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FXUS63 KLOT 271219
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
619 AM CST FRI FEB 27 2026
KEY MESSAGES
- DENSE FREEZING FOG THIS MORNING WILL AFFECT THE COMMUTE IN THE
CHICAGO METRO AREA.
- TODAY WILL BE UNSEASONABLY WARM AND BREEZY WITH A THREAT FOR
RAPID BRUSH FIRE SPREAD.
- A PAIR OF STORM SYSTEMS MAY BRING ACCUMULATING SNOW TO PARTS
OF THE AREA THIS WEEKEND, FAVORING AREAS NEAR AND NORTH OF THE
WISCONSIN STATE LINE SATURDAY AFTERNOON, AND AREAS SOUTH OF
INTERSTATE 80 SUNDAY NIGHT.
- THERE IS A GROWING SIGNAL FOR AN ACTIVE STRETCH FEATURING
PERIODS OF SHOWERS AND POSSIBLY THUNDERSTORMS MID TO LATE NEXT
WEEK AND BEYOND, LIKELY ACCOMPANIED BY MUCH ABOVE AVERAGE
TEMPERATURES AT TIMES.
UPDATE
ISSUED AT 619 AM CST FRI FEB 27 2026
OPTED FOR A SHORT FUSED DENSE FOG ADVISORY IN THE CHICAGO METRO.
STRENGTHENING SOUTHWEST FLOW ALOFT HAS ADVECTED THE OVERNIGHT
FOG BANK NORTHEASTWARD AND IT'S GOTTEN NOTICEABLY THICKER ON
WEBCAMS (AND HERE OUTSIDE THE NWS OFFICE IN ROMEOVILLE).
CONSIDERING THAT A MOVING SHALLOW DENSE FOG BANK CAN BE QUITE
HAZARDOUS FOR DRIVERS, WITH THE FRIDAY MORNING RUSH UPON US,
DECIDED ON THE ADVISORY (VS. CONTINUED SPECIAL WEATHER STATEMENT
ISSUANCE). THE ADVISORY IS IN EFFECT UNTIL 9 AM, THOUGH IT'S
POSSIBLE THE WORST CONDITIONS IMPROVE EARLIER IN THE 8 AM HOUR.
WITHIN THE CITY OF CHICAGO, WARMING CONDITIONS DOWNTOWN MAY HELP
KEEP THE LOWEST VISIBILITY A FEW MILES INLAND OF THE LAKESHORE.
CASTRO/PETR
RC
DISCUSSION
ISSUED AT 350 AM CST FRI FEB 27 2026
THROUGH SUNDAY NIGHT:
LIGHT WINDS AND CLEAR SKIES HAVE ALLOWED SHALLOW FOG TO DEVELOP
MAINLY SOUTHWEST OF THE CHICAGO METRO IN ILLINOIS EARLY THIS
MORNING. BELOW FREEZING TEMPERATURES TEMPERATURES COULD ALSO
LEAD TO PATCHY SLIDE SPOTS DEVELOPING WHERE FOG HAS BECOME
LOCALLY DENSE. GIVEN THE SHALLOW AND PATCHY NATURE OF THE FOG,
HAVE OPTED TO HANDLE THIS WITH AN SPS THROUGH 7 AM CST BUT A
CONSIDERATION FOR A DENSE FOG ADVISORY MAY BECOME WARRANTED IF
THE DENSE AREAL COVERAGE INCREASES TOWARD DAYBREAK. EXPECT ANY
LINGERING FOG TO ERODE WITHIN AN HOUR OR TWO OF SUNRISE.
WE ARE HEADED FOR AN UNSEASONABLY WARM DAY TODAY WITH STRONG
SOUTHWEST WINDS DEVELOPING IN RESPONSE TO A SUB-1000 MB LOW
MOVING ACROSS ONTARIO. STRONG WARM ADVECTION PAIRED WITH DEEP
MIXING WILL ALLOW TEMPERATURES TO WARM INTO THE 60S ACROSS THE
AREA. IN FACT, SOME AREAS SOUTHWEST OF THE CHICAGO METRO COULD
POTENTIALLY APPROACH OR EVEN REACH 70F IF THE MOST DEEPLY MIXED
GUIDANCE (HRRR/RAP) VERIFIES. THE DEPTH OF MIXING WILL ALSO PLAY
A CRUCIAL ROLE IN THE UPPER BOUNDS OF WIND GUSTS AND LOWER
BOUNDS FOR THE DEWPOINT/RELATIVE HUMIDITY, ALL IMPORTANT FACTORS
WHEN ASSESSING THE POTENTIAL FOR RAPID SPREAD OF BRUSH FIRES
(MORE DETAILS ON THIS CAN BE FOUND IN THE FIRE WEATHER SECTION
BELOW). HRRR AND RAP REMAIN FAIRLY CONSISTENT IN A BRIEF WINDOW
WHEN WINDS COULD GUST TO 35-40+ MPH FOR A FEW HOURS LATE IN THE
AFTERNOON BEFORE EASING AROUND SUNSET AS WINDS TURN WEST TO
NORTHWEST BEHIND A COLD FRONT.
ATTENTION THEN TURNS TO A LOW AMPLITUDE SHORTWAVE EXPECTED TO
DIVE OUT OF CANADA TOWARD THE UPPER MIDWEST ON SATURDAY. THIS
CLIPPER-SYSTEM MAY BRING A PERIOD OF F-GEN DRIVEN ACCUMULATING
SNOW SOMEWHERE IN THE REGION SATURDAY AFTERNOON INTO THE EARLY
EVENING; HOWEVER, BIG QUESTION MARKS REMAIN AS TO WHERE THIS
BAND ENDS UP TRACKING. THE LATEST FORECAST LEANS TOWARD THE
MORE NORTHERLY GUIDANCE WHICH KEEPS THE CENTER OF THE SNOW BAND
NORTH OF THE WI-IL STATELINE. THERE REMAIN A FEW SOLUTIONS WITH
A FARTHER SOUTH TRACK WHICH WOULD TAKE THIS BAND ACROSS
NORTHERN ILLINOIS. FORECAST VERTICAL PROFILES ALSO SUGGEST THAT
THERE COULD BE CONVECTIVE SNOW SHOWER ELEMENTS SOUTH OF THE MAIN
BAND OF SNOW, WHICH WOULD INCLUDE NORTHERN ILLINOIS INTO
NORTHWEST INDIANA EVEN WITH A MORE NORTHERLY TRACK PROVIDED
THAT THERE IS SUFFICIENT SATURATION. THUS, OPTED TO MAINTAIN
SNOW CHANCES ACROSS THE AREA (20-50%), HIGHEST NEAR THE WI-IL
STATE LINE. THE TEMPERATURE FORECAST ON SATURDAY WILL ALSO
LARGELY DRIVEN BY THE POSITION OF THIS BAND OF SNOW WHICH COULD
RESULT IN A SHARP GRADIENT IN TEMPERATURES ACROSS THE LOCAL
AREA, FROM AS LOW AS 30S NORTH TO 50S TO AROUND 60 WELL SOUTH OF
I-80.
YET ANOTHER SYSTEM WILL FOLLOW ON THE HEELS OF THE FIRST
BRINGING THE POTENTIAL FOR ACCUMULATING SNOW TO THE REGION
SUNDAY NIGHT. SIMILAR TO THE FIRST SYSTEM THERE REMAINS A LOT
OF UNCERTAINTY IN THE SYSTEM TRACK. THE LATEST BLENDED GUIDANCE
CONTINUES TO HAVE HIGHEST SNOW CHANCES FOR AREAS SOUTH OF I-80
TOWARD CENTRAL IL/IN. AN EXPANSIVE SURFACE HIGH THAT SETS UP
ACROSS THE UPPER MIDWEST AND BROADER GREAT LAKES REGION COULD
HELP SHIFT THE NORTHERN PERIPHERY OF THE SNOW FARTHER SOUTH,
WHICH SOME OF THE GLOBAL GUIDANCE HAS BEEN STARTING TO CATCH
ONTO, THOUGH THE ECMWF REMAINS THE FARTHEST NORTH. WITH
TEMPERATURES IN THE 20S ANY SNOW THAT DOES FALL WOULD READILY
ACCUMULATE ON UNTREATED SURFACES. WILL CONTINUE TO MONITOR
TRENDS OVER THE COMING DAYS. STAY TUNED!
PETR
MONDAY THROUGH THURSDAY (AND BEYOND):
WHILE THE MONTH OF FEBRUARY WILL FINISH UP SOLIDLY ABOVE NORMAL
TEMPERATURE WISE, IT STILL FEATURED PREDOMINANTLY NORTHWEST FLOW
ALOFT, RESULTING IN WELL BELOW AVERAGE PRECIPITATION (AND
SNOWFALL). THIS WILL CHANGE IN A BIG WAY DURING THE UPCOMING
FIRST WEEK OF MARCH FOLLOWING A SEASONABLY CHILLY FIRST COUPLE
DAYS OF THE MONTH (POSSIBLY ACCOMPANIED BY SOME SNOW IN SPOTS).
THE PATTERN WILL TRANSITION TO THE NEGATIVE PHASE OF THE PACIFIC
NORTH AMERICAN (PNA) TELECONNECTION PATTERN, CHARACTERIZED BY
WESTERN CONUS TROUGHING AND EASTERN CONUS RIDGING AT THE MID AND
UPPER LEVELS. SUCH A PATTERN IS COMMONLY ACTIVE LOCALLY, WHICH
SHOULD ENTAIL PERIODS OF BENEFICIAL PRECIPITATION AS WE HEAD INTO
THE GROWING SEASON.
ALSO NOTABLE IN THE UPCOMING PATTERN IS THE LACK OF ANY
CORRESPONDING HIGH LATITUDE BLOCKING IN THE ARCTIC AND NORTH
ATLANTIC (POSITIVE ARCTIC OSCILLATION/AO AND NORTH ATLANTIC
OSCILLATION/NAO). THIS WILL ALLOW FOR THE EASTERN RIDGING TO
BECOME PARTICULARLY PRONOUNCED, SUGGESTING A GENERALLY ABOVE TO
WELL ABOVE AVERAGE TEMPERATURE REGIME POSSIBLY PERSISTING ALL THE
WAY THROUGH MID MARCH. HOWEVER, IN THE EARLY SPRING, EVEN IN A
MILD PATTERN, INDIVIDUAL STORM TRACKS PLAY A LARGE ROLE IN
TEMPERATURE DISTRIBUTIONS, AS THE CHILLY WATERS OF LAKE MICHIGAN
RESULT IN NOTABLY COOLER TEMPS IN ONSHORE FLOW NORTH OF STORM
TRACKS AND/OR REINFORCED WARM FRONTS.
TURNING FROM THE BIG PICTURE TELECONNECTION PATTERN TO THE DAY TO
DAY, SPECIFIC DETAILS ARE RATHER MURKY GIVEN A LARGE RANGE OF
SOLUTIONS OFFERED BY THE VARIOUS ENSEMBLE SOLUTIONS. THE NORTHWARD
EXTENT OF AN ACTIVE BAROCLINIC ZONE WILL BE MODULATED BY THE
PROXIMITY OF SURFACE HIGH PRESSURE TO THE REGION, WHICH IS QUITE
VARIABLE BETWEEN THE ENSEMBLE SYSTEMS AND ACROSS ENSEMBLE MEMBERS.
AN INITIAL ROUND OF PRECIPITATION COULD REACH INTO AT LEAST
PORTIONS OF THE AREA IN THE MONDAY NIGHT-TUESDAY TIMEFRAME, WITH
THE OVERALL HIGHEST POPS SOUTH OF I-80. THIS COULD FEATURE SOME
THREAT FOR WINTRY PRECIP AS SURFACE WETBULB TEMPS MAY STILL BE
FLIRTING WITH FREEZING.
VARIANCE ONLY INCREASES INTO THE MID TO LATE WORKWEEK TIMEFRAME,
LOWERING CONFIDENCE IN MOST OF THE SPECIFIC DETAILS. THE MAIN
EXCEPTION TO THIS IS FOR RAIN BEING THE PREDOMINANT PTYPE WITH
HIGH CONFIDENCE IN THE WEDNESDAY-FRIDAY PERIOD NEXT WEEK. IN
GENERAL, THE GEFS IS FASTER IN BRINGING RAIN BACK TO THE AREA
DURING THE DAY ON WEDNESDAY AND INTO WEDNESDAY NIGHT, WHILE THE
THE FOREIGN PRODUCED ENSEMBLE SYSTEMS ARE MORE FOCUSED ON THE
WEDNESDAY NIGHT AND THURSDAY TIMEFRAME. REGARDLESS OF EXACTLY HOW
THE MID TO LATE WEEK PERIOD EVOLVES, PRECIPITABLE WATER OF
250-300% OF AVERAGE/NORMAL FOR EARLY MARCH COULD CERTAINLY SPELL
CORRIDORS OF HEAVY RAINFALL AND AN ASSOCIATED FLOODING THREAT.
THE EXTENT (OR LACK THEREOF) OF EMBEDDED THUNDERSTORMS WILL LIKELY
PLAY A ROLE AS WELL, THOUGH FOR NOW, THE FORECAST DOES NOT YET
FEATURE ANY EXPLICIT MENTION FOR THUNDERSTORM CHANCES. FINALLY,
THE EXCEPTIONALLY MILD AND MOIST CYCLONE WARM SECTORS IN THE
UPCOMING PATTERN MAY ALSO FEATURE A THREAT FOR ORGANIZED STRONG TO
SEVERE CONVECTION WITHIN IN THE GENERAL REGION.
CASTRO
AVIATION /12Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 606 AM CST FRI FEB 27 2026
MAIN CONCERNS:
- A PERIOD OF LIFR CONDITIONS APPEARS PROBABLE AT ORD AND MDW THIS
MORNING, THOUGH IT'S UNCERTAIN HOW LOW VSBY WILL GET.
- STRENGTHENING SOUTHWEST WINDS THIS AFTERNOON, WITH GUSTS NEAR
TO POSSIBLY ABOVE 35 KT AT TIMES LATE THIS AFTERNOON.
- WINDS WILL LIKELY SHIFT TO NORTHEASTERLY SATURDAY MORNING.
A BANK OF LIFR STRATUS AND DENSE FOG JUST SOUTHWEST OF ORD AND
MDW AS OF THIS WRITING SHOULD MOVE ACROSS THE CHICAGO TERMINALS
(AND DPA) IN SOME FASHION BETWEEN ABOUT 12-14Z, WITH TEMPO LIFR
CONDITIONS INDICATED. ONCE THE LOW CONDITIONS IMPROVE LATER
THIS MORNING, SOUTHWEST WINDS WILL STEADILY INCREASE. THERE
LOOKS TO BE A SHORT PERIOD JUST AHEAD OF AN APPROACHING COLD
FRONT WHERE GUSTS COULD REACH AS HIGH AS 35-40 KT. THE DIRECTION
WILL LIKELY VEER TO WEST-SOUTHWEST DURING THE STRONGEST WINDS.
EARLY THIS EVENING, WINDS WILL SHIFT TO WEST-NORTHWEST WITH
GUSTS IN THE 20-25 KT RANGE BEHIND THE COLD FRONT PASSAGE. WINDS
SHOULD EASE TO AROUND 10 KT FROM THE NORTHWEST OVERNIGHT AND
THEN SHIFT TO NORTHEASTERLY SATURDAY MORNING. EXPECT THICKENING
AND GRADUALLY LOWERING VFR CIGS INTO SATURDAY MORNING.
CASTRO
FIRE WEATHER
ISSUED AT 350 AM CST FRI FEB 27 2026
THREAT FOR BRUSH FIRE SPREAD THIS AFTERNOON...
STRONG SOUTHWESTERLY WINDS ARE EXPECTED TO DEVELOP ACROSS THE
REGION THIS AFTERNOON. AT THIS POINT, OUR FORECAST FAVORS
SUSTAINED WINDS INCREASING TOWARD 15 MPH AND GUSTS RANGING FROM
30 TO 35 MPH LATE MORNING THROUGH EARLY AFTERNOON. IF MORE
AGGRESSIVE MIXING SCENARIOS PAN OUT, SUSTAINED WINDS COULD
EXCEED 20 MPH AND GUSTS COULD EXCEED 40 MPH FOR A BRIEF 2 TO 3
HOUR WINDOW LATE IN THE AFTERNOON. WHEN PAIRED WITH
UNSEASONABLY WARM TEMPERATURES IN THE LOW TO MID 60S AND
AFTERNOON MINIMUM RELATIVE HUMIDITY VALUES OF 25 TO 30 PERCENT,
CONDITIONS MAY APPROACH RED FLAG WARNING CRITERIA ON A LOCALIZED
BASIS, PARTICULARLY SOUTHWEST OF THE CHICAGO METRO AREA.
BORCHARDT/PETR
LOT WATCHES/WARNINGS/ADVISORIES
IL...DENSE FOG ADVISORY UNTIL 9 AM CST THIS MORNING FOR ILZ012-
ILZ013-ILZ020-ILZ021-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 9 PM CST THIS EVENING FOR WINTHROP
HARBOR IL TO GARY IN.
SMALL CRAFT ADVISORY FROM NOON TODAY TO 9 PM CST THIS EVENING
FOR GARY TO BURNS HARBOR IN-BURNS HARBOR TO MICHIGAN CITY
IN.
VISIT US AT WEATHER.GOV/CHICAGO
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