408
FXUS63 KLSX 161954
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
154 PM CST THU JAN 16 2025
KEY MESSAGES
- FRIDAY WILL BE THE WARMEST DAY OF THE WEEK AS HIGHS REACH THE
40S AND 50S AREAWIDE. TEMPERATURES WILL QUICKLY PLUMMET THIS
WEEKEND WITH WIDESPREAD HIGHS IN THE TEENS BY SUNDAY.
- WIDESPREAD LIGHT RAIN IS EXPECTED FRIDAY NIGHT INTO SATURDAY
MORNING WITH THE HIGHEST POTENTIAL (80-90%) IN SOUTHWEST
ILLINOIS AND SOUTHEAST MISSOURI. LIGHT SNOW ON THE BACKSIDE OF
THE SYSTEM IS INCREASINGLY UNLIKELY.
SHORT TERM
(THROUGH LATE FRIDAY NIGHT)
ISSUED AT 153 PM CST THU JAN 16 2025
AS OF 1430Z THIS MORNING, AREAL SURFACE OBSERVATIONS SHOWED
WIDESPREAD TEMPERATURES NEAR AND ABOVE FREEZING. THESE TEMPERATURES
WERE ALREADY WARMER THAN YESTERDAY'S HIGHS FOR MANY LOCATIONS AND
MARKED THE BEGINNING OF A TWO DAY PERIOD OF WARMTH FOR THE REGION
CAUSED BY WARM AIR ADVECTION. ABUNDANT SUNSHINE AND WARMER
CONDITIONS TODAY ARE EXPECTED TO EAT INTO THE REMAINING SNOW,
RESULTING IN MINOR CHANGES TO THE SNOWPACK. THIS IS RELEVANT BECAUSE
THE SNOWPACK WILL DIRECTLY IMPACT THE POTENTIAL FOR FOG TONIGHT.
WARM AIR ADVECTION WILL CONTINUE OVERNIGHT, THREATENING THE
FORMATION OF FOG AS IT MEETS THE SNOW COVERED GROUND. THOUGH MUCH OF
THE FORECAST AREA WILL MEET THE CONDITIONS OF HAVING LIGHT WIND THIS
EVENING AND A SNOWPACK, THE GREATEST POTENTIAL FOR FOG FORMATION AND
PERSISTENCE WILL EXIST IN SOUTH-CENTRAL AND SOUTHWEST ILLINOIS.
THESE LOCATIONS ARE ARE EXPECTED TO SEE EFFICIENT RADIATIONAL
COOLING CONDITIONS ATOP THE SNOW. CONFIDENCE IS INCREASING IN THE
DEVELOPMENT OF FOG IN THESE AREAS TONIGHT, AS SUPPORTED BY UNANIMOUS
CONSENSUS AMONG GUIDANCE IN ITS PRESENCE. CONFIDENCE BEGINS TO WAVER
CONCERNING THE DENSITY OF THE FOG, HOWEVER. MOST HIGH RESOLUTION
GUIDANCE PLUMMETS VISIBILITIES TO LESS THAN 1 MILE LATE TONIGHT, BUT
SOME KEEP WITH A MORE OPTIMISTIC 2-3 MILES. I HAVE NO DOUBT THAT <1
MILE VISIBILITIES ARE POSSIBLE TONIGHT, BUT I HAVE LOW CONFIDENCE IN
EXACTLY WHERE THAT WOULD OCCUR AND FOR HOW LONG. ANY FOG THAT DOES
DEVELOP WILL DISSIPATE FRIDAY MORNING. UNTIL IT DISSIPATES, SLICK
SPOTS ON ELEVATED SURFACES WILL BE POSSIBLE.
FRIDAY WILL BE THE WARMEST DAY OF THE NEXT SEVEN WITH HIGH
TEMPERATURES FORECAST TO REACH THE MID-40S TO LOW-50S AREAWIDE. THIS
SHOT OF WARMTH SHOULD MAKE A DENT IN THE REMAINING SNOW BEFORE A
COLD FRONT TAKES US BACK TO WINTER FRIDAY NIGHT INTO SATURDAY
MORNING. AHEAD OF THE FRONT, MOISTURE WILL ADVECT NORTHWARD AS A
SURFACE LOW APPROACHES THE OHIO VALLEY. CONCURRENTLY, VORTICITY
ADVECTION FROM THE LOW'S PARENT SHORTWAVE WILL BE PROVIDING LIFT TO
THE REGION. THIS WILL RESULT IN WIDESPREAD WARM SECTOR RAIN WITH A
FOCUS ON SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS. RAINFALL TOTALS
OF AROUND 0.25" STILL LOOK REASONABLE FOR THESE LOCATIONS. THE HREF
LPMM DOES PLANT A BULLSEYE OF UP TO 0.5" OF RAIN IN SOUTHWEST
ILLINOIS, SKIRTING THE BORDER BETWEEN OURS AND PADUCAH'S CWAS. THIS
VALUE ALIGNS MORE CLOSELY WITH THE WPC FORECAST WHICH HAS BEEN MORE
ROBUST THAN ENSEMBLES SUGGEST. ENSEMBLE STATISTICS SHOW 24 HOUR
TOTALS OF 0.25" - 0.3", AND PROBABILITIES OF >0.20" AT 40-60%. IN
ALL, 0.5" IS POSSIBLE AS AN OUTLIER, BUT MOST LOCATIONS WILL
PROBABLY NOT EXCEED HALF THAT. RAIN WILL END QUICKLY SATURDAY
MORNING AS A COLD FRONT USHERS IN VERY COLD AND DRY AIR. PREVIOUSLY
DISCUSSED BACK-END SNOW IS BECOMING LESS LIKELY AS THE MID-LEVELS
PRETTY IMMEDIATELY BEHIND THE FRONT. A FEW FLURRIES OR A BRIEF
LIGHT RAIN/SNOW MIX ARE STILL POSSIBLE, BUT INCREASINGLY DOUBTFUL.
JAJA
LONG TERM
(SATURDAY THROUGH NEXT THURSDAY)
ISSUED AT 153 PM CST THU JAN 16 2025
FRIDAY NIGHT'S/SATURDAY MORNING'S COLD FRONT WILL PASS THROUGH WITH
A VENGEANCE. SATURDAY'S HIGH TEMPERATURES WILL VERY LIKELY OCCUR
NEAR MIDNIGHT WITH TEMPERATURES DROPPING THROUGH THE DAY OR HOLDING
STEADY IN THE AFTERNOON. AFTERNOON "HIGHS" ARE ONLY FORECAST TO
REACH THE 20S IN AREAS NORTH OF I-70 AND THE 30S TO THE SOUTH.
ALTHOUGH THESE ARE REASONABLE CONDITIONS FOR JANUARY, NORTHWEST
WINDS WILL ENSURE THE WIND CHILL IS AT LEAST 10 DEGREES COOLER THAN
THE AIR TEMPERATURE. SUNDAY MORNING WILL REALLY KICK OFF OUR COLD
STREAK. MORNING WIND CHILLS ARE EXPECTED TO DIP BELOW ZERO FOR MOST
LOCATIONS NORTH OF I-70. THIS WILL REMAIN TRUE FROM SUNDAY MORNING
THROUGH WEDNESDAY MORNING. ALTHOUGH THERE WILL BE A DIURNAL
TEMPERATURE CURVE EACH DAY, PORTIONS OF FAR NORTHEAST MISSOURI AND
WEST-CENTRAL ILLINOIS MAY NOT SEE WIND CHILLS ABOVE ZERO AT ANY TIME
OF DAY BETWEEN SUNDAY AND WEDNESDAY MORNING. ALTHOUGH WIND CHILLS
REMAIN ABOVE COLD WEATHER ADVISORY CRITERIA, CONDITIONS WILL STILL
BE DANGEROUS FOR THOSE WHO SPEND LONG PERIODS OF TIME OUTDOORS.
WHETHER TEMPERATURES AND WIND CHILLS SWAY WARMER OR COOLER IN THE
COMING DAYS IS DEPENDENT ON THE BEHAVIOR OF SURFACE HIGH PRESSURE
SPILLING INTO THE REGION EARLY NEXT WEEK. IF THE HIGH TRACKS
DIRECTLY THROUGH OUR CWA ON MONDAY OR TUESDAY MORNINGS, EFFICIENT
RADIATIONAL COOLING MAY COOL US ENOUGH TO REACH ADVISORY CRITERIA.
IT'S A SITUATION WE'LL CONTINUE TO MONITOR OVER THE COMING DAYS. THE
COLD SNAP WILL LIKELY END ON WEDNESDAY AS LOW-LEVEL RIDGING EXITS TO
THE EAST AND WE RETURN TO SOUTHERLY FLOW. LREF PROBABILITIES OF NOON
TEMPERATURES <25 DEGREES ARE GENERALLY 20-40% ON WEDNESDAY, A STEEP
DROP FROM THE 100% PROBABILITIES PRESENT ON TUESDAY. HOW WARM IT
ACTUALLY GETS DURING THE WARM-UP IS UNCERTAIN, BUT IT WILL
UNDOUBTEDLY FEEL BETTER THAN THE BITTER COLD WE'LL HAVE JUST GONE
THROUGH.
JAJA
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1130 AM CST THU JAN 16 2025
THIS AFTERNOON'S GUSTY WINDS WILL SUBSIDE THIS EVENING, BECOMING
LIGHT AND VARIABLE FOR SHELTERED LOCATIONS AND IN PORTIONS OF
SOUTHERN ILLINOIS AND SOUTHEAST MISSOURI. THE POTENTIAL FOR FOG
TONIGHT IS GREATEST IN SOUTHERN ILLINOIS WHERE RADIATIONAL COOLING
WILL BE MOST EFFICIENT OVER THE LINGERING SNOWPACK. THE BEST TIMING
FOR THIS WILL BE LATE THIS EVENING INTO VERY EARLY FRIDAY MORNING.
MAINTAINED MVFR VISIBILITY AT KSTL AND IFR VISIBILITY AT KCPS
DURING THIS ISSUANCE. CONFIDENCE IN THE PRESENCE OF FOG IS
INCREASING, BUT CONFIDENCE IN THE WESTERN EXTENT OF THE FOG IS
STILL LOW. WITH THAT IN MIND, I DID NOT HAVE ENOUGH EVIDENCE TO
REMOVE THE FOG COMPLETELY. AFTER FOG DISSIPATES FRIDAY MORNING,
VFR CONDITIONS WILL LAST THROUGH THE AFTERNOON WITH GUSTY WINDS
MAKING A RETURN.
THERE IS A LOW CHANCE OF LOW-LEVEL WIND SHEAR IMPACTS IN CENTRAL
MISSOURI, NORTHEAST MISSOURI, AND WEST-CENTRAL ILLINOIS FRIDAY
MORNING. SINCE SOUNDING DATA SHOWS ELEVATED WINDS AT THE SURFACE
INCREASING INCREMENTALLY TO ~40 KTS AT 1400-2000FT IN THESE
LOCATIONS AND MARGINAL DIRECTIONAL SHEAR, DECIDED TO LEAVE THIS OUT
OF THE TAFS DURING THIS ISSUANCE.
JAJA
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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