261
FXUS63 KLSX 312328
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
628 PM CDT MON MAR 31 2025
KEY MESSAGES
- STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE AGAIN LATE TUESDAY
NIGHT, WITH SEVERE THUNDERSTORMS MORE LIKELY ON WEDNESDAY
AFTERNOON.
- PERIODS OF HEAVY RAIN ARE LIKELY THURSDAY THROUGH SATURDAY,
MAINLY ACROSS SOUTHEAST MISSOURI INTO SOUTHWEST ILLINOIS. THESE
PERIODS OF HEAVY RAIN MAY CAUSE RIVER FLOODING AND FLASH
FLOODING.
SHORT TERM
(THROUGH LATE TUESDAY AFTERNOON)
ISSUED AT 224 PM CDT MON MAR 31 2025
A SURFACE RIDGE IS CURRENTLY ENTERING WESTERN MISSOURI, AND WILL
SLIDE EASTWARD INTO THE LOWER OHIO VALLEY BY EARLY TUESDAY MORNING.
THE COMBINATION OF LIGHT/VARIABLE WINDS MOST OF THE NIGHT AND A
MOSTLY CLEAR SKY SHOULD LEAD TO EFFICIENT RADIATIONAL COOLING
OVERNIGHT, LASTING LONGEST IN SOUTH-CENTRAL ILLINOIS. FARTHER WEST,
LIGHT SOUTHEASTERLY WINDS AND SOME INCREASE IN HIGH-LEVEL CLOUDINESS
SHOULD END THE COOLING TREND AFTER ABOUT 0700-0900 UTC. LOWS ARE
EXPECTED TO RANGE FROM NEAR FREEZING TO THE MID 30S ACROSS THE
REGION. THERE LIKELY WILL BE SOME FROST, BUT FROST THIS EARLY IN THE
SEASON SHOULD NOT POSE ANY SIGNIFICANT PROBLEMS TO VEGETATION.
THEREFORE, NO FROST ADVISORY WAS ISSUED.
TEMPERATURES WILL WARM UP ON TUESDAY AS SOUTHEASTERLY WINDS
INCREASE. DID COOL HIGHS A COUPLE OF DEGREES HOWEVER FROM THE
PREVIOUS FORECAST AS SOUTHEASTERLY WINDS TEND TO UNDERPERFORM ON
TEMPERATURES, ESPECIALLY WITH THE INCREASING MID/HIGH LEVEL
CLOUDINESS THAT IS EXPECTED. HIGHS ARE FORECAST TO RANGE FROM THE
MID 50S TO MID 60S FROM NORTHEAST TO SOUTHWEST.
GOSSELIN
LONG TERM
(TUESDAY NIGHT THROUGH NEXT MONDAY)
ISSUED AT 224 PM CDT MON MAR 31 2025
(TUESDAY NIGHT)
ELEVATED SHOWERS AND THUNDERSTORMS ARE POSSIBLE IN PARTS OF
NORTHEAST MISSOURI AND WEST-CENTRAL ILLINOIS AFTER MIDNIGHT AS THE
LOW-LEVEL JET INCREASES. THE WINDOW FOR THIS ACTIVITY IS PROBABLY
PRETTY NARROW AS THE STRONGER LOW-LEVEL MOISTURE CONVERGENCE QUICKLY
ROCKETS NORTHEASTWARD. DETERMINISTIC MODEL GUIDANCE SHOWS SEVERAL
HUNDRED J/KG OF MUCAPE WITH PLENTY OF DEEP-LAYER SHEAR. ELEVATED
HAILERS ARE POSSIBLE, BUT THE LACK OF MORE INSTABILITY SHOULD KEEP
STORMS FROM GETTING SEVERE.
AT LEAST SCATTERED THUNDERSTORMS ARE FORECAST TO MOVE OUT OF THE MID-
MISSOURI VALLEY AND HEAD TOWARD NORTHEAST MISSOURI AFTER 0600 UTC.
THESE STORMS SHOULD BE DECAYING AS THEY MOVE EASTWARD DUE TO
WEAKENING MID/UPPER LEVEL FORCING AND A LESS UNSTABLE ENVIRONMENT.
ANY CONVECTION MOVING IN STILL MAY HAVE A TENDENCY TO BE MORE
ELEVATED IN NATURE, THOUGH IF A LINE OF STORMS IS A BIT MORE
ORGANIZED THAN ANTICIPATED, MAY BE ABLE TO MIX DOWN SOME MARGINALLY
SEVERE WINDS DOWN TO THE SURFACE. WITH 50+ KNOTS OF FLOW AS LOW AS
ABOUT 3000 FEET AGL, THIS IS CERTAINLY PLAUSIBLE.
(WEDNESDAY)
THE PACIFIC COLD FRONT WILL CONTINUE TO MOVE EASTWARD AND LIKELY
WILL SERVE AS A FOCUS FOR ADDITIONAL CONVECTIVE DEVELOPMENT. THE
MORNING CONVECTION SHOULD WEAKEN AS IT HEADS INTO EASTERN MISSOURI.
THE QUESTION IS HOW QUICKLY AND HOW FAR EAST/SOUTHEAST DOES IT GET
BEFORE DOING SO. WITH THE STRONG VORTICITY MAXIMA QUICKLY MOVING
INTO THE UPPER MIDWEST, THAT SUGGESTS IT COULD HAPPEN FAST. HOWEVER,
THE LOW-LEVEL JET DOESN'T WEAKEN MUCH, WHICH COULD SUGGEST SOME
CONVECTIVE DEVELOPMENT THROUGH THE MORNING. A COMPOSITE OUTFLOW
BOUNDARY MAY EMANATE OUT OF THIS DECAYING CONVECTION, AND COULD EVEN
SERVE AS THE "EFFECTIVE" FRONT DEPENDING ON HOW MUCH IT ALTERS THE
ENVIRONMENT. THIS LEADS TO UNCERTAINTY ON HOW MUCH INSTABILITY THERE
WILL BE AND HOW LARGE OF THE AREA MAY BE UNDER THE GUN FOR RENEWED
DEVELOPMENT IN THE AFTERNOON.
SPEAKING OF WHICH, SOME COOLING ALOFT AND THE SURFACE PACIFIC COLD
FRONT AND/OR THE REMNANT OUTFLOW BOUNDARY LIKELY WILL BE ENOUGH TO
GET AT LEAST ISOLATED CONVECTION GOING BY EARLY AFTERNOON. THIS IS A
CASE WITH VERY LITTLE MID/UPPER AIR FORCING FOR ASCENT, WITH NEUTRAL
HEIGHT TRENDS THROUGH THE EARLY EVENING. IN ADDITION, CONVERGENCE
ALONG THE PACIFIC COLD FRONT IS NOT VERY IMPRESSIVE. THESE FACTORS
POINT TO MORE DISCRETE CONVECTION (I.E., SUPERCELLS). THE DEEP-LAYER
SHEAR VECTORS ARE NEARLY PARALLEL TO THE BOUNDARY THOUGH, SO IT IS
POSSIBLE THAT STORMS GET UNDERCUT BY THE FRONT ITSELF. HODOGRAPHS
ARE PRETTY STRAIGHT AS WELL, SUGGESTING SPLITTING SUPERCELLS ARE
POSSIBLE WHICH WOULD INCREASE THE THREAT FOR MERGERS (AND POSSIBLE
DESTRUCTIVE INTERFERENCE). LARGE HAIL CERTAINLY LOOKS LIKE A THREAT
IN ANY SUPERCELLS, WITH STEEP MIDLEVEL LAPSE RATES HELPING TO
INCREASE CAPE AVAILABLE WITHIN THE HAIL GROWTH ZONE. EXACTLY HOW
MUCH INSTABILITY THERE WILL BE IS DEPENDENT ON HOW EARLY MORNING
CONVECTION EVOLVES AS DISCUSSED ABOVE. REGARDLESS, PROBABILITIES FOR
500 J/KG ARE LIKELY (60+%). GIVEN DEEP-LAYER SHEAR OF 60-70 KNOTS, I
HAVE LITTLE DOUBT THAT THERE WILL BE AT LEAST A FEW STORMS THAT ARE
STRONG TO SEVERE IN THE AREA. THERE WILL ALSO BE A TORNADIC THREAT,
GIVEN A LOT OF SPEED SHEAR IN THE LOWEST 1 KM. WINDS LOOK PRETTY UNI-
DIRECTIONAL THOUGH, WITH NOT MUCH CURVATURE EVIDENT ON HODOGRAPHS IN
THE AREA. IN ADDITION, THE TIMING (AFTERNOON) IS NOT IDEAL AS LCLS
ARE HIGHER THAN IF TIMING WAS LATER (MORE INTO EVENING HOURS).
STORM COVERAGE IS LIKELY TO INCREASE BY EARLY EVENING AS THE LOW-
LEVEL JET INCREASES AND SURFACE CONVERGENCE STRENGTHENS ALONG THE
COLD FRONT. IN OTHER WORDS, CONVECTIVE EVOLUTION LIKELY WILL CONSIST
MORE OF LINE/BOWING SEGMENTS COMPARED TO SUPERCELLS. THE TORNADIC
THREAT WILL ALSO INCREASE AS THERE IS A BIT MORE CURVATURE EVIDENT
ON FORECAST HODOGRAPHS AND 0-1KM SHEAR/SRH INCREASES. HOWEVER,
STORMS MAY ALREADY BE OUT OF OUR AREA NEAR 0000 UTC, BUT IT DEPENDS
ON THE EXACT TIMING OF THE FRONT ITSELF.
(WEDNESDAY NIGHT - SATURDAY NIGHT)
ALL SIGNS CONTINUE TO POINT TOWARD A VERY ACTIVE PERIOD OF TIME, AS
THE SURFACE COLD FRONT STALLS OUT AND ANOMALOUS TROUGHING DIGS INTO
THE DESERT SOUTHWEST. AT LEAST 3 DISTURBANCES WILL EJECT OUT OF THE
SOUTHWEST AND INTERACT WITH THE QUASI-STATIONARY FRONT. THIS MEANS
ROUND AFTER ROUND OF ELEVATED CONVECTION ALONG/NORTH OF THE
BOUNDARY. HOW THIS FRONT EVOLVES THROUGH THE PERIOD IS NOT CERTAIN,
AS CONVECTION TENDS TO SHUNT THE BOUNDARY MORE TO THE SOUTHEAST BUT
RISING MID/UPPER LEVEL HEIGHTS AND THE POTENTIAL FOR A STRONGER WAVE
TO MOVE THROUGH ON SATURDAY COULD HELP PUSH THE FRONT TO THE NORTH.
THE DETAILS WILL NEED TO BE IRONED OUT IN THE COMING DAYS, BUT THE
PATTERN SCREAMS HEAVY RAINFALL. IF WAVE AFTER WAVE IMPACTS THE SAME
AREAS, THERE IS POTENTIAL FOR SOME HISTORIC RAINFALL (12-15+
INCHES). AT THIS EARLY JUNCTURE, THE MOST FAVORED AREA FOR THE
HIGHEST TOTALS ARE ACROSS CENTRAL ARKANSAS INTO THE LOWER OHIO
VALLEY. THIS IS JUST SOUTHEAST OF OUR SOUTHEAST MISSOURI COUNTIES,
BUT NOT BY FAR. AT LEAST SUBTLE SHIFTS ARE POSSIBLE IN THE DAYS
AHEAD, AND A SHIFT NORTHWEST COULD RAISE THE STAKES FOR VERY
SIGNIFICANT RAINFALL AND RIVER/FLASH FLOODING INTO MORE OF THE AREA.
ON THE OTHER SIDE OF THE COIN, A SHIFT TO THE SOUTHEAST WOULD LESSEN
THE THREAT, WITH THE RAINFALL MAINLY BENEFICIAL. SOUTHEAST MISSOURI
HAS BEEN VERY DRY THIS MONTH. A FEW INCHES OF RAIN WOULD BE WELCOME,
BUT 5-8+" WOULD NOT. THE CURRENT AXIS OF RAINFALL WOULD AT LEAST
THREATEN THE BLACK RIVER AND SMALLER STREAMS IN SOUTHEAST MISSOURI,
WITH THE THREAT POTENTIALLY INCLUDING THE MERAMEC AND TRIBUTARIES AS
WELL AS THE KASKASKIA BASINS IF THERE IS ANY SHIFT TO THE NORTHWEST.
(SUNDAY - NEXT MONDAY)
ENSEMBLE GUIDANCE IS IN GOOD AGREEMENT THAT A VERY COOL AND DRY
PATTERN WILL GREET US TO END THE WEEKEND INTO EARLY NEXT WEEK. AFTER
THE BUSY STRETCH OF WEATHER AHEAD, A COOL AND DRY PERIOD WOULD BE
JUST WHAT THE DOCTOR ORDERED. THERE IS A PRETTY GOOD SIGNAL FOR A
LIGHT FREEZE, WITH THE LREF SHOWING PROBABILITIES OF SUBFREEZING
LOWS AT 50-80%. GIVEN THAT THIS IS A WEEK OUT AND THE GROWING SEASON
WILL VERY LIKELY UNDERWAY, FROST/FREEZE PRODUCTS MAY BE NEEDED FOR
THIS TIME PERIOD.
GOSSELIN
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 627 PM CDT MON MAR 31 2025
DRY AND VFR FLIGHT CONDITIONS WILL PERSIST THROUGH THE TAF PERIOD
WITH A WEAK SURFACE RIDGE ALSO LEADING TO WINDS BECOMING LIGHT AND
VARIABLE THIS EVENING. WINDS WILL SHIFT TO SOUTHEASTERLY TUESDAY
MORNING AND STRENGTHEN THROUGH THE DAY WITH OCCASIONAL GUSTS OF OVER
20 KT BY LATE MORNING. THE STRONGEST GUSTS, LIKELY AROUND 30 KT, ARE
EXPECTED AT KCOU, KJEF, AND KUIN DURING TUESDAY EVENING.
PFAHLER
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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