716
FXUS63 KLOT 160503
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1103 PM CST SAT FEB 15 2025
KEY MESSAGES
- PERIOD OF LIGHT ACCUMULATING SNOW EXPECTED WELL SOUTH OF I-80
TONIGHT.
- LAKE EFFECT SNOW EXPECTED ALONG AND NEAR THE IL AND IN LAKE
MICHIGAN SHORES LATE TONIGHT THROUGH SUNDAY MORNING. SOME
LOCALIZED TRAVEL IMPACTS POSSIBLE DUE TO SNOW COVERED ROADS.
- EXPECT BITTERLY COLD CONDITIONS SUNDAY NIGHT THROUGH WEDNESDAY
MORNING WITH DANGEROUSLY LOW WIND PROBABLE IN AT LEAST PARTS OF
THE AREA MONDAY AND TUESDAY MORNINGS. WIND CHILLS MAY STAY NEAR
TO BELOW ZERO ALL THE WAY FROM SUNDAY EVENING THROUGH WEDNESDAY
MORNING.
- THERE'S A LOW CHANCE OF ACCUMULATING SNOW WELL SOUTH OF I-80
MONDAY AFTERNOON AND EVENING, THEN A CHANCE OF FLUFFY
ACCUMULATING SNOW AND ASSOCIATED TRAVEL IMPACTS AREAWIDE ON
WEDNESDAY-WEDNESDAY NIGHT.
UPDATE
ISSUED AT 944 PM CST SAT FEB 15 2025
POCKETS OF VERY LIGHT SNOW, AT TIMES CHANGING TO FREEZING
DRIZZLE ("SNIZZLE") CONTINUES ACROSS THE REGION, COINCIDENT
WITH AN EARLIER RASH OF SEVERE ICING PIREPS, INDICATIVE OF THE
LACK OF CLOUD ICE. RECENTLY, OBSERVATIONS HAVE TRENDED MORE
TOWARDS SNOW WITH CLOUD TOPS GRADUALLY COOLING CLOSER TO -10 C.
GIVEN THE INCREDIBLY LIGHT NATURE OF ANY LINGERING FREEZING
DRIZZLE, NOT OVERLY CONCERNED ABOUT TRAVEL IMPACTS.
ATTENTION IS SHIFTING TO LAKE EFFECT SNOW, WITH THE INITIAL
SIGNS OF DEVELOPMENT IN REGIONAL RADARS TO THE NORTH (TMKE AND
KGRB IN PARTICULAR). FORECAST SOUNDINGS REVEAL THE LES PARAMETER
SPACE IS SORT OF "LOW-MID TIER" WITH INVERSION HEIGHTS BUILDING
TO AROUND 8 KFT AND LAKE INDUCED CAPE OF MAYBE 50-100 J/KG AT
TIMES. INCOMING HIRES GUIDANCE IS CRANKING OUT ANYWHERE FROM A
FEW HUNDREDTHS TO JUST NORTH OF A TENTH OF AN INCH OF LIQUID
EQUIVALENT NEAR THE LAKE. WITH SLRS JUST A BIT NORTH OF 10-11:1,
THIS COULD FLUFF UP TO AN INCH OR A SMIDGE MORE AT THE LAKE.
WITH AIR TEMPERATURES FALLING INTO THE MID/UPPER 20S TONIGHT
INTO SUNDAY MORNING, THIS SNOWFALL MAY LEAD TO SOME SLIPPERY
CONDITIONS, WHICH APPEAR WELL-HIGHLIGHTED BY THE CURRENT SPS
(WHICH WE'LL BE REISSUING HERE SHORTLY).
THE MAIN WINDOW FOR ACCUMULATING SNOW FOR OUR NE ILLINOIS
COUNTIES WILL BE ABOUT 3 AM THROUGH 9 AM BEFORE THE BAND SWINGS
EAST INTO NW INDIANA. WHILE THE BAND'S RESIDENCE TIME STILL
LOOKS FAIRLY BRIEF (2-3 HOURS OR LESS), LAKE PARAMETERS IMPROVE
PERHAPS JUST A HAIR. HOURLY RATES STILL DON'T LOOK OVERLY
CONCERNING, BUT THE EASTERN PARTS OF LAKE COUNTY, INDIANA AND
MUCH OF PORTER COUNTY LOOK LIKE THE AREAS TO WATCH A BIT MORE
CLOSELY WITH A POTENTIAL FOR LOCALLY HIGHER TOTALS (ASSUMING THE
BAND DOESN'T RAPIDLY PIVOT EASTWARD).
CARLAW
DISCUSSION
ISSUED AT 310 PM CST SAT FEB 15 2025
THROUGH SUNDAY:
WHILE THE BAND OF WINTRY PRECIPITATION ACROSS NORTHERN IL IS NOW
EXITING TO EAST OF THE AREA, ATTENTION IS NOW FOCUSED ON THE NEXT
BATCH OF WINTRY PRECIPITATION CURRENTLY NOTED EXPANDING
NORTHEASTWARD ACROSS MO. THIS ACTIVITY IS DEVELOPING WITHIN A
STRENGTHENING DEFORMATION ZONE ORIENTED ALONG THE BAROCLINIC ZONE
CURRENTLY IN PLACE ON THE NORTHWEST PERIPHERY OF A CONSOLIDATING
SURFACE LOW OVER THE OZARKS. AS THIS SURFACE DEEPENS AND SHIFTS
INTO THE OHIO VALLEY TONIGHT, THE EXPECTATION IS FOR THIS AREA OF
PRECIPITATION TO DEVELOP EAST-NORTHEASTWARD ACROSS MY SOUTHERN
COUNTIES (WELL SOUTH OF I-80) THROUGH THE EVENING.
THE PRECIPITATION MAY ONSET IN THIS AREA AS A WINTRY MIX, BUT
SHOULD TRANSITION OVER TO SNOW THROUGH THE EVENING AS A COLDER
AIRMASS SHIFTS INTO THE AREA. SINCE EVEN MY FAR SOUTHERN AREAS
ARE EXPECTED TO REMAIN ALONG THE NORTHERN/NORTHWESTERN PERIPHERY
OF AREA OF SNOW, THE RATES ARE EXPECTED TO BE OVERLY IMPRESSIVE
(GENERALLY A 0.5" OR LESS PER HOUR), THUS LIMITING IMPACTS TO
TRAVEL AND TOTAL SNOWFALL TONIGHT. NEVERTHELESS, WITH AN INCH OR
TWO OF SNOW, AND LIGHT TRAVEL IMPACTS, WE OPTED TO HIGHLIGHT AREAS
SOUTH OF I-80 WITH AN SPS. LITTLE OR NO SNOW EXPECTED I-80 AND
NORTHWARD WITH THIS PARTICULAR BATCH OF PRECIPITATION TONIGHT.
WINDS WILL BE INCREASINGLY FROM THE NORTH-NORTHWEST TONIGHT IN
RESPONSE TO THE DEEPENING LOW SHIFTING UP THE OHIO VALLEY. AS THEY
DO, THE NORTHERLY FETCH OVER LAKE MICHIGAN WILL COMBINE WITH
INCREASINGLY FAVORABLE THERMODYNAMICS TO SUPPORT THE DEVELOPMENT
OF A LAKE EFFECT BAND OF SNOW. THIS BAND OF SNOW SHOULD SET UP
ALONG THE WI SHORE THIS EVENING, BEFORE SHIFTING SOUTHWARD DOWN
THE WESTERN SHORE OF THE LAKE OVERNIGHT. IT DOES APPEAR THAT A
PERIOD OF ACCUMULATING LAKE EFFECT SNOW WILL IMPACT AREAS NEAR AND
ALONG THE IL AND IN LAKE MICHIGAN SHORES LATE TONIGHT THROUGH
SUNDAY MORNING.
WHILE THIS MAY RESULT IN SOME LOCALIZED AMOUNTS OF 2 TO
3", IT APPEARS THE BAND OF SNOW WILL REMAIN PROGRESSIVE ENOUGH TO
LIMIT ITS DURATION IN ANY GIVEN LOCATION. ACCORDINGLY, WE HAVE
OPTED TO HOLD OFF ON ANY TYPE OF WINTER HEADLINE AT THIS TIME.
EXPECT THIS LAKE EFFECT BAND TO BECOME FOCUSED MAINLY ACROSS THE
NORTHWESTERN IN SHORE SUNDAY MORNING BEFORE SHIFTING EAST OF THE
AREA IN THE AFTERNOON.
OUTSIDE OF THE LAKE EFFECT SNOW INTO SUNDAY MORNING, IT APPEARS
SOME SCATTERED SNOW SHOWERS AND FLURRIES WILL BE POSSIBLE FOR MOST
AREAS IN THE AFTERNOON AS THE AIRMASS QUICKLY TURNS MUCH COLDER.
GUSTY NORTHWESTERLY WINDS OF 35+ MPH WILL ALSO RESULT IN SOME
PATCHY AREAS OF BLOWING SNOW IN THE OPEN AREAS OF NORTHERN IL, AND
WILL ALSO MAKE FOR SOME VERY COLD WIND CHILLS, PARTICULARLY INTO
SUNDAY NIGHT. STRONG COLD AIR ADVECTION ON THESE NORTHWESTERLY
WINDS WILL SEND TEMPERATURES DOWN THROUGH THE DAY, WITH READINGS
EXPECTED TO FALL INTO THE LOW 20S BY LATE AFTERNOON. MOST NOTABLE,
HOWEVER, WILL BE THE WIND CHILLS, WHICH WILL BE DROPPING BELOW
ZERO BY EARLY SUNDAY EVENING.
KJB
SUNDAY NIGHT THROUGH SATURDAY:
A QUASI-STATIONARY BLOCKING REGIME WILL SET UP THIS WEEK DUE TO
GENERALLY ABOVE NORMAL MID-LEVEL HEIGHT ANOMALIES FROM NEAR ALASKA
TO GREENLAND. LOBES OF THE TROPOSPHERIC POLAR VORTEX ASSOCIATED
WITH BITTERLY COLD ARCTIC AIR MASSES WILL REMAIN TRAPPED SOUTH
OF THE HIGH-LATITUDE BLOCKING. IN TERMS OF TEMPERATURES AND WIND
CHILLS, THE UPCOMING WORK WEEK MAY RIVAL OR SURPASS THE COLDEST
STRETCH OF THIS WINTER THUS FAR, BACK IN MID TO LATE JANUARY.
BUT WITH RESPECT TO DAILY NORMALS, THIS WEEK WILL BE COLDER THAN
THE JANUARY COLD SNAP SINCE OUR AVERAGE TEMPS STEADILY CLIMB IN
MID TO LATE FEBRUARY.
WHILE TEMPERATURES ALOFT (AT 850 MB) WILL NOT BE AS COLD AS IN
THE JANUARY COLD SNAP, THE MAIN DIFFERENCE THIS WEEK WILL BE THE
EXPANSIVE SNOW COVER ACROSS MUCH OF THE REGION, PARTICULARLY
UPSTREAM, WHICH IS OUR SOURCE REGION. AS THE -16 TO -20C AIR MASS
AT 850 MB BUILDS IN SUNDAY NIGHT, THE PRESSURE GRADIENT WILL
REMAIN TIGHT, RESULTING IN BLUSTERY WEST-NORTHWEST WINDS GUSTING
TO 35 MPH IN THE EVENING AND 25-30 MPH OVERNIGHT INTO EARLY
MONDAY. ENSEMBLE PROBABILITIES FOR LOWS OF 0F OR COLDER SUPPORT
NEAR TO A FEW/SEVERAL DEGREE BELOW ZERO LOWS FOR ABOUT THE
NORTHERN 2/3 OF THE AREA, COLDEST ACROSS INTERIOR NORTHERN
ILLINOIS. THIS WILL TRANSLATE TO MINIMUM WIND CHILLS OF -15 TO
-25F, AGAIN COLDEST ACROSS INTERIOR NORTHERN ILLINOIS, AND WE'LL
LIKELY NEED A COLD WEATHER ADVISORY FOR MUCH OF IF NOT THE ENTIRE
AREA.
THE BLOCKING IN PLACE WILL UNFORTUNATELY RESULT IN LITTLE AIR MASS
CHANGE MONDAY-TUESDAY, WITH LIKELY EVEN A REINFORCING COLD SHOT
KNOCKING DOWN 850 MB TEMPS A BIT MONDAY NIGHT INTO TUESDAY.
DESPITE THE STEADILY STRENGTHENING MID FEBRUARY SUN, THE SNOW
COVER AND CLOUD COVER (ESPECIALLY ON MONDAY) WILL RESULT IN HIGHS
BELOW 10F FOR A MAJORITY OF THE AREA. BREEZY WESTERLY WINDS MONDAY
AFTERNOON WILL KEEP WIND CHILLS BELOW ZERO THROUGH THE DAY.
AS THE REINFORCING COLD ARRIVES MONDAY NIGHT INTO TUESDAY WITH A
~1050 (!) MB BUILDING INTO THE NORTHERN PLAINS, THE MAIN WILD CARD
FOR HOW COLD IT MAY GET WILL BE WHETHER SKIES CAN CLEAR OUT
SUFFICIENTLY. AS IT STANDS, OUR FORECAST HAS LOWS AROUND -10F NEAR
AND WEST OF THE FOX VALLEY, WITH LOW-MID MINUS SINGLE DIGITS
ELSEWHERE. NORTHWEST WINDS OF 5-15 MPH WILL BRING ANOTHER NIGHT OF
DANGEROUSLY LOW WIND CHILLS OF 15 TO 25 BELOW (LOCALLY -25 TO -30F
POSSIBLE ACROSS INTERIOR NORTHERN IL). IT SHOULD CLOUD UP AGAIN
TUESDAY NIGHT, RESULTING IN LOW TEMPS A FEW TO SEVERAL DEGREES
HIGHER THAN MONDAY NIGHT.
REGARDING SNOW CHANCES IN THE EARLY PART OF THE WORK WEEK, THE
MAIN TIMEFRAME OF INTEREST IS MONDAY AFTERNOON AND EVENING AS A
FRONTOGENESIS DRIVEN BAND OF SNOW COULD POSSIBLY EXTEND INTO AREAS
WELL SOUTH OF I-80, IF DRY AIR IS ERODED ENOUGH. WE ONLY HAVE
SLIGHT CHANCE POPS (~20%) FOR THIS FOR NOW, BUT GIVEN HOW COLD
IT'LL BE, IT DOESN'T TAKE MUCH SNOW TO CAUSE TRAVEL ISSUES.
THERE'S A BETTER CHANCE OF FLUFFY SNOW AREAWIDE DURING THE
WEDNESDAY THROUGH WEDNESDAY NIGHT TIMEFRAME AS A MID-LEVEL SHORT-
WAVE . IN ADDITION, FAVORABLE LAKE INDUCED THERMODYNAMICS AND
CONVERGENCE COULD YIELD A MODERATE TO HEAVY SNOW BAND OVER THE
SOUTHERN PART OF THE LAKE (GENERAL LOCATION TBD, BUT IT COULD
INCLUDE SOME OF OUR LAKE EFFECT PRONE COUNTIES).
ASIDE FROM THE LAKE EFFECT SNOW POTENTIAL ON WEDNESDAY INTO EARLY
THURSDAY, MOST ENSEMBLE GUIDANCE POINTS TOWARDS A HIGH POP AND
GENERALLY LIGHT QPF SCENARIO. BUT WITH THE LOWER LEVELS OF THE
COLUMN IN THE DGZ (-12 TO -18C), AS LONG AS THERE'S AT LEAST
MODEST ASCENT WELL ALIGNED WITH THE DGZ, RATIOS COULD BE WELL
ABOVE CLIMO. REGARDLESS OF THE SNOW RATIOS, AS ALREADY NOTED RE.
MONDAY PM SNOW CHANCE SOUTH, WITH TEMPS THIS COLD, IT REALLY
DOESN'T TAKE MUCH SNOW TO RESULT IN HAZARDOUS TRAVEL CONDITIONS.
THE MAIN CHANGE WITH THIS ISSUANCE WAS TO EXPAND THE COVERAGE OF
CHANCE POPS TO INCLUDE MOST OF THE CWA.
IN THE WAKE OF WHATEVER PLAYS OUT WEDNESDAY-WEDNESDAY NIGHT, THE
COLD WILL FINALLY LOSE ITS GRIP BY THE WEEKEND. HOWEVER, THE
PRESENCE OF EXPANSIVE ~1040 MB SURFACE HIGH PRESSURE OVER THE
CENTRAL CONUS (AND SLOWLY TRANSLATING EASTWARD) WILL KEEP TEMPS
WELL BELOW NORMAL, ALBEIT MODERATING, ALL THE WAY THROUGH
SATURDAY. THE EXTENDED DURATION OF WELL BELOW FREEZING TEMPS WILL
INCREASE THE RISK FOR ICE JAM RELATED FLOODING NEAR RIVERS.
CASTRO
AVIATION /06Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 1103 PM CST SAT FEB 15 2025
LOWER-END MVFR CEILINGS WITH INTERMITTENT FLURRIES WILL PERSIST
THROUGH THE NIGHT AS NNW WINDS GUST TO AROUND 25 KNOTS. LAKE
EFFECT SNOW WILL BRUSH THE ILLINOIS SHORE FROM THE PRE-DAWN
HOURS THROUGH AROUND 13-14Z, POSSIBLY BRINGING A PERIOD OF MVFR
VISIBILITY AT ORD AND IFR VISIBILITY AT MDW. ANY LAKE EFFECT
SNOW BANDS OVER NORTHEAST ILLINOIS SHOULD BE BRIEF (1-2 HOURS)
BEFORE SHIFTING ACROSS NORTHWEST INDIANA THROUGH THE MORNING AND
AFTERNOON. MVFR CEILINGS WILL CONTINUE TODAY AMIDST STRONG COLD
AIR ADVECTION OVER THE AREA. STRATOCUMULUS WILL SUPPORT
ISOLATED TO SCATTERED FLURRIES OR BRIEF LIGHT SNOW SHOWERS LATE
MORNING THROUGH MID AFTERNOON. DRY CONDITIONS ARE THEN EXPECTED
TONIGHT.
NNW WINDS CURRENTLY GUSTING TO AROUND 25 KNOTS WILL INCREASE TO
30 KNOTS FROM AROUND SUNRISE THROUGH MID-MORNING. NW WINDS WILL
CONTINUE TO GUST OVER 25 KNOTS THROUGH THE REMAINDER OF THE DAY
AND UP TO 25 KNOTS TONIGHT.
KLUBER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 6 AM CST MONDAY FOR THE IL
NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL 6 AM CST SUNDAY FOR THE IN
NEARSHORE WATERS.
GALE WARNING FROM 6 AM SUNDAY TO MIDNIGHT CST SUNDAY NIGHT FOR
THE IN NEARSHORE WATERS.
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