916
FXUS63 KLOT 200011
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
611 PM CST TUE NOV 19 2024
KEY MESSAGES
- MUCH COLDER WEATHER MID-LATE WEEK -- COLDEST AIR MASS OF THE
AUTUMN THUS FAR.
- SNOW SHOWERS LATE WEDNESDAY AFTERNOON THROUGH WEDNESDAY NIGHT
MAY PRODUCE THE SEASON'S FIRST MEASURABLE ACCUMULATION IN
SOME LOCATIONS.
- CHANCE OF WET SNOW THURSDAY WITH POTENTIAL FOR SOME SLUSHY
ACCUMULATION -- ESPECIALLY COOLER/GRASSY SURFACES.
DISCUSSION
ISSUED AT 301 PM CST TUE NOV 19 2024
PATTERN SYNOPSIS/FORECAST: EARLY AFTERNOON ANALYSIS YIELDS ~985 MB
OVER NORTH-CENTRAL MN WITH AN OCCLUDED FRONT EXTENDING ACROSS
NORTHERN WI INTO SOUTHWEST MI. SECONDARY COLD FRONT CURRENTLY MAKING
EASTWARD HEADWAY ACROSS SOUTHERN WI AND NORTHERN IL. THE ATTENDANT
PARENT CLOSED, NEGATIVELY TILTED, UPPER WAVE FOLLOWING SUIT ACROSS
THE NORTHERN PLAINS. THIS UPPER WAVE COMBINED WITH A SECONDARY PIECE
OF ENERGY EMANATING FROM THE SOUTHERN ROCKIES ARE EXPECTED TO PHASE
OVER THE REGION TONIGHT WITH AMPLIFIED TROUGHING CROSSING THE GREAT
LAKES REGION WEDNESDAY INTO THURSDAY. THIS IS EXPECTED TO YIELD A
STRONGER PUSH OF COLDER AIR INTO THE REGION TONIGHT THROUGH LATE
THIS WEEK -- LIKELY THE COLDEST AIR SO FAR THIS AUTUMN -- WHILE
APPROACHING ROCKIES ENERGY INDUCES ASCENT AIDED BY INCREASING LOW-
LEVEL FRONTOGENESIS.
A SECONDARY AREA OF LOW PRESSURE EXPECTED TO SPIN UP TO THE EAST
OVER SOUTHEAST MI/LAKE HURON DURING THE DAY WEDNESDAY, WITH LATEST
TRENDS SUPPORTING THIS SYSTEM RETROGRADING TO VICINITY NORTHERN LAKE
MICHIGAN WEDNESDAY NIGHT EVENTUALLY TREKKING SOUTH THE LENGTH OF
LAKE MICHIGAN THROUGH THURSDAY. A RATHER FASCINATING EVOLUTION OF
NOT ONLY THE SURFACE FEATURE, BUT ALSO THE MID-LEVEL WAVE
ESSENTIALLY FUJIWHARA-ING AROUND AND PHASING WITH THE PARENT UPPER
LOW WEDNESDAY NIGHT.
LONGER RANGE TRENDS SUPPORT MID-LEVEL RIDGING FOLDING OVER THE
REGION THIS WEEKEND WITH ATTENDANT SFC HIGH PRESSURE SUPPORTING
QUIETER SENSIBLE WEATHER. RENEWED CHANCES FOR MORE ACTIVE WEATHER
RETURN EARLY NEXT WEEK AS ADDITIONAL SHORTWAVE(S) MEANDER THE
NATION'S MIDSECTION.
THROUGH WEDNESDAY NIGHT:
LITTLE IN THE WAY OF SENSIBLE WEATHER THIS EVENING WITH THIS
AFTERNOON'S ABOVE NORMAL TEMPERATURES GIVING WAY TO A STRONGER PUSH
OF COLD ADVECTION LATER THIS EVENING AND ESPECIALLY TONIGHT INTO
WEDNESDAY. AS WAS ALLUDED TO ABOVE, APPROACHING ROCKIES SHORTWAVE
COMBINED WITH A STRENGTHENING LOW-LEVEL FGEN RESPONSE SHOULD PROVE
TO BE ENOUGH TO KICK OFF A BATCH OF RAIN SHOWERS TONIGHT, MAINLY
AFTER 09Z. SHOWERS SHOULD BE RELATIVELY QUICK-MOVING WITH MINIMAL
QPF AND LARGELY EXITING STAGE RIGHT BY 15Z WEDNESDAY. SHORT-LIVED
BREAK IN PRECIP EXPECTED LATE WEDNESDAY MORNING THROUGH MID-
AFTERNOON BEFORE ADDITIONAL RAIN/SNOW SHOWER CHANCES ARRIVE FROM THE
NORTHWEST. COOLING THERMAL PROFILES SHOULD SUPPORT SHOWERS
EVENTUALLY MIXING WITH AND CHANGING OVER TO WET SNOW BY LATE
AFTERNOON ACROSS WESTERN REACHES OF THE FORECAST AREA, AND
EVENTUALLY OVER THE METRO BY MID-EVENING ONWARD. FORECAST THERMAL
PROFILES CONTINUE TO SUPPORT SCATTERED TO NUMEROUS SNOW SHOWERS
WEDNESDAY NIGHT, ESPECIALLY GIVEN AN UPTICK OF LOW-MID LEVEL
MOISTURE EXTENDING THROUGH A 5-7 KFT DEEP DGZ. WOULDN'T BE SURPRISING
FOR SOME OF THESE SNOW SHOWERS TO BE RATHER ROBUST WITH BRIEF, BUT
LOCALLY SIGNIFICANT VISIBILITY DROPS, ESPECIALLY CONSIDERING
NORTHWEST WIND GUSTS AS HIGH AS 25-30 MPH DURING THE LATTER HALF OF
THE OVERNIGHT. LATEST SUITE OF PROBABILISTIC GUIDANCE WITH RESPECT
TO THE SEASON'S FIRST SNOW ACCUMULATION (0.1" OR MORE) CONTINUES TO
INCREASE WITH PROBABILITIES RANGING FROM 50-80%+ ACROSS THE FORECAST
AREA. PROBABILITIES FOR >0.5" DROP SIGNIFICANTLY THROUGH 12Z THURSDAY
-- 35% OR LESS AREA-WIDE, WITH MANY LOCATIONS <10%.
THURSDAY THROUGH TUESDAY:
LINGERING SCATTERED SNOW SHOWERS EARLY THURSDAY MORNING LIKELY TO
GIVE WAY TO THE EAST RATHER QUICKLY. HOWEVER, ATTENTION QUICKLY
REFOCUSES ON POTENTIAL FOR ANOTHER ROUND OF WINTRY WEATHER/
ACCUMULATING SNOW DURING THE DAY THURSDAY AS AFOREMENTIONED LOW
PRESSURE PINWHEELS DOWN THE LENGTH OF THE LAKE MICHIGAN. LATEST
SUITE OF ENSEMBLE TRENDS CONTINUE TO SHIFT TO FAVOR THIS SOLUTION,
ALTHOUGH STILL QUITE A BIT OF UNCERTAINTY EXISTS ON JUST HOW FAR
WEST WET SNOW SPREADS (E.G. ALL THE DAY TO THE FAR WESTERN FORECAST
AREA OR MORE CONFINED TO AREAS CLOSER TO LAKE MICHIGAN/NORTHWEST
IN). NONETHELESS, PROBABILITIES CONTINUE TO INCREASE FOR
ACCUMULATING SNOW WITH LREF PROBS FOR 1" OR MORE AS HIGH AS 60-65%
FOR AREAS EAST OF I-39 AND NORTH OF I-80. SUSPECT THAT SINCE THE
MAJORITY OF THIS SNOW IS PROGGED TO FALL DURING THE DAYLIGHT HOURS
THAT COOLER/GRASSY SURFACES WILL BE MOST SUSCEPTIBLE FOR SLUSHY
ACCUMULATIONS, BUT SOME IMPACT TO ROADS NOT RULED OUT AT THIS POINT
-- DEPENDENT ON THE INTENSITY AS TO WHICH SNOW FALLS. POTENTIAL FOR
GUSTY NORTHWEST WINDS AS HIGH AS 35 MPH CONTINUES THROUGH THIS TIME
FRAME.
SNOW MAY TRANSITION BACK TO A BIT OF RAIN SHOWER ACTIVITY LATER
THURSDAY AFTERNOON AND EVENING ON THE BACKSIDE OF THIS SYSTEM AS WE
ACTUALLY WARM ADVECT FROM THE NORTH (ODD!) BEFORE DIMINISHING
ENTIRELY THURSDAY NIGHT/EARLY FRIDAY IN IL. LINGERING LAKE INDUCED
SHOWERS EXPECTED TO CONTINUE IN NORTHWEST IN LAKE BELTS AT LEAST
THROUGH FRIDAY, IF NOT ALL THE WAY THROUGH FRIDAY NIGHT. HIGHER
HEIGHTS BUILD ACROSS THE WESTERN GREAT LAKES THIS WEEKEND WITH
LITTLE IN THE WAY OF SENSIBLE WEATHER ANTICIPATED. NEXT SHOT OF
PRECIP ARRIVES TOWARDS THE TAIL END OF THE LONG RANGE AS MID-LEVEL
WAVE(S) EJECT LEE OF THE ROCKIES.
GILLEN
AVIATION /00Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 611 PM CST TUE NOV 19 2024
FORECAST CONCERNS FOR THE TERMINALS...
- POTENTIAL FOR A PERIOD OF MVFR CEILINGS TONIGHT, MAINLY NEAR
IL-WI LINE
- BRIEF PERIOD OF RAIN SHOWERS WEDNESDAY MORNING
- BREEZY WESTERLY WINDS THROUGH THE DAY ON WEDNESDAY
- SECOND ROUND OF RAIN AND SNOW SHOWERS WEDNESDAY AFTERNOON
TRANSITIONING TO SNOW WEDNESDAY EVENING AND OVERNIGHT
AN UPPER LOW CONTINUES TO ORGANIZE OVER THE NORTHERN PLAINS THIS
EVENING WITH A NOTABLE SHORTWAVE DISTURBANCE TRAVERSING ACROSS
THE CENTRAL PLAINS. AS A RESULT OF THESE FEATURES, A BROAD AREA
OF 2500-3500 FT STRATUS HAS DEVELOPED OVER THE UPPER MISSISSIPPI
VALLEY AND HAS STARTED TO SHOW SIGNS OF SOUTHWARD EXPANSION
TOWARDS NORTHERN IL. SINCE MOST OF THE UPSTREAM CEILING
OBSERVATIONS SHOW VFR VALUES I HAVE DECIDED TO MAINTAIN VFR
CONDITIONS IN THE TAFS FOR TONIGHT, BUT DID INCLUDE A SCT025
MENTION TO HINT AT THE POTENTIAL FOR SOME MVFR CEILINGS ESPECIALLY
NEAR THE IL-WI LINE.
IN ADDITION TO THE CEILINGS, THERE IS ALSO A BAND OF RAIN
SHOWERS ASSOCIATED WITH THE AFOREMENTIONED SHORTWAVE THAT IS
PROGRESSING TOWARDS THE AREA ALONG AN ELEVATED FRONTAL BOUNDARY.
THIS BAND IS EXPECTED TO BECOME MORE LINEAR ALONG THE FRONT
OVERNIGHT AND PIVOT ACROSS NORTHERN IL AND NORTHWEST IN BETWEEN
10Z AND 15Z WEDNESDAY MORNING. GIVEN THE CONVECTIVE NATURE OF
THE SHOWERS AND THEIR ANTICIPATED QUICK MOVEMENT, SHOWERS SHOULD
ONLY LAST 1-2 HOURS AT ANY ONE LOCATION.
AS THE UPPER LOW MOVES INTO THE GREAT LAKES ON WEDNESDAY, WINDS
WILL INCREASE IN SPEED. THEREFORE, EXPECT WESTERLY WIND GUSTS OF
20-25 KTS WEDNESDAY MORNING FOLLOWED BY STRONGER GUSTS OF 25-30
KTS WEDNESDAY AFTERNOON. WHILE IT DOES LOOK AS IF GUSTS WILL
EASE SOMEWHAT WEDNESDAY EVENING, SOME OCCASIONAL 17-20 KT GUSTS
WILL REMAIN POSSIBLE THROUGH THE END OF THE FORECAST PERIOD.
ALONG WITH THE WINDS, THE LOW WILL ALSO KICK OFF ANOTHER ROUND
OF SHOWERS WEDNESDAY AFTERNOON THROUGH WEDNESDAY NIGHT.
INITIALLY, SHOWERS SHOULD START OFF AS RAIN OR A RAIN/SNOW MIX
AS THE SNOW GROWTH REGION SATURATES. HOWEVER, AS SURFACE
TEMPERATURES COOL WEDNESDAY EVENING THE RAIN IS EXPECTED TO
TRANSITION TO ALL SNOW AFTER 02Z AND REMAIN AS SUCH THROUGH THE
REST OF WEDNESDAY NIGHT. THAT SAID, ACCUMULATIONS ARE EXPECTED
TO BE SOMEWHAT MUTED AND MAINLY CONFINED TO GRASSY AND ELEVATED
SURFACES DUE TO TEMPERATURES FORECAST TO BE NEAR OR JUST ABOVE
FREEZING. THOUGH, FORECAST SOUNDINGS DO SHOW NOTABLE AMOUNTS OF
LOW-LEVEL INSTABILITY WHICH COULD CAUSE SNOW RATES TO BE HIGHER
THAN FORECAST WHICH COULD LEAD TO LOCALIZED ACCUMULATIONS IN
EXCESS OF A QUARTER INCH.
YACK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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