909
FXUS63 KLOT 132335
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
635 PM CDT TUE MAY 13 2025
KEY MESSAGES
- DENSE FOG NEAR THE ILLINOIS LAKE MICHIGAN SHORE THIS AFTERNOON IS
LIKELY TO SPREAD INLAND ACROSS PARTS OF NORTHEASTERN IL AND
NORTHWESTERN IN TONIGHT.
- SUMMER-LIKE WARMTH AWAY FROM THE LAKE EXPECTED THROUGH MIDWEEK.
THERE IS A CHANCE FOR NEAR-RECORD TEMPERATURES ON THURSDAY.
- 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.
DISCUSSION
ISSUED AT 307 PM CDT TUE MAY 13 2025
THROUGH WEDNESDAY NIGHT:
SMALL SCALE MID-LEVEL IMPULSES WILL CONTINUE TO SWING
NORTHWESTWARD INTO OUR AREA ALONG THE NORTHERN PERIPHERY OF THE
UPPER LOW SHIFTING INTO EASTERN KY INTO THIS EVENING. THESE WILL
FOSTER ISOLATED TO WIDELY SCATTERED SHOWERS AND A FEW
THUNDERSTORMS LATE THIS AFTERNOON AND EVENING, WITH MOST OF THE
COVERAGE FAVORED ACROSS NORTHWESTERN IN. THIS ACTIVITY IS THEN
EXPECTED TO WANE DURING THE MID TO LATE EVENING HOURS. WHILE
SEVERE WEATHER IS NOT ANTICIPATED WITH ANY OF THESE STORMS, SOME
BRIEF DOWNPOURS AND LOCALLY GUSTY WINDS TO 40 MPH COULD RESULT
WITH THE STRONGEST STORMS.
OTHERWISE, THE MAIN FOCUS FOR TONIGHT INTO WEDNESDAY MORNING
WILL REVOLVE AROUND DENSE FOG POTENTIAL, PARTICULARLY NEAR LAKE
MICHIGAN. RECENT SATELLITE IMAGERY AND AREA MARINE WEBCAMS
CONFIRM THAT AREAS OF DENSE FOG CONTINUE OVER SOUTHWESTERN LAKE
MICHIGAN RIGHT UP TO THE NORTHEASTERN IL SHORE. THIS FOG IS
LIKELY TO OOZE INLAND ACROSS PARTS OF NORTHEASTERN IL WITH
SUNSET THIS EVENING, LIKELY IMPACTING AREAS WITHING ABOUT 5-10
MILES FROM THE LAKESHORE THROUGH THE EVENING AND OVERNIGHT. THE
FOG MAY THEN BEGIN TO DEVELOP/SPREAD FARTHER INLAND ACROSS
NORTHEASTERN IL AND NORTHWESTERN IN LATER THIS EVENING AND
OVERNIGHT. ACCORDINGLY, AREAS OF DENSE FOG, WITH VISIBILITIES
UNDER A HALF MILE, APPEAR TO BE A GOOD BET TONIGHT, WITH THE
HIGHEST PROBABILITIES OF THIS (70%+) EXPECTED ACROSS THE COLLAR
COUNTIES OF LAKE MICHIGAN (EG, LAKE IL, COOK, LAKE IN AND
PORTER).
WHILE CONFIDENCE CONTINUES TO INCREASE WITH AREAS OF DENSE FOG
TONIGHT, WE HAVE OPTED TO HOLD OFF ON ISSUING A DENSE FOG
ADVISORY AT THIS TIME. THIS IS MAINLY DUE TO THE FACT THAT SOME
UNCERTAINTY CONTINUES WITH THE INLAND EXTENT OF THE DENSEST FOG.
ACCORDINGLY, WILL LET THE EVENING SHIFT GET A BETTER HANDLE ON
THE OBSERVATION TRENDS THIS EVENING BEFORE LOCKING INTO A FOG
HEADLINE. THE FOG IS LIKELY TO LINGER INTO THE EARLY TO MID
MORNING HOURS OF WEDNESDAY BEFORE DIURNALLY IMPROVING.
FOLLOWING THE FOGGY START TO THE EARLY MORNING, WEDNESDAY WILL
BE ANOTHER WARM DAY FOR INLAND SECTIONS OF THE AREA, AS
TEMPERATURES WARM INTO THE LOWER 80S INTO WEDNESDAY AFTERNOON.
HOWEVER, CONTINUED ONSHORE FLOW WILL AGAIN KEEP CONDITIONS MUCH
COOLER ALONG THE LAKESHORE (60S). SOME ADDITIONAL ISOLATED TO
WIDELY SCATTERED SHOWERS AND THUNDERSTORMS WILL ALSO BE POSSIBLE
(20-30% CHANCE) WEDNESDAY AFTERNOON. SIMILAR TO TODAY, THE
PRIMARILY THREAT FOR THESE WILL BE ACROSS INTERIOR SECTIONS OF
NORTHERN IL AND NORTHWESTERN IN. SEVERE WEATHER IS NOT
ANTICIPATED WITH THIS ACTIVITY.
KJB
THURSDAY THROUGH FRIDAY NIGHT:
NOT A LOT HAS CHANGED RECENTLY IN THE THINKING FOR THURSDAY'S
STORM POTENTIAL OR FOR FRIDAY'S FIRE WEATHER CONCERNS. LEADING
UP TO THE STORM POTENTIAL, SOUTHERLY WINDS WILL BE GUSTING TO 25
TO 30 MPH, POSSIBLY HIGHER, AHEAD OF THE SYSTEM. THE EFFICIENT
WARM ADVECTION BOTH AT THE SURFACE AND ALOFT WILL PROVIDE NEAR-
RECORD WARMTH ON THURSDAY WITH HIGHS FORECAST IN THE UPPER 80S
TO AROUND 90 DEGREES. SEE THE CLIMATE SECTION OF THE AFD BELOW
FOR SPECIFICS ON RECORDS.
THE POTENTIAL FOR STORMS SHOULD ARRIVE IN OUR WEST MID-LATE
AFTERNOON AHEAD OF AN IMPENDING OCCLUDED COLD FRONT/DRYLINE.
THIS FEATURE AND THE ASSOCIATED STORM CHANCES WILL MOVE ACROSS
THE AREA BEFORE DEPARTING TO THE EAST AROUND MID-EVENING. IT
REMAINS A VERY CONDITIONAL THREAT WITH A CAPPING INVERSION, DRY
LAYER AIR, AND UNIMPRESSIVE FORCING ALL FACTORS THAT COULD
INHIBIT STORM DEVELOPMENT, AT LEAST TO AN EXTENT. BUT, IF STORMS
DO INITIALIZE, STRONG TO SEVERE CONVECTION WILL LIKELY ENSUE.
IN THE OPEN WARM SECTOR AHEAD OF THE BOUNDARY, GUIDANCE IS
GENERATING ANYWHERE FROM 2,000 TO 3,000 J/KG OF MLCAPE. THIS IS
MADE POSSIBLE BY SUCH WARM LOW-LEVEL AIR LEADING TO MID-LEVEL
LAPSE RATES IN THE NEIGHBORHOOD OF 8-9 K/KM. ELS ARE EVEN BEING
MODELED ALL THE WAY UP ABOVE 200MB. STORMS WILL NOT BE GETTING
ANYWHERE NEAR THAT TALL WITH SO MUCH DRY MID-UPPER AIR, BUT IT
GOES TO SHOW JUST HOW MUCH COOL AIR RESIDES ALOFT. 50 TO 60 KT
OF EFFECTIVE SHEAR AND A DEEP INFLOW LAYER ARE ALSO MORE THAN
SUPPORTIVE OF ORGANIZED SEVERE CONVECTION. SO IF STORMS DEVELOP,
THE ENVIRONMENT ALOFT IS PRIMED FOR PRETTY ERUPTIVE UPDRAFTS.
IT'S JUST A MATTER OF IF WE CAN MAKE ANY USE OF THOSE BETTER
INGREDIENTS. IN ORDER TO DO THAT, THE CAP WILL EITHER HAVE TO
BREAK OR BE FORCED THROUGH AND ENOUGH MOISTURE WILL NEED TO
GATHER TO SUPPORT CONVECTIVE INITIATION, BUT IT'S NOT CLEAR IF
EITHER OF THOSE WILL OCCUR.
THERE REMAINS DISCREPANCIES IN AFTERNOON TEMPERATURES AND
DEWPOINTS AHEAD OF THE BOUNDARY WHICH EXTENDS TO DISAGREEMENTS
ON THE LEVEL OF CAPPING THAT HOLDS. MOST GUIDANCE NOW SUGGESTS
THAT THE CAP WILL EITHER BREAK PRIOR TO FROPA OR ONLY WEAK
CAPPING WILL REMAIN. HOWEVER, ANY WEAK CAPPING COULD BE ENOUGH
TO KEEP STORMS AT BAY. FORCING LOOKS ALL AROUND VERY MEAGER BUT
ESPECIALLY ABOVE THE CAP. THE MORE APPRECIABLE OF THE ALREADY
MODEST FORCING FOR US WILL BE FOCUSED IN THE LOW LEVELS AND WILL
COME VIA PRESSURE FALLS. THE BETTER DEEP FORCING WILL BE
DISPLACED TO OUR NORTH AND WEST AND WE WON'T BE GETTING A TON OF
HELP FROM FEATURES ALOFT HERE. FORCED ASCENT ALONG THE BOUNDARY
COULD PROVIDE SOME EXTRA OOMF, BUT MOST GUIDANCE IS SUGGESTING
THAT DEEP MIXING INTO SW FLOW MAY CAUSE SURFACE WINDS TO TAKE ON
MORE OF A SW DIRECTION AHEAD OF THE FRONT, WHICH WOULD REALLY
HINDER CONVERGENCE ALONG THE FRONT COMPARED TO IF WINDS CAN
REMAIN EAST OF SOUTH. LASTLY, WILL THERE EVEN BE ENOUGH BOUNDARY
LAYER MOISTURE TO GENERATE DEEP CONVECTION? THE INVERTED-V
SOUNDING WILL MAKE THAT DIFFICULT TO ACHIEVE VIA MIXING AND A
NUMBER OF FORECAST SOUNDINGS STRUGGLE TO SATURATE BENEATH THE
INVERSION.
IF STORMS OCCUR, THE PRIMARY CONCERNS WOULD BE LARGE HAIL AND
DAMAGING WINDS. SOUNDING ANALOGS FOR THURSDAY SUGGEST
DESTRUCTIVE HAIL MAY EVEN BE POSSIBLE, ALTHOUGH HOPEFULLY ALL
THAT DRY UPPER AIR CAN HAMPER HAIL GROWTH A BIT. THE STEEP LAPSE
RATES AND DRY AIR, ESPECIALLY THROUGH THE LOW LEVELS, ARE
FAVORABLE FOR STRONG DOWNDRAFT WINDS. THERE IS A LESSER THREAT
FOR TORNADOES, BUT THE POTENTIAL IS CERTAINLY THERE. ANY STORMS
THAT GO SHOULD BE SURFACE-BASED AND ABLE TO TAKE FULL ADVANTAGE
OF THE LOW-LEVEL HODOGRAPH. AGAIN THOUGH, THERE ARE UNCERTAINTY
REGARDING SURFACE WINDS NEAR THE FRONT AND THE TORNADO THREAT
WILL BE HIGHER IF THEY CAN REMAIN BACKED (SE). THE SHEAR PROFILE
RELATIVE TO THE BOUNDARY FAVOR A DISCRETE OR SEMI-DISCRETE
MODE, AND THE DRY AIR MAY ALSO HELP KEEP MODE RATHER DISCRETE.
THE GENERALLY BEST CHANCES AT SEEING CONVECTIVE INITIATION IS
ACROSS OUR NORTH WHERE SLIGHTLY MORE FAVORABLE PROFILES CAN BE
FOUND. THE NBM'S 30-50% POPS ACROSS THE AREA MATCH WELL WITH THE
30-50% POPS FROM THE GRAND ENSEMBLE (GEFS, GEPS, AND EPS
CONGLOMERATE).
WE'RE STILL EYEING FIRE WEATHER CONCERNS FOR FRIDAY FOR THE
COMBINATION OF WARM, DRY AIR AND GUSTY WINDS. AN ENHANCED LOW-
LEVEL WIND FIELD WILL GENERATE ON THE SOUTHERN PERIPHERY OF THE
LOW TO OUR NORTH, BUT IT'S UNCLEAR HOW MUCH OF THAT MOVES OVER
THE AREA AND WHAT THE MAGNITUDE OF THOSE WINDS WILL LOOK LIKE.
THE EURO/EPS HAS BEEN THE MOST AGGRESSIVE WITH BOTH THE WINDS
AND DRY SURFACE AIR ON FRIDAY. THE EPS MEAN AS WELL AS THE
DETERMINISTIC EURO MIX 40 TO 50 MPH GUSTS DOWN TO THE SURFACE
DURING THE LATE MORNING AND AFTERNOON. THE GFS AND GEFS KEEP THE
CORE OF THESE STRONGER LOW-LEVEL WINDS AWAY FROM THE AREA AND
RESOLVE GUSTS MORE IN THE 30 TO 35 MPH RANGE. THE EPS MEAN HAS
40 TO 50 MPH GUSTS IN THE LATE MORNING AND AFTERNOON AND 18Z RHS
BETWEEN 20 AND 25%. BY 21Z, THE DETERMINISTIC EURO MIXES RHS
DOWN TO 15 TO 20%. THE GEFS IS NOT QUITE AS DRY AS KEEPS MIDDAY
RHS GENERALLY ABOVE 30%. GFS ALSO KEEPS THE STRONGER LOW-LEVEL
WIND FIELD DISPLACED TO OUR NORTHWEST AND RESOLVES GUSTS CLOSER
TO 30 TO 35 MPH. SO AT THE LEAST A MARGINAL THREAT FOR FIRE
SPREAD WILL EXIST ON FRIDAY, BUT MORE LIKELY IT WILL BE A
CONSIDERABLE FIRE WEATHER DAY, POSSIBLY LOOKING AT RED FLAG
CRITERIA.
AN ADDITIONAL SYSTEM OF SHOWERS AND THUNDERSTORMS IS EXPECTED
TO GO UP AHEAD OF A SECONDARY COLD FRONT LATE FRIDAY. THE GFS
HAS BEEN WANTING TO BRING A LARGE SWATH OF PRECIP ACROSS THE
AREA DURING THE AFTERNOON. BUT, THE GFS IS AN OUTLIER IN TERMS
OF LAYER MOISTURE AND IS EVEN NOTABLY MORE AGGRESSIVE THAN JUST
ABOUT ALL 30 INDIVIDUAL GEFS MEMBERS. MOST OTHER CAMPS RESOLVE
ISOLATED TO WIDELY SCATTERED ACTIVITY HERE AND THERE THROUGH THE
AFTERNOON. A MARGINAL SEVERE RISK MAY EXIST IN OUR FAR SOUTH
LATER IN THE DAY, BUT THE FAR BETTER CHANCES SHOULD REMAIN SOUTH
OF THE AREA.
DOOM
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/KJB
AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 635 PM CDT TUE MAY 13 2025
FORECAST CONCERNS INCLUDE...
DENSE FOG WITH VLIFR CIGS/VIS OVERNIGHT/EARLY WEDNESDAY MORNING.
CIGS/VIS QUICKLY LIFTING THROUGH IFR/MVFR WEDNESDAY MORNING.
ISOLATED THUNDERSTORMS THIS EVENING, SOUTHWEST OF THE TERMINALS.
DENSE FOG OVER SOUTHERN LAKE MICHIGAN WILL MOVE INLAND AFTER
SUNSET, FIRST AS A LOW MVFR CIG, THEN AN IFR CIG AND THEN
VISIBILITIES WILL STEADILY LOWER. MUCH OF GUIDANCE NOW TANKS
THE VIS AT ORD/MDW/GYY TO 1/4SM IN THE PREDAWN HOURS AND HAVE
FOLLOWED THESE TRENDS WITH TEMPO 1/4SM. IT IS POSSIBLE THAT
THERE WILL BE A 4-5 HOUR PERIOD OF PREVAILING 1/4SM VIS THAT
MAY BE NEEDED WITH LATER FORECASTS. THERE SHOULD BE RAPID
IMPROVEMENT IN BOTH THE VIS AND CIGS IN THE 13Z-15Z TIME PERIOD
WEDNESDAY MORNING. DENSE FOG MAY MOVE EVEN FURTHER INLAND THAN
JUST ORD/MDW AND TRENDS WILL NEED TO BE MONITORED BUT SOME FOG
IS EXPECTED FOR MUCH OF THE AREA ALONG WITH IFR/LIFR CIGS EARLY
WEDNESDAY MORNING.
THERE IS THE POTENTIAL FOR ADDITIONAL FOG AND LOWER CIGS
WEDNESDAY EVENING INTO EARLY THURSDAY MORNING, BUT CONFIDENCE
FOR TIMING IS TOO LOW FOR MENTION WITH THE NEW 30 HOUR ORD/MDW
TAFS.
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL CONTINUE INTO
THIS EVENING FOR AREAS SOUTHWEST OF THE TERMINALS AND ARE NOT
EXPECTED AT THE TERMINALS.
EASTERLY WINDS WILL CONTINUE THROUGH THE PERIOD FOR THE CHICAGO
TERMINALS, WITH SOUTHEAST WINDS FOR THE REST OF THE AREA AND RFD
WEDNESDAY. CMS
CLIMATE
ISSUED AT 613 PM 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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