392
FXUS63 KLSX 281940
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
240 PM CDT FRI MAR 28 2025
KEY MESSAGES
- THERE IS A CHANCE OF SHOWERS ACROSS SOUTHEAST MISSOURI AND SOUTHERN
ILLINOIS LATE TONIGHT INTO SATURDAY MORNING.
- SEVERE WEATHER IS LIKELY SUNDAY AFTERNOON INTO EARLY EVENING WITH
DAMAGING WIND, LARGE HAIL, AND TORNADOES ALL POSSIBLE.
SHORT TERM
(THROUGH LATE SATURDAY NIGHT)
ISSUED AT 238 PM CDT FRI MAR 28 2025
TONIGHT'S FORECAST LOWS IN THE UPPER 50S TO LOW 60S ARE 20 TO 25
DEGREES ABOVE NORMAL FOR LATE MARCH - ON PAR WITH OUR AVERAGE HIGHS.
THIS WILL BE DUE TO CONTINUING LOW-LEVEL WARM AIR ADVECTION AND
INSULATING CLOUD COVER OVERNIGHT. LOW-LEVEL MOISTURE FROM THE GULF
WILL CONTINUE TO ADVECT INTO THE REGION AS OVERNIGHT AS WELL. THIS
MOISTURE IS EXPECTED TO CONVERGE WITH A LOW-LEVEL JET AND, WITH THE
AID OF MID-LEVEL VORTICITY LOBES MOVING THROUGH, PRODUCE SHOWERS
ALONG OUR SOUTHEASTERN BORDER LATE TONIGHT. AS THE VORTICITY LOBES
MOVE NORTHEAST THROUGH SATURDAY MORNING, COVERAGE OF SHOWERS WILL
INCREASE OVER THE SOUTHERN AND EASTERN PORTIONS OF THE CWA. BY MID-
AFTERNOON, THESE SHOWERS WILL BE EAST OF THE AREA AND THE REST OF
THE DAY WILL BE MOSTLY DRY.
OTHERWISE, SATURDAY WILL BE ANOTHER UNSEASONABLY WARM DAY, THOUGH
NOT AS INTENSE THAN TODAY. PERSISTENT CLOUD COVER AND MORNING RAIN
IN SOUTHEAST MISSOURI AND SOUTHERN ILLINOIS WILL KEEP THESE AREAS
FROM REACHING 70 DEGREES. ELSEWHERE, HIGHS WILL CLIMB INTO THE LOW
TO MID-70S.
JAJA
LONG TERM
(SUNDAY THROUGH NEXT FRIDAY)
ISSUED AT 238 PM CDT FRI MAR 28 2025
BY EARLY SUNDAY MORNING, A NEGATIVELY TILTED LONGWAVE TROUGH WILL BE
CROSSING THE PLAINS WITH ITS SURFACE REFLECTION CENTERED SOMEWHERE
NEAR THE IOWA/MISSOURI BORDER. THE UNCERTAINTY IN ITS PLACEMENT
DIRECTLY IMPACTS THE POSITION OF SURFACE FRONT, AND THUS OUR SHOWER
AND THUNDERSTORM POTENTIAL SUNDAY MORNING AND AGAIN SUNDAY
AFTERNOON. SOME DETERMINISTIC GUIDANCE HAS REMAINED CONSISTENT IN
DEPICTING A FRONT EXTENDING ACROSS FAR WESTERN MISSOURI BY 12Z
SUNDAY WITH CONVECTION DEVELOPING ALONG THE FRONT OVERNIGHT. LATEST
CAMS SUGGEST THAT CONVECTION MAY DEVELOP NEAR THE KANSAS/MISSOURI
BORDER WITH AN MCS MOVING ACROSS SOUTHERN MISSOURI. THIS WOULD
LIKELY WEAKEN WITH EASTERN EXTENT, LEAVING US WITH MARGINALLY SEVERE
REMNANTS. IF THE FRONT IS FASTER AND CONVECTION DEVELOPS CLOSER TO
THE CWA, UP TO 500 J/KG OF MUCAPE IS FORECAST TO EXIST OVER A STOUT
CAP, SO SEVERE POTENTIAL WILL LIKELY BE LIMITED REGARDLESS. IF
SEVERE WEATHER DOES OCCUR, THE THREAT WOULD LIKELY BE LIMITED TO
LARGE HAIL AND GUSTY WINDS.
THIS WILL NOT BE THE CASE FOR SUNDAY AFTERNOON. ALTHOUGH SOME
DETAILS ARE STILL UNCLEAR AND THERE IS ROOM FOR FAILURE, CONFIDENCE
IN THE POTENTIAL FOR SEVERE WEATHER IS HIGH. HOW THE ENVIRONMENT
LINES UP TO PRODUCE SEVERE WEATHER IS THE QUESTION. ON SUNDAY THE
CWA WILL BE WITHIN A REGION OF UPPER LEVEL DIVERGENCE AND THE AMOUNT
OF LIFT AVAILABLE WILL BE OF NO CONCERN. ONGOING WARM AIR AND
MOISTURE ADVECTION WILL ENSURE AMPLE INSTABILITY WITH 2000+ J/KG
SBCAPE POTENTIALLY AVAILABLE DURING THE PEAK OF THE EVENT.
SOUTHWESTERLY 0-6 KM BULK SHEAR VECTOR OF 40 TO 60 KTS AT THE
BEGINNING OF THE EVENT MAY NOT BE COMPLETELY PERPENDICULAR TO THE
FRONT DEPENDING ON ITS ORIENTATION, BUT SUGGESTS SEMI-DISCREET
SUPERCELLS WILL BE THE STARTING STORM MODE WITH A TRANSITION TO A
QLCS AS THE SYSTEM MOVES EAST. IN THIS CASE, VERY STEEP LAPSE RATES
OF UP TO 8 C/KM AND STRONG SHEAR WILL SUPPORT ROBUST UPDRAFTS
CAPABLE OF PRODUCING LARGE HAIL. IN THE LOW-LEVELS, A DRY ADIABATIC
BOUNDARY LAYER AND VEERED WINDS SUPPORT THE POTENTIAL FOR DAMAGING
WINDS. TORNADOES WOULD ALSO BE POSSIBLE.
BUT WHAT ARE THE CAVEATS? AS MENTIONED PREVIOUSLY, THERE ARE
UNCERTAINTIES REGARDING THE SURFACE FRONT THAT WILL IMPACT THE
EVOLUTION OF SUNDAY AFTERNOON'S EVENT AND ONE OF THEM IS THE
ORIENTATION OF THE BULK SHEAR VECTORS TO THE FRONT. RECENT GUIDANCE
HAS BEEN TRENDING TOWARD THESE VECTORS BEING MORE PARALLEL TO THE
FRONT INITIALLY, WHICH WOULD RESULT IN A QLCS EVENT RATHER THAN SEMI-
DISCREET CONVECTION EVOLVING INTO A LINE. IN THIS CASE, THE TORNADO
THREAT WOULD BE LOWER AND DAMAGING WIND WOULD BE THE PRIMARY HAZARD.
ANOTHER FAILURE POINT IS THE AFOREMENTIONED SUNDAY MORNING MCS. IT'S
UNCLEAR HOW LONG THE MCS AND CLOUD COVER WILL LINGER IN THE AREA, IF
AT ALL, AND THAT WILL DIRECTLY IMPACT THE AMOUNT OF INSTABILITY
AVAILABLE FOR THE AFTERNOON ROUND. THE DECAYING MCS COULD ALSO LAY
OUT A BOUNDARY THAT CONVECTION WOULD INITIATE ON. THAT FEATURE MAY
NOT EVEN RESIDE IN OUR CWA. NEEDLESS TO SAY, THE SEVERE POTENTIAL IF
THIS OCCURS WOULD DECREASE SIGNIFICANTLY IF EXIST AT ALL.
TO SUMMARIZE: THE WORST CASE SCENARIO SEES SEMI-DISCREET SUPERCELLS
WITH ALL HAZARDS POSSIBLE, BUT MULTIPLE FAILURE MODES EXIST. MODELS
ARE TRENDING TOWARD THE SOLUTION IN WHICH A QLCS DEVELOPS QUICKLY
AND WE ARE LEFT WITH A DAMAGING WIND THREAT AND LOWER TORNADO
THREAT. ALTHOUGH MODELS ARE TRENDING TOWARD THIS, ANY OF THE
SOLUTIONS DISCUSSED ARE STILL POSSIBLE.
THE COLD FRONT AND ASSOCIATED WEATHER IS FORECAST TO EXIT THE
FORECAST AREA SUNDAY EVENING. COLD AIR WILL FILTER IN BEHIND THE
FRONT BRINGING JACKET WEATHER BACK INTO THE FORECAST FOR MONDAY AND
TUESDAY WITH LOWS IN THE 30S AND 40S AND HIGHS LARGELY IN THE 50S.
ANOTHER POTENTIALLY IMPACTFUL SYSTEM IS FORECAST TO BRING WEATHER TO
THE AREA DURING THE MIDDLE OF THIS WEEK, THOUGH GUIDANCE IS TOO
VARIABLE TO EXPOUND ON THAT JUST YET.
JAJA
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1233 PM CDT FRI MAR 28 2025
DRY AND VFR CONDITIONS WILL CONTINUE INTO TONIGHT BEFORE SHOWERS
ENTER THE FORECAST AREA FROM THE SOUTH. THESE SHOWERS WILL
INCREASE IN COVERAGE TOMORROW MORNING AND CEILINGS WILL DROP TO
MVFR AREAWIDE. IFR CEILINGS ARE POSSIBLE WHERE RAIN IS EXPECTED
(SOUTHEAST MISSOURI/SOUTHERN ILLINOIS). CONFIDENCE IN IFR
CONDITIONS IMPACTING THE ST. LOUIS METROPOLITAN TERMINALS IS TOO
LOW TO INCLUDE IN THE TAFS AT THIS JUNCTURE. OTHERWISE, TODAY'S
WIND GUSTS WILL DIMINISH TONIGHT BEFORE INCREASING AGAIN TOMORROW
AFTERNOON.
JAJA
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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