883
FXUS63 KLOT 190352
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
952 PM CST MON NOV 18 2024
KEY MESSAGES
- INCREASINGLY STRONG AND GUSTY WINDS TONIGHT INTO TUESDAY,
GUSTS TO, OR EVEN A LITTLE OVER, 40 MPH ARE POSSIBLE
- UNSEASONABLY WARM WEATHER WILL CONTINUE THROUGH TUESDAY,
FOLLOWED BY MUCH COLDER WEATHER, COLDEST AIR MASS OF THE
AUTUMN
- INTERMITTENT LIGHT SHOWERS POSSIBLE AT TIMES TUES NIGHT
THROUGH WED NIGHT, WITH SOME WET SNOW FLAKES POSSIBLY MIXED IN
- CHANCE OF WET SNOW OR RAIN/WET SNOW MIX THURSDAY, LOW
PROBABILITY OF SOME SLUSHY ACCUMULATIONS, MAINLY ON GRASSY
SURFACES
UPDATE
ISSUED AT 952 PM CST MON NOV 18 2024
THE NEXT ROUND OF SHOWERS IS BEGINNING TO LIFT INTO THE AREA
LATE THIS EVENING AND HAS AT TIMES BEEN ACCOMPANIED WITH
ISOLATED EMBEDDED THUNDERSTORMS. DUE TO HOW CLOSE THIS ACTIVITY
IS GETTING TO THE AREA, OPTED TO INTRODUCE A SLIGHT CHANCE OF
THUNDER BACK INTO THE FORECAST WITH THE EVENING UPDATE TO
ACCOUNT FOR AN OCCASIONAL LIGHTNING STRIKE OVER THE NEXT FEW
HOURS.
WIND SPEEDS ARE ALSO STEADILY ON THE INCREASE WITH PEAK WIND
GUSTS IN THE 35-40 MPH RANGE OCCURRING WITHIN THE BAND OF RAIN.
HI-RES GUIDANCE CONTINUES TO BE RATHER BULLISH ON HOW STRONG
THE WINDS INCREASE OVERNIGHT, LIKELY DUE TO MIXING A BIT DEEPER
INTO THE STRENGTHENING LOW-LEVEL JET OVERHEAD. WHILE
SPORADICALLY HIGHER GUSTS REMAIN POSSIBLE, HAVE HELD OFF ON
ISSUING A WIND ADVISORY WITH THIS UPDATE. WILL CONTINUE TO
MONITOR OBSERVATIONAL TRENDS.
PETR
DISCUSSION
ISSUED AT 259 PM CST MON NOV 18 2024
VIGOROUS MID-LATITUDE CYCLONE OVER THE CENTRAL U.S. WILL PROVIDE FOR
SOME ACTIVE WEATHER OVER THE NEXT 24 HOURS. AT 19Z, A 987MB SURFACE
LOW WAS ANALYZED OVER CENTRAL KANSAS WITH A WARM FRONT EXTENDING
NORTH EXTREME NORTHWEST MISSOURI, THEN EAST ACROSS DOWN STATE IL.
NORTH OF THIS WARM FRONT, OUR CWA IS COVERED WITH WIDESPREAD RAIN,
LOW CLOUDINESS, AND LIGHT FOG THIS AFTERNOON. AS THE KS SFC LOW
MOVES NORTH TO NEAR KMSP BY DAYBREAK TUESDAY, IT WILL DRAG THE WARM
FRONT NORTH ACROSS OUR AREA THIS EVENING, BRINGING A TEMPORARY END
TO THE RAIN THIS EVENING.
THE BREAK SHOULD BE RELATIVELY SHORT LIVED AS A PREFRONTAL BAND OF
SHOWERS ACROSS EASTERN OKLAHOMA AND EASTERN KANSAS LIFTS QUICKLY
NORTHEASTWARD AND ACROSS OUR CWA LATE THIS EVENING INTO THE EARLY
PORTIONS OF THE OVERNIGHT PERIOD. GUIDANCE IS IN PRETTY GOOD
AGREEMENT THAT THERE WILL BE LITTLE IF ANY UPRIGHT INSTABILITY AND
GIVEN THE LACK OF LIGHTNING UPSTREAM, THINK THE CHANCES OF THUNDER
IN OUR CWA IS TOO LOW TO MAINTAIN A CHANCE OF THUNDERSTORMS IN THE
GRIDS. HAVING SAID THAT, SOME OF THE MORE ROBUST CONVECTIVE-Y
SHOWERS (WITHOUT LIGHTNING) COULD LEAD TO SOME LOCALLY STRONGER WIND
GUSTS LATE THIS EVENING INTO THE OVERNIGHT HOURS.
IN ADDITION TO SOME STRONGER GUSTS IN A FEW OF THE SHOWERS, THERE IS
ALSO CONCERN WITH THE POTENTIAL FOR STRONG SYNOPTIC WINDS TONIGHT.
AS THE DEEP LOW PRESSURE TRACKS NORTH INTO THE MID-UPPER MISSISSIPPI
VALLEY TONIGHT, VERY STRONG PRESSURE FALLS (>6MB/3HR) IN ADVANCE OF
THE LOW SHOULD RESULT IN A SIGNIFICANT ISALLOBARIC RESPONSE TO THE
WINDS OVER THE AREA THIS EVENING. ANTICIPATE WINDS WILL RAMP UP TO
20-30 MPH THIS EVENING WITH GUSTS OF 30-40 MPH A PRETTY GOOD BET.
CERTAINLY CAN'T RULE OUT STRONGER GUSTS, PARTICULARLY IF
TEMPERATURES OVERPERFORM THIS EVENING, BUT CONFIDENCE IN GUSTS 45+
MPH ISN'T HIGH ENOUGH TO JUSTIFY ISSUING A WIND ADVISORY, BUT WILL
BRIEF ONCOMING EVENING SHIFT ON THE POTENTIAL.
INTERESTINGLY, BEHIND THE BAND OF SHOWERS, THE HRRR AND 3KM NAM SHOW
ANOTHER SURGE OF STRONGER WIND GUSTS (45-50+ MPH). THIS WILL
COINCIDE WITH VERY STRONG LOW LEVEL JET MOVING ACROSS THE REGION
WITH >50KT AT 925MB AND >70KT AT 850MB. BY THIS LATER TONIGHT, THE
STRONGER ISALLOBARIC WIND COMPONENT SHOULD HAVE SHIFTED NORTH OF THE
AREA, SO CONFIDENCE IN HOW MUCH OF VERY HIGH MOMENTUM AIR ASSOCIATED
WITH THE LOW-LEVEL JET WILL BE ABLE TO MIX TO THE SFC IN GUSTS
IS LOW. THIS WOULD ALSO BE A PERIOD WORTH MONITORING FOR
POTENTIAL WIND ADVISORY SHOULD WINDS OVERPERFORM. SFC TROUGH
TRAILING WELL BEHIND THE INITIAL BAND OF SHOWERS WILL MOVE
ACROSS THE AREA EARLY TUESDAY MORNING. COULD BE A FEW HOURS OF
STRONGER SOUTHWESTERLY WINDS BEHIND THAT BOUNDARY TUESDAY
MORNING (ROUGHLY 11-17Z) WITH SOME 40+ MPH GUSTS AGAIN POSSIBLE.
UNSEASONABLY WARM TEMPERATURES ARE EXPECTED TONIGHT. AS THE WARM
FRONT LIFTS NORTH, LOOK FOR SFC TEMPS TO RISE INTO THE UPPER 50S TO
LOWER 60S AND LIKELY REMAIN THERE THROUGH THE NIGHT. JUST TO PUT
INTO PERSPECTIVE HOW UNUSUALLY WARM THIS IS, OUR AVERAGE HIGH
TEMPERATURES THIS TIME OF YEAR ARE IN THE 40S! NOT GOING TO THREATEN
ANY DAYTIME RECORD WARM LOW TEMPERATURES AS TEMPS WILL TUESDAY
EVENING PRIOR TO MIDNIGHT.
CONFIDENCE IN THE LARGE SCALE PATTERN EVOLUTION IS QUITE HIGH FOR
THE MIDDLE AND END OF THE WEEK, HOWEVER, UNFORTUNATELY, CONFIDENCE
IS QUITE LOW IN THE FINER SCALE DETAILS. AMONG THESE "SMALLER SCALE
DETAILS" WOULD INCLUDE THE POTENTIAL FOR SNOW, POSSIBLY ENOUGH TO
WHITEN THE GROUND IN PORTIONS OF OUR CWA THURSDAY,
TO THE WEST OF CENTRAL U.S. CYCLONE IS A VIGOROUS NORTHERN STREAM
TROUGH OVER THE NORTHERN ROCKIES AND PACIFIC NORTHWEST. THESE TWO
TROUGHS ARE PROGGED TO PHASE OVER THE NORTHERN PLAINS TUESDAY NIGHT,
EVOLVING INTO A LARGE AND DEEP CLOSED MID-UPPER LEVEL LOW. IN CASE
THINGS WEREN'T COMPLICATED ENOUGH ALREADY, ANOTHER SHORTWAVE TROUGH
AND ASSOCIATED MID-UPPER LEVEL JET STREAK ABOUT TO MOVE ONSHORE
CALIFORNIA THIS AFTERNOON IS PROGGED TO QUICKLY MOVE EASTWARD ON THE
SOUTHERN FLANKS OF THE POWERFUL NORTHERN PLAINS CUT OFF LOW. THIS
WAVE WILL MOVE ACROSS THE MID-MISSISSIPPI VALLEY BY EARLY WEDNESDAY
MORNING, WHICH COULD LEAD TO SOME CHANCE OF SHOWERS STARTING
WEDNESDAY MORNING.
THE 12Z ECMWF AND 12Z GFS BOTH NOW DEPICTING A FAIRLY
FASCINATING EVOLUTION WITH THE AFOREMENTIONED SHORTWAVE NOW
ESSENTIALLY FUJIWHARA-ING AROUND AND PHASING WITH THE UPPER LOW
OVER THE UPPER MIDWEST LATE WEDNESDAY INTO WEDNESDAY NIGHT.
INTERESTINGLY, THAT SECOND SHORTWAVE IS PROGGED TO PIVOT ALL THE
WAY AROUND THE MID-UPPER LEVEL CIRCULATION AND PIVOT WEST AND
SOUTHWARD ACROSS MICHIGAN LATE WED NIGHT INTO THURSDAY. BOTH THE
GFS AND ECMWF DEPICT A NEW SFC LOW DEVELOPING IN THE VICINITY
OF LAKES HURON AND ERIE LATE WEDNESDAY AFTERNOON, THEN SHOWING
RAPID DEEPENING OF THIS LOW AS IT CYCLONICALLY LOOPS NORTH, THEN
WEST, AND EVENTUALLY SOUTHWEST ACROSS LOWER MICHIGAN WED NIGHT
INTO THURSDAY.
IN THIS SCENARIO, A BAND OF FORMIDABLE WARM AIR ADVECTION DRIVEN
PRECIPITATION WOULD DEVELOP ON THE NORTH THEN WESTERN FLANKS OF THIS
LOW. THIS PRECIPITATION IS THEN PROGGED TO MOVE SOUTHWEST INTO OUR
CWA LATE WED NIGHT/EARLY THURSDAY MORNING. TEMPERATURES INITIALLY
WOULD LIKELY BE COLD ENOUGH TO SUPPORT WET SNOW, POSSIBLY MIXING
WITH OR CHANGING TO RAIN DURING THE DAY THURSDAY AS NORTHERLY WIND
ADVECT IN A WARMER AIR MASS THAT WILL HAVE COMPLETELY ROTATED AROUND
THIS CYCLONE. IN THIS GENERAL SCENARIO THAT THE 12Z GFS/ECMWF ARE
DEPICTING, SOME PORTIONS OF OUR CWA COULD SEE SOME SLUSHY SNOW
ACCUMULATION, MAINLY ON GRASSY SURFACES AND AWAY FROM THE IMMEDIATE
LAKESHORE.
HARD TO STRESS JUST HOW MUCH UNCERTAINTY EXISTS IN THIS FORECAST FOR
THURSDAY. NOT ONLY WAS THIS A VERY SIGNIFICANT CHANGE FROM PREVIOUS
RUNS, BUT IT IS ALSO AN EXTREMELY COMPLEX EVOLUTION WITH MANY MOVING
PIECES. MODELS OFTEN STRUGGLE WITH HANDLING PHASING WAVES AND IN
THIS CASE IT IS 3 MAIN DIFFERENT WAVES PHASING. IT IS INTERESTING
THAT THE OPERATIONAL 12Z GFS AND ECMWF BOTH MADE THIS SIGNIFICANT
CHANGE IN UNISON, BUT GIVEN THE COMPLEXITY OF THE SET-UP, I'D BE
VERY CAUTIOUS IN PUTTING TOO MUCH STOCK IN THESE RUNS UNTIL THERE IS
MORE ENSEMBLE SUPPORT AND SOME RUN-TO-RUN CONSISTENCY.
IN THE WAKE OF THIS SYSTEM, NEAR AVERAGE TEMPERATURES ARE EXPECTED
HEADING INTO NEXT WEEKEND WITH LIKELY DRIER WEATHER CONDITIONS.
- IZZI
AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 600 PM CST MON NOV 18 2024
FORECAST CONCERNS FOR THE TERMINALS...
- ANOTHER PERIOD OF SHOWERS TONIGHT INTO EARLY TUESDAY MORNING
- BRIEF PERIOD OF VFR CEILINGS THIS EVENING BECOMING MVFR TO
NEAR IFR TONIGHT THEN GRADUALLY IMPROVING TUESDAY AFTERNOON
- BREEZY SOUTHEAST WINDS TONIGHT BECOMING SOUTHWEST AND GUSTY
TUESDAY MORNING WITH GUSTS AROUND 35 KTS POSSIBLE
AN STRONG STORM SYSTEM CONTINUES TO INTENSIFY OVER THE CENTRAL
PLAINS THIS EVENING AND IS EXPECTED TO LIFT INTO THE UPPER
MIDWEST OVERNIGHT. THE SYSTEMS WARM FRONT DID MOVE THROUGH
NORTHERN IL AND NORTHWEST IN EARLIER TODAY WHICH IS GENERATING
THE ONGOING SHOWERS AND LIFR CEILINGS. AS THIS INITIAL WAVE OF
SHOWERS TAPERS OVER THE NEXT HOUR, CEILINGS WILL LIFT INTO THE
IFR CATEGORY AND THEN EVENTUALLY VFR BETWEEN 02Z AND 03Z. THOUGH,
POCKETS OF SCT TO BKN 2500-3000 FT CEILINGS MAY LINGERING THIS
EVENING. A SECOND ROUND OF SHOWERS IS EXPECTED TO MOVE INTO THE
AREA AROUND MIDNIGHT (BETWEEN 04Z-06Z) AND PERSIST THROUGH THE
NIGHT AS THE SYSTEM'S COLD FRONT MOVES THROUGH. WHILE THE MORE
CONVECTIVE NATURE OF THIS ROUND OF SHOWERS SHOULD KEEP CEILINGS
HIGHER, MVFR TO NEAR IFR CEILINGS AND IFR VISIBILITIES ARE
STILL EXPECTED TO OCCUR WITH THE SHOWERS OVERNIGHT. THE COLD
FRONT SHOULD EXIT THE AREA BY 12Z TUESDAY WHICH WILL ALLOW
SHOWERS TO COME TO AN END LEAVING DRY CONDITIONS FOR THE REST OF
THE FORECAST PERIOD.
ASIDE FROM THE SHOWERS, WINDS ARE EXPECTED TO INCREASE IN SPEED
THIS EVENING AS THE SURFACE LOW TRAVERSES ACROSS IA INTO MN.
GUSTS THIS EVENING WILL GENERALLY BE IN THE 25-30 KT RANGE OUT
OF THE SOUTHEAST, BUT A FEW HIGHER GUSTS WILL BE POSSIBLE IN THE
WAKE OF THE SHOWERS. WINDS WILL BECOME SOUTHWESTERLY BEHIND THE
FRONT TUESDAY MORNING ALONG WITH A QUICK UPTICK IN WINDS AS THE
ATMOSPHERE MIXES INTO THE LOW-LEVEL JET AROUND 12-13Z.
THEREFORE, EXPECT A PERIOD OF 30-35 KT GUSTS TUESDAY MORNING
WITH LOCALLY HIGHER GUSTS TO 40 KTS POSSIBLE. WIND SPEEDS WILL
GRADUALLY EASE TUESDAY AFTERNOON AND EVENING, BUT A FEW TEEN TO
20 KT GUSTS MAY PERSIST THROUGH THE END OF THE FORECAST PERIOD.
FINALLY, ANY MVFR TO NEAR IFR CEILINGS WITH THE AFOREMENTIONED
SHOWERS TONIGHT WILL LIFT TO MVFR TUESDAY MORNING AND CONTINUE
TO GRADUALLY IMPROVE THROUGH REST OF THE DAY. HOWEVER, THERE IS
A STRONG SIGNAL IN GUIDANCE THAT SOME 3000-4000 FT CEILINGS
SHOULD PERSIST THROUGH THE END OF THE FORECAST PERIOD.
FURTHERMORE, THERE IS ALSO A POTENTIAL FOR SOME 2500-3000 FT
STRATUS TO REDEVELOP TUESDAY NIGHT BUT THIS IS SOMEWHAT LOW
CONFIDENCE DUE TO UNCERTAINTY IN HOW MIXED THE ATMOSPHERE WILL
REMAIN. GIVEN THE NOTABLE SIGNAL IN GUIDANCE FOR THIS POTENTIAL
HAVE DECIDED TO INCLUDE A SCT025 MENTION IN THE 30-HOUR TAFS AS
A PRECAUTION.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 3 PM CST TUESDAY FOR THE IL AND IN
NEARSHORE WATERS.
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