427
FXUS63 KILX 162209
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
409 PM CST SAT NOV 16 2024
KEY MESSAGES
- RAIN AND GUSTY WINDS WILL OVERSPREAD THE REGION ON MONDAY. THE
RAINFALL FORECAST IS GENERALLY BETWEEN 0.25" - 1", AND WE ARE
ANTICIPATING 30-40 MPH WIND GUSTS BY MONDAY EVENING.
- A POWERHOUSE AUTUMN STORM SYSTEM WILL PUSH INTO THE REGION
WEDNESDAY AND THURSDAY, BRINGING GUSTY WINDS (30-40 MPH) AND
SHOWERY PRECIPITATION (40-60% CHANCE).
- MUCH COLDER TEMPERATURES ARRIVE THURSDAY - SATURDAY WITH SUB-
FREEZING OVERNIGHT LOWS LIKELY (> 60% CHANCE) AT SOME POINT
DURING THIS STRETCH.
DISCUSSION
ISSUED AT 149 PM CST SAT NOV 16 2024
AFTERNOON WATER VAPOR IMAGERY CURRENTLY DEPICTS TWO AREAS OF
INTEREST: (1) A SHORT-WAVE TROUGH MOVING ACROSS THE BLACK HILLS,
AND (2) A DEEP TROUGH DIGGING INTO BAJA CALIFORNIA. WHILE BOTH
WAVES WILL BE RESPONSIBLE FOR BRINGING SENSIBLE WEATHER TO
CENTRAL ILLINOIS, THE LATTER IS EXPECTED TO BE MORE IMPACTFUL IN
THE WEEK AHEAD.
BY LATE TONIGHT, A PRE-FRONTAL SURFACE TROUGH AND TRAILING COLD
FRONT ASSOCIATED WITH THE NORTHERN TRACK SHORTWAVE WILL MOVE
ACROSS THE MID-MISSISSIPPI VALLEY. A PLUME OF LOW-LEVEL MOISTURE
AND WEAK ISENTROPIC ASCENT AHEAD OF THIS FEATURE COULD RESULT IN
A FEW SPRINKLES SUNDAY MORNING WEST OF I-55. SOME GUIDANCE (E.G.
RAP & NAM) SUPPORTS SPRINKLES THROUGH MUCH OF THE DAY ON SUNDAY AS
THE COLD FRONT PUSHES INTO CENTRAL ILLINOIS AND STALLS OUT.
WHATEVER PRECIP WE'RE ABLE TO SQUEEZE OUT SUNDAY, IT'S GOING TO
HAVE TO BE FROM LOW- LEVEL PROCESSES, WITH THE UPPER FORCING
SAILING WELL OUT OF OUR AREA.
ATTENTION THEN QUICKLY TURNS TO MONDAY AS THE SOUTHERN STREAM
TROUGH LIFTS ACROSS THE SOUTHERN ROCKIES AND PIVOTS INTO THE
PLAINS. STRONG TEMPERATURE ADVECTION ASSOCIATED WITH THIS
DISTURBANCE WILL INCREASE BAROCLINIC INSTABILITY AND RESULT IN
RAPID CYCLOGENESIS THROUGHOUT MONDAY. WHILE THE MAIN IMPACT FROM
THIS SYSTEM, AT LEAST FOR CENTRAL ILLINOIS, APPEARS TO BE GUSTY
WINDS, THERE WILL BE WIDESPREAD RAINFALL AS WELL. A ROBUST INFLUX
OF SUB-TROPICAL MOISTURE SURGING NORTHWARD FROM THE WESTERN GULF
WILL HELP BRING 1.5" PWATS INTO CENTRAL ILLINOIS, WHICH EXCEEDS
THE 99TH PERCENTILE OF AVAILABLE MOISTURE FOR MID-NOVEMBER
CLIMATOLOGY. WITH STRONG SYNOPTIC LIFT (JET DYNAMICS) JUXTAPOSED
TO A MOISTURE-LADEN AIRMASS, WE SHOULD BE ABLE TO TAKE ANOTHER
HEALTHY BITE OUT OF OUR DROUGHT. WITH HI-RES GUIDANCE NOT OUT FAR
ENOUGH TO RESOLVE THIS FRONTAL SYSTEM, WE ARE RELYING ON NBM AND
LREF GUIDANCE FOR OUR RAINFALL GOALPOSTS (10TH-90TH PERCENTILE),
WHICH LOOK TO FALL BETWEEN 0.25"-1". MORE IMPACTFUL, HOWEVER, WILL
THE BE THE GUSTY WINDS. WITH THE DEEPENING SURFACE LOW POSITIONED
TO OUR NORTHWEST, SYNOPTIC WIND GUSTS WILL BE IN THE 30-40 MPH
RANGE. WORTH MONITORING, THOUGH, WILL BE THE POTENTIAL FOR
CONVECTIVE SHOWERS TO HELP TRANSFER MOMENTUM DOWNWARD FROM A 50
KT, 925-MB JET CORE. IF THIS WERE TO HAPPEN, WE COULD BE DEALING
WITH A FEW 40-50 MPH GUSTS, PARTICULARLY MONDAY NIGHT.
AFTER THE MONDAY SYSTEM GOES THROUGH ITS OCCLUSION AND PHASES
TOGETHER WITH ANOTHER TROUGH DIGGING OUT OF THE PACIFIC
NORTHWEST, THE MIDWEST WILL ONCE AGAIN BE FACING A POWERHOUSE
LATE-AUTUMN STORM SYSTEM. WHILE ALL SIGNS POINT TO A DEEPENING
UPPER- LEVEL LOW BOTTOMING-OUT SOMEWHERE OVER THE GREAT LAKES,
JUST HOW DEEP AND EXACTLY WHERE IT DEVELOPS REMAINS AN ENIGMA.
HONING-IN ON DETERMINISTIC GLOBAL GUIDANCE SUCH AS THE GFS AND
ECMWF HAS LARGELY BEEN USELESS, WITH THE STORM TRACK FRUSTRATINGLY
BOUNCING BACK-AND-FORTH SOMEWHERE BETWEEN INDY AND CLEVELAND.
THIS, OF COURSE, CAN DRAMATICALLY CHANGE OUR WIND AND SNOW
FORECAST. BUT, IF WE KEY-IN ON THE BLENDED (NBM) AND ENSEMBLE
(LREF) GUIDANCE, WE CAN TAKE A MORE PROBABILISTIC APPROACH WHICH
LEADS US TO A FEW EARLY CONCLUSIONS: (1) GUSTY WINDS IN THE 30-40
MPH REALM; (2) A LOW PROBABILITY (< 15% CHANCE) FOR A 2" SNOWFALL;
AND (3) A HIGH PROBABILITY (> 50%) CHANCE FOR SUB-FREEZING
OVERNIGHT TEMPERATURES SOMETIME BETWEEN WEDNESDAY NIGHT AND FRIDAY
NIGHT. AS ALWAYS, WE WILL NEED SOME MORE TIME TO MONITOR SNOW
TRENDS. EVEN TAKING AN ENSEMBLE APPROACH, THE MEAN OFTEN
CAMOUFLAGES THE VARIANCE.
MJA
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1124 AM CST SAT NOV 16 2024
MVFR CEILINGS WILL PERSIST INTO THIS EVENING BEFORE BREAKING AND
LIFTING TO VFR AS SURFACE WINDS TURN MORE SOUTHERLY. AFTER A
PERIOD TONIGHT IN WHICH VFR IS THE PRIMARY FLIGHT CATEGORY,
CLOUDS WILL FILL AND LOWER BACK INTO THE MVFR RANGE AHEAD OF A
FRONTAL SYSTEM.
MJA
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
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