057
FXUS63 KLSX 052314
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
614 PM CDT FRI JUN 5 2026
KEY MESSAGES
- DAILY, VARYING CHANCES OF SHOWERS AND THUNDERSTORMS WILL EXIST
THROUGH TUESDAY. THERE IS A THREAT OF LOCALLY HEAVY RAINFALL
SUNDAY AND MONDAY.
- TEMPERATURES AND HUMIDITY WILL INCREASE AFTER MONDAY WITH PEAK
AFTERNOON/EVENING HEAT INDEX VALUES POTENTIALLY REACHING 100 F.
SHORT TERM
(THROUGH LATE SATURDAY NIGHT)
ISSUED AT 225 PM CDT FRI JUN 5 2026
WITH THIS MORNING'S UPPER-LEVEL TROUGH DEPARTING AND THE NEXT TROUGH
PASSING NORTH OF THE MID-MISSISSIPPI RIVER VALLEY, ANY REDEVELOPMENT
OF SHOWERS AND THUNDERSTORMS THIS EVENING AND OVERNIGHT IS UNCERTAIN
OWING TO A LACK OF CLEAR LOW-LEVEL FORCING MECHANISM. A FEW CAMS
HAVE INCONSISTENTLY INDICATED POTENTIAL SHOWERS AND THUNDERSTORMS IN
NORTHEASTERN MO/WEST-CENTRAL IL THIS EVENING AS WELL AS CLUSTERS/MCS
OF SHOWERS AND THUNDERSTORMS ACROSS IA AND NORTHERN IL ALONG A QUASI-
STATIONARY FRONT SAGGING SOUTHWARD INTO THE LLJ OVERNIGHT. HOWEVER,
LATEST HREF PROBABILITIES OF MEASURABLE RAINFALL ARE 20 PERCENT OR
LESS, FURTHER DIMINISHING CONFIDENCE. IF THUNDERSTORMS OCCUR THIS
EVENING, 2000 TO 3000 J/KG MLCAPE AND MODEST 15 TO 25 KT OF DEEP-
LAYER WIND SHEAR, A BRIEFLY SEVERE THUNDERSTORM WITH DAMAGING WINDS
AND MARGINALLY SEVERE HAIL CANNOT BE RULED OUT. BUT THIS
CONDITIONALITY AND AN ALREADY MARGINAL ENVIRONMENT KEEPS CONFIDENCE
TOO LOW TO ADVERTISE THE THREAT.
ON SATURDAY, THE CWA WILL BE SANDWICHED BETWEEN THE AFOREMENTIONED
UPPER-LEVEL TROUGH PASSING TO THE NORTHEAST AND ANOTHER SOUTHERN
STREAM LOW/TROUGH APPROACHING FROM THE SOUTH. SINCE THE QUASI-
STATIONARY FRONT IS ALSO EXPECTED TO STAY NORTHEAST OF THE CWA, LOW-
LEVEL FORCING MECHANISMS ARE ONCE AGAIN NOT CLEAR. WITH A WEAK
CAPPING INVERSION, AT LEAST ISOLATED SHOWERS AND THUNDERSTORMS ARE
EXPECTED DURING PEAK AFTERNOON HEATING OF THE WARM AND MOIST
AIRMASS. THERE ARE TIMING DIFFERENCES IN THE ARRIVAL OF LARGE-SCALE
ASCENT LEADING THE APPROACHING LOW/TOUGH WITH THE EARLIEST BEING
LATE SATURDAY AFTERNOON, WHICH WOULD SUPPORT INCREASING COVERAGE OF
SHOWERS AND THUNDERSTORMS IF THERE IS AN OVERLAP WITH PEAK HEATING.
THE EXACT LOCATION, COVERAGE, AND TIMING OF THUNDERSTORMS IS
UNCLEAR, WITH CAMS ALSO ADVERTISING NOTABLY DIFFERENT SOLUTIONS. AN
ISOLATED MICROBURST WITH GUSTY WINDS IS POSSIBLE, BUT SUB-15 KT DEEP-
LAYER WIND SHEAR WILL LIMIT THE THREAT OF SEVERE WEATHER. HIGH
TEMPERATURES WILL GENERALLY BE SIMILAR TO TODAY, IF NOT A COUPLE OF
DEGREES WARMER WHERE CLOUDS ARE LESS PREVALENT DURING THE AFTERNOON
BETWEEN EARLY DAY STRATOCUMULUS AND INCREASING UPPER-LEVEL CLOUDS.
PFAHLER
LONG TERM
(SUNDAY THROUGH NEXT FRIDAY)
ISSUED AT 225 PM CDT FRI JUN 5 2026
THE UPPER-LEVEL LOW/TROUGH WILL PROPAGATE NORTHWARD OVER THE CENTRAL
PLAINS AND MID-MISSISSIPPI RIVER VALLEY SUNDAY AND MONDAY,
ACCOMPANIED BY THE MOST FAVORABLE PERIOD OF MORE WIDESPREAD SHOWERS
AND THUNDERSTORMS WITH 60 TO 90 PERCENT OF ENSEMBLE MEMBERSHIP
CONTAINING MEASURABLE RAINFALL. PROBABILITIES ARE HIGHEST DURING
EACH AFTERNOON AND EVENING BUT THERE ARE INDICATIONS THAT NOCTURNAL
LLJS COULD ALSO SUPPORT SOME OVERNIGHT SHOWERS AND THUNDERSTORMS.
THERE WILL BE A LOCALLY HEAVY RAINFALL THREAT DURING THIS TIME
PERIOD WITH PRECIPITABLE WATER NEARING 2" (99TH CLIMATOLOGICAL
PERCENTILE) AND VERY DEEP WARM CLOUD DEPTHS COMBINED WITH KINEMATIC
PROFILES SUGGESTING POTENTIAL BACKBUILDING OR TRAINING OF SOME
THUNDERSTORMS. HOWEVER, FLASH FLOODING WOULD CONCEPTUALLY REQUIRE
LOCATIONS TO RECEIVE MULTIPLE ROUNDS OF HEAVY RAINFALL AND/OR
THUNDERSTORMS TO LOOSELY ORGANIZE INTO MCSS OR CLUSTERS, WHICH
CANNOT BE SAID WITH MUCH CONFIDENCE AT THIS RANGE. THE MAJORITY OF
THE NBM HIGH TEMPERATURE DISTRIBUTION IS COOLER (UPPER 70S TO 80S F)
BOTH SUNDAY AND MONDAY, BUT HOW COOL TEMPERATURES ACTUALLY REMAIN
WILL COME DOWN TO THE AMOUNT OF PRECIPITATION AND CLOUD COVER.
FOLLOWING THE DEPARTURE OF THE UPPER-LEVEL LOW/TROUGH LATE MONDAY,
GLOBAL MODEL GUIDANCE CONTINUES TO ADVERTISE A BLOSSOMING RIDGE
DOMINATING THE MID-MISSISSIPPI RIVER VALLEY WITHIN VARYING
DEPICTIONS OF AN OMEGA BLOCK TUESDAY THROUGH LATE NEXT WEEK. IN THIS
PATTERN, THE WARM AND MOIST AIRMASS WILL REMAIN IN PLACE AND EVEN BE
REINFORCED BY WEAK, BUT PERSISTENT LOW-LEVEL SOUTHERLY FLOW. AS 850-
HPA TEMPERATURES RISE TO NEAR THE 99TH CLIMATOLOGICAL PERCENTILE AND
THE RIDGE INHIBITS DAILY SHOWER AND THUNDERSTORM DEVELOPMENT, HIGH
TEMPERATURES WILL WARM TO THE UPPER 80S TO MID-90S F. WITH DEWPOINTS
IN THE 70S F, PEAK AFTERNOON AND EVENING HEAT INDEX VALUES ARE
PROJECTED TO REACH 100 F, BUT VALUES WILL DEPEND ON THE BALANCE OF
DIURNAL BOUNDARY LAYER MIXING ALLOWING WARMER TEMPERATURES WITH
LOWERING DEWPOINTS.
PFAHLER
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 614 PM CDT FRI JUN 5 2026
VFR CONDITIONS ARE EXPECTED TO BE ACCOMPANIED BY LIGHT SOUTH AND
SOUTHWESTERLY FLOW THROUGH TONIGHT. BY SATURDAY, THERE IS THE LOW
POTENTIAL THAT AN ISOLATED THUNDERSTORM COULD IMPACT ANY OF THE
TERMINALS. WITHIN THE BROADER SPREAD OF LOW POTENTIAL (15%) ARE
LOCALLY HIGHER CHANCES (25-30%) AROUND KJEF/KCOU AND KUIN. MANY OF
THESE WILL BE HIT-OR-MISS AND MAY NOT IMPACT ANY TERMINAL AT ALL.
HOWEVER, A DISTURBANCE OVER OKLAHOMA WILL CONTINUE TO ADVECT
MOISTURE INTO THE REGION ON THE BACK SIDE OF A SURFACE HIGH
PRESSURE RIDGE, AND A SEPARATE, LINGERING BOUNDARY OVER NORTHERN
MISSOURI AND WEST CENTRAL ILLINOIS MAY TRIGGER A FEW ISOLATED TO
WIDELY SCATTERED THUNDERSTORMS SATURDAY AFTERNOON. THUNDERSTORMS
WILL BE CAPABLE OF LOCALLY HEAVY RAIN WITH MVFR CIGS (3K FEET) AND
VIS (4SM). THUNDERSTORMS THAT DEVELOP ARE EXPECTED TO FADE
THROUGH SATURDAY AFTERNOON WITH THE LOSS OF DAYTIME HEATING.
BETTER CHANCES ARRIVE LATE SATURDAY NIGHT, JUST BEYOND THE TAF
PACKAGE.
MAPLES
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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