736
FXUS63 KLOT 182059
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
259 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
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 /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1202 PM CST MON NOV 18 2024
KEY AVIATION MESSAGES:
- SHRA WITH PERIODS OF IFR CEILINGS THIS AFTERNOON AND AGAIN
LATE THIS EVENING THROUGH THE OVERNIGHT HOURS.
- 10-20% CHANCE OF TS WITH THE SECOND ROUND OF SHRA TONIGHT.
- SE WINDS GUSTING TO 30 KNOTS VEERING SSW AROUND SUNRISE
TUESDAY. A COUPLE HOUR PERIOD OF STRONGER SOUTH-SOUTHWEST
WINDS (GUST 35+ KT) POSSIBLE AROUND SUNRISE TUESDAY MORNING.
CONDITIONS CONTINUE TO QUICKLY DETERIORATE ACROSS THE NORTHERN
IL AND NORTHWESTERN IN TERMINALS THIS MIDDAY HOUR. THE
EXPECTATION THROUGH MID TO LATE THIS AFTERNOON IS FOR IFR (SOME
PATCHY LIFR) CIGS AND VSBYS TO PERSIST AHEAD OF A SURFACE WARM
FRONT. PERIODS OF RAIN CAN ALSO BE EXPECTED AS WARM FRONTAL BAND
OF RAIN CONTINUES TRACKING NORTHWARD ACROSS THE AREA. IT APPEARS
THE STEADIER RAIN WILL BECOME MORE SHOWERY, OR EVEN STOP FOR A
FEW HOUR PERIOD, AROUND SUNSET LATE THIS AFTERNOON (22-23Z) AS
THIS INITIAL FRONTAL DRIVEN BAND OF RAIN TRACKS NORTH OUT OF
THE AREA. WHILE VSBYS WILL IMPROVE WITH THE END OF THE RAIN,
SOME LOWER CIGS COULD LINGER FOR A COUPLE HOURS INTO EARLY THIS
EVENING BEFORE A PERIOD OF IMPROVING CIGS (VFR) IS LIKELY.
ANY IMPROVEMENT THIS EVENING WILL BE SHORT LIVED, HOWEVER, AS
ANOTHER BAND OF SHOWERS (POSSIBLY EVEN A FEW THUNDERSTORMS) IS
SLATED TO SLIDE EASTWARD INTO THE AREA IN ADVANCE OF AN
APPROACHING COLD FRONT. THE BEST TIMING FOR THIS LINE OF SHOWERS
WILL BE IN THE 05 TO 08Z TIMEFRAME AT THE CHICAGO AREA
TERMINALS, AND SLIGHTLY EARLIER AT KRFD. THE CURRENT TEMPO IN
THE TAFS HIGHLIGHTS THIS TIMING. ABOUT A 5-15% CHANCE FOR A
FEW RUMBLES OF THUNDER ALSO EXISTS WITH THIS LINE OF SHOWERS
TONIGHT, BUT WITH THE CHANCES BEING TOO LOW, THERE CONTINUES TO
BE NO FORMAL MENTION IN THE TAF.
WINDS WILL BECOME INCREASINGLY GUSTY (25-30 KT) FROM THE
SOUTHEAST THIS EVENING AND TONIGHT AS A STRONG SURFACE LOW
TRACKS NORTHEASTWARD ACROSS THE MID-MISSOURI VALLEY. WINDS WILL
THEN SHIFT SOUTH-SOUTHWESTERLY AROUND (OR A BIT BEFORE) DAYBREAK
TUESDAY MORNING AS A SURFACE COLD FRONT SWEEPS EASTWARD ACROSS
THE AREA. A PERIOD OF STRONG WIND GUSTS (35+KT) IS POSSIBLE
(40-50% CHANCE) WITH THE PASSAGE OF THIS FRONT. THESE STRONG
GUSTY WINDS WILL GRADUALLY EASE THROUGH THE AFTERNOON AS THEY
TURN WEST-SOUTHWESTERLY.
KJB
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 3 PM CST TUESDAY FOR THE IL
NEARSHORE WATERS.
SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 3 PM CST
TUESDAY FOR THE IN NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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