847
FXUS63 KLOT 172054
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
254 PM CST MON NOV 17 2025
KEY MESSAGES
- RAIN AND DRIZZLE EXPECTED TONIGHT THROUGH TUESDAY.
- ANOTHER PERIOD OF RAIN POSSIBLE TOWARDS LATE WEEK.
DISCUSSION
ISSUED AT 254 PM CST MON NOV 17 2025
THROUGH TUESDAY:
A SURFACE HIGH CONTINUES TO SLOWLY MOVE EAST ACROSS THE AREA
THIS AFTERNOON AS A SHORTWAVE TROUGH EJECTS INTO THE CENTRAL
PLAINS. THIS SHORTWAVE WILL PIVOT INTO THE MISSISSIPPI VALLEY
LATE TONIGHT INTO TUESDAY MORNING AND THEN ACROSS NORTHERN IL
AND NORTHWEST IN TUESDAY AFTERNOON. AS A RESULT, THE DEVELOPING
RAIN SHOWERS IN IA AND MO WILL LIFT INTO OUR AREA AROUND
MIDNIGHT AND PERSIST THROUGH TUESDAY MORNING AS THE SYSTEM MOVES
THROUGH. GIVEN THAT FORECAST SOUNDINGS SHOW THE ENVIRONMENT TO
BE LARGELY ABOVE FREEZING, EXPECT PRECIPITATION TO REMAIN AS
RAIN THROUGH ITS DURATION BUT THERE WILL BE SOME MODEST
INSTABILITY ALOFT WHICH MAY SUPPORT SOME INSTANCES OF GRAUPEL AS
RAIN BEGINS. ADDITIONALLY, A STRAY LIGHTNING STRIKE CANNOT BE
RULED OUT EITHER THOUGH THE BEST CHANCE FOR SUCH WILL LIKELY
STAY IN CENTRAL IL CLOSER TO THE SURFACE LOW.
WHILE THE BROADER RAIN WILL GRADUALLY TAPER THROUGH TUESDAY
MORNING AS THE MID-LEVEL DRY SLOT MOVES OVERHEAD, SOME LINGERING
LOW-LEVEL MOISTURE IN THE PRESENCE OF SOME MODEST ASCENT SHOULD
ALLOW SOME OCCASIONAL LIGHT SHOWERS AND DRIZZLE TO PERSIST
THROUGH TUESDAY AFTERNOON. OTHERWISE, EXPECT CLOUD SKIES AND
EASTERLY WINDS AROUND 10-15 MPH. TEMPERATURES ON TUESDAY WILL BE
A BIT COOLER THAN TODAY WITH HIGHS IN THE LOW TO MID-40S
AREAWIDE.
TUESDAY NIGHT THROUGH MONDAY:
THE AFOREMENTIONED SHORTWAVE TROUGH WILL EJECT TO THE EAST
TUESDAY EVENING AS MID-LEVEL HEIGHT RISES MOVE INTO THE GREAT
LAKES. THE HEIGHT RISES SHOULD CUT OFF THE ASCENT AND ALLOW THE
LIGHT SHOWERS/DRIZZLE TO TAPER BY MID-EVENING. WHILE DRY
CONDITIONS ARE THEN EXPECTED TO PREVAIL THROUGH THE MIDDLE OF
THE WEEK, A PLUME OF LOW-LEVEL MOISTURE IS FORECAST TO GET
TRAPPED BENEATH THE SUBSIDENCE INVERSION. AS A RESULT A
PREVAILING STRATUS DECK IS EXPECTED TO REMAIN IN PLACE THROUGH
WEDNESDAY NIGHT AND POSSIBLY THROUGH THE DAY ON THURSDAY. WITH
THE LOWER SUN ANGLE AND CLOUD COVER, TEMPERATURES BETWEEN
TUESDAY NIGHT AND WEDNESDAY LIKELY WON'T VARY MUCH (MAYBE 5- 8
DEGREES OR SO) WITH HIGHS CURRENTLY FORECAST TO BE IN THE
MID-40S AT BEST. DEPENDING ON HOW QUICKLY THE LOW-LEVEL MOISTURE
ERODES ON THURSDAY WILL DETERMINE WHETHER THURSDAY IS ANOTHER
COOL AND GLOOMY DAY OR IF TEMPERATURES ARE ABLE TO REBOUND INTO
THE 50S. FOR NOW THE OFFICIAL FORECAST HAS LEANED TOWARDS THE
CLOUDS SCATTERING AND A WARMER SOLUTION, BUT THIS COULD CHANGE
AS WE GET CLOSER SO DON'T BE SURPRISED IF TEMPERATURES VERIFY
SEVERAL DEGREES COOLER FOR THURSDAY.
HEADING INTO THE LATER HALF OF THE WEEK, OUR ATTENTION TURNS
TOWARDS THE EVOLUTION OF THE UPPER LOW AND ASSOCIATED BROAD
TROUGH THAT IS JUST OFFSHORE OF SOUTHERN CALIFORNIA AS OF THIS
WRITING. THIS TROUGH/LOW IS FORECAST TO SLOWLY MEANDER INTO THE
SOUTHWEST CONUS THROUGH WEDNESDAY AND POSSIBLY ATTEMPT TO PHASE
WITH ANOTHER TROUGH THAT WILL BE DIVING OUT OF THE PACIFIC
NORTHWEST ON THURSDAY. AS THIS FEATURE BEGINS TO EJECT INTO THE
SOUTHERN PLAINS ON THURSDAY, ANOTHER SHORTWAVE TROUGH IS PROGGED
TO PIVOT ACROSS THE NORTHERN GREAT LAKES. IT IS DURING THIS
THURSDAY THROUGH FRIDAY TIMEFRAME THAT THE FORECAST BECOMES VERY
UNCERTAIN. THE REASON IS BECAUSE IF THE SOUTHERN TROUGH MOVES
QUICK ENOUGH IT MAY LIMIT THE OVERALL MOISTURE RETURN INTO
NORTHERN IL AND NORTHWEST IN AND THUS KEEP THE BULK OF ANY
ASSOCIATED PRECIPITATION TO THE SOUTH OF OUR AREA IN THE OHIO
AND TENNESSEE RIVER VALLEYS. HOWEVER, IF THE TROUGH IS SLOWER
THEN SUFFICIENT MOISTURE MAY BE ABLE TO RETURN AHEAD OF THIS
SYSTEM AND THE NORTHERN STREAM TROUGH AND ALLOW PRECIPITATION TO
RETURN TO THE AREA AS EARLY AS THURSDAY. THOUGH, ANY
PRECIPITATION AT THIS POINT LOOKS TO FALL MAINLY AS RAIN DUE TO
TEMPERATURES GENERALLY ABOVE FREEZING.
AT THIS POINT ENSEMBLE GUIDANCE IS SPLIT ON WHICH OF THESE
AFOREMENTIONED SCENARIOS WILL COME TO FRUITION AND THUS WHETHER
OR NOT WE SEE ANY RAIN THURSDAY AND/OR FRIDAY IS VERY UNCERTAIN.
THAT SAID, IT SEEMS THE GENERAL TREND IS FOR RAIN TO STAY MORE
TO OUR SOUTH WHICH IS WHY THE NBM POPS HAVE ONCE AGAIN TRENDED
DOWNWARD. FOR NOW HAVE OPTED TO MAINTAIN THE 20-50% POPS OFFERED
BY THE NBM FOR LATE THURSDAY INTO FRIDAY IN CASE THE WETTER
SOLUTION PANS OUT BUT SUSPECT IF THE DRIER TREND CONTINUES WE
MAY BE ABLE TO CUT POPS ALL TOGETHER IN THE NEXT COUPLE DAYS.
REGARDLESS OF HOW THIS PERIOD PANS OUT, TEMPERATURES LOOK TO
REMAIN SEASONABLE THROUGH THE WEEKEND WITH HIGHS IN THE 40S TO
LOWER 50S WITH OVERNIGHT LOWS IN THE 30S. ON THAT NOTE THE
WEEKEND DOES LOOK DRY WITH HIGH PRESSURE FORECAST TO MOVE BACK
INTO THE AREA.
YACK
AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1136 AM CST MON NOV 17 2025
THE PRIMARY AVIATION CONCERNS ARE AS FOLLOWS:
* PERIODS OF SHOWERS TONIGHT AND TOMORROW MORNING, TURNING INTO
DRIZZLE
* GRADUALLY LOWERING CIGS FROM VFR TO MVFR AND EVENTUALLY IFR
* POTENTIAL FOR LONG-DURATION LOW STRATUS EVENT CONTINUING WELL
BEYOND THE END OF THE TAF PERIOD
DISCUSSION:
LIGHT AND VARIABLE WINDS WILL CONTINUE THROUGH THE EARLY
AFTERNOON HOURS THANKS TO THE PASSAGE OF A SURFACE RIDGE AXIS.
DIRECTIONS SHOULD TREND EASTERLY BY EARLY-EVENING OWING TO LAKE
INFLUENCE, BEFORE INCREASING IN MAGNITUDE TOWARD 10KT THROUGH
THE OVERNIGHT HOURS. AN EASTERLY WIND DIRECTION WILL THEN
PREVAIL THROUGH THE REMAINDER OF THE TAF PERIOD.
SHOWERS ARE BEGINNING TO DEVELOP FROM FAR SOUTHEASTERN SOUTH
DAKOTA SOUTHEASTWARD INTO MISSOURI WITHIN A STRENGTHENING
REGION OF BROAD LOW-LEVEL WARM AIR ADVECTION INDUCED BY AN
UPPER-LEVEL WAVE ENTERING WESTERN NEBRASKA. SHOWER COVERAGE WILL
INCREASE MARKEDLY THIS EVENING AND SPREAD EASTWARD, REACHING
THE TERMINALS IN THE 06-08Z TIMEFRAME. CIGS SHOULD REMAIN VFR
THROUGH THE OVERNIGHT HOURS OWING TO TOP-DOWN SATURATION
PROCESSES ERODING A LOW-LEVEL DRY LAYER. VISBYS SHOULD REMAIN
MORE OR LESS BETWEEN 4 AND 6 MILES IN SHOWERS OVERNIGHT.
AFTER DAYBREAK, SHOWERS SHOULD GRADUALLY TRANSITION TO DRIZZLE
AS A LOW-LEVEL INVERSION STRENGTHENS ACROSS THE REGION. CIGS
SHOULD LOWER INTO MVFR AND IFR AS THE TRANSITION TO DRIZZLE
OCCURS. VISIBILITY MAY DROP AS LOW AS 2-3 MILES WHERE DRIZZLE
CELLS ARE MOST PREVALENT, PERHAPS BETWEEN 18-00Z (LAST 6 HOURS
OF THE 30-HOUR TAF WINDOW AT ORD/MDW) TIED TO WHEN THE UPPER-
LEVEL WAVE SLIDES DIRECTLY OVERHEAD. FOR NOW, WILL ADVERTISE 6SM
RADZ IN FAVOR OF DOWNWARD ADJUSTMENTS IN VISIBILITY AS MODEL
AND OBSERVATIONAL TRENDS ALLOW.
FINALLY, THE POTENTIAL EXISTS FOR IFR TO MVFR STRATUS TO LINGER
WELL BEYOND THE END OF THE TAF PERIOD AS LOW-LEVEL MOISTURE GETS
TRAPPED BENEATH THE STRONG INVERSION.
BORCHARDT
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 6 AM TUESDAY TO 3 AM CST WEDNESDAY
FOR THE IL NEARSHORE WATERS.
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