181
FXUS63 KLOT 131739
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1239 PM CDT TUE MAY 13 2025
KEY MESSAGES
- FOG NEAR THE ILLINOIS SHORE THIS MORNING MAY SPREAD FARTHER
INLAND TONIGHT WITH AT LEAST PATCHY DENSE FOG POSSIBLE.
- SUMMER-LIKE WARMTH AWAY FROM THE LAKE EXPECTED THROUGH MIDWEEK.
THERE IS A CHANCE FOR NEAR-RECORD TEMPERATURES ON THURSDAY.
- SHOWERS AND STORM CHANCES EXIST THROUGH WEDNESDAY AFTERNOON,
THOUGH MANY HOURS AND AREAS WILL REMAIN DRY.
- THERE IS A LEVEL 2 OF 5 THREAT FOR SEVERE WEATHER THURSDAY
AFTERNOON AND EVENING, CONTINGENT ON STORMS DEVELOPING.
- AN ELEVATED TO POTENTIALLY SIGNIFICANT FIRE SPREAD RISK
EXISTS ON FRIDAY DUE TO A COMBINATION OF STRONG WINDS AND DRY
CONDITIONS.
UPDATE
ISSUED AT 704 AM CDT TUE MAY 13 2025
DENSE FOG QUICKLY DEVELOPED OVER SOUTHERN LAKE MICHIGAN THIS
MORNING AND OOZED IN ALONG THE ILLINOIS SHORE. WEBCAMS NEAR AND
ALONG THE SHORELINE SUGGEST AT LEAST PATCHY DENSE FOG. WE WENT
AHEAD AND ISSUED A SPECIAL WEATHER STATEMENT (IN EFFECT UNTIL
11AM) AND PUT OUT A GRAPHICAL NOWCAST FOR THE SHORE-HUGGING FOG
THIS MORNING. IT'S UNCERTAIN IF/WHEN THE FOG WILL IMPROVE, SO
WE'LL NEED TO MONITOR OBSERVATIONS, WEBCAMS, AND GUIDANCE
TRENDS. HOWEVER THE REST OF THE DAYTIME PLAYS OUT, EXPECT FOG TO
SPREAD FURTHER INLAND FROM THE LAKE TONIGHT WITHOUT THE BENEFIT
OF THE STRONG MAY SUN AND RECENT GUIDANCE SUGGESTS AREAS OF
DENSE FOG WILL BE POSSIBLE.
CASTRO/PETR
DISCUSSION
ISSUED AT 337 AM CDT TUE MAY 13 2025
THROUGH WEDNESDAY:
GOES WATER VAPOR IMAGERY SHOWS AN EXPANSIVE CLOSED MID-UPPER
LOW SPINNING ACROSS THE EASTERN HALF OF THE CONUS, CURRENTLY
CENTERED OVER WESTERN TENNESSEE. THIS FEATURE WILL CONTINUE TO
BRING ISOLATED TO WIDELY SCATTERED (MAINLY DIURNAL) SHOWER AND
STORM CHANCES TO PARTS OF THE AREA THROUGH WEDNESDAY AFTERNOON.
LOCATIONS OF THE GREATEST COVERAGE WILL LARGELY BE DICTATED BY
SMALLER SCALE VORT LOBES THAT ROTATE AROUND THE LOW, THOUGH A
LAKE SHADOW (THANKS TO CONTINUED ONSHORE FLOW) WILL LIKELY LIMIT
COVERAGE ACROSS FAR NORTHEAST ILLINOIS TODAY.
SIMILAR TO YESTERDAY, ANY STORMS THAT DEVELOP WILL BE CAPABLE
OF OCCASIONAL LIGHTNING STRIKES, LOCALLY HEAVY DOWNPOURS, AND
DUE TO THEIR PULSE-LIKE NATURE, GUSTY WINDS UP TO AROUND 30-40
MPH WILL BE POSSIBLE AS STORMS COLLAPSE. COLD AIR FUNNELS WERE
REPORTED IN CENTRAL ILLINOIS YESTERDAY, AND GIVEN THAT SIMILAR
CONDITIONS ARE EXPECTED TO PIVOT INTO THE AREA TODAY, (LOW-
LEVEL INSTABILITY PAIRED WITH SURFACE VORTICITY) SUSPECT THAT
THEY WILL BE POSSIBLE WITH ANY SHOWERS/STORMS THAT DEVELOP
TODAY.
THE SUMMER-LIKE WARMTH IS EXPECTED TO CONTINUE TODAY WITH
TEMPERATURES FORECAST TO WARM INTO THE MID 70S TO AROUND 80
DEGREES. THE EXCEPTION TO THIS BEING NEAR THE LAKESHORE WHERE
CONTINUED ONSHORE FLOW WILL HOLD HIGHS IN THE 60S. WITH WARM AND
MOIST AIR LIFTING ACROSS THE AREA, FOG DEVELOPMENT OVER THE
LAKE IS LIKELY TODAY THROUGH WEDNESDAY. AS LOW-LEVEL FLOW TURNS
MORE EAST NORTHEASTERLY LATE THIS EVENING AND OVERNIGHT, THIS
FOG MAY OOZE INLAND. ACCORDINGLY, INTRODUCED AREAS OF FOG ALONG
THE IMMEDIATE LAKESHORE LATE THIS EVENING THROUGH EARLY
WEDNESDAY MORNING AND PATCHY FOG FURTHER INLAND ACROSS FAR
NORTHEAST ILLINOIS.
WEDNESDAY WILL BE SIMILAR TO TODAY THOUGH PERHAPS SLIGHTLY
WARMER FOR INLAND AREAS (LOW TO MID 80S FOR HIGHS). THE MID-
UPPER LOW WILL BEGIN TO SHIFT FURTHER EAST WHICH SHOULD HELP
LIMIT SHOWER COVERAGE OVERALL. HOWEVER, A SURFACE CONVERGENCE
AXIS THAT SETS UP DURING THE AFTERNOON EXTENDING FROM NEAR
ROCKFORD TO RENSSELAER COULD COULD AID IN GREATER SHOWER/STORM
COVERAGE IN THOSE AREAS.
PETR
WEDNESDAY NIGHT:
THE MAIN CONCERN IS FOR FOG OVER THE LAKE TO POSSIBLY BLEED BACK A
BIT INLAND ALONG THE IMMEDIATE ILLINOIS SHORE GIVEN LOW-LEVEL
EAST-SOUTHEAST FLOW. IF THERE'S STILL DENSE FOG OVER THE LAKE
DURING THE DAY ON WEDNESDAY, THEN LOCALLY DENSE FOG WOULD BE
POSSIBLE ALONG THE ILLINOIS SHORELINE. ASIDE FROM THIS CONCERN,
EXPECT A QUIET AND MILD NIGHT WITH LOWS IN THE LOWER TO MID 60S
EXCEPT 50S ALONG THE ILLINOIS SHORE AND FAR NORTHEAST ILLINOIS.
THURSDAY-THURSDAY EVENING:
HOT, NEAR RECORD HIGH TEMPS (SEE FORTHCOMING CLIMATE AFD
SECTION FOR MORE) ARE THE FIRST ITEM OF NOTE FOR THURSDAY.
EXCEPTIONALLY WARM LOW- LEVEL TEMPS ARE EXPECTED AT PEAK
HEATING. IN FACT, PROGGED 925 MB TEMPS IN THE MID TO PERHAPS
UPPER 20S CELSIUS ARE ABOVE THE 90TH PERCENTILE OF DVN AND ILX
MID MAY SOUNDING CLIMATOLOGY. WITH THESE VERY WARM TEMPS ALOFT
(AND PUSHING +20C AT 850 MB!), SOUTHERLY WINDS GUSTING TO 30-35
MPH, AND PLENTY OF SUNSHINE SHOULD TRANSLATE TO HIGHS IN THE
UPPER 80S TO LOWER 90S.
THESE TEMPS PAIRED WITH DEW POINTS IN THE 60S AMIDST VERY STEEP
MID-LEVEL LAPSE RATES AROUND 8C/KM WILL LIKELY YIELD 2-3KG OF
MLCAPE. IN ADDITION TO THE LARGE INSTABILITY, STRONG MID-LEVEL
SHEAR (EFFECTIVE DEEP LAYER SHEAR PUSHING 50 KT) FROM SEASONABLY
ROBUST SOUTHWESTERLY MID-LEVEL FLOW VEERING TO WESTERLY ABOVE 500
MB WILL SET UP A CONDITIONALLY VOLATILE AIR MASS REGARDING THE
THREAT FOR SEVERE WEATHER. THE AFOREMENTIONED INGREDIENTS SUGGEST
SUPERCELL MODE WITH LARGE TO DESTRUCTIVE HAIL BEING THE MOST
NOTABLE THREAT (AND A PERSISTENT FEATURE ON SOUNDING ANALOGS). A
COLD FRONT/DRY-LINE TRAILING FROM THE POWERHOUSE 980S MB
CYCLONE OVER MN WILL BE THE SOURCE OF LOWER-LEVEL CONVERGENCE.
MEANWHILE, THE STRONGEST FORCING FROM THE DEEP, NEGATIVELY
TILTED MID-UPPER TROUGH WILL REMAIN OFF TO OUR NORTHWEST, THOUGH
MODEST 500 MB HEIGHT FALLS WILL OVERSPREAD THE MID-UPPER MS
VALLEY LATE IN THE AFTERNOON.
AS ALREADY ALLUDED TO ABOVE, THIS LOOKS TO BE ANOTHER CONDITIONAL
SEVERE WEATHER THREAT SCENARIO (CONDITIONAL UPON STORMS ACTUALLY
FORMING). SOME OF THE GUIDANCE VEERS THE SOUTHERLY WINDS TO
SOUTHWESTERLY OUT AHEAD OF THE FRONT, WHICH WOULD GREATLY CURTAIL
LOW-LEVEL CONVERGENCE. EVEN IF A PRE-FRONTAL TROUGH OR SURFACE
WAVE KEEPS FLOW MORE BACKED, THE LARGE SCALE FORCING IS RATHER
MEAGER GIVEN THE VERY WARM EML BASE AND ASSOCIATED CAPPING FROM
IT. VERSUS THE APRIL 28TH FAILED CONDITIONAL POTENTIAL, THIS SETUP
APPEARS MUCH MORE LIKELY TO HAVE STRONG HEATING THROUGH
INSOLATION, HELPING TO ERODE THE CAPPING TO AN EXTENT. FINALLY,
ANOTHER COMPETING FACTOR APPEARS TO BE VERY DRY AIR AT THE MID-
LEVELS THAT COULD PROVIDE DELETERIOUS DRY AIR ENTRAINMENT INTO
SOME UPDRAFT ATTEMPTS.
GIVEN THE COMPETING AND LIMITING FACTORS, POPS IN THE 30-40% RANGE
IN THE LATE AFTERNOON AND EARLY EVENING APPEAR SUFFICIENT. EVEN IF
CI (CONVECTIVE INITIATION) OCCURS, COVERAGE MAY ONLY END UP
ISOLATED TO PERHAPS WIDELY SCATTERED. TAKEN IN SUM, THE IMPRESSIVE
INGREDIENTS FOR SEVERE WEATHER, BUT CONDITIONAL NATURE SUPPORT THE
LEVEL 2 OF 5 THREAT FOR MOST OF THE AREA IN SPC'S DAY 3
OUTLOOK. IN ADDITION TO DAMAGING TO POTENTIALLY DESTRUCTIVE
HAIL, AND STRONG DOWNBURST WINDS, ELEVATED LCL HEIGHTS AND
COMPARABLY MORE MODEST LOW-LEVEL SHEAR FORECAST MAY LIMIT THE
TORNADO THREAT SOMEWHAT, IF A FEW SUPERCELLS DO INDEED OCCUR.
THE THREAT FOR THUNDERSTORMS AND SEVERE WEATHER SHOULD END
FAIRLY QUICKLY BY THE MID EVENING AS THE DRYLINE/FRONT SWEEPS
ACROSS THE AREA.
FRIDAY:
THE MAIN FORECAST CONCERN IS THE POTENTIAL FOR HIGH FIRE DANGER
DUE TO STRONG WEST-SOUTHWEST WINDS AND VERY WARM TEMPS (WELL INTO
THE 80S) PLUS DEW POINTS IN THE 40S (OR LOWER) YIELDING RH IN THE
20-30% RANGE (OR LOWER). FRIDAY'S FORECAST ADMITTEDLY IS A BIT
LOWER CONFIDENCE DUE TO OVERALL CONSIDERABLE VARIANCE AMONG
GUIDANCE MEMBERS. WITH THAT SAID, THE MOST CONSISTENT SUITE HAS
BEEN THE ECMWF/EPS, WHICH ALSO (UNFORTUNATELY) HAPPENS TO
FEATURE THE MOST CONCERNING SCENARIO FROM A FIRE WEATHER
PERSPECTIVE. ONE OF THE KEY ITEMS TO WATCH FOR THE FORECAST WILL
BE HOW FAST AND HOW FAR SOUTH THE UPPER TROUGH ASSOCIATED WITH
THE STRONG LOW PRESSURE TO THE NORTH CLOSES OFF, WHICH WOULD ACT
TO KEEP THE 980S MB SURFACE LOW FARTHER SOUTH. SHOULD THIS
OCCUR, A VERY TIGHT PRESSURE GRADIENT WILL REMAIN IN PLACE OVER
OUR AREA WITH DEW POINTS MIXING OUT INTO THE 40S OR LOWER. IN
ADDITION, STRONGER SOUTHWESTERLY 850 MB FLOW WOULD BE IN PLACE
TO TAP INTO WITH DEEP MIXING.
SINCE IT'S ONLY TUESDAY, THE MAIN FORECAST TWEAK WAS TO NUDGE UP
THE WIND GUSTS A BIT FROM THE NBM INITIALIZATION INTO THE 35-40
MPH RANGE, STRONGEST I-80 AND NORTH. ALSO SLIGHTLY NUDGED TD
LOWER. THESE STEPS WERE TAKEN WITH THE GOOD RUN TO RUN CONSISTENCY
OF THE ECMWF/EPS IN MIND. WE'LL NEED TO CLOSELY MONITOR GUIDANCE TRENDS
FOR THIS PERIOD, NEEDLESS TO SAY.
LATER FRIDAY AND ESPECIALLY INTO FRIDAY EVENING, DESPITE THE
WARM, DRY, AND WINDY CONDITIONS DURING THE DAY, AN IMPULSE COMING
UP THE OH VALLEY MAY BE ABLE TO YIELD SOME HIGH BASED SHOWERS AND
EVEN A STORM OR TWO, ESPECIALLY SOUTHEAST OF I-55. SUSPECT THE
GEFS/GFS DEPICTIONS ARE AN OUTLIER FOR THE MUCH WETTER SCENARIO ON
FRIDAY, THOUGH LOW POPS IN THE 20-30% RANGE APPEAR SUFFICIENT.
CASTRO
SATURDAY THROUGH TUESDAY:
GENERALLY COOLER AND DRY CONDITIONS ARE FORECAST FOR THE WEEKEND.
WHILE CONFIDENCE IN THE DETAILS REMAIN LOW THIS FAR OUT, LONG-RANGE
GUIDANCE SUPPORTS A RETURN TO A MORE ACTIVE WEATHER PERIOD AS
MULTIPLE IMPULSES EJECTING OFF THE ROCKIES NEXT WEEK WHICH COULD
BRING ADDITIONAL SHOWER AND THUNDERSTORM CHANCES TO THE REGION.
PETR
AVIATION /18Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 1239 PM CDT TUE MAY 13 2025
KEY AVIATION MESSAGES FOR THE CURRENT TAF PERIOD:
- IFR/LIFR CIGS/VIS EXPECTED OVERNIGHT INTO TUESDAY MORNING
EAST WINDS WILL BECOME LIGHT TONIGHT, IF NOT BECOMING CALM
ALTOGETHER OVERNIGHT. INCREASING MOISTURE ACROSS THE AREA HAS
CREATED SCT/BKN CLOUDS MAINLY ABOVE 2500 FEET ACROSS THE REGION.
THERE IS A CHANCE FOR SHOWERS AND THUNDERSTORMS AWAY FROM THE
CHICAGO METRO THIS AFTERNOON, BUT WITH THE PROBABILITY LESS THAN
25 PERCENT, IT WAS KEPT OUT OF THE TAF. PERHAPS KGYY HAS THE
BEST CHANCE, BUT MODELS ARE KEEPING IT SOUTH OF THE TERMINAL.
THE MAIN IMPACT TO TERMINALS IS THE LOWERING OF CIGS AND VIS
THROUGH THE NIGHT. THERE IS INCREASING CONFIDENCE THAT AFTER
DARK, CLOUDS OUT OVER THE LAKE WILL SLOWLY OOZE INLAND AND LOWER
CIGS AND VIS THROUGH TUESDAY MORNING WITH A THREAT OF
POTENTIALLY DENSE FOG (VIS LESS THAN 1/2SM). THE GREATEST THREAT
FOR FOG WILL BE TERMINALS CLOSER TO THE LAKE (ORD, MDW, GYY).
THERE IS STILL SOME UNCERTAINTY ON IMPROVEMENT WEDNESDAY
MORNING, THOUGH VIS IS EXPECTED TO IMPROVE AFTER 15Z, WITH AN
EVENTUAL RETURN TO VFR AFTER 18Z.
DK
CLIMATE
ISSUED AT 420 AM CDT TUE MAY 13 2025
RECORD HIGH TEMPERATURES ARE POSSIBLE ON THURSDAY MAY 15TH.
HERE ARE THE CURRENT RECORD HIGHS FOR MAY 15TH:
CHICAGO: 91 IN 1962
ROCKFORD: 90 IN 1944
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY UNTIL 1 PM CDT WEDNESDAY FOR THE IL AND IN
NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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