908
FXUS63 KLSX 151133
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
533 AM CST WED JAN 15 2025
KEY MESSAGES
- ARCTIC AIR WILL REMAIN IN PLACE THROUGH TODAY. TEMPERATURES WILL
BEGIN TO WARM THURSDAY WITH ABOVE NORMAL TEMPERATURES ON FRIDAY.
ARCTIC AIR COMES CRASHING BACK IN THROUGH SATURDAY WITH
BITTERLY COLD TEMPERATURES SUNDAY INTO NEXT WEEK.
- LIGHT RAIN IS LIKELY LATE FRIDAY EVENING THROUGH EARLY SATURDAY
MORNING. THE HIGHEST CHANCES (60-80%) RUN FROM WHITE HALL, IL TO
HERMANN, MO AND POINTS SOUTH/EAST. PRECIPITATION MAY BRIEFLY END
AS LIGHT RAIN/SNOW/FLURRIES. NO ACCUMULATION IS EXPECTED.
SHORT TERM
(THROUGH LATE THURSDAY AFTERNOON)
ISSUED AT 327 AM CST WED JAN 15 2025
A RESPECTABLE 1036 MB SURFACE HIGH IS CENTERED OVERHEAD THIS MORNING
WITH CALM TO LIGHT/VARIABLE SURFACE WINDS. A WEAK, UNIMPACTFUL
CLIPPER SYSTEM IS POSITIONED OVER THE PLAINS WITH NIGHTTIME
MICROPHYSICS SATELLITE IMAGERY SHOWING BROKEN/OVERCAST SKIES
EXTENDING FROM SOUTHEASTERN SOUTH DAKOTA THROUGH CENTRAL MISSOURI.
CLOUD COVER WILL TRY TO NUDGE EASTWARD INTO WESTERN SECTION OF THE
CWA, BUT LIKELY WON'T HAVE MUCH PROGRESS WITH MID-LEVEL RH VALUES
DROPPING OFF FROM WEST TO EAST. WHERE SKIES REMAIN CLEAR THROUGH
EARLY MORNING, TEMPERATURES WILL COOL EFFICIENTLY. LOWS WERE
ADJUSTED TO REFLECT THIS WITH WIDESPREAD SINGLE DIGITS (ABOVE ZERO)
AND A FEW SUB-ZERO LOWS GENERALLY OVER INTERIOR SECTIONS OF
ILLINOIS. THE ONLY OTHER CONCERN IS THE POTENTIAL FOR STEAM FOG
ADJACENT TO LARGER RIVERS IN LOWER ELEVATIONS. I WOULDN'T EXPECT
THIS TO DEPART TOO FAR FROM STREAMS CONSIDERING DEWPOINT DEPRESSIONS
ARE 10-12 DEGREES AWAY FROM THESE LOCATIONS.
TODAY IS THE LAST OF THE ARCTIC COLD BEFORE AIR BEGINS TO WARM
THURSDAY. FORTUNATELY, MUCH OF THE AREA REMAINS DEVOID OF CLOUD
COVER TO HELP OFFSET THE COLD. SURFACE RIDGING SHIFTS INTO THE
OHIO/TENNESSEE VALLEYS WITH SOUTHERLY RETURN FLOW COMMENCING FROM
WEST TO EAST BETWEEN MID-MORNING AND EARLY THIS AFTERNOON. WHILE
HIGHS IN THE 20S WILL COVER MUCH OF THE AREA, SECTIONS OF CENTRAL
AND SOUTHEAST MISSOURI WARM INTO THE LOW TO MID-30S.
TEMPERATURES WILL BE 15-20 DEGREES WARMER TONIGHT THAN THIS MORNING
AS WARMER AIR OVER THE PLAINS GRADUALLY EXHIBITS MORE INFLUENCE IN
TIME. THE EASTWARD EXTENT OF THE MILDER AIR REMAINS ALONG AND WEST
OF THE MISSISSIPPI RIVER. TEENS CLAIM LESS REAL ESTATE OVER INTERIOR
SECTIONS OF ILLINOIS WITH 20S TO THE WEST. BOTH WINDS AND CLOUDS
BEGIN TO INCREASE TONIGHT AS A TROUGH ATTEMPTS TO BRIEFLY REINFORCE
COLD AIR TO THE SOUTH. THIS IS RATHER SHORT-LIVED, HOWEVER, WITH
WINDS TURNING WESTERLY.
WARMER AIR EVENTUALLY WINS OUT AS AN AMPLIFIED RIDGE SHIFTS EASTWARD
FROM THE PLAINS THURSDAY. MUCH OF THE CWA WILL REACH THE MID TO
UPPER 30S WITH LOW TO MID-40S PUSHING INTO CENTRAL MISSOURI THROUGH
FAR SOUTHWESTERN ILLINOIS.
MAPLES
LONG TERM
(THURSDAY NIGHT THROUGH TUESDAY)
ISSUED AT 327 AM CST WED JAN 15 2025
THE MID-MISSISSIPPI VALLEY REMAINS UNDER NORTHWESTERLY FLOW ALOFT
THURSDAY NIGHT, BUT WILL BE DIVIDED BY A DEPARTING TROUGH THAT
EXTENDS SOUTHWEST THROUGH THE GREAT LAKES REGION AND RIDGING OVER
THE INTERMOUNTAIN WEST. WARM AIR ADVECTION WILL BEGINS TO
STRENGTHEN, THOUGH LATEST MEDIUM RANGE GUIDANCE (NAM) HAS DELAYED
ITS ARRIVAL SLIGHTLY.
THE MAIN CONCERN THURSDAY NIGHT INTO EARLY FRIDAY MORNING WILL BE
THE POTENTIAL FOR ADVECTION FOG WITH WARMER AIR ADVANCING OVER COOL,
SATURATED SURFACES, COMPLEMENTS OF REMAINING SNOWPACK. IT HAS BEEN
NOTED THAT HRRR GUIDANCE IS QUITE A BIT MORE AGGRESSIVE WITH SNOW
DEPTH, HOLDING ONTO AMOUNTS (12+ INCHES) THAT ARE SEVERAL INCHES
HIGHER THAN LATEST NOHRSC ASSESSMENTS. CONSIDERING THURSDAY'S
WARMTH, PART OF THE QUESTION WITH FOG POTENTIAL WILL STEM FROM HOW
MUCH SNOW IS LEFT OVER THURSDAY NIGHT. WHILE THERE IS GOOD POTENTIAL
FOR ADVECTION FOG, I HAVE CAPPED IT AT PATCHY WITH SOME UNCERTAINTY
IN THE LINGERING SNOW DEPTH/COVERAGE THROUGH FRIDAY MORNING.
WARM AIR ADVECTION GETS INTO FULL SWING FRIDAY WITH ABOVE NORMAL
TEMPERATURES LIKELY. ONCE AGAIN, LINGERING SNOW MAY DETERMINE HOW
FAR NORTHEAST THE 50S MAKE IT. MID-LEVEL 850 MB AIR OF 10-15C OVER
THE PLAINS MODERATES SLIGHTLY AS IT SHIFTS INTO THE MID-MISSISSIPPI
VALLEY WITH 5-8C ENCOMPASSING THE CWA. A MAJORITY OF ECM/GFS
ENSEMBLES ARE SOLIDLY IN THE LOW TO MID-40S, INCHING NEAR 50 FURTHER
SOUTH AND WEST OF ST. LOUIS AND COLUMBIA. LREF GUIDANCE ISN'T TOO
BULLISH WITH 50S, PLOTTING 20-30% PROBABILITIES IN THE AFOREMENTIONED
AREAS OF CENTRAL AND SOUTHEAST MISSOURI. HOWEVER, PROBABILITIES JUMP
(40% NEAR KUIN/80-90% FROM ROLLA TO FESTUS, MO) ALONG AND WEST OF
THE MISSISSIPPI RIVER FOR TEMPERATURES ABOVE 45 DEGREES. IF THERE'S
ANY GUARANTEE, IT WILL BE FOR A PRODUCTIVE DAY FOR SNOWMELT.
THE NEXT CHANCE OF PRECIPITATION ARRIVES LATE FRIDAY INTO FRIDAY
NIGHT BEFORE EXITING EARLY SATURDAY MORNING. THE PROMINENT FEATURE
IS A STRONG 984 MB LOW THAT TRAVERSES SOUTHERN CANADA, WHERE THE
COLD AIR MASS ORIGINATES. LOCALLY, PRECIPITATION CHANCES COME FROM A
WEAKER SURFACE LOW THAT TRACKS FROM THE TEXAS PANHANDLE AND SOUTH OF
THE MO/AR BORDER. THE GOOD NEWS IS THAT THERE ISN'T MUCH QUESTION
WITH PRECIPITATION TYPE AS WE ARE WELL WITHIN THE WARM AIR UPON ITS
ARRIVE. LATEST GLOBAL GUIDANCE CONTINUES TO SHIFT THE SYSTEM SOUTH
(REFERENCING DP/DT) WITH A EARLIER ARRIVAL (MAYBE AN HOUR OR TWO) OF
THE COLD FRONT. THE MAIN CHANGE SINCE THE LAST UPDATE HAS BEEN A
SLIGHTLY LATER ONSET OF PRECIPITATION WITH ONLY SLIGHT CHANCE (BELOW
20%) POPS FRIDAY EVENING AND LOWER PRECIPITATION AMOUNTS BY THE TIME
IT ALL ENDS. LREF MEANS HAVE TIGHTENED THE NORTHERN GRADIENT WITH
LESS THAN 0.10" NEAR KUIN AND UP TO 0.3" SOUTHEAST OF I-44 AND SOUTH
OF I-64 IN ILLINOIS. LREF PROBABILITIES FOR 0.25" OR MORE PEAK AT 50-
60% OVER THESE AREAS AND QUICKLY DROP OFF TO THE NORTHWEST.
FORTUNATELY, THE BACK SIDE OF THE SYSTEM LACK MUCH SUPPORT FOR
WINTRY PRECIPITATION WITH LITTLE MID-LEVEL SUPPORT AND ADVANCING
DEEP, COLD AND DRY AIR MASS BEHIND THE COLD FRONT. A VERY BRIEF
PERIOD OF LIGHT SNOW/FLURRIES CANNOT BE RULED OUT BUT ACCUMULATIONS
LOOK UNLIKELY, ESPECIALLY CONSIDERING 36-48 HOURS OF WARMER AIR THAT
LIES AHEAD OF THE FRONT.
THE COLD WILL BE THE MAIN STORY OVER THE WEEK INTO NEXT WEEK.
TEMPERATURES WILL BE SEASONABLY COOL SATURDAY WITH LITTLE UPWARD
MOVEMENT THROUGH THE AFTERNOON. THE BRUNT OF THE COLD MOVES IN
SUNDAY, EXTENDING INTO THE EARLY PORTION OF NEXT WEEK. TEENS AND 20S
RETURN TO THE REGION FOR DAYTIME HIGHS. WIDESPREAD SINGLE DIGITS ARE
EXPECTED ACROSS THE REGION MONDAY AND TUESDAY MORNING, POSSIBLY AS
LATE AS WEDNESDAY MORNING. SUB-ZERO TEMPERATURES CANNOT BE RULED
OUT, SHOULD SKIES REMAIN CLEAR AND WINDS CALM. GFS IS POSITIONING AN
IMPRESSIVE 1052 MB SURFACE HIGH OVERHEAD, WHILE THE ECM CENTERS A
1045 MB HIGH OVER THE TX/OK PANHANDLES. THE POSITION OF THE HIGH
WILL BE PARAMOUNT TO ANY POTENTIAL FOR SUB-ZERO READINGS WITH LFREF
MEMBERS LINING UP PROBABILITIES (30-60%) NORTH OF I-70.
PROBABILITIES ARE HIGHEST (40-60%) ACROSS NORTHEAST MISSOURI TUESDAY
MORNING.
MAPLES
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 524 AM CST WED JAN 15 2025
OBSERVATIONS SHOW NOTABLE FOG, WHICH HAS ALSO BEEN ABSENT ON
NIGHTTIME MICROPHYSICS PRODUCTS. A SMALL BANK OF MID-LEVEL CLOUDS
ARE SLOWLY MOVING ACROSS CENTRAL AND EAST CENTRAL MISSOURI, WHICH
WILL FURTHER INHIBIT DEVELOPMENT. THIS COMBINATION WITH THE DRY
AIR MASS AWAY FROM AREA STREAM/RIVERS SHOULD BE ABLE TO STAVE OFF
THE POTENTIAL AND HAS THEREFORE BEEN REMOVED.
VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD WITH MID-LEVEL
CEILINGS AROUND OR ABOVE 10K FEET. SHORT TERM GUIDANCE HINTS AT
LLWS LATE TONIGHT INTO EARLY THURSDAY. HOWEVER, SURFACE WINDS OF
5-10 KNOTS ONLY INCREASE TO AROUND 25 KNOTS THROUGH THE TOP OF THE
INVERSION (1200 FEET OR SO) WITH 10-15 KNOTS SPEED DIFFERENCE
THROUGH 2000 FEET. LLWS WAS NOT ADDED AT THIS TIME BUT WILL BE
MONITORED FOR ANY POTENTIAL CHANGES SHOULD IT NEED TO BE ADDED IN
LATER UPDATES.
MAPLES
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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