657
FXUS63 KLSX 251928
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
128 PM CST SAT JAN 25 2025
KEY MESSAGES
- A DRY COLD FRONT PASSING THROUGH THE REGION TONIGHT WILL
BRIEFLY COOL US DOWN BEFORE A RETURN TO MILD TEMPERATURES
THROUGH THE MIDDLE OF NEXT WEEK.
- DRY WEATHER STAYS IN PLACE THROUGH ROUGHLY MID-WEEK, BUT
PRECIPITATION CHANCES RAMP UP CLOSER TO NEXT WEEKEND.
SHORT TERM
(THROUGH LATE SUNDAY NIGHT)
ISSUED AT 125 PM CST SAT JAN 25 2025
ZONAL FLOW ALOFT RESULTING FROM A BROAD LONGWAVE TROUGH IS PROMOTING
A DECK OF CIRRUS AND CIRROSTRATUS ACROSS THE CENTRAL GREAT PLAINS
AND LOWER MIDWEST. DESPITE THE OPAQUE SKY AND OBSCURED SUNSHINE,
WEAK SOUTHWEST WINDS PROMOTED WELCOMED WARMTH THROUGHOUT MOST OF
MISSOURI AND ILLINOIS TODAY WHILE FURTHER ERODING THE REMNANT
SNOWPACK. WHILE MILD TEMPERATURES ARE IN STORE FOR US GOING
FORWARD, A WEAK SHORTWAVE TRACKING THROUGH THE UPPER MIDWEST AND
ATTENDANT COLD FRONT WILL PULL COOLER AIR INTO THE BI- STATE
REGION TONIGHT THROUGH SUNDAY. NO PRECIPITATION IS FORECAST WITH
THE FRONT'S PASSAGE, OWING TO WEAK FORCING ALOFT AND A MOISTURE-
STARVED ATMOSPHERE.
THE MAGNITUDE OF THE COOLDOWN WILL VARY FROM NORTH TO SOUTH SUNDAY,
WITH AREAS IN NORTHERN MISSOURI/WEST-CENTRAL ILLINOIS STRUGGLING TO
WARM ABOVE FREEZING AND THE OZARKS TOPPING OUT IN THE LOW 40S.
THAT SPATIAL DIFFERENCE ASIDE, THE VERY SMALL INTERQUARTILE RANGE
FOR TEMPERATURES IN THE SHORT-RANGE GUIDANCE LENDS ME CONFIDENCE
THAT THE ENTIRE REGION WILL COOL NEARLY 10 DEGREES COMPARED TO
TODAY. HIGH SURFACE PRESSURE SAGS SOUTH OF THE REGION OVERNIGHT
SUNDAY INTO MONDAY ALONG THE GULF COAST, PROMOTING DRY SOUTHERLY
RETURN FLOW THAT WILL RE-ESTABLISH WARM TEMPERATURES FOR THE MID-
MISSISSIPPI VALLEY TO START THE WORK WEEK.
MRB
LONG TERM
(MONDAY THROUGH NEXT SATURDAY)
ISSUED AT 125 PM CST SAT JAN 25 2025
WITH A DEEPER, MORE PRONOUNCED LONGWAVE TROUGH SETTING UP OVER THE
EASTERN HALF OF THE CONUS, A CUTOFF UPPER-LEVEL LOW WILL DEVELOP
CENTERED ROUGHLY OVER THE CALIFORNIA COAST BY LATE SUNDAY. DESPITE
THE MID-MISSISSIPPI VALLEY BEING UNDER NORTHWEST FLOW IN THE MID-
AND UPPER LEVELS, LOW LEVEL FLOW WILL BE MORE WESTERLY OR
SOUTHWESTERLY, WHICH WILL PROMOTE WARMING TEMPERATURES FOR THE FIRST
HALF OF THE WORK WEEK. THE RANGE OF REASONABLE TEMPERATURES THROUGH
WEDNESDAY IS NOT ONLY RELATIVELY SMALL (5-6 DEGREE IQR AT MOST), BUT
DECIDEDLY TRENDING WARMER INTO THE 40S MONDAY AND 50S TUESDAY AND
WEDNESDAY. WHILE SHORTWAVE IMPULSES WILL APPROACH THE REGION FROM
THE UPPER LEVEL LOW TO OUR NORTHWEST, THERE IS NO SUPPORT IN ANY
GUIDANCE THAT THEY WOULD BE STRONG ENOUGH OR CLOSE ENOUGH TO US TO
CAUSE CHANGES TO OUR SENSIBLE WEATHER. THE WARM, DRY SOUTHWEST FLOW
OFF THE OZARKS THAT WILL OCCUR BOTH DAYS WILL LEAD TO LOWER RH
VALUES DURING THE AFTERNOON PARTICULARLY IN SOUTHEAST AND EAST-
CENTRAL MISSOURI. THAT SAID, THE COMBINATION OF DRY AIR AND STRONG
WINDS LOOKS UNLIKELY (10-20%) TO RESULT IN ELEVATED FIRE DANGER.
MORE INFORMATION CAN BE FOUND IN THE FIRE WEATHER FORECAST PRODUCT.
MEANWHILE, THE CUTOFF LOW OFF THE WEST COAST WILL MEANDER AROUND THE
DESERT SOUTHWEST UNDER SOMEWHAT OF A REX BLOCK FOR THE FIRST FEW
DAYS OF THE WEEK. IT WILL REMAIN FAR FROM THE MIDWEST UNTIL AT LEAST
THURSDAY. MOST ENSEMBLE GUIDANCE AND DETERMINISTIC COUNTERPARTS
DEPICT A CLIPPER QUICKLY SWEEPING ACROSS THE GREAT LAKES LATE
WEDNESDAY AMIDST THE NORTHWEST FLOW ALOFT. WHILE PRECIPITATION
CHANCES WITH THIS SYSTEM ARE NEAR-ZERO FOR OUR AREA, IT WILL DRAG A
COLD FRONT SOUTH THROUGH THE REGION. EXACTLY HOW COOL THE POST-
FRONTAL AIR WILL BE ON THURSDAY IS STILL IN QUESTION, WITH AN 8-10
DEGREE IQR PRESENT IN THE NBM HIGH TEMPERATURE OUTPUT. REGARDLESS OF
THAT, THERE IS HIGHER CONFIDENCE (80% CHANCE) THAT HIGHS REACH THE
LOW 40S AT LEAST AREAWIDE.
WHILE HIGH SURFACE PRESSURE AND COOLER TEMPERATURES ESTABLISH
THEMSELVES OVER US THURSDAY, A UPPER LEVEL WAVE APPROACHING THE WEST
COAST WILL DISLODGE THE STALLED CUTOFF LOW. AS THE LOW TRACKS OVER
THE ROCKIES, IT WILL FORCE A SURFACE LOW TO FORM NEAR THE TEXAS
COASTLINE. ALL GUIDANCE HAS THIS FEATURE IMPACTING OUR REGION NEAR
THE END OF THE WEEK, BUT CONSIDERABLE TIMING, AMPLITUDE, AND TRACK
DIFFERENCES STILL EXIST THAT MAKE PINPOINTING DETAILS DIFFICULT.
THAT SAID, THERE IS GROWING CONSENSUS THAT PRECIPITATION ONSET WILL
BE DELAYED UNTIL FRIDAY AT THE EARLIEST. THE CURRENT FORECAST DOES
BRING PRECIPITATION CHANCES EARLIER THAN THAT, OWING TO LINGERING
POTENTIAL FOR AN EARLIER START, BUT THAT SCENARIO IS BECOMING LESS
LIKELY.
THERE IS ANYWHERE FROM A 20-40% CHANCE THAT WINTRY PRECIPITATION
WILL KICK OFF THIS ROUND OF PRECIPITATION LATE FRIDAY WITH COOLER
AIR IN PLACE AHEAD OF THE SYSTEM, PARTICULARLY IN NORTHERN MISSOURI
AND WEST-CENTRAL ILLINOIS. WHILE THERE IS A THREAT FOR FREEZING RAIN
PRESENT IN THE ENSEMBLE GUIDANCE, THE PROBABILITY OF SEEING
SUBFREEZING TEMPERATURES WITH PRECIPITATION FALLING IS LOW (5-10%)
AMIDST ALL SOLUTIONS. EVEN IF WARM AIR LAGS BEHIND, AS SOME
SOLUTIONS SUGGEST, ANTECEDENT WARM TEMPERATURES AT THE SURFACE WILL
INHIBIT ICE ACCRETION. AS A RESULT, THE MORE LIKELY OUTCOME IS SNOW
OR A RAIN/SNOW MIX AT FIRST BEFORE WARMER AIR OVERTAKES THE SHALLOW
COOLER LAYER AND WE TRANSITION TO ALL RAIN. WITH NO INSTABILITY TO
SPEAK OF AVAILABLE TO THIS SYSTEM, IT WILL LIKELY PASS THROUGH WITH
LITTLE SIGNIFICANCE BEYOND THE RAIN ITSELF. EXACTLY HOW QUICKLY THE
LOW EJECTS IS STILL UNCERTAIN, AND WILL IMPACT RAINFALL TOTALS AND
TEMPERATURES GOING INTO EARLY NEXT WEEK. A QUICK LOOK BEYOND THE
FORECAST PERIOD SUGGESTS AN ACTIVE SOUTHWEST FLOW PATTERN ALOFT TO
BEGIN FEBRUARY, WITH THE CPC 6-10 DAY OUTLOOK HIGHLIGHTING THE
REGION FOR INCREASED PROBABILITY FOR ABOVE-NORMAL PRECIPITATION.
MRB
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1102 AM CST SAT JAN 25 2025
DRY VFR CONDITIONS WILL EXIST ACROSS THE REGION THROUGH THE VALID
TAF PERIOD, WITH NO IMPACTS TO AVIATION INTERESTS CURRENTLY
FORECAST. A DRY COLD FRONT WILL PASS THROUGH THE TERMINALS
TONIGHT, VEERING LIGHT WINDS OUT OF THE NORTHWEST THROUGH LATE
SUNDAY NIGHT AT THE LEAST.
MRB
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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