609
FXUS63 KLOT 200929
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
329 AM CST THU FEB 20 2025
KEY MESSAGES
- LIGHT LAKE EFFECT SNOW SHOWERS WILL CLIP NORTHEAST PORTER
COUNTY AT TIMES THROUGH THIS AFTERNOON.
- A RETURN TO NEAR TO ABOVE NORMAL TEMPERATURES IS EXPECTED NEXT
WEEK.
DISCUSSION
ISSUED AT 329 AM CST THU FEB 20 2025
THROUGH FRIDAY:
A SPRAWLING 1040+ MB SURFACE HIGH IS CURRENTLY CENTERED ACROSS
THE NATION'S MID-SECTION WHERE DANGEROUS COLD CONTINUES TO OUR
WEST. MEANWHILE A MID- TO UPPER-LEVEL WAVE IS TRAVERSING
THE GREAT LAKES REGION. WHILE A FEW FLURRIES HAVE BEEN OBSERVED
AT TIMES OVERNIGHT HERE LOCALLY, THE MAJORITY OF THIS ACTIVITY
HAS REMAINED LARGELY SOUTH AND EAST OF THE LOCAL AREA DUE TO
VERY DRY LOW-LEVELS KEEPING SNOW FROM REACHING THE SURFACE.
PERIODS OF LOW CLOUDS ARE EXPECTED AT TIMES TODAY WHICH MAY
LIMIT SOME OF OUR DAYTIME WARMING. HOWEVER, HIGHS ARE STILL
EXPECTED TO WARM INTO THE LOW TO MID 20S TODAY FOR SOME THIS
AFTERNOON WITH UPPER TEENS TO AROUND 20 EXPECTED ACROSS
INTERIOR NORTHERN ILLINOIS.
LAKE EFFECT SNOW PARAMETERS REMAIN MAXIMIZED EAST OF THE AREA
WHERE MORE DOMINANT BUT TRANSIENT LAKE EFFECT BAND(S)/EMBEDDED
MESO-LOWS ARE EXPECTED TO CONTINUE ACROSS PORTIONS OF SOUTHWEST
LOWER MICHIGAN AND NORTHWEST INDIANA THROUGH TODAY. HAVE
MAINTAINED A 20-30% CHANCE OF LAKE EFFECT SNOW SHOWERS ACROSS
NORTHEAST PORTER COUNTY THROUGH THIS AFTERNOON TO ACCOUNT FOR
LIGHT MEASURABLE SNOW OCCURRING AT TIMES ON THE WESTERN FRINGES
OF THE LAKE EFFECT BAND.
TEMPERATURES WILL BE COLD YET AGAIN TONIGHT DUE TO CONDITIONS
BECOMING FAVORABLE FOR MORE EFFICIENT RADIATIONAL COOLING
COMPARED TO THE PAST COUPLE OF NIGHTS (MOSTLY CLEAR SKIES AND
LIGHTER WINDS). EXPECT SINGLE DIGIT LOWS OUTSIDE OF CHICAGO WITH
NEAR TO SLIGHTLY BELOW ZERO TEMPS POSSIBLE ACROSS INTERIOR
NORTHERN ILLINOIS. THE LIGHTER WINDS SHOULD KEEP WIND CHILLS
MOSTLY IN CHECK, WITH FORECAST MINIMUM WIND CHILL VALUES IN THE
0 TO -10 DEGREE RANGE THROUGH EARLY FRIDAY MORNING.
WINDS BEGIN TO TAKE ON A MORE SOUTHWESTERLY COMPONENT DURING
THE DAY ON FRIDAY AS THE CENTER OF THE SURFACE HIGH BEGINS TO
GRADUALLY DRIFT SOUTH OF THE AREA. THIS COMBINED WITH MID-LEVEL
RIDGING BUILDING BACK INTO THE REGION SHOULD ALLOW TEMPERATURES
TO WARM A BIT MORE ON FRIDAY WITH MID-UPPER 20S FORECAST
NEAR/EAST OF I-55 AND LOWER 20S ACROSS INTERIOR NORTHERN
ILLINOIS.
PETR
FRIDAY NIGHT THROUGH THURSDAY:
AFTER A COLD START TO THE DAY ON SATURDAY (THOUGH COMPARATIVELY
NOT AS COLD AS EARLIER IN THE WEEK), WARM AIR ADVECTION OFF OF
SOUTHWESTERLY WINDS WILL ALLOW TEMPERATURES TO MODERATE OVER THE
WEEKEND AND INTO EARLY NEXT WEEK. WHILE THERE ARE STILL SOME
UNCERTAINTIES TIED TO CLOUD COVER AND HOW QUICKLY OUR EXISTING
SNOWPACK WILL MELT, NEAR TO ABOVE NORMAL TEMPERATURES ARE LIKELY
TO BE PRESENT ACROSS THE AREA EARLY NEXT WEEK WITH EVEN SOME 50
DEGREE READINGS APPEARING TO BE ATTAINABLE ACROSS OUR SOUTHERN
COUNTIES. DURING THIS WARMUP, WE'LL NEED TO MONITOR THE
POTENTIAL FOR ICE JAM-RELATED LOCALIZED FLOODING ALONG SOME
AREA RIVERS AS RIVER ICE MELTS AND ICE JAMS BREAK UP.
A MORE ACTIVE NORTHWEST FLOW PATTERN ALOFT IS PROGGED TO SET UP
ACROSS THE REGION OVER THE WEEKEND AND INTO NEXT WEEK WITH
MULTIPLE SUCCESSIVE SHORTWAVE TROUGHS DIVING SOUTHEASTWARD INTO
THE MIDWEST/GREAT LAKES. THE FIRST TWO OF THESE SHORTWAVES ARE
SLATED TO PASS BY ON SATURDAY AND ON SUNDAY, THOUGH ENSEMBLE
GUIDANCE IS NOW IN ALMOST UNANIMOUS AGREEMENT THAT NEITHER OF
THESE SHORTWAVES WILL DO ANYTHING MORE THAN JUST CAUSING AN
UPTICK IN MID- TO HIGH-LEVEL CLOUD COVER. LOW-LEVEL WARM AIR
ADVECTION/ISENTROPIC UPGLIDE COULD HELP YIELD SOME LOWER CLOUDS
DURING THIS TIME AS WELL, THOUGH GFS AND ECMWF FORECAST
SOUNDINGS SUGGEST THAT THIS LOWER CLOUD LAYER LIKELY WON'T GROW
DEEP ENOUGH TO SUPPORT PRECIPITATION.
A PAIR OF MORE ROBUST SHORTWAVE TROUGHS THEN LOOK TO TRAVERSE
THE REGION DURING THE FIRST HALF OF THE UPCOMING WORKWEEK, WITH
THE FIRST OF THESE COMING LATE SUNDAY NIGHT INTO MONDAY AND THE
SECOND SWINGING BY MONDAY NIGHT OR TUESDAY. RELATIVE TO THE
WEEKEND SHORTWAVES, THERE IS BETTER ENSEMBLE AGREEMENT ON BOTH
OF THESE WAVES INDUCING PRECIPITATION IN THE REGION, BUT STILL
SOME NON-TRIVIAL DIFFERENCES IN THEIR EXACT TRACKS, AND HENCE
THEIR RESULTANT QPF FOOTPRINTS -- PARTICULARLY WITH THE SECOND
WAVE. THE NBM'S POPS FOR THIS PERIOD ARE PROBABLY A BIT LOWER
THAN THEY SHOULD BE, BUT COULDN'T REALLY JUSTIFY MAKING NOTABLE
CHANGES TO THEM GIVEN THE EXISTING SPATIAL AND TEMPORAL
UNCERTAINTIES AND WHEN CONSIDERING THAT THERE HAS NOW BEEN SOME
MORE CONSISTENT SUPPORT FOR THE BULK OF THE PRECIPITATION
ASSOCIATED WITH THE MONDAY SHORTWAVE REMAINING TO OUR NORTHEAST.
EITHER WAY, THE QUICK-MOVING NATURE OF THESE SHORTWAVES AND THE
LESS-THAN-STELLAR MOISTURE QUALITY THAT THEY'LL HAVE TO WORK
WITH SUGGESTS THAT ANY PRECIPITATION THAT DOES OCCUR WON'T
PRODUCE MUCH IN TERMS OF QPF/AMOUNTS.
YET ANOTHER TROUGH IN THIS CAVALCADE OF UPPER-LEVEL
DISTURBANCES IS PROGGED TO DIG INTO THE REGION ON WEDNESDAY OR
THURSDAY OF NEXT WEEK. WHILE THERE ARE STILL A LOT OF INHERENT
UNCERTAINTIES WITH IT BEING 6-7 DAYS OUT, THE GENERAL PICTURE
BEING PAINTED BY FORECAST GUIDANCE SUGGESTS THAT THIS WOULD
PROBABLY GIVE US OUR BEST OVERALL CHANCE FOR PRECIPITATION NEXT
WEEK WITH PRETTY MUCH ALL OF THE LATEST GLOBAL DETERMINISTIC
MODEL RUNS DEPICTING A MORE ORGANIZED CYCLOGENETIC RESPONSE AT
THE SURFACE AS THIS TROUGH MOVES THROUGH THE REGION. THE MILDER
TEMPERATURES NEXT WEEK TEND TO FAVOR RAIN OVER SNOW AS THE
DOMINANT PRECIPITATION TYPE WITH EACH OF NEXT WEEK'S
PRECIPITATION CHANCES, THOUGH SNOW WOULDN'T BE OUT OF THE
QUESTION AT THIS POINT EITHER, ESPECIALLY IF PRECIPITATION WERE
TO OCCUR DURING THE NIGHTTIME WHEN TEMPERATURES WILL BE COOLER.
OGOREK
AVIATION /06Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 1115 PM CST WED FEB 19 2025
THERE ARE NO MAJOR AVIATION CONCERNS THROUGH THE TAF PERIOD.
VIRGA WILL CONTINUE THROUGH THE OVERNIGHT HOURS WITH PERHAPS A
FLURRY OR TWO MAKING IT TO THE GROUND (NO FORMAL MENTION IN THE
OUTGOING TAFS). TOWARD OR JUST AFTER DAYBREAK, A VFR STRATUS
DECK CURRENTLY IN WISCONSIN AND MICHIGAN MAY SLOSH SOUTHWESTWARD
INTO NORTHERN ILLINOIS AND NORTHWESTERN INDIANA, THOUGH
CONFIDENCE IS LOWER THAN AVERAGE OWING TO A POCKET OF DRY LOW-
LEVEL AIR AHEAD OF THE CLOUDS. EVEN IF CLOUDS DO NOT MAKE IT IN
TOMORROW MORNING, STEEPENING LOW-LEVEL LAPSE RATES MAY ALLOW FOR
AN MVFR STRATOCUMULUS DECK TO DEVELOP BY MID-AFTERNOON. WINDS
WILL BE OUT OF THE WEST-NORTHWEST THROUGH THE TAF PERIOD.
BORCHARDT
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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