811
FXUS63 KLOT 190500
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1100 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 /06Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 1100 PM CST MON NOV 18 2024
- SHOWERS TO CONTINUE THROUGH EARLY TUESDAY MORNING WITH A NON-
ZERO CHANCE FOR AN ISOLATED RUMBLE OF THUNDER
- CEILINGS GRADUALLY LOWERING BACK TO MVFR OVERNIGHT WITH
POCKETS OF IFR POSSIBLE WITH THE SHOWERS
- BREEZY SOUTHEAST WINDS TONIGHT WILL BECOME SOUTHWESTERLY
AND INCREASE TUESDAY MORNING WITH GUSTS IN EXCESS OF 35 KTS
POSSIBLE
THE NEXT WAVE OF SHOWERS IS WORKING ITS WAY INTO NORTHERN IL
THIS EVENING AHEAD OF A COLD FRONT ASSOCIATED WITH THE STRONG
STORM SYSTEM MOVING ACROSS IA AND MN. WHILE THERE HAVE BEEN A
COUPLE OF ISOLATED LIGHTNING STRIKES IN WESTERN IL, INSTABILITY
HAS BEEN WANING WITH EASTWARD EXTENT SO NOT EXPECTING MUCH IN
THE WAY OF LIGHTNING AT THE TERMINALS. THOUGH A STRAY STRIKE OR
TWO CANNOT BE COMPLETELY RULED OUT JUST YET. OTHERWISE, EXPECT
SHOWERS TO PREVAIL AT THE TERMINALS THROUGH DAYBREAK WITH
REDUCED VISIBILITIES IN THE 2- 5 SM RANGE POSSIBLE.
OUTSIDE OF THE SHOWERS, WINDS HAVE CONTINUED TO INCREASE THIS
EVENING WITH MOST AREAS REPORTING 25-30 KT GUSTS. THOUGH, SOME
LOCALLY HIGHER GUSTS IN THE 30-40 KT RANGE HAVE BEEN OBSERVED
WITH SOME OF THE MORE ROBUST SHOWERS IN IA. WINDS ARE EXPECTED
TO INCREASE THROUGH THE NIGHT AS A STRONG LOW-LEVEL JET RAMPS UP
OVERHEAD WITH GUSTS IN THE 30-35 KT RANGE EXPECTED BY DAYBREAK.
THE STRONGEST WINDS ARE EXPECTED TO OCCUR AROUND DAYBREAK
THROUGH MID-MORNING WITH GUSTS FORECAST TO GRADUALLY DIMINISH
TUESDAY AFTERNOON. WHILE DIRECTIONS OVERNIGHT WILL BE OUT OF
THE SOUTHEAST, WINDS WILL BECOME SOUTHWESTERLY IN THE WAKE OF
THE SHOWERS BETWEEN 10-12Z TUESDAY MORNING.
FINALLY, CEILINGS HAVE RISEN TO VFR THIS EVENING AS THE
ATMOSPHERE HAS BEEN BETTER MIXED. HOWEVER, CEILINGS ARE EXPECTED
TO LOWER BACK INTO THE MVFR CATEGORY AS THE SHOWERS MOVE
THROUGH AND PERSIST AS SUCH THROUGH TUESDAY MORNING. WHILE THERE
HAVE BEEN SOME ISOLATED POCKETS OF IFR WITH THE SHOWERS, THE
CONFIDENCE IN WIDESPREAD IFR IS DECREASING BUT HAVE LEFT IN THE
TEMPO GROUPS FOR NOW. VFR CONDITIONS ARE FORECAST TO RETURN TO
THE TERMINALS TUESDAY AFTERNOON AND SHOULD PREVAIL THROUGH THE
REST OF THE FORECAST PERIOD. THERE REMAINS THE POTENTIAL FOR
SOME 2000-3000 FT STRATUS TO REDEVELOP TUESDAY NIGHT, BUT
CONFIDENCE IS STILL SOMEWHAT LOW DUE TO UNCERTAINTY IN
ATMOSPHERIC MIXING.
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.
VISIT US AT WEATHER.GOV/CHICAGO
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