151
FXUS63 KLOT 191546 CCA
AFDLOT
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
946 AM CST TUE NOV 19 2024
KEY MESSAGES
- GUSTY SOUTHWEST WINDS AROUND 40 MPH THOUGH MIDDAY, GRADUALLY
EASING THIS AFTERNOON.
- UNSEASONABLY WARM WEATHER WILL CONTINUE TODAY, FOLLOWED BY
MUCH COLDER WEATHER, COLDEST AIR MASS OF THE AUTUMN
- SNOW SHOWERS LATE WEDNESDAY AFTERNOON THROUGH WEDNESDAY NIGHT
MAY PRODUCE THE FIRST MINOR MEASURABLE ACCUMULATION OF THE
SEASON.
- CHANCE OF WET SNOW THURSDAY, WITH THE POTENTIAL FOR SOME
SLUSHY ACCUMULATIONS, MAINLY ON GRASSY SURFACES.
DISCUSSION
ISSUED AT 246 AM CST TUE NOV 19 2024
THROUGH WEDNESDAY:
MAIN FORECAST CONCERNS THROUGH THE NEAR-TERM PERIOD ARE STRONG,
GUSTY WINDS NEAR ADVISORY CRITERIA AT TIMES THROUGH MIDDAY
TODAY, THEN REDEVELOPMENT OF PRECIPITATION LATE TONIGHT INTO
WEDNESDAY. MILD, ABOVE-AVERAGE TEMPERATURES TODAY WILL GIVE WAY
TO COLDER, MORE TYPICAL READINGS BY WEDNESDAY. COLDER AIR MAY
ALLOW FOR SOME WET SNOW TO MIX IN LATE IN THE WEDNESDAY
AFTERNOON ACROSS OUR WESTERN CWA.
EARLY MORNING SURFACE ANALYSIS PLACES DEEP 983 HPA LOW OVER
SOUTHWEST MN, WITH AN OCCLUDING COLD FRONT EXTENDING THROUGH
NORTHEAST IA THEN SOUTH THROUGH CENTRAL IL. THE PARENT SHORT
WAVE, A POTENT NEGATIVELY-TILTED DISTURBANCE, CONTINUES TO LIFT
NORTHWARD ACROSS THE UPPER MIDWEST, WITH THE SYSTEM'S MID-LEVEL
DRY SLOT SPREADING NORTH ACROSS IL. THE MAIN AXIS OF RAIN
AND ISOLATED EMBEDDED THUNDERSTORMS MOVED NORTH AND EAST OF THE
CWA IN THE PAST FEW HOURS, WITH ONLY WEAKER SCATTERED SHOWERS
LINGERING BENEATH THE UPPER TROUGH. THESE TOO WILL END FROM
SOUTHWEST TO NORTHEAST THROUGH MID-MORNING AS THE MID-LEVEL
VORT EXITS TO OUR NORTH.
GIVEN THE TIGHT SURFACE PRESSURE GRADIENT AND STRONG WIND
FIELDS ASSOCIATED WITH THE DEEP LOW TO OUR NORTHWEST, SOUTH-
SOUTHEAST WINDS HAVE BEEN STRONG AND GUSTY THROUGH THE NIGHT.
WHILE A FEW SPORADIC HIGHER GUSTS HAVE BEEN NOTED, SURFACE OBS
GENERALLY INDICATE WINDS IN THE 20-25 MPH RANGE WITH GUSTS OF
35-40 MPH. THESE WINDS WILL SHIFT SOUTHWEST THIS MORNING WHILE
MAINTAINING SIMILAR SPEEDS MIDDAY BEFORE EASING BUT REMAINING
BREEZY THIS AFTERNOON. WITH SPEEDS NEAR/JUST UNDER WIND ADVISORY
CRITERIA, ELECTED TO ISSUE A SPECIAL WEATHER STATEMENT EARLIER
TO CALL ATTENTION TO THE STRONG WINDS.
AS GUIDANCE HAS BEEN ADVERTISING OVER THE PAST SEVERAL DAYS,
OUR UPPER-MIDWEST SHORT WAVE, AND ANOTHER STRENGTHENING VORT
TRACKING EAST FROM THE SOUTHERN ROCKIES LATER TODAY, WILL AID IN
AMPLIFYING AN UPPER TROUGH AND A DEEP CLOSED UPPER LOW ACROSS
THE REGION INTO WEDNESDAY. THIS WILL DEVELOP A STRONGER PUSH OF
COLDER AIR INTO THE REGION TONIGHT, WHILE THE APPROACHING
ROCKIES VORT INDUCES ASCENT AIDED BY STRENGTHENING LOW-LEVEL
FRONTOGENESIS AND UPPER LEVEL DIVERGENCE IN THE LEFT EXIT
REGION OF THE UPPER JET. THIS, IN TURN, WILL LIKELY LEAD TO
REDEVELOPMENT OF RAIN SHOWERS ACROSS PARTS OF THE AREA BY
MORNING WHICH WILL PERSIST INTO THE DAY WEDNESDAY AS THE UPPER
TROUGH AND MID-LEVEL COLD POOL DEVELOP SOUTHEAST ACROSS THE
AREA. COOLING OF THE COLUMN, AS WELL AS FALLING SURFACE
TEMPS/WET BULBS, WILL LIKELY SUPPORT PRECIPITATION EVENTUALLY
MIXING WITH WET SNOW LATE IN THE AFTERNOON ACROSS THE WESTERN
HALF OF OUR FORECAST AREA.
AFTER AN EXTENDED PERIOD OF ABOVE-AVERAGE TEMPERATURES THIS
MONTH, AND ANOTHER DAY OF 50S/LOW 60S TEMPS TODAY, WEDNESDAY'S
READINGS IN THE 40S (FALLING INTO THE 30S WEST LATE) AND
BLUSTERY WEST WINDS AROUND 25 MPH WILL MAKE FOR A MUCH CHILLIER
FEEL.
RATZER
WEDNESDAY NIGHT THROUGH MONDAY:
STRONG CAA WILL BE ONGOING WEDNESDAY EVENING AS THE CORE OF 850
HPA AIR AS LOW AS -10 TO -12C CROSSES OVER THE AREA LATE
WEDNESDAY NIGHT INTO THURSDAY MORNING. THERMAL PROFILES SUPPORT
SCATTERED TO NUMEROUS SNOW SHOWERS ACROSS THE AREA, ESPECIALLY
OVERNIGHT AS LOW TO MID-LEVEL MOISTURE INCREASES WITHIN A
COMPACT MID-LEVEL WAVE. WITH A RELATIVELY DEEP DGZ IN THE MID-
LEVELS, SOME OF THESE SHOWERS COULD PRODUCE LOCALIZED BURSTS OF
SNOW AMID BLUSTERY NW WINDS GUSTING TO 30 MPH. MEASURABLE SNOW
(AT LEAST 0.1") SEEMS PROBABLE FOR SOME OF THE AREA, BUT THE
PATHS OF INDIVIDUAL SHOWERS/FILAMENTS WILL DICTATE WHO SEES A
DUSTING ON GRASSY SURFACES.
AS A BROAD UPPER-LEVEL LOW ROTATES ACROSS THE GREAT LAKES
REGION WEDNESDAY THROUGH FRIDAY, AN INITIAL WAVE ORIGINATING
FROM THE COLORADO ROCKIES ON TUESDAY WILL CROSS LOWER MICHIGAN
ON WEDNESDAY BEFORE CYCLONICALLY ROTATING SOUTHWARD ROUGHLY
ALONG LAKE MICHIGAN THURSDAY INTO THURSDAY EVENING. THERE HAS
BEEN A SUBSTANTIAL SHIFT WITH ENSEMBLE GUIDANCE TO FAVOR THIS
SCENARIO OVER THE PAST COUPLE DAYS, SO THE FORECAST REFLECTS
THIS TREND. AHEAD OF AND WITHIN THE PROMINENT MID-LEVEL VORT
LOBE, DYNAMIC COOLER OF THE LOWER TROPOSPHERE WILL FAVOR
POTENTIALLY ACCUMULATING SNOW INTO NORTHEAST ILLINOIS AND
NORTHWEST INDIANA DURING THIS TIME. WITH THE INTRICACIES OF A
MULTIPLE WAVES ROTATING AROUND THE UPPER-LEVEL, IT CAN BE
EXPECTED THAT THE FOCUS FOR SNOW WILL CHANGE LONGITUDINALLY WITH
SUBSEQUENT FORECAST CYCLES. WHETHER THIS REMAINS FAR ENOUGH
WEST TO AFFECT SOME (OR MOST) OF THE CWA OR SHIFT FAR ENOUGH
EAST TO AFFECT PRIMARILY INDIANA AND LOWER MICHIGAN REMAINS TO
BE SEEN. NONETHELESS, THE ODDS OF ACCUMULATING SNOW (EVEN MORE
THAN 1") CONTINUE TO GRADUALLY INCREASE FOR AT LEAST THE EASTERN
HALF OF THE AREA ON THURSDAY. ADDITIONALLY, AN ASSOCIATED
STRONG NORTHWESTERLY GRADIENT FLOW WITH THIS SYSTEM COULD YIELD
STRONG GUSTS TO 35MPH+.
BEYOND THURSDAY EVENING, RESIDUAL SHOWER ACTIVITY WILL END
ACROSS ALL BUT THE NW WIND LAKE BELTS OF NORTHWEST INDIANA.
THERE, LAKE EFFECT RAIN SHOWERS WILL PERSIST INTO AT LEAST
SATURDAY. RIDGING SHOULD THEN BRING QUIET CONDITIONS ON SUNDAY
BEFORE A LONGWAVE TROUGH OVER THE NORTHERN GREAT PLAINS
INTERACTS WITH A POCKET OF PACIFIC MOISTURE TO PRODUCE AN AREA
OF RAIN SOMEWHERE OVER THE WESTERN GREAT LAKES MONDAY INTO
MONDAY NIGHT.
KLUBER
AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 537 AM CST TUE NOV 19 2024
S WINDS GUSTING TO AROUND 30 KNOTS, SPORADICALLY TO AROUND 35
KNOTS THROUGH MID-MORNING, WILL GRADUALLY VEER SW THROUGH THE
DAY WHILE DIMINISHING TO UNDER 25 KNOTS. WSW WINDS WITH
OCCASIONAL GUSTS AS HIGH AS 20 KNOTS ARE THEN EXPECTED TONIGHT
BEHIND A COLD FRONT BEFORE INCREASING WITH GUSTS TO AROUND 25
KNOTS BY LATE WEDNESDAY MORNING.
PERIODS OF HIGH-END MVFR TO LOW-END VFR CEILINGS WILL PERSIST
THROUGH THE PERIOD. WHILE THE CURRENT TAF SHOWS A DRY FORECAST,
THERE IS A LESS THAN 30% CHANCE THAT -RA DEVELOPS OVER THE
TERMINALS BEGINNING AROUND SUNRISE WEDNESDAY AND CONTINUES
THROUGH MID-MORNING.
KLUBER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 3 PM CST THIS AFTERNOON FOR THE IL
AND IN NEARSHORE WATERS.
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