618
FXUS63 KLOT 211130
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
530 AM CST TUE JAN 21 2025
KEY MESSAGES
- ARCTIC EPISODE PEAKS THIS MORNING. WIND CHILLS AROUND 30 TO 35
BELOW ACROSS INTERIOR NORTHERN AND NORTHWEST ILLINOIS, AND
AROUND 25 BELOW ELSEWHERE.
- ANOTHER COLD NIGHT TONIGHT, BUT TEMPERATURES MODERATE WEDNESDAY
INTO THE END OF THE WEEK.
- THREAT FOR ACCUMULATING SNOW (COATING TO AN INCH) INCREASING
WEDNESDAY AND PARTICULARLY WEDNESDAY NIGHT. MAY LEAD TO
SLIPPERY TRAVEL GIVEN VERY COLD GROUND TEMPERATURES.
DISCUSSION
ISSUED AT 246 AM CST TUE JAN 21 2025
THROUGH WEDNESDAY NIGHT:
THIS LATEST ARCTIC BLAST IS REACHING PEAK INTENSITY OVER THE
REGION EARLY THIS MORNING AS A SUBTLE REINFORCING FRONT HAS
USHERED IN THE COLDEST AIRMASS OF THE STRETCH. UPSTREAM, AIR
TEMPERATURES ARE FALLING AT A RATE OF ABOUT 1 TO 2 DEGREES PER
HOUR, AND LOOK TO BOTTOM OUT NEAR 10 TO EVEN LOCALLY 12 BELOW IN
SPOTS ACROSS OUR FAR NORTH AND WESTERN LOCALES. WITH A
PERSISTENT WESTERLY BREEZE, WIND CHILLS WILL LIKELY END UP IN
THE 30 TO 35 BELOW RANGE ACROSS OUR NORTH AND WEST COUNTIES--
RIGHT UNDER THE CORE OF THE COLDEST PART OF THE 850 MB AIRMASS.
FURTHER SOUTH AND EAST, WIND CHILLS WILL BE NEAR 25 BELOW. THE
COLDEST PERIOD THIS MORNING WILL BE FROM ROUGHLY 5 AM TO 10 AM,
ALTHOUGH WIND CHILLS WILL BE SLOW TO RECOVER EVEN INTO THE
AFTERNOON, AND MAY NOT MEANINGFULLY RISE ABOVE 20 BELOW UNTIL
AFTER ABOUT 3 PM. WITH ALL OF THIS SAID, HAVE UPGRADED A PORTION
OF THE COLD WEATHER ADVISORY TO AN EXTREME COLD WARNING WHERE
WIND CHILLS LOOK TO SETTLED INTO THE 30 TO 35 BELOW RANGE.
OTHERWISE, WHILE GENERALLY MOSTLY SUNNY CONDITIONS ARE EXPECTED
TODAY, HAVE HELD ON TO A SMALL CHANCE FOR FLURRIES THIS MORNING
MAINLY ACROSS THE NORTHEASTERN THIRD OF THE AREA. IR SATELLITE
LOOPS REVEAL SOME LINGERING "STRINGY" STRATOCU, AND GIVEN HOW
EASY IT'S BEEN TO CRANK OUT FLURRIES FROM THESE SHALLOW CLOUDS,
FELT IT PRUDENT TO CONTINUE THE MENTION FOR A BIT LONGER. NO
ACCUMULATIONS ARE EXPECTED, HOWEVER.
WARM ADVECTION WILL COMMENCE IN EARNEST TONIGHT AS WINDS FLIP
OUT OF THE SOUTH AND SOUTHWEST. THIS SHOULD RESULT IN LOW
TEMPERATURES BEING HIT DURING THE EVENING AND THEN EITHER FLAT
LINING OR SLOWLY RISING THROUGH THE REST OF THE NIGHT. WINDS
SHOULD ALSO GRADUALLY INCREASE AFTER MIDNIGHT, SO THE NET RESULT
OF THIS IS WIND CHILL VALUES REMAINING FAIRLY STAGNANT AROUND 15
BELOW. WITH THE BURGEONING WAA AND A SOMEWHAT SPLOTCHY NATURE
TO ANY SUB -20 F WIND CHILLS TONIGHT, ELECTED TO FORGO AN
ADDITIONAL ADVISORY, BUT IT'S CONCEIVABLE A FINAL ONE MIGHT BE
NEEDED TODAY. REGARDLESS, WE'LL FINALLY BE EXITING THIS COLD
SPELL ON WEDNESDAY AND BEYOND.
FOR THE WEDNESDAY TO WEDNESDAY NIGHT PERIOD: THE MAIN CHANGE WAS
TO BOOST LIGHT SNOW CHANCES, PARTICULARLY WEDNESDAY EVENING AND
OVERNIGHT AS A SERIES OF WAVES TRAVERSE THE REGION OVERHEAD.
WHILE FORCING GENERALLY DOESN'T LOOK SUPER SIGNIFICANT,
PERSISTENT MODEST UVVS AROUND 2 TO 4 UBAR/SECOND, COMBINED WITH
FORECAST PROFILES THAT LOOK INCREASINGLY SATURATED SHOULD
SUPPORT LIGHT PRECIP ACROSS MOST OF THE REGION. THIS INITIALLY
WILL FOCUS ACROSS FAR NORTHERN ILLINOIS WEDNESDAY MORNING AND
AFTERNOON, BEFORE MARCHING SOUTH AND EAST WITH TIME OVERNIGHT.
FAIRLY DEEP DGZS (NEAR 3 KM AT TIMES) SHOULD SUPPORT EFFICIENT
SNOWFLAKE PRODUCTION, LIKELY ENOUGH TO HELP PUNCH THROUGH ANY
REMAINING DRY SUB-CLOUD LAYER.
QPF AMOUNTS THROUGH WEDNESDAY NIGHT LOOK FAIRLY LIGHT, BUT WITH
HIGH SLRS PROBABLY IN EXCESS OF 15-18:1, A FLUFFY COATING TO
INCH SEEMS REASONABLE TO EXPECT. WITH GROUND TEMPERATURES LIKELY
TO STILL BE VERY COLD FROM THE RECENT STRETCH, CONCERN IS THAT
EVEN THIS LIGHT SNOW MAY LEAD TO TRAVEL IMPACTS. CARLAW
THURSDAY THROUGH MONDAY:
AS THIS SYSTEM EXITS TO THE EAST, WINDS OVER THE WATERS WILL
TURN TO THE NORTHWEST FOR BETTER FETCH INTO NORTHWEST INDIANA.
MODEL SOUNDINGS ARE SHOWING SOME LOW LEVEL SATURATION AND
INSTABILITY FOR THE POTENTIAL OF LAKE EFFECT SNOW THROUGH THE
DAY ON THURSDAY BEFORE WINDS TURN WEST AT NIGHT. THE ONE MAIN
QUESTION WILL BE ICE COVERAGE OVER THE LAKE AS WEBCAMS IN
MICHIGAN CITY ON MONDAY ALREADY SHOWED EXPANSIVE PANCAKE ICE
FORMING. NEVERTHELESS, IT WAS DECIDED TO ADD CHANCE POPS IN THE
NORTHEAST PORTION OF PORTER COUNTY FOR THURSDAY.
TEMPERATURES WILL SLOWLY STAIR-STEP UPWARDS TOWARD MORE SEASONAL
NORMS INTO THIS WEEKEND. ENSEMBLE GUIDANCE IS SUGGESTING ANOTHER
COUPLE OF UPPER LEVEL WAVES, ONE ON FRIDAY AND ANOTHER ON
SATURDAY, MOVING OVER THE AREA. THE CURRENT SIGNAL FOR THE
FRIDAY WAVE IS TOO DRY, BASED ON CURRENT PROJECTIONS, TO ADD ANY
POPS TO THE FORECAST. AS FOR THE SATURDAY SYSTEM, MODEL
SOUNDINGS DO SHOW A LITTLE ASCENT THROUGH A MORE SATURATED
COLUMN OF THE DGZ. IT IS NOT A STRONG SIGNAL SO THE FORECAST WAS
KEPT DRY FOR NOW, THOUGH IT WOULD NOT BE SURPRISING IF IN LATER
PACKAGES A MENTION OF FLURRIES MIGHT NEED TO BE ADDED. BEYOND
THIS WEEKEND, ZONAL FLOW LOOKS TO DEVELOP. MAYBE THERE IS
ANOTHER WEAK WAVE EARLY NEXT WEEK, BUT NOTHING OF CONSEQUENCE AT
THIS DISTANCE, OTHER THAN A CHANCE FOR ABOVE NORMAL
TEMPERATURES AROUND TUESDAY.
DK
AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 530 AM CST TUE JAN 21 2025
KEY AVIATION MESSAGES FOR THE CURRENT TAF PERIOD:
- BITTERLY COLD WIND CHILLS THROUGH THIS AFTERNOON
THERE ARE NO MAJOR AVIATION WEATHER CONCERNS THROUGH THE
CURRENT TAF PACKAGE. HOWEVER, IT SHOULD BE NOTED THAT THERE ARE
DANGEROUS WIND CHILLS EXPECTED THROUGH THIS AFTERNOON THAT WILL
IMPACT GROUND STAFF WORKING OUTDOORS.
AS AN UPPER LEVEL WAVE EXITS THE REGION, ALL CHANCES FOR
FLURRIES IN THE SHORT TERM HAVE FOR THE MOST PART MOVED OUT OVER
LAKE MICHIGAN. PERHAPS A BRIEF FLURRY MOVES OVER GYY IN THE
NEXT COUPLE HOURS, BUT NO ACCUMS ARE EXPECTED.
WINDS WILL REMAIN OUT OF THE WEST TO NORTHWEST THROUGH THE DAY.
THERE HAVE BEEN ISOLATED GUSTS UP TO 20 KNOTS, BUT NOT
PERSISTENT ENOUGH TO INCLUDE IN A PREVAILING LINE ANYWHERE.
HOWEVER, WIND GUSTS ARE EXPECTED TO BE MORE PERSISTENT THIS
AFTERNOON WITH GUSTS BETWEEN 20 TO 25 KNOTS. AS WINDS SUBSIDE
THIS EVENING, THEY WILL GRADUALLY TURN TO THE SOUTHWEST. THE
NEXT WAVE STARTS TO MOVE DOWN FROM THE NORTHWEST LATE TONIGHT.
A STRONG LOW LEVEL JET WILL INCREASE TOMORROW MORNING AHEAD OF
IT WITH CLOSE TO 50 KNOT WINDS AROUND 3000 FEET. THERE WILL BE
WIND GUSTS BETWEEN 20 TO 25 KT AT THE SURFACE, BUT THERE IS A
CHANCE FOR ISOLATED GUSTS UP TO 30 KNOTS. THIS NEXT SYSTEM WILL
LIKELY HAVE CHANCES FOR ACCUMULATING SNOW WITH IT, BUT THE
BETTER CHANCES ARE OUTSIDE OF THE CURRENT TAF WINDOW (WEDNESDAY
AFTERNOON/EVENING). PERHAPS THERE ARE A FEW VFR FLURRIES AHEAD
OF IT, BUT FOR NOW THE TAFS WERE KEPT DRY.
DK
LOT WATCHES/WARNINGS/ADVISORIES
IL...EXTREME COLD WARNING UNTIL NOON CST TODAY FOR ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ019.
COLD WEATHER ADVISORY UNTIL 2 PM CST THIS AFTERNOON FOR ILZ013-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
ILZ105-ILZ106-ILZ107-ILZ108.
IN...COLD WEATHER ADVISORY UNTIL 2 PM CST /3 PM EST/ THIS AFTERNOON
FOR INZ001-INZ002-INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 6 PM CST
WEDNESDAY FOR THE IL AND IN NEARSHORE WATERS.
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