922
FXUS63 KLSX 211048
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
548 AM CDT WED MAY 21 2025
KEY MESSAGES
- COOL, BREEZY, AND DRY CONDITIONS ARE EXPECTED TODAY AND
TOMORROW, WITH ONLY LOW CHANCES (20-30%) FOR SHOWERS ACROSS THE
OZARKS TONIGHT AND ILLINOIS TOMORROW NIGHT. COOL CONDITIONS ARE
LIKELY TO PERSIST THROUGH THE HOLIDAY WEEKEND.
- CHANCES FOR WIDESPREAD RAIN INCREASE OVER THE WEEKEND AND EARLY
NEXT WEEK, WITH SOME POTENTIAL FOR HEAVY RAIN AND THUNDERSTORMS
AS WELL. WHILE CONFIDENCE IS GROWING THAT HEAVY RAIN WILL FALL
ACROSS THE REGION, THERE IS LESS CONFIDENCE IN EXACTLY WHERE THE
HEAVIEST RAIN (AND IMPACTS) WILL OCCUR.
SHORT TERM
(THROUGH LATE THURSDAY AFTERNOON)
ISSUED AT 253 AM CDT WED MAY 21 2025
COOLER, MOSTLY DRY CONDITIONS ARE SET TO FILTER INTO THE AREA OVER
THE NEXT FEW DAYS THANKS TO PERSISTENT NORTHWEST FLOW. WHILE THE
CHANCES FOR MEANINGFUL PRECIPITATION WILL BE LOW BETWEEN TODAY AND
TOMORROW, THERE MAY BE A COUPLE OF OPPORTUNITIES FOR SOME LINGERING
LIGHT SHOWER ACTIVITY WORTH DISCUSSING.
WHILE THE SURFACE COLD FRONT HAS SURGED SOUTH OF THE AREA AND
COOLER, MORE STABLE AIR IS IN PLACE, A SUBTLE SHORTWAVE MOVING
THROUGH THE CYCLONIC FLOW ALOFT MAY PROVIDE ENOUGH FORCING TO
PRODUCE SOME ELEVATED POST FRONTAL SHOWERS OVERNIGHT TONIGHT. THE
FOCUS OF THIS ACTIVITY IS EXPECTED TO BE ACROSS SOUTHERN MISSOURI,
WHERE SOME MODEST MUCAPE MAY ALSO YIELD SOME THUNDERSTORMS (MAYBE
EVEN A FEW STRONG/SEVERE STORMS) AS WELL. WHILE OUR SOUTHERN
AREAS MAY BE GRAZED BY THE NORTHERN FRINGES OF THIS ACTIVITY LATE
THIS EVENING AND OVERNIGHT, INSTABILITY IS EXPECTED TO BE QUITE
MEAGER THIS FAR NORTH OF THE SURFACE BOUNDARY, AND THIS LIMITS OUR
POTENTIAL TO SEE MORE ROBUST CONVECTION AND PRECIPITATION. WHILE
IT WON'T BE IMPOSSIBLE TO SEE A THUNDERSTORM OR TWO ACROSS THE
OZARKS, BETTER CHANCES EXIST FARTHER SOUTH. THE NEXT OPPORTUNITY
FOR PRECIPITATION WILL BE A LOW CHANCES (20%) FOR A FEW COLD-CORE
SHOWERS MOVING THROUGH THE CYCLONIC FLOW ACROSS MAINLY ILLINOIS
LATE TOMORROW, BUT THESE ARE NOT EXPECTED TO BE SIGNIFICANT.
OTHERWISE, DRY CONDITIONS ARE EXPECTED THROUGH AT LEAST FRIDAY
MORNING.
OTHERWISE, THE MOST NOTABLE CHANGE OVER THE NEXT TWO DAYS WILL BE A
SIGNIFICANT COOLING TREND, WHICH IS EXPECTED TO PERSIST THROUGH THE
WEEKEND AND INTO EARLY NEXT WEEK. WHILE THE CORE OF THE POST-FRONTAL
AIRMASS WON'T ARRIVE UNTIL TOMORROW, TEMPERATURES TODAY WILL BE
NOTICEABLY COOLER THAN YESTERDAY (NOT TO MENTION LESS HUMID), WITH
HIGHS GENERALLY IN THE MID 60S TO MID 70S. THESE TEMPERATURES WILL
CONTINUE TO DROP THURSDAY AS NORTHWEST FLOW PERSISTS, WITH MORNING
LOWS IN THE 40S TO LOW 50S AND HIGHS ANOTHER 5 DEGREES COOLER THAN
TODAY. BRISK NORTHWEST WINDS WILL ALSO MAKE THIS FEEL A LITTLE
COOLER STILL, WITH SUSTAINED SPEEDS OF AROUND 15 TO 20 MPH AND GUSTS
TO AROUND 30 MPH THROUGH THE DAY TODAY, AND SIMILAR IF NOT SLIGHTLY
LOWER SPEEDS TOMORROW.
BRC
LONG TERM
(THURSDAY NIGHT THROUGH TUESDAY)
ISSUED AT 253 AM CDT WED MAY 21 2025
WHILE NORTHWEST FLOW WILL HANG ON INTO THE WEEKEND, A GRADUAL
PATTERN SHIFT WILL LEAD TO MORE UNSETTLED CONDITIONS AND AN
OPPORTUNITY FOR MORE RAIN...INCLUDING POSSIBLY SOME HEAVY RAIN.
BEGINNING FRIDAY, THE AXIS OF AN UPPER RIDGE ACROSS THE HIGH PLAINS
WILL SLOWLY NUDGE EASTWARD, CAUSING UPPER HEIGHTS TO BUILD WHILE
MAINTAINING NORTHWEST FLOW ALOFT. BEHIND THIS RIDGE, A SHORTWAVE
WILL SLOWLY MOVE ACROSS THE INTERMOUNTAIN WEST, AND A LEE SURFACE
TROUGH WILL GRADUALLY DEVELOP ACROSS THE HIGH PLAINS IN RESPONSE. AS
THIS SURFACE LOW SLOWLY DEEPENS AND MOVES EAST OVER THE WEEKEND,
A SOUTHWESTERLY LOW LEVEL JET WILL GRADUALLY STRENGTHEN AND BEGIN
TO DRAW RICH GULF MOISTURE INTO THE CENTRAL PLAINS AND EVENTUALLY
EASTWARD INTO THE LOWER MISSOURI BASIN.
MEANWHILE, THE PREVIOUSLY DISCUSSED SURFACE FRONT IS EXPECTED TO
REMAIN STALLED SOMEWHERE ACROSS THE AREA, PROVIDING A FOCUS FOR LIFT
AS THE LOW LEVEL JET STRENGTHENS AND OVERRUNS IT. THE PREVIOUSLY
MENTIONED MOISTURE CONTENT IS ALSO EXPECTED TO STEADILY INCREASE,
WITH LREF MEDIAN VALUES REACHING AROUND 1.5 INCHES AREA WIDE, WHICH
IS GREATER THAN THE 90TH PERCENTILE OF CLIMATOLOGY FOR THIS TIME
OF YEAR. GIVEN THESE FACTORS, ALONG WITH THE POTENTIAL FOR STORM
MOTIONS ROUGHLY PARALLEL TO THE STALLED BOUNDARY, THE PATTERN
SUPPORTS THE POTENTIAL FOR HEAVY RAIN DUE TO MULTIPLE ROUNDS OF
SHOWERS AND THUNDERSTORMS. CURRENT NBM AND LREF PROBABILITIES
SUGGEST A ROUGHLY 50-60% CHANCE OF MORE THAN 2 INCHES OF RAIN
ACROSS A BROAD AREA OF CENTRAL AND SOUTHERN MISSOURI BETWEEN
SATURDAY AND TUESDAY, WITH 90TH PERCENTILE VALUES REACHING CLOSE
TO 5 INCHES.
WHILE CONFIDENCE IS GROWING THAT SOME AREAS WILL SEE HEAVY RAIN
DURING THIS WINDOW, THERE REMAINS CONSIDERABLE UNCERTAINTY REGARDING
EXACTLY WHERE THE CORRIDOR OF HEAVIEST RAIN WILL FALL. THIS WILL
LIKELY BE CLOSELY TIED TO THE POSITION OF THE FRONT, WHICH
REMAINS HIGHLY VARIABLE AMONG ENSEMBLE MEMBERS. LREF CLUSTER
ANALYSIS MAINTAINS CONSIDERABLE SPREAD IN THE PLACEMENT OF THE
HEAVIEST RAIN AS A RESULT, WHICH RANGES FROM ROUGHLY THE I-70
CORRIDOR AND ACROSS MUCH OF OUR AREA, TO FAR SOUTHERN MISSOURI AND
MOSTLY TO OUR SOUTH. THESE DETAILS WILL BE REFINED OVER THE NEXT
FEW DAYS, BUT IT SHOULD BE NOTED THAT LATEST MODEL TRENDS HAVE
SHIFTED HIGHER RAIN TOTALS AND PROBABILITIES FARTHER NORTH.
FINALLY, THE POTENTIAL FOR STRONG OR SEVERE THUNDERSTORMS REMAINS
SOMEWHAT LOW GIVEN THE POSITION OF THE FRONT AND THE LIKELIHOOD OF
COOLER, MORE STABLE AIR REMAINING IN PLACE. HOWEVER, THIS IS NOT SET
IN STONE CONSIDERING THE VARIABILITY IN THE POSITION OF THE FRONT,
AS A NORTHWARD SURGE IN THIS BOUNDARY MAY LEAD TO GREATER
INSTABILITY AHEAD OF THE APPROACHING SHORTWAVE LATE IN THE WEEKEND.
MODEST WIND SHEAR MAY ALSO PROVE TO BE A LIMITING FACTOR, BUT
PERHAPS NOT A DISQUALIFYING ONE. SO WHILE HIGHER PROBABILITIES OF
STRONGER CONVECTION REMAIN TO OUR SOUTH, THERE IS A PLAUSIBLE
SCENARIO THAT COULD PUT OUR AREA IN PLAY FOR THIS AS WELL.
OTHERWISE, THE PRIMARY STORY OVER THE WEEKEND WILL BE THE
PERSISTENCE OF BELOW-AVERAGE TEMPERATURES, WHICH MAY BE EXACERBATED
BY THE POTENTIAL FOR MULTIPLE ROUNDS OF SIGNIFICANT PRECIPITATION.
IT SHOULD BE NOTED THAT THERE IS SOME NON-TRIVIAL SPREAD IN THE HIGH
TEMPERATURE FORECASTS THROUGH THE WEEKEND, LIKELY OWING TO
VARIABILITY IN THE POSITION OF THE COLD FRONT AND THE TIMING OF
ROUNDS OF PRECIPITATION.
BEYOND TUESDAY, AN OVERALL DRYING AND GRADUAL WARMING TREND IS
EXPECTED, ALTHOUGH EVEN THIS IS SOMEWHAT IN DOUBT AS THERE ARE SOME
INDICATIONS THAT THE UPPER TROUGH MAY CUT-OFF AND LINGER ACROSS THE
OHIO VALLEY FROM MID TO LATE WEEK. THIS SCENARIO WOULD LIKELY SLOW
OUR WARMUP, AND MAINTAIN CHANCES FOR SHOWERS FOR A BIT LONGER.
BRC
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 543 AM CDT WED MAY 21 2025
VFR CONDITIONS ARE LIKELY FOR A MAJORITY OF THE TAF PERIOD, WITH A
FEW POSSIBLE EXCEPTIONS. SOME LOW CLOUDS ARE PRESENT AROUND UIN AT
THE START OF THE PERIOD, AND MVFR CEILINGS MAY DEVELOP
PERIODICALLY EARLY IN THE DAY. VFR CONDITIONS ARE LIKELY TO RETURN
DURING THE AFTERNOON. ELSEWHERE, VFR CONDITIONS ARE LIKELY TO
PERSIST THROUGH THE DAY.
BREEZY WEST-NORTHWEST WINDS CAN BE EXPECTED AT ALL TERMINALS FROM
LATE MORNING THROUGH LATE AFTERNOON, AND WIND SPEEDS WILL WEAKEN
DURING THE EVENING AND OVERNIGHT.
THERE IS A LOW CHANCE (LESS THAN 20%) OF SHOWERS AND THUNDERSTORMS
AT COU AND JEF LATE THIS EVENING, GENERALLY AFTER 00Z. HOWEVER,
PROBABILITIES REMAIN TOO LOW FOR INCLUSION IN THE TAF AT THIS
TIME.
BRC
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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