074
FXUS63 KLOT 161804
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1204 PM CST SAT NOV 16 2024
KEY MESSAGES
- PERIODS OF RAIN ARE EXPECTED MONDAY THROUGH TUESDAY MORNING.
- ANOTHER SYSTEM WILL MOVE IN WEDNESDAY THROUGH THURSDAY WITH
ADDITIONAL CHANCES FOR PRECIPITATION.
- A COLDER AIR MASS WILL SETTLE IN LATE NEXT WEEK WITH MORNING
LOW TEMPERATURES AT OR BELOW FREEZING.
DISCUSSION
ISSUED AT 258 AM CST SAT NOV 16 2024
THROUGH SUNDAY:
AFTER STALLING CLOSE THE IN/IL LINE LATE FRIDAY AFTERNOON AND
EVENING, THE WESTERN EXTENT OF AN EXPANSIVE AREA OF STRATUS HAS
STARTED TO ADVECT NORTHWEST BEHIND A PASSING RIDGE. AREAS EAST
OF I-39 ARE GENERALLY OVERCAST AS OF 2AM, AND THE CLOUD COVER
SHOULD CONTINUE TO EXPAND ACROSS THE REMAINDER OF THE FORECAST
AREA THROUGH SUNRISE. FLOW WILL MORE OR LESS BE UNIFORM THROUGH
THE CLOUD LAYER AND ACROSS A SLOWLY LOWERING SUBSIDENCE
INVERSION, SO OVERALL MIXING WILL REMAIN LOW AT BEST. BUT GIVEN
THE EXPECTED SHALLOW CLOUD DEPTH, ANY HOLES THAT DEVELOP WITHIN
THE CLOUD LAYER MAY CASCADE INTO LARGER AREAS OF CLEARING BY
THIS AFTERNOON. WILL MAINTAIN A MORE PESSIMISTIC FORECAST WITH
CLOUD COVER AND TEMPS TODAY, WITH THE POTENTIAL FOR THE FORECAST
TO VARY CONSIDERABLY DEPENDING ON THE CLOUD COVER TRENDS.
A HIGHLY OCCLUDED LOW/UPPER-TROUGH LIFTING NORTHEAST ACROSS THE
DAKOTAS TODAY WILL DRAG A WEAKENING COLD FRONT ACROSS THE
FORECAST AREA LATE THIS EVENING INTO SUNDAY MORNING. INITIALLY,
A POCKET OF MODEST MID-LEVEL MOISTURE MAY HELP INITIATE SOME
VERY HIGH-BASED (APPROACHING 15KFT) SHOWERS CLOSER TO THE
MISSISSIPPI RIVER EARLY THIS EVENING. THE SHOWERS MAY SURVIVE
THROUGH A DEEP DRY SUB-CLOUD LAYER AND PRODUCE SPARSE SHOWERS OR
SPRINKLES ACROSS THE NORTHWEST HALF OF THE CWA LATE THIS
EVENING INTO THE EARLY OVERNIGHT HOURS. LATE TONIGHT THROUGH
SUNDAY MORNING, VEERING LOW-LEVEL FLOW WITHIN A FEED OF WEAK
MOISTURE ADVECTION AHEAD OF THE STALLING FRONT WILL RESULT IN
BROAD BUT WEAK LOW-LEVEL ISENTROPIC ASCENT ACROSS MUCH OF THE
AREA. THIS SHOULD RESULT IN AT LEAST SOME PATCHY DRIZZLE THROUGH
THE MORNING BEFORE DECREASING INVERSION HEIGHTS AND SOME LOW-
LEVEL DRYING ENDS THE PRECIP POTENTIAL IN THE AFTERNOON.
KLUBER
SUNDAY NIGHT THROUGH FRIDAY:
MAIN FOCUS THROUGH NEXT WEEK IS ON A PAIR OF PRECIPITATION-
PRODUCING SYSTEMS WHICH WILL AFFECT THE AREA MONDAY INTO EARLY
TUESDAY, AND WEDNESDAY INTO THURSDAY. AFTER A MILD START TO THE
WEEK, A PATTERN SHIFT TOWARD COOLER, MORE SEASONABLE
TEMPERATURES IS ALSO EXPECTED WITH THE MID-LATE WEEK SYSTEM.
THIS MAY POSSIBLY BRING SOME OF THE FIRST WET SNOW FLAKES OF THE
SEASON TO PARTS OF THE AREA.
A WEAK COLD FRONT WILL BE PUSHING SLOWLY SOUTH-SOUTHEAST ACROSS
THE FORECAST AREA SUNDAY EVENING, AS THE SOUTHERN PERIPHERY OF
A MID- LEVEL SHORT WAVE TROUGH AXIS TRANSITS THE AREA. MOISTURE
DEPTH LOOKS QUITE SHALLOW PER MODEL FORECAST SOUNDINGS, THOUGH
CAN'T COMPLETELY RULE OUT SOME PATCHY LIGHT RAIN/DRIZZLE IN THE
VICINITY OF THE LOW- LEVEL BAROCLINIC ZONE DURING THE EVENING
MAINLY SOUTH OF I-80. WELL TO OUR SOUTHWEST, GUIDANCE CONTINUES
TO BE IN GOOD AGREEMENT IN A STRONG MID-LEVEL SHORT WAVE
EMERGING FROM NM/WESTERN TX BY MONDAY MORNING, WHICH IS PROGGED
TO LIFT NORTHEAST ACROSS THE CENTRAL PLAINS AND A DEEPENING
(SUB-990 HPA) SURFACE LOW DEVELOPING INTO NORTHEAST KS BY MONDAY
EVENING. IN RESPONSE TO INCREASING FORCING FOR ASCENT AND A
NORTHWARD-LIFTING WARM FRONTAL ZONE, RAIN IS EXPECTED TO DEVELOP
ACROSS THE FORECAST AREA DURING THE DAY. RAIN SHOULD BECOME
MORE WIDESPREAD MONDAY NIGHT, AS THE MID-LEVEL WAVE AND
OCCLUDING SURFACE LOW CONTINUE TO LIFT NORTHEAST INTO THE UPPER
MISSISSIPPI VALLEY AND THE OCCLUDED COLD FRONT AND WARM FRONTAL
BOUNDARY PUSHES INTO IL. RAIN LOOKS TO TAPER OFF FROM SOUTHWEST
TO NORTHEAST TUESDAY MORNING, AS THE NEGATIVELY-TILTED SHORT
WAVE CONTINUES TO LIFT NORTH-NORTHEAST ACROSS THE REGION AND THE
MID- LEVEL DRY SLOT SPREADS IN ALOFT. THE FORECAST AREA WILL
REMAIN ON THE WARM SIDE OF THIS FIRST SYSTEM, WITH DAYTIME
TEMPERATURES IN THE 50S TO AROUND 60/LOWER 60S THROUGH TUESDAY
AND BREEZY SOUTHEAST TO SOUTH WINDS GUSTING TO 25 MPH OR SO AT
TIMES.
BACK TO THE WEST, EXTENDED GUIDANCE/GLOBAL ENSEMBLES CONTINUE
TO DEPICT ANOTHER STRONG JET STREAK DIGGING ACROSS THE CENTRAL
AND SOUTHERN ROCKIES ON TUESDAY, LEADING TO AMPLIFICATION OF A
LONG-WAVE UPPER TROUGH AND DEVELOPMENT OF A CLOSED UPPER LOW
ACROSS THE CENTRAL CONUS TUESDAY NIGHT. THE EVOLUTION OF THIS
UPPER LOW BECOMES RATHER COMPLEX AS IT MOVES EAST ACROSS THE
MIDWEST MID-WEEK HOWEVER, WITH A STRONG SHORT WAVE WRAPPING
AROUND THE SOUTHERN PERIPHERY OF THE LOW INTO THE REGION BY
EARLY WEDNESDAY AND THE FORMER UPPER MIDWEST VORT WRAPPING
AROUND THE CIRCULATION IN A PSEUDO FUJIWHARA EFFECT FURTHER
DEEPENING THE UPPER LOW ACROSS THE REGION INTO THURSDAY. THIS
RESULTS IN A NEW DEEPENING SURFACE LOW TAKING SHAPE SOMEWHERE IN
THE VICINITY OF THE LOWER OH VALLEY, IN AND OH LATER WEDNESDAY
INTO WEDNESDAY NIGHT.
OBVIOUSLY, THERE REMAINS GUIDANCE SPREAD WITHIN THIS COMPLEX
EVOLUTION (INCLUDING HOW QUICKLY IT MOVES EAST OF THE AREA LATE
IN THE WEEK) AND FURTHER REFINEMENT OF THE DETAILS WILL NEED TO
OCCUR AS THIS CURRENT DAYS 5-6 EVENT DRAWS NEARER. IN GENERAL
HOWEVER, THIS EVOLUTION CURRENTLY SUPPORTS A REDEVELOPMENT OF
PRECIPITATION ACROSS PARTS OF THE FORECAST AREA WEDNESDAY INTO
THURSDAY. AN INTRUSION OF COLDER AIR INTO THE SYSTEM IS
EXPECTED, PARTICULARLY AROUND THE WESTERN/SOUTHERN PERIPHERY OF
THE CIRCULATION AND INTO THE OH VALLEY REGION WHERE H8 TEMPS DIP
BELOW 0C. OF FAIRLY HIGH CONFIDENCE IS THE WELL-ADVERTISED
PATTERN SHIFT TOWARD COOLER, MORE SEASONABLE (HIGHS IN LOW-40S,
LOWS AROUND FREEZING) TEMPERATURES FROM MID-WEEK ON. OF LOWER
CONFIDENCE IS THE POTENTIAL FOR THE FIRST WET SNOW FLAKES OF THE
SEASON TO OCCUR ACROSS SOME PART OF THE FORECAST AREA LATER
WEDNESDAY INTO THURSDAY IN ASSOCIATION WITH THE DEEPENING LOW,
THOUGH CURRENT ENSEMBLES SUGGEST GREATER POTENTIAL FOR POSSIBLY
ACCUMULATING SNOWS MAY BE EAST/SOUTHEAST OF OUR AREA.
RATZER
AVIATION /18Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 1203 PM CST SAT NOV 16 2024
THE MAIN AVIATION WEATHER CONCERNS FOR THE 18Z TAF PERIOD
INCLUDE:
* CONTINUED MVFR WITH UNCERTAINTY IN TIMING OF A RETURN TO VFR
AN EXPANSIVE MVFR DECK BLANKETS A BIG PORTION OF THE MIDWEST
LATE THIS MORNING, AND CHICAGOLAND IS NO EXCEPTION. THERE IS A
CONSIDERABLE AMOUNT OF UNCERTAINTY AS TO WHEN CONDITIONS WILL
RETURN TO VFR. VISIBLE SATELLITE IMAGERY SHOWS THIS OVERCAST
DECK HAS RECENTLY BEGUN TO GRADUALLY BREAK APART. WHILE THERE IS
REASON TO BELIEVE THAT WE COULD POSSIBLY SCATTER OUT BY LATE
THIS AFTERNOON, THE MUCH STRONGER SIGNAL SUPPORTS MVFR HOLDING
STEADY FOR THE REMAINDER OF THE DAY. LATER THIS EVENING INTO
TONIGHT IS WHERE CONFIDENCE REALLY BEGINS TO DROP. AT LEAST
SCATTERED SUB-3KFT COVERAGE IS ANTICIPATED THROUGH THE PERIOD,
BUT BEST GUESS IS THAT THE MVFR WILL PREVAIL THROUGH TONIGHT AND
THE BETTER PART OF TOMORROW. IT'S WORTH NOTING THAT THERE HAS
BEEN A RECENT TREND AMONG MODEL GUIDANCE IN FAVOR OF VFR
RETURNING AROUND MID-MORNING OR SO TOMORROW. DIDN'T THINK THIS
SIGNAL WAS STRONG OR PERSISTENT ENOUGH TO JUSTIFY REMOVING MVFR
FROM THE TAF AT THIS POINT.
MEANWHILE, SSE WINDS AROUND 10 TO 15 KT MAY CONTINUE TO GUST TO
AROUND 20 KT THROUGH THE DAY. DIRECTION WILL GRADUALLY VEER
DURING THE EVENING PUSHING WEST OF SOUTH LATE IN THE EVENING.
WINDS ACTUALLY LOOK TO INCREASE A FEW TICS FOR THE TONIGHT
PERIOD WITH SSW GUSTS TO 20 TO AS HIGH AS 25 KT EXPECTED. EXPECT
SW WINDS WITH GUSTS TO NEAR 20 KT DURING THE DAY TOMORROW.
DOOM
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 3 AM CST SUNDAY
FOR WINTHROP HARBOR TO WILMETTE HARBOR IL.
VISIT US AT WEATHER.GOV/CHICAGO
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