945
FXUS63 KLOT 210459
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1059 PM CST THU FEB 20 2025
KEY MESSAGES
- TWO MORE NIGHTS OF WELL BELOW NORMAL TEMPERATURES ARE IN STORE,
COLDEST TONIGHT ACROSS INTERIOR NORTHERN ILLINOIS.
- TEMPERATURES WILL MODERATE TO CLOSER TO NORMAL ON SATURDAY AND
THEN ABOVE NORMAL SUNDAY THROUGH TUESDAY.
- THE NEXT DECENT CHANCE FOR PRECIPITATION (40-50% POPS) IS NEXT
WEDNESDAY-WEDNESDAY NIGHT.
DISCUSSION
ISSUED AT 224 PM CST THU FEB 20 2025
THROUGH FRIDAY NIGHT:
THOUGH HIGH TEMPERATURES WERE WELL BELOW NORMAL (MID-UPPER 30S
IS NORMAL FOR 2/20) AGAIN THIS AFTERNOON, READINGS FROM THE
UPPER TEENS TO LOWER-MID 20S PAIRED WITH THE STRENGTHENING LATE
FEBRUARY SUN DOES HELP. SPRAWLING SURFACE HIGH PRESSURE OF ABOUT
1040-1045 MB WILL CENTER OVER MISSOURI TONIGHT, WITH UPPER 1030S
TO AROUND 1040 MB PRESSURES EXTENDING ACROSS OUR AREA. SOME OF
THE NEAR TERM MODEL GUIDANCE WAS FAR TOO AGGRESSIVE WITH CLOUD
COVER THIS AFTERNOON, SO WITH MORE OF THE NIGHT LIKELY TO BE
CLEAR/MOSTLY CLEAR, ANOTHER VERY COLD NIGHT IS IN STORE. THIS
WILL ESPECIALLY BE THE CASE NEAR AND WEST OF THE FOX VALLEY
WHERE DEEPER SNOW COVER AND BEING CLOSER TO THE RIDGE AXIS WILL
RESULT IN GOOD RADIATIONAL COOLING. EXPECTING LOWS FROM NEAR 0F
TO A COUPLE DEGREES BELOW ZERO IN THESE AREAS, WITH POSITIVE
SINGLE DIGITS TO AROUND 10F FOR THE REST OF THE AREA (HIGHEST
IN/NEAR DOWNTOWN CHICAGO).
ON FRIDAY, PLENTY OF SUNSHINE, THE STILL DRY MODIFIED ARCTIC
AIRMASS, 925 MB TEMPS RISING TO ABOUT -9C, AND FURTHER MELTING
OF SNOW COVER SHOULD TRANSLATE TO HIGHS IN THE UPPER 20S TO
LOWER 30S FOR MOST OF THE AREA. WENT ABOVE MOST OF THE GUIDANCE
TOWARDS THE HRRR, AS IT APPEARS THE COOLER GUIDANCE IS NOT
MELTING ENOUGH OF THE SNOW COVER. IF ANY LOCATIONS REACH
32-33F, THAT WILL BE THE FIRST TIME AT OR ABOVE FREEZING SINCE
LAST SATURDAY. THE SURFACE HIGH WILL BE CENTERED NEAR AND SOUTH
OF THE OHIO VALLEY ON SATURDAY NIGHT, STILL CLOSE ENOUGH FOR
SOUTHWEST WINDS TO DIMINISH AND SUPPORT GOOD RADIATIONAL COOLING
OUTSIDE OF CHICAGO, WITH LOWS IN THE MID POSITIVE SINGLE DIGITS
TO AROUND 10F, WHILE THE URBAN HEAT ISLAND SEES LOWS GENERALLY
IN THE MID TEENS.
SATURDAY THROUGH THURSDAY:
SATURDAY WILL LIKELY REACH THE MID 30S IN AT LEAST THE SOUTHWEST
HALF OF THE CWA (UPPER 20S TO LOWER 30S NORTHWEST) AMIDST
BREEZY SOUTHWEST WINDS. A NORTHWESTERLY, BUT MILDER (THANKFULLY),
MID AND UPPER LEVEL FLOW PATTERN WILL PREVAIL SUNDAY THROUGH
TUESDAY, RESULTING IN THE FIRST STRETCH OF SOLIDLY ABOVE NORMAL
TEMPERATURES SINCE DURING THE FIRST WEEK OF THIS MONTH. SUNDAY
SHOULD REACH THE 40-45F RANGE FOR A GOOD CHUNK OF THE AREA,
EXCEPT PERHAPS PORTIONS OF INTERIOR FAR NORTHERN ILLINOIS. THEN
ON MONDAY AND TUESDAY, TEMPS WILL LIKELY BE WELL INTO THE 40S
AND EVEN NEAR TO ABOVE 50F IN SPOTS (MILDEST SOUTH OF I-80). A
FAST MOVING CLIPPER-LIKE SHORT-WAVE MAY BRING A PERIOD OF LIGHT
RAIN OR SHOWERS MONDAY NIGHT, THOUGH THE VARIANCE IN SOLUTIONS
LENDS TO ONLY 20-30% POPS IN THE GRIDDED FORECAST.
CONFIDENCE FURTHER DIMINISHES BY NEXT WEDNESDAY-WEDNESDAY NIGHT
DUE TO LARGE SPREAD IN THE HANDLING OF THE NEXT SHORT-WAVE
APPROACHING FROM THE NORTHWESTERN CONUS. THE SPECTRUM OF
PLAUSIBLE OUTCOMES RANGES FROM A PRIMARILY DRY AND EVEN MILDER
WEDNESDAY (WIDESPREAD 50S?) TO COOLER (POSSIBLY MUCH COOLER AT
THAT) WITH PRECIPITATION OVERSPREADING THE AREA. OUR FORECAST IS
THE RELATIVE MIDDLE GROUND, WITH A CHANCE OF RAIN WEDNESDAY
(30-40% POPS DURING THE AFTERNOON), AND THEN 40-50% CHANCE OF
PRECIP IN THE FORM OF RAIN OR SNOW WEDNESDAY NIGHT TO ACCOUNT
FOR THE UNCERTAINTY. REGARDLESS OF THE WEDNESDAY-WEDNESDAY NIGHT
OUTCOME, ENSEMBLE GUIDANCE FAVORS A RETURN OF BELOW NORMAL
TEMPERATURES NEXT THURSDAY, WITH SOME LIGHT LINGERING PRECIP
POSSIBLE.
CASTRO
AVIATION /00Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 1059 PM CST THU FEB 20 2025
NO SIGNIFICANT AVIATION WEATHER CONCERNS THOUGH THIS TAF PERIOD.
SURFACE HIGH PRESSURE WILL SPREAD SLOWLY EAST FROM THE LOWER
MISSOURI VALLEY INTO THE LOWER OHIO VALLEY THROUGH FRIDAY.
COMBINED WITH LINGERING DRY MODIFIED ARCTIC AIR, THIS WILL
RESULT IN A PERIOD OF LARGELY CLOUDLESS VFR SKIES AND MODEST
WESTERLY WINDS GRADUALLY BACKING TO SOUTHWEST BY LATE FRIDAY AND
FRIDAY NIGHT.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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