666
FXUS63 KLSX 160913
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
313 AM CST THU JAN 16 2025
KEY MESSAGES
- MILDER AIR WILL BUMP TEMPERATURES BACK TO NORMAL TODAY WITH
ABOVE NORMAL WARMTH FRIDAY. THE WARMUP WILL BE BRIEF, HOWEVER,
AS ARCTIC AIR MAKES A STRONG RETURN THIS WEEKEND INTO EARLY NEXT
WEEK.
- WIDESPREAD LIGHT RAIN IS EXPECTED (70-90%) LATE FRIDAY THROUGH
EARLY SATURDAY. PRECIPITATION THAT LINGERS INTO SATURDAY MORNING
MAY BRIEFLY MIX WITH OR CHANGE TO SNOW BEFORE EXITING. NO
ACCUMULATION IS EXPECTED.
SHORT TERM
(THROUGH LATE FRIDAY AFTERNOON)
ISSUED AT 312 AM CST THU JAN 16 2025
A LONGWAVE TROUGH EXTENDS SOUTHWARD OUT OF CANADA THIS MORNING AND
COVERS ROUGHLY THE EASTERN THIRD OF THE U.S. EARLY THIS MORNING. A
WEAK LOBE OF VORTICITY IS EMBEDDED IN THE SOUTHERN QUADRANT OF THE
MEAN FLOW, PASSING AROUND THE SOUTHERN END OF LAKE MICHIGAN. THE
FEATURE IS LARGELY BENIGN WITH EXCEPTION TO A THIN VEIL OF
SATURATION AROUND 700 MB, WHICH IS PRODUCING MID-LEVEL CLOUDS OVER
PARTS OF MISSOURI AND ILLINOIS. THERE HAS BEEN JUST ENOUGH MOISTURE
TO PRODUCE A FEW FLURRIES, ALL OF WHICH WILL CONTINUE TO PUSH EAST-
SOUTHEAST BEFORE SUNRISE.
THE HIGHLY-ANTICIPATED WARMING TREND HAS ALREADY BEGUN EARLY THIS
MORNING AS THE 0C 850 MB ISOTHERM BISECTS THE STATE OF MISSOURI FROM
NORTH TO SOUTH. THE LONGWAVE TROUGH INITIALLY MAKES A SLOW SHIFT TO
THE EAST, RESULTING IN A MODEST PUSH OF MILDER AIR INTO THE REGION
EARLY THIS MORNING THROUGH THE DAY TODAY. TEMPERATURES, WHILE
SIGNIFICANTLY WARMER THAN THE PAST FEW DAYS, WILL RETURN TO NEAR
NORMAL (MID-30S TO LOW-40S) WITH A FEW LOCATIONS OVER FAR SOUTHEAST
MISSOURI IN THE UPPER 40S.
AS THE UPPER TROUGH MOVES FURTHER EAST, IT IS REPLACED BY AN UPPER
RIDGE. THE LAST FEW FORECAST CYCLES HAVE BEEN CONSISTENTLY WARMING
850 MB TEMPERATURES IN THE POSITIVE SINGLE DIGITS (5-8C) WITH FEW
INDICATIONS THAT CENTRAL MISSOURI BRIEFLY TOUCHES 10C. IN THIS
PROCESS, ADD WARMTH, MOISTURE AND LINGER SNOW COVER SUPPORTS AN
ADVECTION FOG SCENARIO. THE BEST POTENTIAL LOOKS TO BE ON THE
ILLINOIS SIDE OF THE RIVER WITH HRRR BEING MOST AGGRESSIVE IN
REDUCING VISIBILITY BELOW 1 MILE. THE UNCERTAINTY HERE WILL BE THE
PLACEMENT OF THE FRONT EARLY FRIDAY MORNING. GIVEN THE UNCERTAINTY,
THE LOWER END WAS CAPPED AT 1-2 MILES, WHICH CAN BE ADJUSTED LATER
AS NEAR-TERM ANALYSIS PROVIDES BETTER DETAIL.
STRONG SOUTHWESTERLY FLOW STRENGTHENS AHEAD OF A COLD FRONT THAT
APPROACHES FROM THE NORTHWEST LATE FRIDAY. TEMPERATURES WILL BE SOME
OF THE WARMEST IN THE LAST 2 WEEKS WITH THE INNER QUARTILE (25TH-
75TH PERCENTILE) SPREAD OF 4-5 DEGREES. THERE IS HIGH CONFIDENCE
THAT HIGHS WILL RISE WELL INTO THE 40S WITH AT LEAST LOW-50S
EXTENDING FROM CENTRAL TO SOUTHWESTERN MISSOURI. THOUGH THE LOW
LEVEL JET STRENGTHENS TO AROUND 60 KNOTS, SHALLOW MIXING OF 1-2K
FEET WILL LIMIT MOST GUSTS TO 20-25 KNOTS WITH ISOLATED GUSTS IN THE
MID-20KT TO NEAR 30 KNOTS RANGE. THE NEXT CHANCE FOR RAIN BEGINS TO
APPROACH OUT OF THE SOUTHWEST WITH THE BULK OF IT ARRIVING FRIDAY
NIGHT. LOW CHANCES (<30%) ENCROACH ON CENTRAL AND SOUTHWESTERN
MISSOURI LATE FRIDAY AFTERNOON.
MAPLES
LONG TERM
(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 312 AM CST THU JAN 16 2025
A STRONG COLD FRONT WILL EXTEND FROM THE GREAT LAKES REGION THROUGH
THE SOUTHERN PLAINS LATE FRIDAY. THE FRONT ENTERS NORTHERN MISSOURI
AS EARLY AS 00Z FRIDAY EVENING WITH A SURFACE LOW AT THE TRAILING
END OF THE FRONT NEAR THE OK/TX BORDER.
THE SURFACE LOW TRACKS EASTWARD INTO THE ARKLATEX REGION AS STRONG
SOUTHWESTERLY FLOW SLINGSHOTS MOISTURE NORTHWARD OUT OF THE WESTERN
GULF OF MEXICO. MODEL SOUNDING FROM MEDIUM AND LONG RANGE GUIDANCE
SHOW DEEP SATURATION BY 03Z FRIDAY EVENING. THOUGH THE SURFACE LOW
IS WELL TO THE SOUTH, MID/UPPER LEVEL VORTICITY PROVIDES THE
NECESSARY ASCENT TO SUPPORT WIDESPREAD LIGHT RAIN FRIDAY NIGHT INTO
EARLY SATURDAY. QPF TRENDS HAVE LOWERED SLIGHTLY THROUGH EACH
CONSECUTIVE FORECAST CYCLE WITH 0.25" AMOUNTS FAVORED SOUTH OF I-44
IN MISSOURI AND SOUTH OF I-64 IN ILLINOIS. WPC OUTLOOKS SHOW UP TO
0.50" IN THE FAR SOUTHEAST SECTION OF THE CWA, WHICH LEANS TOWARD
THE 75TH PERCENTILE OF ENSEMBLE DATA. THIS IS LIKELY A PRODUCT OF
THE GFS INFLUENCE WITH IT BEING AMONG THE HIGHER TALLIES. HALF-INCH
AMOUNTS CANNOT BE ENTIRELY RULES OUT, BUT MEAN RAINFALL OVER THIS
AREA WILL LARGELY BE LESS WITH LREF PROBABILITIES FOR A HALF-INCH AT
OR LESS THAN 10% AND INNER QUARTILE RANGE AT 0.10-0.30". AMOUNTS
TRAIL OFF QUICKLY TO THE NORTH, GENERALLY LESS THAN 0.20" DECREASING
TO LESS THAN 0.10" OVER NORTHEASTERN MISSOURI.
THE BRIEF PERIOD OF WARMTH COMES TO AN ABRUPT END EARLY SATURDAY
MORNING AS THE COLD FRONT CONTINUES TO THE SOUTHEAST. LINGERING
MOISTURE COULD MIX WITH OR CHANGE TO SNOW. THE ARGUMENT AGAINST THIS
IS THAT DRY AIR SURGES IN AT THE MID-LEVELS AND THE DENDRITIC GROWTH
ZONE BECOME UNSATURATED RATHER QUICKLY WITH LITTLE LIFT LEFT BEHIND
THE BOUNDARY. IT IS NEXT TO DOUBTFUL THAT SNOW WILL LAST LONG AT
ALL, IF IT EVEN OCCURS. WITH THAT IN MIND, CONCERNS FOR IMPACTS ARE
NEXT TO ZERO WITH NO ACCUMULATION EXPECTED. ARCTIC AIR CONTINUES TO
FILTER IN THROUGH THE DAY SATURDAY, PREVENTING TEMPERATURES FROM
MOVING MUCH HIGHER THAN SATURDAY MORNING LOWS (20S). HIGHS RANGE
FROM THE MID-20S TO THE NORTH TO MID-30S TO THE SOUTH.
COLD, ARCTIC AIR SETTLES IN SATURDAY NIGHT THROUGH TUESDAY NIGHT AS
MASSIVE LONGWAVE UPPER TROUGH SWALLOWS MUCH OF THE U.S. THIS IS WHEN
THE BRUNT OF THE COLD IS FELT MONDAY MORNING AND TUESDAY MORNING.
GFS DETERMINISTIC HAS BACKED OFF THE ANOMALOUSLY IMPRESSIVE 1052 HPA
SURFACE HIGH AND COME MORE IN LINE WITH THE ECM 1045 HPA SCENARIO.
THAT BEING SAID, THERE IS STILL DISAGREEMENT IN THE EXACT POSITION
OF THE SURFACE HIGH, WHICH WILL HAVE AN IMPACT ON THE DEPTH OF THE
COLD AIR AND EFFICIENCY OF RADIATIONAL COOLING. I'VE BEEN KEEPING AN
EYE ON LREF PROBABILITIES FOR BELOW ZERO TEMPERATURES EACH MORNING,
WHICH HAVE CONSISTENTLY HELD ONTO 30-50% PROBABILITIES NORTH OF I-
70. THIS WOULD BE MORE PLAUSIBLE IF THE SURFACE HIGH CENTERS
OVERHEAD EITHER MORNING WITH LIGHT WINDS AND CLEAR SKIES. EITHER
WAY, IT'S NEARLY CERTAIN TO BE BITTERLY COLD ONCE AGAIN.
ENSEMBLE SPREAD INCREASES TOWARD THE TAIL END OF THE FORECAST.
HOWEVER, THE LONGWAVE TROUGH MOVES EAST WITH MEAN MID/UPPER FLOW
TURNING WESTERLY THROUGH MIDWEEK. THOUGH NBM TEMPERATURES SHOW INNER
QUARTILE SPREAD OF 10-12 DEGREES, THIS IS LIKELY A RESULT OF
DISAGREEMENTS IN ARRIVAL TIME OF THE WARMER AIR. TRENDS ARE
ENCOURAGING AS THEY SHOW A GRADUAL RISE TO NEAR NORMAL WEDNESDAY.
MAPLES
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1036 PM CST WED JAN 15 2025
CONFIDENCE IS HIGH IN VFR FLIGHT CONDITIONS THROUGH THE FORECAST
PERIOD AT ALL LOCAL TERMINALS. FLURRIES ARE POSSIBLE AT KUIN
DURING THE FIRST HOUR OR TWO OF THE PERIOD, AND IF THESE OCCUR,
IMPACTS ARE NOT EXPECTED. WINDS WILL GRADUALLY SHIFT TO OUT OF THE
NORTHWEST AND STRENGTHEN THURSDAY BEFORE BECOMING VARIABLE TO
CALM THURSDAY NIGHT. THESE CALM WINDS MAY AID IN THE DEVELOPMENT
OF FOG, BUT CONFIDENCE IN FOG OCCURRING IN PROXIMITY TO THE LOCAL
TERMINALS IS LOW AT THE MOMENT.
ELMORE
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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