350
FXUS63 KLOT 140856
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
356 AM CDT WED MAY 14 2025
KEY MESSAGES
- SUMMER-LIKE WARMTH CONTINUES THROUGH FRIDAY, WITH RECORD
BREAKING HEAT POSSIBLE THURSDAY.
- CONDITIONAL THREAT OF SEVERE WEATHER EXISTS THURSDAY AFTERNOON
AND EVENING (THREAT LEVEL 2 TO 3 OUT OF 5), DEPENDENT ON
STORMS FORMING.
- THREAT OF RAPID FIRE SPREAD THURSDAY AND ESPECIALLY FRIDAY DUE
TO A COMBINATION OF STRONG WINDS AND DRY CONDITIONS.
DISCUSSION
ISSUED AT 355 AM CDT WED MAY 14 2025
THROUGH THURSDAY MORNING:
DENSE FOG AND LOW STRATUS CONTINUES TO DRIFT INLAND ACROSS
NORTHEAST ILLINOIS EARLY THIS MORNING. THIS WILL LEAD TO FURTHER
DETERIORATION OF VISIBILITY AS IT CONTINUES ITS SLOW MARCH
INLAND, WITH FURTHER EXPANSIONS OF THE DENSE FOG ADVISORY
POSSIBLE. OUTSIDE OF THE MARINE-BASED FOG INFLUENCE, PATCHY FOG
(SOME LOCALLY DENSE) HAS DEVELOPED FURTHER INLAND ACROSS EAST
CENTRAL IL AND NORTHWEST IN DUE TO LIGHT WINDS AND RESIDUAL HIGH
LOW-LEVEL MOISTURE. VISIBILITY WILL IMPROVE QUICKLY BY 8-9 AM
CST FOR INLAND AREAS.
EXPECT ANOTHER ROUND OF MAINLY LOW COVERAGE SHOWERS AND ISOLATED
THUNDERSTORMS THIS AFTERNOON SOUTHWEST OF THE CHICAGO METRO
ALONG A NARROW CONFLUENCE AXIS. AS HAS BEEN THE CASE THE PAST
COUPLE OF DAYS THE MAIN HAZARDS WITH ANY STORMS THAT DEVELOP
WILL BE LIGHTNING STRIKES, LOCALLY HEAVY DOWNPOURS, AND GUSTY
WINDS UP TO AROUND 30-40 MPH UPON THE STORM COLLAPSING (IF THEY
DEVELOP). WILL NOTE THAT ANY OUTFLOW BOUNDARIES FROM THESE
AFTERNOON STORMS COULD LEAD TO ADDITIONAL DEVELOPMENT DURING THE
LATE AFTERNOON/EARLY EVENING PERIOD. HAVE INCLUDED SOME LOW-END
SLIGHT CHANCES (15-20%) INTO THE CHICAGO METRO TO ACCOUNT FOR
THIS POTENTIAL.
IT WILL BE ANOTHER WARM AND HUMID DAY TODAY, WITH HIGH
TEMPERATURES IN THE UPPER 70S TO MID 80S. CONTINUED ONSHORE FLOW
WILL KEEP TEMPERATURES COOLER, IN THE MID 60S TO LOWER 70S NEAR
THE LAKESHORE WITH FOG OVER THE LAKE DRIFTING INLAND ALONG THE
IMMEDIATE LAKESHORE POSSIBLE AT TIMES THROUGH THE DAY. THIS MAY
PUSH A BIT FARTHER INLAND ACROSS FAR NORTHEAST ILLINOIS AGAIN
TONIGHT.
STEEPENING LAPSE RATES AHEAD OF DEEPENING LOW PRESSURE ACROSS
THE NORTH CENTRAL PLAINS, ALONG WITH STRONG WARM ADVECTION AND
ISENTROPIC ASCENT COULD SUPPORT AN AXIS OF ELEVATED
THUNDERSTORMS DEVELOPING. GIVEN THIS IS A NEW TREND IN ONLY A
FEW MODELS, OPTED TO INTRODUCE SLIGHT CHANCES (15-20%) FOR
THUNDERSTORMS OVERNIGHT THROUGH MID THURSDAY MORNING. WHILE
CONFIDENCE IS LOW IN THIS POTENTIAL, FOR WHAT IT'S WORTH THE 00Z
OPERATIONAL ECMWF WAS ON THE MORE AGGRESSIVE SIDE WITH THE
ELEVATED CONVECTION FOOTPRINT AND ITS ENSEMBLE CAME IN WITH
15-30% OF MEMBERS FORECASTING QPF. IF STORMS WERE TO FORM THEY
WOULD BE CAPABLE OF LARGE HAIL AND LIGHTNING STRIKES.
PETR
THURSDAY AFTERNOON THROUGH THURSDAY NIGHT:
HOT, NEAR TO RECORD HIGH TEMPS STILL APPEAR ON TRACK FOR
THURSDAY. IF ELEVATED CONVECTION DOES OCCUR IN THE MORNING AS
MENTIONED IN PREVIOUS SECTION, ITS ASSOCIATED DEBRIS CLOUD COVER
COULD SLOW THE WARMING TREND FOR A COUPLE HOURS AND LEAVE SOME
RESIDUAL BOUNDARIES IN PLACE. CLOUD COVER SHOULD THIN OUT FOR
THE MIDDAY-MID AFTERNOON TIMEFRAME, WHEN TEMPS SHOULD BE OFF TO
THE RACES AWAY FROM THE IL SHORE (HELD COOLER BY SOUTHEAST
WINDS UNTIL TOWARDS EVENING). 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 30-40 MPH, AND PLENTY OF SUNSHINE
SHOULD TRANSLATE TO HIGHS FROM AROUND 90F TO THE LOWER 90S.
IT'S EVEN NOT OUT OF THE QUESTION THAT A FEW 94F READINGS OCCUR
IN PORTIONS OF THE SOUTHWEST CWA. THE HEAT INDICES, WHILE NOT
NECESSARILY PROBLEMATIC FOR MOST FOR MID SUMMER, WILL BE
UNUSUALLY HOT FOR MID MAY, PEAKING IN THE MID-UPPER 90S F IN
SPOTS.
THE HOT AND MODERATELY HUMID CONDITIONS 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 HIGH INTENSITY 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. THIS
AND THE DRYLINE SURGING EASTWARD MORE QUICKLY WOULD SCOUR THE
AIR MASS OUT MORE QUICKLY. EVEN IF A PRE-FRONTAL TROUGH OR
SURFACE WAVE KEEPS FLOW MORE BACKED (SIMILAR TO THE UNCANNILY
CONSISTENT OPERATIONAL ECMWF DEPICTIONS THE LAST SEVERAL CYCLES),
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. IT'S WORTH NOTING THAT THE
ECMWF/EPS SUITE HAS BEEN VERY CONSISTENT SHOWING CI (~75% OF 00Z
MEMBERS SHOWING QPF BETWEEN 18-00Z), EVEN WITHOUT DEW POINTS
INTO THE 70S AS SOME GUIDANCE IS DEPICTING.
YET ANOTHER COMPETING FACTOR APPEARS TO BE VERY DRY AIR AT THE
MID-LEVELS, ESPECIALLY WITH WESTWARD EXTENT THAT COULD PROVIDE
DELETERIOUS DRY AIR ENTRAINMENT INTO SOME UPDRAFT ATTEMPTS.
GIVEN THE COMPETING AND LIMITING FACTORS, POPS IN THE 30-40%
RANGE FROM THE MID AFTERNOON THROUGH THE EARLY EVENING (~2PM-9PM
CDT) APPEAR SUFFICIENT. EVEN IF CI (CONVECTIVE INITIATION)
OCCURS, COVERAGE MAY ONLY END UP ISOLATED TO PERHAPS WIDELY
SCATTERED. GIVEN THE IMPRESSIVE INGREDIENTS FOR HIGHER END
SEVERE WEATHER, ESPECIALLY HAIL, AND ALSO DOWNBURST WINDS, SPC
INTRODUCED A LEVEL 3 OF 5 THREAT INTO A PORTION OF THE CWA
(LEVEL 2 OF 5 FOR THE REST OF THE AREA) ON ITS DAY 2 OUTLOOK.
THREATS WISE, IN ADDITION TO DAMAGING TO POTENTIALLY DESTRUCTIVE
HAIL, AND STRONG DOWNBURST WINDS (FROM STEEP LOW- LEVEL LAPSE
RATES), ELEVATED LCL HEIGHTS AND COMPARABLY MORE MODEST LOW-
LEVEL SHEAR FORECAST MAY LIMIT THE TORNADO THREAT SOMEWHAT VS
THE OTHER HAZARDS, IF A FEW SUPERCELLS DO INDEED OCCUR. WE'LL
CONTINUE TO MESSAGE THE UNCERTAINTY/CONDITIONALITY OF THE SETUP
IN OUR GRAPHICS.
IT'S WORTH A BRIEF MENTION THAT THE FASTER DRYLINE SCENARIOS
COULD BRING A SHORT-FUSED ELEVATED FIRE DANGER SCENARIO INTO
PLAY FROM THE LATE AFTERNOON THROUGH A BIT AFTER SUNSET,
ESPECIALLY FOR THE WESTERN HALF OR THIRD OF THE CWA. THIS WILL
BE DUE TO SOUTHWEST WINDS GUSTING TO NEAR 40 MPH, AND DEW POINTS
DROPPING INTO THE 50S IF NOT 40S WITH TEMPS STILL AROUND
90F/LOW 90S. 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 STILL A
BIT LOWER CONFIDENCE DUE TO OVERALL CONSIDERABLE VARIANCE AMONG
GUIDANCE MEMBERS. WITH THAT SAID, THE MOST CONSISTENT SUITE HAS
CONTINUED TO BE 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 LOW-MID 40S
OR EVEN LOWER. IN ADDITION, STRONGER SOUTHWESTERLY 850 MB FLOW
WOULD BE IN PLACE TO TAP INTO WITH DEEP MIXING.
WIND GUSTS WERE NUDGED UPWARDS A BIT FROM THE NBM INITIALIZATION
INTO THE 35-40 MPH RANGE, STRONGEST I-80 AND NORTH. ALSO
SLIGHTLY NUDGED TD LOWER, WITH SOME EXPLICIT MID 40S VALUES IN
SPOTS. 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. A FIRE
WEATHER WATCH MAY NEED TO BE CONSIDERED THIS AFTERNOON FOR AT
LEAST PORTIONS OF THE AREA AFTER CONSULTATION WITH LOCAL FIRE
WEATHER/LAND MANAGEMENT PARTNERS.
LATER FRIDAY AND ESPECIALLY INTO FRIDAY EVENING, DESPITE THE
WARM, DRY, AND WINDY CONDITIONS DURING THE DAY, ANOTHER IMPULSE
TRACKING FROM THE MID-MS VALLEY TO THE OH VALLEY AND EASTERN
GREAT LAKES SHOULD INDUCE SOME MOISTURE RETURN BACK INTO THE
CWA. THE LATE MOISTURE RETURN SHOULD GENERALLY BE MOST EFFECTIVE
INTO AREAS GENERALLY SOUTHEAST OF I-55. WITH STEEP MID-LEVEL
LAPSE RATES STILL IN PLACE, HIGH BASED SHOWERS AND ISOLATED TO
WIDELY SCATTERED THUNDERSTORMS ARE POSSIBLE, ESPECIALLY
SOUTHEAST OF I-55. SUPPORTIVE DEEP LAYER SHEAR COULD EVEN
SUPPORT AN ISOLATED SEVERE THREAT IN OUR SOUTH/SOUTHEAST CWA,
BUT THE BETTER CHANCES LOOK TO BE FARTHER SOUTH. SUSPECT THE
NCEP (NAM/GFS/GEFS) DEPICTIONS REMAIN A TOO WET OUTLIER FOR
FRIDAY, THOUGH POPS IN THE 20-50% RANGE (HIGHEST SOUTHEAST OF
I-55) APPEAR SUFFICIENT.
ONCE THE EVENING CONVECTIVE THREAT ENDS, THE REST OF THE NIGHT
WILL BE BREEZY AND COOLER IN THE WAKE OF ANOTHER COLD FRONT
PASSAGE. FORECAST LOWS ARE IN THE MID-UPPER 50S.
CASTRO
SATURDAY THROUGH TUESDAY:
GENERALLY COOLER AND DRY CONDITIONS ARE FORECAST FOR THE WEEKEND.
THE MAIN WEATHER ITEM OF NOTE OVER THE WEEKEND IS YET ANOTHER
DAY OF BREEZY/WINDY CONDITIONS ON SATURDAY, ALBEIT NOT QUITE AS
WINDY AS FRIDAY. WESTERLY WINDS WILL GUST UP TO 30-35 MPH, WITH
UPSIDE POTENTIAL TO 35-40 MPH BASED ON THE MORE AGGRESSIVE
GUIDANCE. THE COOLER TEMPS (70S) WILL LIMIT THE FIRE DANGER
VERSUS FRIDAY AS WELL. LOOKING AHEAD TO NEXT WORK WEEK, 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 /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 1245 AM CDT WED MAY 14 2025
KEY AVIATION MESSAGES:
- PERIOD OF LIFR TO POTENTIALLY VLIFR CIGS/VSBYS EARLY THIS
MORNING
- LOW CONFIDENCE IN SHRA/VCTS LATE AFTERNOON/EARLY EVENING (LESS
THAN 20% CHANCE)
FOCUS IN THE NEAR TERM REMAINS THE LOW STRATUS AND DENSE FOG
OVER LAKE MICHIGAN THAT HAS BEEN SLOWLY DRIFTING INLAND EARLY
THIS MORNING ACROSS NORTHEAST ILLINOIS. THERE HAS BEEN A SLOWING
TREND WITH HOW QUICKLY CEILINGS AND VISIBILITY DROP WITH
SOUTHWEST EXTENT SO HAVE OPTED TO DELAY THE ONSET OF VLIFR
VSBYS AT ORD TO THE 10-13Z TIMEFRAME, WITH LOWER CONFIDENCE IN
IT REACHING MDW (NUDGED UP TO 1/2 SM). 500FT CIGS ARE ON THE
DOORSTEP OF ORD AND EXPECT A STEADY STAIR STEP DOWN IN
CONDITIONS OVER THE NEXT FEW HOURS, EVENTUALLY REACHING MDW,
DPA, AND GYY AS WELL. RFD MAY END UP THE WESTERN FRINGES OF THE
VSBY/CIG REDUCTIONS.
SHOWER AND ISOLATED THUNDERSTORM ACTIVITY IS EXPECTED TO DEVELOP
SOUTHWEST OF THE TERMINALS THIS AFTERNOON. CURRENTLY MAINTAIN A
DRY TAF WITH THIS UPDATE FOR ALL SITES, BUT WILL HAVE TO KEEP AN
EYE ON WHETHER ANY REMNANT OUTFLOW BOUNDARIES FROM THOSE STORMS
(IF THEY FORM) SERVE AS A FORCING MECHANISM FOR ADDITIONAL
DEVELOPMENT PRIOR TO SUNSET (~22-01Z) CLOSER TO THE TERMINALS.
HEADING INTO THIS EVENING, FOG OVER THE LAKE MAY TRY TO DRIFT
INLAND ONCE AGAIN INTO NORTHEAST ILLINOIS. SOME GUIDANCE HAS
TRENDED A BIT LESS PESSIMISTIC WITH THIS, HOWEVER, AND KEEPS
THE LIFR/IFR CONDITIONS CLOSER TO THE LAKESHORE AND JUST TO THE
NORTHEAST OF ORD/MDW. THIS WILL BE SOMETHING TO MONITOR OVER THE
NEXT FEW TAF UPDATES.
WINDS WILL REMAIN GENERALLY EASTERLY THROUGH THE PERIOD, VARYING
FROM NORTHEAST TO SOUTHEAST AT TIMES.
PETR
CLIMATE
ISSUED AT 613 PM CDT TUE MAY 13 2025
RECORD HIGH TEMPERATURES ARE POSSIBLE ON THURSDAY MAY 15.
HERE ARE THE CURRENT RECORD HIGHS FOR MAY 15:
CHICAGO: 91 IN 1962
ROCKFORD: 90 IN 1944
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...DENSE FOG ADVISORY UNTIL 10 AM CDT THIS MORNING FOR ILZ005-
ILZ006-ILZ103.
IN...NONE.
LM...DENSE FOG ADVISORY UNTIL 1 PM CDT THIS AFTERNOON FOR THE IL
AND IN NEARSHORE WATERS.
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