OF
THE CWA, AND THUS LOWEST WIND CHILLS (LOCATIONS THAT HAVE 5+ MPH
WIND SPEEDS) SHOULD HOVER AT -10 TO -15, LOCALLY AS LOW AS -15
TO -20F. WITH THE ABOVE THINKING IN MIND, WE'RE NOT CURRENTLY
EXPECTING TO NEED A COLD WEATHER ADVISORY DURING TUESDAY'S
EVENING COLDEST TEMPS.
LATE TUESDAY NIGHT INTO WEDNESDAY MORNING, THE SURFACE HIGH WILL
SHIFT INTO THE EASTERN OHIO VALLEY AS BROAD WEAK LOW PRESSURE
APPROACHES FROM THE NORTHWEST. EXPECT GRADUALLY INCREASING
SOUTHERLY WINDS AND INCREASED MID-LEVEL CLOUD COVER TO RESULT IN
RISING TEMPS OVERNIGHT THROUGH DAYBREAK WEDNESDAY. WINDS SHOULD
QUICKLY BECOME GUSTY AFTER SUNRISE (UP TO 30 MPH), SO DESPITE THE
MODERATING TEMPS, IT CERTAINLY WON'T BE PLEASANT (IE. EARLY MORNING
WIND CHILLS ABOUT -10F RISING TO ABOUT 0F BY MIDDAY).
ALSO OF NOTE WEDNESDAY-WEDNESDAY NIGHT AND EVEN INTO THURSDAY,
THERE IS SOME CHANCE FOR PERIODS OF SNOW/SNOW SHOWERS. THE MID AND
UPPER PATTERN IS A BIT COMPLEX DURING THIS TIME, WHICH HAS
RESULTED IN FAIRLY SIZABLE RUN TO RUN CHANGES IN THE
DETERMINISTIC GUIDANCE. GENERALLY SPEAKING, A CLIPPER-LIKE
SHORT-WAVE TROUGH SHOULD MOVE ACROSS THE REGION IN THE
WEDNESDAY-WEDNESDAY NIGHT TIMEFRAME, FOLLOWED BY ANOTHER TROUGH
AND MODEST CAA ON THURSDAY. DESPITE THE AFOREMENTIONED
DETERMINISTIC VARIANCE, THERE HAS BEEN A CONSISTENT SIGNAL AMONG
SOME OF THE ENSEMBLE MEMBERS, TOPPING OUT AT ABOUT 20 TO 40%
WEDNESDAY-WEDNESDAY EVENING, HIGHEST NORTH OF I-80, AND THEN
GENERALLY IN THE 20-30% RANGE ON THURSDAY. IT CERTAINLY DOESN'T
LOOK LIKE A BIG DEAL SNOWFALL WISE, WITH LIMITED MOISTURE TO
WORK WITH, THOUGH SUB-FREEZING TEMPS (AND VERY COLD ROAD
SURFACES) COULD RESULT IN SOME TRAVEL IMPACTS AT TIMES. IN
COLLABORATION WITH NEIGHBORING WFOS, WE ADDED LOW POPS (20-30%
RANGE WED-WED NIGHT, HIGHEST NORTH OF I-80, AND ~20% ON
THURSDAY) INTO THE FORECAST.
MEDIUM-RANGE GUIDANCE IS MIXED ON WHETHER THE PREDOMINANTLY DRY
NORTHWESTERLY MID AND UPPER FLOW PATTERN WILL EASE OR BECOME
WEST-SOUTHWEST FOR A TIME NEXT WEEKEND, WHICH MAY OPEN THE DOOR
FOR A RETURN OF PRECIP CHANCES (SNOW OR RAIN/SNOW/WINTRY MIX)
SATURDAY NIGHT INTO SUNDAY. THE GFS/GEFS IS MUCH MORE BULLISH IN
THIS REGARD THAN THE OTHER NWP SYSTEMS, SO SAW NO REASON TO STRAY
FROM THE SLIGHT (~20%) CHANCE POPS OFFERED BY THE NBM, PRIMARILY
SOUTHEAST OF I-55. TEMPERATURES MAY FLIRT WITH 32F IN SPOTS
THURSDAY-FRIDAY (UPPER 20S TO AROUND 30F ELSEWHERE), WITH A BETTER
CHANCE OF MORE WIDESPREAD ABOVE FREEZING HIGHS NEXT WEEKEND.
CASTRO
AVIATION /00Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 541 PM CST SUN JAN 19 2025
THERE ARE NO MAJOR AVIATION WEATHER CONCERNS FOR THE 00Z TAF
PERIOD.
WNW WINDS NEAR OR JUST OVER 10 KT WILL OCCASIONALLY GUST INTO
THE TEENS KTS THROUGH THE NIGHT. GUSTS TO 25 TO 30 KT WILL
BUILD AFTER MID-MORNING MONDAY AND PERSIST INTO EARLY EVENING
BEFORE GRADUALLY SUBSIDING. ADDITIONALLY, SOME LIGHT FLURRIES
MAY MATERIALIZE DURING THE AFTERNOON AND EARLY EVENING ON
MONDAY. WHILE THESE LOOK TO BE LARGELY NON-IMPACTFUL, IT'S NOT
OUT OF THE QUESTION THAT THEY COULD PRODUCE MINOR VSBY
REDUCTIONS AT TIMES. OTHERWISE, EXPECT VFR THROUGHOUT THE
PERIOD.
DOOM
LOT WATCHES/WARNINGS/ADVISORIES
IL...COLD WEATHER ADVISORY UNTIL NOON CST MONDAY FOR ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
ILZ105-ILZ106-ILZ107-ILZ108.
COLD WEATHER ADVISORY FROM 9 PM MONDAY TO NOON CST TUESDAY FOR
ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-
ILZ013-ILZ019-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-ILZ106-
ILZ107-ILZ108.
IN...COLD WEATHER ADVISORY UNTIL NOON CST /1 PM EST/ MONDAY FOR
INZ001-INZ002-INZ010-INZ011-INZ019.
COLD WEATHER ADVISORY FROM 9 PM MONDAY TO NOON CST TUESDAY FOR
INZ001-INZ002.
LM...SMALL CRAFT ADVISORY UNTIL 4 AM CST MONDAY FOR WINTHROP HARBOR
IL TO GARY IN.
SMALL CRAFT ADVISORY UNTIL 10 PM CST MONDAY FOR GARY TO BURNS
HARBOR IN-BURNS HARBOR TO MICHIGAN CITY IN.
HEAVY FREEZING SPRAY WARNING UNTIL 4 AM CST MONDAY FOR GARY TO
BURNS HARBOR IN-BURNS HARBOR TO MICHIGAN CITY IN.
VISIT US AT WEATHER.GOV/CHICAGO
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