862
FXUS63 KLSX 041956
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
256 PM CDT THU JUN 4 2026
KEY MESSAGES
- WARM AND INCREASINGLY HUMID AIR WILL BECOME ESTABLISHED ACROSS
THE REGION, PERSISTING WELL INTO NEXT WEEK.
- DAILY CHANCES OF SHOWERS AND THUNDERSTORMS ARE EXPECTED INTO
NEXT WEEK. SUNDAY AND MONDAY ARE FAVORED FOR THE HIGHEST CHANCE
AND GREATEST COVERAGE WITH PLENTY OF DRY TIME OTHERWISE.
SHORT TERM
(THROUGH LATE FRIDAY NIGHT)
ISSUED AT 255 PM CDT THU JUN 4 2026
LOW-LEVEL SOUTH-SOUTHWESTERLY FLOW CONTINUES TO TRANSPORT
INCREASINGLY MOIST AIR INTO THE REGION, EVIDENCED BY DEWPOINTS
RUNNING ABOUT 15 TO 20 F HIGHER THAN WEDNESDAY AND WIDESPREAD
DIURNAL CUMULUS. A SUBTLE MID-LEVEL PERTURBATION IS ALSO PROMOTING
THE DEVELOPMENT OF ISOLATED TO SCATTERED SHOWERS ACROSS
SOUTHERN/SOUTHWESTERN MO THAT COULD SPREAD INTO CENTRAL AND
NORTHEASTERN MO THROUGH THIS EVENING WITH A STRAY THUNDERSTORM
POSSIBLE AS WELL.
FURTHER TO THE WEST ACROSS NORTHERN KS/EASTERN NE, AN UPPER-LEVEL
TROUGH IS DRIVING AN MCS THAT IS PROGGED TO TRACK SLOWLY
NORTHEASTWARD WITH TRAILING SHOWERS AND THUNDERSTORMS PROGRESSING
EASTWARD NORTH OF I-70 OVERNIGHT, SUPPORTED BY A VEERING, NOCTURNAL
LLJ. THESE SHOWERS AND THUNDERSTORMS ARE NOT EXPECTED TO REACH THE
CWA UNTIL FRIDAY MORNING WITH THE HIGHEST HREF PROBABILITIES (60 TO
80 PERCENT) OF MEASURABLE RAINFALL ACROSS NORTHEASTERN MO/WEST-
CENTRAL IL, BUT SOME CAMS HAVE SHOWERS AND THUNDERSTORM REACHING AS
FAR SOUTH AS I-70 AND EAST AS I-44 (MO) AND I-55 (IL) THROUGH LATE
MORNING AND EARLY AFTERNOON. HOWEVER, COVERAGE SHOULD BE DECREASING
THROUGH THAT TIME AS LARGE-SCALE ASCENT DEPARTS WITH THE THROUGH TO
THE EAST AND THE LLJ ABATES. SUBSEQUENT DEVELOPMENT OF SHOWERS AND
THUNDERSTORMS (LOCALLY SPEAKING) IS UNCERTAIN FRIDAY EVENING INTO
OVERNIGHT, SEEMING TO RELY ON A NOCTURNAL LLJ INTERFACING A
POTENTIAL REMNANT OUTFLOW BOUNDARY SOMEWHERE NORTH OF I-70
(NORTHEASTERN MO/WEST-CENTRAL IL) AND/OR A THUNDERSTORM CLUSTER/MCS
SAGGING SOUTHWARD INTO THE LLJ. IF THERE ARE THUNDERSTORMS IN THE
CWA DURING THE EVENING, 1500 TO 2500 J/KG MLCAPE AND 15 TO 25 KT OF
DEEP-LAYER WIND SHEAR WOULD SUPPORT TRANSIENT SEVERE THUNDERSTORMS
WITH DAMAGING WINDS AND MARGINALLY SEVERE HAIL. HOWEVER, CONFIDENCE
IS MUCH HIGHER IN SHOWERS AND THUNDERSTORMS DEVELOPING TO THE NORTH
AND NORTHWEST OF THE CWA, CLOSER TO A QUASI-STATIONARY FRONT, WHICH
IS REFLECTED BY HREF PROBABILITIES AS WELL, PRECLUDING MESSAGING OF
ANY SEVERE WEATHER AT THIS TIME. EVEN WITH MORNING SHOWERS AND
THUNDERSTORMS ON FRIDAY, BREAKING CLOUDS AND PREDOMINANTLY DRY
CONDITIONS DURING THE AFTERNOON WILL LEAD TO HIGH TEMPERATURES A
COUPLE DEGREES WARMER THAN TODAY.
PFAHLER
LONG TERM
(SATURDAY THROUGH NEXT THURSDAY)
ISSUED AT 255 PM CDT THU JUN 4 2026
ON SATURDAY, THE CWA WILL SPEND MOST, IF NOT ALL, OF THE DAYTIME
HOURS BETWEEN THE UPPER-LEVEL TROUGH PROPAGATING TO THE NORTHEAST
AND ANOTHER SOUTHERN STREAM LOW/TROUGH APPROACHING FROM THE SOUTH.
WITH A LACK OF DISCERNIBLE LOW-LEVEL FORCING MECHANISM EITHER, THE
LOCATION, TIMING, AND COVERAGE OF ANY SHOWERS AND THUNDERSTORMS
DEVELOPING IS HIGHLY UNCERTAIN. HOWEVER, AT LEAST ISOLATED SHOWERS
AND THUNDERSTORMS ARE EXPECTED DURING PEAK AFTERNOON AND EVENING
HEATING WITH A WEAK CAPPING INVERSION ADVERTISED IN FORECAST
SOUNDINGS. GREATER COVERAGE WOULD HAVE TO DEPEND ON EITHER A REMNANT
OUTFLOW BOUNDARY FROM MORNING THUNDERSTORMS AND/OR EARLIER ARRIVAL
OF THE SOUTHERN STREAM LOW/TROUGH. WITH LESS OVERALL
PRECIPITATION/CLOUDS AND SLIGHTLY WARMER 850-HPA TEMPERATURES, HIGH
TEMPERATURES ON SATURDAY ARE FORECAST TO BE WARMER AND IN THE MID-
80S TO AROUND 90 F.
THE AFOREMENTIONED UPPER-LEVEL LOW/TROUGH IS ANTICIPATED TO TRACK
NORTHWARD THROUGH THE CENTRAL PLAINS AND MID-MISSISSIPPI RIVER
VALLEY SUNDAY AND MONDAY WITH THE GREATEST CORRESPONDING SUPPORT FOR
SHOWERS AND THUNDERSTORMS IN ENSEMBLE MODEL GUIDANCE THOSE DAYS.
PROBABILITIES OF MEASURABLE RAINFALL PEAK EACH AFTERNOON AND EVENING
AT 60 TO 90 PERCENT ACROSS THE ENTIRE CWA. WITH GREATER COVERAGE AND
PREVALENCE OF PRECIPITATION AND CLOUDS, CONFIDENCE IS HIGH THAT
THOSE DAYS WILL BE RELATIVELY COOLER, BUT EXACT VALUES ARE VERY
UNCERTAIN AND SENSITIVE TO THOSE FACTORS WITH WIDER (5 TO 7 F) NBM
HIGH TEMPERATURE INTERQUARTILE RANGES. IT IS NOT OUT OF THE QUESTION
THAT TEMPERATURES REMAIN IN THE 70S F WHERE PRECIPITATION LINGERS
MOST OF THE DAY.
DEEP-LAYER WIND SHEAR SATURDAY THROUGH MONDAY WILL BE 20 KT OR LESS,
INDICATING THAT THUNDERSTORMS WILL BE UNORGANIZED OR VERY LOOSELY
ORGANIZED AT BEST DESPITE POTENTIALLY MODERATE AMOUNTS (1500 TO 3000
J/KG) OF INSTABILITY. THESE FACTORS LIMIT THE THREAT OF SEVERE
WEATHER AND FLASH FLOODING BUT ISOLATED MICROBURSTS WITH GUSTY WINDS
AND LOCALLY HEAVY RAINFALL WILL NEED TO BE MONITORED, CONSIDERING
THAT WARM RAIN PROCESSES WILL BE VERY EFFICIENT WITH PRECIPITABLE
WATER PROJECTED TO FLIRT WITH 2" OR THE 99TH CLIMATOLOGICAL
PERCENTILE IN COMBINATION WITH DEEP WARM CLOUD DEPTHS.
AFTER THE UPPER-LEVEL TROUGH DEPARTS LATE MONDAY, GLOBAL MODEL
GUIDANCE HAS SIGNIFICANT HEIGHT RISES TAKING PLACE ACROSS THE MID-
MISSISSIPPI RIVER VALLEY AS AN UPPER-LEVEL RIDGE BLOSSOMS IN PART OF
A DEVELOPING OMEGA BLOCK. IN EFFECT, THIS PATTERN ACTS TO STAGNATE
THE RESIDENT WARM AND MOIST AIRMASS WITH AIDED INFLUX OF WARMTH AND
MOISTURE UPON WEAK LOW-LEVEL SOUTHERLY FLOW. THIS EVOLUTION SUPPORTS
HIGH TEMPERATURES IN THE UPPER 80S TO LOW-90S F AND HEAT INDEX
VALUES REACHING AROUND 100 F EACH AFTERNOON WITH DEWPOINTS IN THE
70S F. THE AMOUNT OF ENSEMBLE MODEL MEMBERSHIP WITH SHOWERS AND
THUNDERSTORMS DECREASES EACH DAY AFTER MONDAY WITH THE INCREASINGLY
DOMINANT RIDGE.
PFAHLER
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1215 PM CDT THU JUN 4 2026
LARGELY DRY AND VFR FLIGHT CONDITIONS WILL CONTINUE THROUGH TONIGHT,
ASIDE FROM A STRAY SHOWER OR THUNDERSTORM IN CENTRAL/NORTHEASTERN MO
LATE THIS AFTERNOON/EVENING. HOWEVER, CONFIDENCE IN IMPACTS AT KCOU
OR KJEF IS TOO LOW TO MENTION. THERE IS HIGHER CONFIDENCE IN SHOWERS
AND THUNDERSTORMS ENTERING NORTHEASTERN MO/WEST-CENTRAL IL FRIDAY
MORNING, WITH IMPACTS MOST LIKELY AT KUIN. ELSEWHERE, CONFIDENCE IS
MUCH LOWER AT THIS TIME DUE TO LOWER EXPECTED COVERAGE.
PFAHLER
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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