515
FXUS63 KLOT 240537
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1237 AM CDT FRI SEP 24 2021
SHORT TERM
256 PM CDT
THROUGH FRIDAY NIGHT...
A VERTICALLY STACKED STORM SYSTEM OVER EASTERN LOWER MICHIGAN HAS
REMAINED JUST FAR ENOUGH EAST OF THE AREA TO KEEP THE SHOWERS
TODAY OVER LAKE MICHIGAN AND ADJACENT AREAS OF LAKE AND PORTER
COUNTIES IN IN. HOWEVER, THE CHICAGO METRO AREA HAS BEEN ON THE
FAR WESTERN PERIPHERY OF THE LARGE CLOUD SHIELD ASSOCIATED WITH
THIS SYSTEM. THIS HAS RESULTED IN A BIT A TEMPERATURE CONTRAST
ACROSS THE AREA. LOCATIONS WEST OF THE CITY HAVE SEEN A GOOD DEAL
OF SUN THROUGH THE DAY, THUS ALLOWING THEIR TEMPERATURES TO CLIMB
INTO THE UPPER 60S TO AROUND 70. HOWEVER, PLACES UNDER THE CLOUD
SHIELD, ESPECIALLY INTO NORTHWESTERN IN ARE ONLY IN THE UPPER 50S
TO THE LOW 60S. THE LINGERING SHOWERS OVER PORTER COUNTY IN WILL
DISSIPATE LATER THIS AFTERNOON AND SKIES WILL CLEAR AREA- WIDE,
SETTING UP A SEASONABLY CHILLY NIGHT ACROSS THE AREA. EXPECT LOW
TEMPERATURES TO FALL INTO THE 40S OUTSIDE OF THE CHICAGO METRO
AREA.
ON FRIDAY WINDS WILL TURN SOUTHWESTERLY AND BECOME RATHER GUSTY
INTO THE AFTERNOON IN RESPONSE TO A STRENGTHENING SURFACE
GRADIENT IN ADVANCE OF AN APPROACHING COLD FRONTAL TROUGH. WIND
GUSTS ARE LIKELY TO GUST UP TO 35 MPH FROM THE SOUTHWEST DURING
THE AFTERNOON AND EVENING. A WARMER AIRMASS WILL FILTER INTO THE
AREA VIA THESE GUSTY WINDS, WHICH WILL SUPPORT HIGHS AREA-WIDE
REACHING INTO THE UPPER 70S ON FRIDAY AFTERNOON.
MILD AND BREEZY CONDITIONS WILL CONTINUE FRIDAY EVENING AS THE
FRONT BEGINS TO SHIFT INTO NORTHWESTERN IL. THE FRONT WILL SHIFT
ACROSS ALL OF NORTHERN IL BY AROUND, OR SHORTLY AFTER MIDNIGHT,
THEN ACROSS MY NORTHWESTERN IN COUNTIES BY 4 AM. WHILE LOW-LEVEL
MOISTURE WILL BE RATHER SPARSE TOMORROW, WITH SURFACE DEWPOINTS
LIKELY IN THE 40S, DEWPOINTS LOOK TO POOL A BIT INTO THE LOW TO
MID 50S ALONG THE FRONTAL BOUNDARY FRIDAY EVENING. GIVEN THE SHARP
MID-LEVEL TROUGH WITH DECENT HEIGHT FALLS ALOFT SHIFTING
OVERHEAD, THE EXPECTATION CONTINUES TO BE THAT A PERIOD OF SHOWERS
WITH SOME EMBEDDED THUNDERSTORMS WILL DEVELOP WITH THE FRONTAL
BOUNDARY. SEVERE WEATHER IS NOT ANTICIPATED, AND ANY SHOWERS AND
STORMS SHOULD END FROM NORTHWEST TO SOUTHEAST FOLLOWING THE
FRONTAL PASSAGE. COOLER TEMPERATURES WILL FOLLOW THE FRONTAL
BOUNDARY INTO SATURDAY.
KJB
LONG TERM
110 PM CDT
SATURDAY THROUGH THURSDAY...
A TREND OF PLEASANT AND WARMING CONDITIONS THROUGH THE WEEKEND AND
INTO NEXT WEEK IS EXPECTED.
THE COLD FRONT THAT WILL BRING US RAIN CHANCES FRIDAY NIGHT IS
EXPECTED TO CLEAR THE AREA BY SATURDAY MORNING AS HIGH PRESSURE
BEGINS TO MOVE IN AND DRY US OUT. WINDS BEHIND THE FRONT WILL BE
WESTERLY AT 10-15 MPH. MOST OF US ON SATURDAY WILL SEE SUNNY
CONDITIONS WITH THE EXCEPTION OF A FEW CLOUDS NEAR THE LAKE WITH
AFTERNOON HIGHS IN THE LOWER 70S.
HIGH PRESSURE WILL CONTINUE TO MOVE EAST HEADING INTO SUNDAY
WHICH WILL TURN OUR WINDS OUT OF THE SOUTH AND TRANSPORT WARMER
AIR NORTHWARD TO THE GREAT LAKES. WINDS WILL REMAIN LIGHT THROUGH
THE PERIOD WITH SPEEDS OF 5 TO 10 MPH. HIGH TEMPERATURES SUNDAY
THROUGH THURSDAY WILL REACH THE MID TO UPPER 70S WITH SOME PLACES
POSSIBLY GETTING INTO THE LOWER 80S. IN ADDITION TO THE WARM
TEMPERATURES, HIGH PRESSURE WILL KEEP US DRY WITH NO RAIN CHANCES
AND MOSTLY CLOUD-FREE SKIES WITH THE EXCEPTION OF A FEW PASSING
CLOUDS FROM TIME TO TIME.
YACK
FIRE WEATHER
256 PM CDT
SOUTHWEST WINDS SHOULD QUICKLY INCREASE LATER FRIDAY MORNING INTO
THE AFTERNOON. CURRENTLY LOOKS LIKE A FEW HOURS OF PEAK 20FT
WINDS AROUND 15-20 MPH WITH HIGHER GUSTS. CURRENT FORECASTS FOR
MINIMUM AFTERNOON RH VALUES NORTHWEST OF I-55 ARE BETWEEN 30-40
PERCENT, BUT IT IS WORTH NOTING THAT SET-UPS LIKE FRIDAY'S
FORECAST SET-UP CAN SOMETIME SEE RH VALUES DROPPING LOWER THAN
FORECAST DUE TO DEEP MIXING AND STRONG WINDS TAPPING INTO DRY AIR
ABOVE THE SURFACE. THE 10-HOUR FUEL STICK MOISTURE VALUES SHOULD
REMAIN JUST ABOVE CRITICAL THRESHOLDS AS WELL, SO AT THIS TIME IT
APPEARS THE THREAT OF REACHING RED FLAG CRITERIA IS QUITE LOW.
HOWEVER, THE STRONG WINDS, LOW RH, AND ANTECEDENT DRY CONDITIONS
SHOULD RESULT IN A HEIGHTENED (MAINLY GRASS) FIRE DANGER,
PARTICULARLY NORTHWEST OF I-55 ACROSS NORTHERN ILLINOIS.
- IZZI
AVIATION
FOR THE 06Z TAFS...
AVIATION WEATHER CONCERNS THIS PERIOD CONSIST OF:
* DEVELOPING GUSTY SOUTHWESTERLY WINDS THROUGH THIS AFTERNOON WITH
SOME OCCASIONAL 30 KT GUSTS POSSIBLE, ESPECIALLY INVOF RFD LATE
* QUICK-HITTING PERIOD OF SHOWERS THIS EVENING WITH A LOW CHANCE
FOR A STORM
* BREEZY NORTHWEST WIND SHIFT THIS EVENING WITH A COLD FRONT
VFR CONDITIONS AND MOSTLY CLEAR SKIES WILL PREVAIL TONIGHT AND
INTO THIS MORNING. WINDS WILL GRADUALLY INCREASE AND BECOME GUSTY
THROUGH THE MORNING, WITH THE PERIOD OF STRONGEST WINDS EXPECTED
TO OCCUR LATER IN THE AFTERNOON. LATEST GUIDANCE SUGGESTS THE
PERIOD OF STRONGEST WINDS OCCURRING IN THE 19-00Z TIME FRAME, WITH
A BRIEF WINDOW WHERE GUSTS COULD NEAR OR EXCEED 30 KTS, ESPECIALLY
INVOF RFD. A QUICK-HITTING ROUND OF SHOWERS IS ANTICIPATED, WITH
CONFIDENCE IN COVERAGE HIGH ENOUGH TO JUSTIFY TEMPO GROUPS AT ALL
THE REGIONAL TAF SITES. INSTABILITY WILL BE LACKING WITH THIS
SYSTEM GIVEN THE MAGNITUDE OF DRY AIR IN PLACE, BUT A FEW
LIGHTNING STRIKES CAN'T BE RULED OUT--PROBABILITIES HOWEVER ARE
WELL UNDER 20% AT THIS TIME.
A NORTHWEST WIND SHIFT WILL OCCUR IN THE WAKE OF A COLD FRONT
SOMETIME TOWARDS MID-LATE EVENING ALTHOUGH SOME UNCERTAINTY
REMAINS WITH EXACT FROPA TIMING. WINDS SHOULD REMAIN A BIT
ELEVATED/BREEZY BEHIND THE FRONT, BUT WILL GRADUALLY EASE AS THE
STRONGEST FLOW SHIFTS OFF TO THE EAST OF THE REGION.
CARLAW
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...BEACH HAZARDS STATEMENT...INZ001-INZ002 UNTIL 4 AM FRIDAY.
LM...GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...5 PM
FRIDAY TO 1 AM SATURDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 5 PM FRIDAY.
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