536
FXUS63 KLOT 191133
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
533 AM CST WED FEB 19 2025
KEY MESSAGES
- BITTERLY COLD CONDITIONS ARE EXPECTED THROUGH THURSDAY MORNING.
- INTERMITTENT FLURRIES ARE EXPECTED LATE THIS AFTERNOON
THROUGH TONIGHT WITH A CHANCE (20-40%) OF LIGHT ACCUMULATIONS
AND SLIPPERY TRAVEL, HIGHEST NEAR/EAST OF I-55.
- LIGHT LAKE EFFECT SNOW WILL CLIP NORTHEAST PORTER COUNTY AT
TIMES THROUGH THURSDAY, WITH THE BEST CHANCE (40%) OF LIGHT
ACCUMULATIONS AND SLIPPERY TRAVEL TONIGHT.
- TEMPERATURES ARE EXPECTED TO GRADUALLY WARM BACK TOWARD AND
EVEN ABOVE NORMAL LATE THIS WEEK INTO EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 307 AM CST WED FEB 19 2025
THROUGH THURSDAY:
AN EXPANSIVE 1050+ MB SURFACE HIGH CENTERED OVER THE NORTHERN
PLAINS CONTINUES TO EXTEND ITS INFLUENCE ACROSS MUCH OF THE
CONUS WITH WELL BELOW NORMAL TEMPERATURES CONTINUING. HIGH
CLOUDS HAVE LIMITED OUR COOLING THUS FAR EARLY THIS MORNING WITH
TEMPERATURES STILL ABOVE ZERO AT PRESS TIME AREAWIDE. AS WE
APPROACH DAYBREAK, THINNING OF THESE HIGH CLOUDS COULD ALLOW
PORTIONS OF INTERIOR NORTHERN ILLINOIS TO BRIEFLY DIP BELOW
ZERO, WITH WIND CHILLS THEN DROPPING INTO THE -15 TO -20 DEGREE
RANGE. WHILE WE MAY REMAIN JUST SHY OF ADVISORY CRITERIA (-20F),
PLAN TO MAINTAIN THE COLD WEATHER ADVISORY THROUGH 10 AM CST.
A MID-LEVEL WAVE EVIDENT ON GOES WATER VAPOR IMAGERY IS
CURRENTLY MOVING ACROSS NE/SD/IA/MN TOWARD THE REGION. NEAR AND
SOUTH OF THIS FEATURE, PATCHES OF LIGHT SNOW AND FLURRIES ARE
ONGOING ACROSS MUCH OF NEBRASKA AND KANSAS. THIS IS EXPECTED TO
CONTINUE EAST WITH TIME. DESPITE THE DRY ARCTIC AIR MASS IN
PLACE, CONCERN REMAINS FOR VERY SMALL SNOWFLAKES ("ARCTIC
DUST"), WHICH WOULD BE CAPABLE OF CAUSING SLIPPERY TRAVEL
CONDITIONS AND REDUCED VISIBILITY. ACCORDINGLY, HAVE MAINTAINED
A MENTION OF INTERMITTENT FLURRIES AREAWIDE LATE THIS AFTERNOON
THROUGH TONIGHT WITH THE BEST POTENTIAL FOR A COATING OF SNOW
(20-40%) MAINLY NEAR/EAST OF I-55. ANY SNOW THAT DOES FALL WOULD
READILY COAT UNTREATED PAVEMENT GIVEN THE COLD TEMPERATURES.
LAKE EFFECT SNOW PARAMETERS BECOME MAXIMIZED MAINLY EAST OF THE
AREA WHERE A DOMINANT BUT TRANSIENT LAKE EFFECT BAND IS
EXPECTED TO IMPACT PORTIONS OF SOUTHWEST LOWER MICHIGAN AND
NORTHWEST INDIANA. HAVE MAINTAINED A 20-40% CHANCE OF LAKE
EFFECT SNOW ACROSS NORTHEAST PORTER COUNTY THROUGH THURSDAY TO
ACCOUNT FOR LIGHT MEASURABLE SNOW OCCURRING AT TIMES LEADING TO
SLICK TRAVEL. WE WILL HAVE TO KEEP A CLOSE EYE ON THE MORE
DOMINANT BAND IN CASE IT HAPPENS TO SHIFT FURTHER WEST INTO
PORTER COUNTY.
LINGERING CLOUD COVER AND FLURRIES WILL LIKELY LIMIT OUR
OVERNIGHT COOLING TONIGHT WITH FORECAST LOWS IN SINGLE DIGITS
ABOVE ZERO FOR MOST OF THE AREA, WITH THE EXCEPTION BEING NEAR
AND EAST OF I-39. THERE REMAINS SOME VARIABILITY IN GUIDANCE AS
TO WHETHER CLOUDS MANAGE TO CLEAR OUT EARLY ENOUGH FOR
TEMPERATURES TO DROP BACK BELOW ZERO FURTHER EAST. GIVEN THIS
UNCERTAINTY, OPTED TO HOLD OFF ON ISSUING ANOTHER COLD WEATHER
ADVISORY ON THIS SHIFT. IF CONFIDENCE IN A FASTER CLEARING OF
CLOUDS INCREASES AND ACCORDINGLY COLDER TEMPERATURES, ONE MAY BE
NEEDED FOR AT LEAST PARTS OF THE AREA. REGARDLESS, EXPECT ONE
MORE CHILLY NIGHT ACROSS THE AREA WITH WIND CHILLS IN THE -10 TO
-20 DEGREE RANGE.
THURSDAY WILL FEATURE WARMER TEMPERATURES IN THE UPPER TEENS TO
LOWER 20S AS WE BEGIN THE VERY GRADUAL STAIR STEP UP TO CLOSER
TO NORMAL TEMPERATURES FOR LATE FEBRUARY THROUGH THE END OF THE
WEEK.
PETR
THURSDAY NIGHT THROUGH TUESDAY:
FRIDAY MORNING LOOKS TO BE THE LAST MORNING OF THIS MID-
FEBRUARY COLD SPELL WHERE PARTS OF OUR FORECAST AREA COULD SEE
SUB-ZERO AIR TEMPERATURES. THIS WOULD BE IN PORTIONS OF INTERIOR
NORTHERN ILLINOIS, WITH THE REMAINDER OF OUR FORECAST AREA
LIKELY TO SEE LOWS IN THE POSITIVE SINGLE DIGITS TO LOW TEENS.
WINDS SHOULD BE LIGHTER BY THIS TIME AS THE CENTER OF A STRONG
1040+ MB CANADIAN SURFACE HIGH SETTLES INTO THE MID-MISSISSIPPI
RIVER VALLEY, SO WIND CHILLS WON'T BE AS BAD AS THEY WERE
EARLIER IN THE WEEK, BUT THEY WILL STILL LIKELY END UP BEING
NEAR OR BELOW ZERO ACROSS OUR FORECAST AREA -- POSSIBLY AS LOW
AS 10 TO 15 BELOW ZERO ACROSS PORTIONS OF INTERIOR NORTHERN
ILLINOIS, WHERE AIR TEMPERATURES WILL BE COLDEST.
BY SATURDAY, THE SURFACE HIGH WILL HAVE DRIFTED OFF TO OUR
SOUTHEAST, RESULTING IN SOUTHWESTERLY SURFACE WINDS BECOMING
ESTABLISHED ACROSS THE REGION OVER THE WEEKEND. THESE
SOUTHWESTERLY WINDS WILL HELP FACILITATE A WARMUP THAT WILL SEE
TEMPERATURES CLIMB CLOSER TO AND EVENTUALLY ABOVE CLIMATOLOGICAL
NORMALS FOR THIS TIME OF YEAR OVER THE WEEKEND AND INTO EARLY
NEXT WEEK. 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.
OTHERWISE, THE WORKWEEK SHOULD END ON A DRY NOTE ON FRIDAY WITH
THE STRONG CANADIAN HIGH EXERTING ITS INFLUENCE ON THE REGION.
THEREAFTER, A MORE ACTIVE NORTHWEST FLOW PATTERN 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 OF THESE SHORTWAVES IS
SLATED TO PASS CLOSE BY ON SATURDAY. THE MINORITY OF ENSEMBLE
MEMBERS THAT WERE SUGGESTING THAT PRECIPITATION COULD OCCUR ON
SATURDAY AS THIS SHORTWAVE SWOOPED BY HAVE LARGELY BACKED OFF
THAT IDEA IN THE LATEST ENSEMBLE SUITES, AND THUS, THE CURRENT
THINKING IS THAT ITS PASSAGE SHOULD RESULT IN NO MORE THAN JUST
AN UPTICK IN MID- TO HIGH-LEVEL CLOUD COVER. A SECOND SHORTWAVE
THEN LOOKS TO PASS BY THE AREA ON SUNDAY, THOUGH AGAIN, THE QPF
SIGNAL IN GUIDANCE AT THE TIME OF ITS ARRIVAL IS QUITE MUTED --
BASICALLY RESTRICTED TO LIGHT QPF IN JUST A FEW GEFS MEMBERS
PLUS THE DETERMINISTIC GFS AMONGST THE LATEST 00Z GUIDANCE
SUITE. THUS, HAVE MAINTAINED THE NBM'S DRY FORECAST THROUGH THE
WEEKEND.
TWO TO THREE ADDITIONAL SHORTWAVES WILL DIVE INTO THE REGION
DURING THE UPCOMING WORKWEEK, EACH OF WHICH LOOK TO BE STRONGER
THAN THE WEEKEND SHORTWAVES AND HENCE BRING A BETTER CHANCE TO
YIELD PRECIPITATION IN OUR FORECAST AREA. HOWEVER, THERE ARE
STILL SIZABLE DIFFERENCES IN THEIR PRECISE TRACKS AND OVERALL
EVOLUTION AMONGST THE GLOBAL ENSEMBLE SYSTEMS, SO CONFIDENCE IN
THE PRECISE TIMING, PLACEMENT, AND OVERALL LIKELIHOOD OF NEXT
WEEK'S PRECIPITATION CHANCES REMAINS LOW ON THE WHOLE.
OGOREK
AVIATION /12Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 533 AM CST WED FEB 19 2025
KEY MESSAGES:
- LIGHT SNOW/FLURRIES MAY AFFECT THE TERMINALS LATE THIS
AFTERNOON INTO TONIGHT.
- MVFR CEILINGS AND/OR VISIBILITIES MAY ACCOMPANY THE
SNOW/FLURRIES.
AN UPPER-LEVEL DISTURBANCE COULD BRING A PERIOD OF FLURRIES/LIGHT
SNOW TO THE TERMINALS LATE THIS AFTERNOON INTO TONIGHT.
CONFIDENCE ISN'T PARTICULARLY HIGH IN SNOW OCCURRING LATER
TODAY, BUT UPSTREAM OBSERVATIONS IN EASTERN NEBRASKA SUGGEST
THAT MVFR VISIBILITIES WOULD BE POSSIBLE IF IT DID, SO OPTED TO
ERR ON THE SIDE OF CAUTION AND INTRODUCED A PROB30 FOR THIS
POSSIBILITY IN THE CHICAGO METRO TAFS. COULDN'T RULE MVFR
VISIBILITIES BEING OBSERVED AT RFD EITHER, BUT THE ODDS OF THAT
OCCURRING THERE APPEAR TO BE LOWER (ABOUT A 20% CHANCE) THAN
FARTHER TO THE SOUTH AND EAST. GIVEN THE COLD TEMPERATURES IN
THE TEENS AND SINGLE DIGITS, THIS VERY LIGHT SNOW COULD RESULT
IN A DUSTING ON ANY SURFACE IF IT WERE TO OCCUR FOR A LONG
ENOUGH PERIOD OF TIME.
VFR CEILINGS ARE EXPECTED TO PERSIST INTO THIS AFTERNOON,
THOUGH PERIODS OF MVFR CEILINGS WILL BE POSSIBLE LATE THIS
AFTERNOON INTO TONIGHT, PARTICULARLY IF IT DOES END UP SNOWING.
OTHERWISE, EXPECT WINDS TO REMAIN OUT OF THE NORTHWEST GENERALLY
NEAR 10 KTS, BUT PERHAPS GUSTING OCCASIONALLY CLOSER TO 20 KTS
TOMORROW MORNING.
OGOREK
LOT WATCHES/WARNINGS/ADVISORIES
IL...COLD WEATHER ADVISORY UNTIL 10 AM CST THIS MORNING FOR ILZ003-
ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012.
IN...NONE.
LM...NONE.
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