589
FXUS63 KLOT 182031
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
231 PM CST SAT JAN 18 2025
KEY MESSAGES
- DANGEROUSLY COLD WIND CHILLS (FROSTBITE POTENTIAL IN ~30
MINUTES) EXPECTED EARLY SUNDAY ACROSS INTERIOR FAR NORTHERN
ILLINOIS, AREAWIDE SUNDAY NIGHT-MONDAY MORNING, AND AGAIN
MONDAY NIGHT-EARLY TUESDAY.
- NORTHEAST PORTER COUNTY MAY BE CLIPPED BY LIGHT LAKE EFFECT
SNOW ACCUMULATIONS AND ASSOCIATED TRAVEL IMPACTS TONIGHT
THROUGH SUNDAY EVENING, WITH THE LAKE EFFECT THEN SHIFTING
EAST FOR THE REST OF THE COLD SNAP. FLURRIES ARE POSSIBLE
AREAWIDE MON PM.
DISCUSSION
ISSUED AT 231 PM CST SAT JAN 18 2025
THROUGH SUNDAY NIGHT:
THANKS TO THE MELTING OF MUCH OF THE SNOW COVER FROM YESTERDAY'S
BRIEF BUT IMPRESSIVE WARM-UP AND PLENTY OF SUNSHINE, TEMPERATURES
WERE ABLE TO HOLD NEAR SEASONABLE TODAY (UPPER 20S-LOWER 30S)
AMIDST 850 MB TEMPS AROUND -10C. THIS UNFORTUNATELY WILL BE THE
LAST TIME WE CAN SAY THIS UNTIL LATER NEXT WEEK. THE FIRST
SIGNIFICANT SURGE OF STOUT COLD AIR ADVECTION (CAA) WILL ARRIVE
TONIGHT AND CAUSE A RESUMPTION OF BLUSTERY NORTHWEST WINDS
GUSTING TO 25-30 MPH FOLLOWING A LULL THIS EVENING. 850 MB TEMPS
WILL PLUNGE TO -20 TO -25C SUNDAY MORNING, LOWEST OVER THE
NORTHWEST HALF OF THE AREA. INITIALLY STEADY TEMPERATURE DROP
THIS EVENING WILL RAMP UP IN THE PRE-DAWN HOURS, WITH READINGS
DOWN NEAR 0F AND LOCALLY JUST BELOW IT ACROSS INTERIOR FAR
NORTHERN ILLINOIS AFTER SUNRISE (SINGLE DIGITS TO AROUND 10F
ELSEWHERE). CONTINUED GUSTY NORTHWEST WINDS WILL KNOCK WIND
CHILLS DOWN TO AROUND -20F FOR THE INITIAL COLD WEATHER ADVISORY
AREA, WHICH WAS EXPANDED TO INCLUDE LEE COUNTY.
850 MB TEMPS WILL CONTINUE TO FALL THROUGH THE DAY ON SUNDAY
FOLLOWING A MID-LEVEL SHORT-WAVE TROUGH PASSAGE. THUS DESPITE
MID-LEVEL CLOUDS CLEARING OUT IN THE AFTERNOON, THERE WILL BE
LITTLE IF ANY AFTERNOON TEMPERATURE AND WIND CHILL RECOVERY.
MOSTLY CLEAR SKIES AND ONLY GRADUALLY EASING WESTERLY WINDS
SUNDAY NIGHT WILL ENABLE LOWS BY EARLY MONDAY TO REACH THE LOWER
TO MID MINUS SINGLE DIGITS. CONFIDENCE IS A BIT LOWER IN SUB-ZERO
LOWS BEING ATTAINED IN DOWNTOWN CHICAGO AND ALONG THE PORTER
COUNTY SHORE GIVEN THE LACK OF SNOW COVER, THOUGH THIS DOESN'T
EFFECT THE MESSAGE OF DANGEROUSLY COLD WIND CHILLS AREA WIDE.
WITH FORECAST WIND CHILLS APPROACHING OR BELOW -20F SUNDAY
EVENING, THE NEW COLD WEATHER ADVISORY ISSUED STARTS AT 6PM AND
RUNS THROUGH 12PM MONDAY. IN ADDITION, FOR THE INITIAL ADVISORY
AREA, WITH WIND CHILLS HOVERING IN THE MID MINUS TEENS SUNDAY
AFTERNOON AND THEN DROPPING BACK TOWARD OR BELOW -20F AROUND OR
JUST AFTER SUNSET SUNDAY, WE OPTED TO JUST EXTEND THIS ADVISORY
ALL THE WAY THROUGH MIDDAY MONDAY. THE NEXT ROUND OF DANGEROUSLY
COLD WIND CHILLS (LATER MONDAY INTO TUESDAY MORNING) CAN BE
FOUND IN THE LONG TERM SECTION BELOW.
LAKE EFFECT SNOW FOR NORTHEAST PORTER COUNTY:
IMPROVING LAKE INDUCED THERMODYNAMICS TONIGHT WITH THE ARRIVAL OF
THE MUCH COLDER AIR MASS WILL HELP EXPAND COVERAGE AND INTENSITY
OF LAKE EFFECT SNOW SHOWERS INTO SOUTHWEST LOWER MICHIGAN AND
NORTHERN INDIANA. PROGGED BOUNDARY LAYER FLOW IS MORE WESTERLY
THAN IS IDEAL FOR PORTER COUNTY (NW FORECAST VS. NORTH TO NNW THAT
IS MORE FAVORABLE). WITH THAT SAID, IN THESE BITTERLY COLD (AND
THUS UNSTABLE) AIR MASSES, LIGHTER SNOW SHOWERS OFTEN DEVELOP
FARTHER WEST THAN IN LESS COLD AIR MASSES. PREFERRED THE NAM AND
WRF DEPICTIONS OF THIS, WHICH ENTAILED HOLDING ONTO CHANCE
(PEAKING IN 30-40% RANGE) POPS FOR NORTHEAST PORTER COUNTY LATE
TONIGHT THROUGH THE DAY ON SUNDAY. OUR FORECAST INCLUDES ISOLATED
TO SCATTERED SNOW SHOWER MENTION DURING THE PERIOD OF HIGHEST
CONFIDENCE. LIGHT SNOW ACCUMULATION OF A COATING TO UP TO 1" IN
FAR NORTHEAST PORTER COUNTY MAY CAUSE SLIPPERY TRAVEL, CONSIDERING
THAT ROAD TREATMENTS WILL BECOME LESS EFFECTIVE WITH THE VERY COLD
TEMPS.
CASTRO
MONDAY THROUGH SATURDAY:
REGARDING THE BITTERLY COLD TEMPERATURES MONDAY THROUGH WEDNESDAY
MORNING:
OUR INCOMING ARCTIC AIRMASS WILL BE IN PLACE ACROSS THE AREA ON
MONDAY. THE COMBINATION OF BLUSTERY WESTERLY WINDS OF 10 TO 20
MPH AND AIR TEMPERATURES ONLY CLIMBING TO 5 TO 10 ABOVE ZERO,
WILL RESULT IN CONTINUED SUBZERO WIND CHILLS ALL DAY LONG. SO,
IN SPITE OF THE FACT THAT THE CURRENT END TIME OF THE COLD
ADVISORY IS SET TO BE AROUND NOON ON MONDAY, DON'T EXPECT MUCH
OF AN IMPROVEMENT IN THE WIND CHILLS DURING THE AFTERNOON.
ANY SLIGHT IMPROVEMENT IN THE WIND CHILLS MONDAY AFTERNOON WILL
BE SHORTED LIVED. IN FACT, A SECOND PUSH OF EVEN COLDER AIR IS
EXPECTED FOLLOWING YET ANOTHER COLD FRONTAL PASSAGE LATE MONDAY
AFTERNOON. IN ITS WAKE, AN EXTRA PUSH OF EVEN COLD AIR WILL
RESULT IN THIS ARCTIC AIRMASS PEAKING IN INTENSITY (850 MB
TEMPERATURES AROUND -30C) ACROSS THE AREA TUESDAY MORNING. THE
SHEER MAGNITUDE OF THIS COLD AIRMASS WILL UNDOUBTEDLY SUPPORT
ACTUAL SURFACE TEMPERATURES BOTTOMING OUT SEVERAL DEGREES BELOW
0F (POSSIBLY AS LOW AS -10F IN PARTS OF INTERIOR SECTIONS OF FAR
NORTHERN IL) MONDAY NIGHT INTO TUESDAY MORNING, WHICH IS QUITE
REMARKABLE CONSIDERING MUCH OF THIS AREA HAS LITTLE OR NO
SNOWPACK.
WHILE WIND SPEEDS WILL NOT BE AS STRONG DURING THE PEAK PERIOD
OF COLD WEATHER EARLY TUESDAY MORNING, THE COMBINATION OF THE
BITTERLY COLD TEMPERATURES WITH UP AROUND 10 MPH OF WIND WILL
SUPPORT DANGEROUS WIND CHILLS VALUES OF -20 TO -30F AREAWIDE
TUESDAY MORNING. ACCORDINGLY, EITHER ANOTHER COLD ADVISORY WILL
BE NEEDED, OR THE CURRENT ONE WILL NEED TO BE EXTENDED THROUGH
TUESDAY. WE WILL ALSO HAVE TO KEEP AN EYE ON THE POTENTIAL FOR
THE NEED FOR A EXCESSIVE COLD WARNING ACROSS MY NORTHERN TIER
COUNTIES, WHERE SUB -30F WIND CHILLS COULD RESULT FOR A SHORT
PERIOD EARLY TUESDAY MORNING.
FOLLOWING A BITTERLY COLD DAY TUESDAY, WITH ACTUAL AIR
TEMPERATURES ONLY CLIMBING A FEW DEGREES ABOVE 0F, TEMPERATURES
WILL FALL BACK A COUPLE OF DEGREES BELOW ZERO TUESDAY NIGHT.
WIND CHILLS MAY CONTINUE TO HOVER NEAR -20F THROUGH TUESDAY
NIGHT, SO ANY NEW COLD HEADLINE COULD NEED TO RUN THROUGH EARLY
WEDNESDAY MORNING. THEREAFTER, TEMPERATURES WILL BE ON A WARMING
TREND. IN FACT, WE SHOULD SEE READINGS REBOUNDING BACK UP TO
AROUND 30F BY THURSDAY.
SNOW CHANCES DURING THE COLD SNAP:
AS WE'VE MENTIONED IN THE PREVIOUS FEW DISCUSSIONS, A VORT MAX
EMBEDDED WITHIN THE FAST CYCLONIC FLOW IS FORECAST TO SLICE
THROUGH THE REGION MONDAY AFTERNOON AND EVENING. WHILE FORECAST
SOUNDINGS DON'T DEPICT PARTICULARLY THICK CLOUD LAYERS, JUST A
BIT OF ASCENT THROUGH A NEAR-SATURATED -30 C LAYER MAY BE ENOUGH
TO SQUEEZE OUT SOME VERY FINE SNOW. THERE'S EVEN A SIGNAL ON
TUESDAY IN THE GFS TO SUGGEST SOME FLURRY ACTIVITY CONTINUE THEN
AS WELL.
FROM WEDNESDAY THROUGH THE END OF THE WEEK, EXTENDED GUIDANCE
SUGGESTS, TO VARYING DEGREES, A POTENTIAL FOR SOME ADDITIONAL
PRECIPITATION CHANCES AS A BROAD TROUGH SWINGS ACROSS THE
CENTRAL CONUS. SIGNIFICANT SPREAD IN THE GUIDANCE AT THIS POINT
PRECLUDES MAKING ANY CHANGES TO THE DRY NBM-DELIVERED FORECAST,
HOWEVER.
KJB/CARLAW
AVIATION /18Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 1137 AM CST SAT JAN 18 2025
FORECAST CONCERNS INCLUDE...
NORTHERLY WINDS THIS AFTERNOON.
GUSTY NORTH/NORTHWEST WINDS THROUGH THE PERIOD.
MVFR CIGS THIS AFTERNOON ACROSS NORTHWEST IN.
WIND DIRECTIONS WILL REMAIN NORTHERLY FOR MUCH OF THIS AFTERNOON
AND MAY TURN NORTH/NORTHEAST AT TIMES FOR THE CHICAGO TERMINALS.
CONFIDENCE IS LOW IF WIND DIRECTIONS WILL BECOME PREVAILING 010
OR 020 AND TRENDS WILL NEED TO BE MONITORED. WIND GUSTS INTO THE
LOWER 20KTS ARE ALSO EXPECTED THIS AFTERNOON. WINDS WILL TURN
MORE TO THE NORTH/NORTHWEST THIS EVENING WITH GUSTS LIKELY
CONTINUING BUT ITS POSSIBLE GUSTS MAY BE MORE SPORADIC. WINDS
WILL TURN MORE TO THE NORTHWEST SUNDAY WITH GUSTS LIKELY
INCREASING BACK INTO THE MID 20KT RANGE.
LAKE EFFECT MVFR CIGS WILL CONTINUE ACROSS NORTHWEST IN THIS
AFTERNOON, SLOWLY SHIFTING TO THE EAST AND TO THE EAST OF GYY BY
LATE THIS AFTERNOON. A FEW FLURRIES WILL ALSO BE POSSIBLE ACROSS
NORTHWEST IN THIS AFTERNOON. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...COLD WEATHER ADVISORY FROM 3 AM SUNDAY TO NOON CST MONDAY FOR
ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-ILZ012.
COLD WEATHER ADVISORY FROM 6 PM SUNDAY TO NOON CST MONDAY FOR
ILZ006-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-
ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.
IN...COLD WEATHER ADVISORY FROM 6 PM CST /7 PM EST/ SUNDAY TO NOON
CST /1 PM EST/ MONDAY FOR INZ001-INZ002-INZ010-INZ011-
INZ019.
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 FROM NOON SUNDAY TO 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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