698
FXUS63 KLSX 161116
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
616 AM CDT SAT AUG 16 2025
KEY MESSAGES
- DANGEROUS HEAT AND HUMIDITY IS EXPECTED TO CONTINUE THROUGH
MONDAY, AND POTENTIALLY INTO TUESDAY FOR PORTIONS OF THE AREA.
- BETTER RAIN CHANCES RETURN LATE TUESDAY INTO MIDWEEK.
SHORT TERM
(THROUGH LATE SUNDAY AFTERNOON)
ISSUED AT 333 AM CDT SAT AUG 16 2025
IR SATELLITE SHOWS CLOUD DEBRIS THAT IS PRIMARILY IN THE UPPER
LEVELS AS A RESULT OF DECAYING CONVECTION OVER ILLINOIS. MUCH OF THE
CLOUD COVER HAS STAYED ALONG AND EAST OF THE MISSISSIPPI RIVER,
THINNING OUT WESTWARD OVER MISSOURI. SURFACE OBSERVATIONS SHOWS
FAIRLY UNIFORM TEMPERATURES RANGING FROM THE UPPER 70S TO AROUND 80
DEGREES WITH THE ST. LOUIS METRO BEING THE EXCEPTION DUE TO THE
URBAN HEAT ISLAND (84 DEGREES AS OF 08Z).
THE UPPER LEVEL RIDGE, CURRENTLY CENTERED OVER MISSOURI, HAS STEERED
MORE ACTIVE WEATHER TO THE NORTH/EAST AND WILL CONTINUE TO BE THE
PRIMARY FACTOR IN THE CONTINUATION OF DANGEROUS HEAT THROUGH THE
REMAINDER OF THE WEEKEND. THE ONE CAVEAT TO WHAT IS EXPECTED TO BE A
MOSTLY DRY FORECAST IS THE POTENTIAL FOR AN ISOLATED SHOWER AND/OR
THUNDERSTORM THIS AFTERNOON/EARLY EVENING. OUTFLOW FROM EARLIER
CONVECTION CONTINUES TO SLOWLY SINK SOUTHWARD THROUGH THE FORECAST
AREA THIS MORNING, LIKELY BECOMING MORE DIFFUSE WITH TIME. HRRR HAS
BEEN PERSISTENT IN DEVELOPING ISOLATED CONVECTION ALONG THE OUTFLOW,
AND WHILE IT HAS ITS LIMITATIONS, A NUMBER OF OTHER HI-RES MODELS
HAVE BEGUN TO INDICATE THE SAME. HOWEVER, GUIDANCE MAY NOT BE
COMPLETELY RELYING ON THIS MORNING'S OUTFLOW, BUT RATHER AN
ADDITIONAL COMPOSITE OUTFLOW FROM CONVECTION CURRENTLY OVER SOUTH
DAKOTA.
PAINTBALL PLOTS ARE IN GOOD AGREEMENT WITH DRIVING THE CONVECTION
FROM SOUTH DAKOTA THROUGH SOUTHERN WISCONSIN AND NORTHERN ILLINOIS.
THIS SENDS THE SECOND OUTFLOW SOUTHEAST INTO THE AREA, INTERACTING
WITH THE REMNANT, DIFFUSE OUTFLOW THAT HANGS UP THROUGH THE AREA
THIS AFTERNOON. MEANWHILE, HREF GUIDANCE SHOWS MEAN LAYER CAPE
BUILDING BETWEEN 2800-3500 J/KG BY MID-AFTERNOON IN A WEAKLY
SHEARED (10-15 KNOTS) ENVIRONMENT. CONSIDERING SUBSIDENCE ALOFT,
THERE'S NOT A HIGH CHANCE THAT MUCH WILL MATERIALIZE AND WHAT DOES
WOULD STRUGGLE TO LAST LONG. TO PINPOINT ISOLATED CELLS OF THIS
NATURE IS EXTREMELY DIFFICULT WITH THE LIMITING FACTORS PRESENT,
BUT I SUPPOSE IT CANNOT BE ENTIRELY RULED OUT WITH A NUMBER OF
SHORT RANGE, HI-RES GUIDANCE DEPICTING SOME SEMBLANCE OF ISOLATED
SHOWERS AND/OR THUNDERSTORMS, MAINLY ACROSS THE SOUTHEASTERN HALF
OF THE CWA. THE LIMITED COVERAGE, SHORT-LIVED NATURE AND LOW
POTENTIAL DID NOT GIVE MUCH MORE CONFIDENCE THAN YESTERDAY'S
FORECAST AND THEREFORE MAINTAINED POPS JUST BELOW 15 PERCENT. A
SIMILAR THEME LIKELY PLAYS OUT SUNDAY, DEPENDENT ON CONVECTION TO
THE NORTH AND ORIENTATION OF THE MID/UPPER LEVEL RIDGING PATTERN,
WHICH REMAINS INTACT AND ENCOMPASSES MUCH OF THE AREA.
OUTSIDE OF ANY ISOLATED SHOWER/THUNDERSTORM, TEMPERATURES WILL CLIMB
BACK INTO THE MID/UPPER 90S EACH AFTERNOON WITH DEWPOINTS IN THE LOW
TO MID-70S. HEAT INDEX VALUES WILL REACH SIMILAR TERRITORY AS
FRIDAY, MAYBE A TOUCH WARMER IN SOME LOCATIONS. THE ONE CHANGE TO
THE HEADLINES, IN COORDINATION WITH NWS PADUCAH/SPRINGFIELD, WAS
TO INCLUDE REYNOLDS, IRON AND MADISON COUNTIES IN THE HEAT
ADVISORY (SEE LONG TERM FOR MORE DETAILS).
MAPLES
LONG TERM
(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 333 AM CDT SAT AUG 16 2025
LREF 500 MB MEAN HEIGHTS MAINTAIN LONGWAVE UPPER LEVEL RIDING OVER A
LARGE PORTION OF THE CONUS MONDAY, CONTINUING THE STRETCH OF HEAT
AND DANGEROUS HEAT INDEX VALUES. MEAN HEIGHTS OF 594 DAM ARE
CENTERED OVERHEAD, SUGGESTING YET ANOTHER DAY OF HEAT INDICES THAT
EXCEED 100 DEGREES AREAWIDE. THE SUBTLE CHANGE IS THE SLIGHT
FLATTENING TO THE TOP OF THE RIDGE ACROSS THE UPPER MISSISSIPPI
VALLEY, WHERE ACTIVE WEATHER CONTINUES TO BE FOCUSED. THIS MAY BE
THE SUBTLE START TO THE WESTWARD SHIFT IN THE RIDGE AS WE HEAD INTO
THE DAY TUESDAY.
CONFIDENCE IS SOMEWHAT SPLIT ACROSS THE REGION BY TUESDAY. THERE HAS
BEEN GROWING CONFIDENCE IN HEAT PERSISTING WITH DANGEROUS HEAT INDEX
VALUES MORE LIKELY ALONG AND SOUTH OF I-70. NBM IQR REMAINS VERY
TIGHT WITH ONLY A FEW DEGREES OF SEPARATION IN HIGH TEMPERATURES
BETWEEN THE 25TH/75TH PERCENTILES (MID/UPPER 90S). ADDITIONALLY,
LREF PROBABILITIES FOR HEAT INDEX VALUES OF 100+ DEGREES CONTINUE TO
INCH HIGHER FOR THESE AREA WITH 60-70% PROBABILITIES EXTENDING ALONG
I-70 FROM JEFFERSON CITY TO UNION AND 70-85% PROBABILITIES OVER EAST-
CENTRAL AND SOUTHEAST MISSOURI INTO SOUTHWEST ILLINOIS. AS MENTIONED
IN THE SHORT TERM, REYNOLD, IRON AND MADISON COUNTIES WERE ADDED TO
THE ADVISORY THIS MORNING GIVEN THE INCREASING CONFIDENCE IN
TUESDAY'S HEAT WITH THE INCREASING POTENTIAL THAT THE HEADLINES WILL
NEED TO BE EXTENDED ACROSS THE SOUTHERN SECTIONS OF THE CWA.
THE UNCERTAINTY IS ACROSS NORTHEAST MISSOURI AND WEST-CENTRAL
ILLINOIS, WHICH MAY BE MORE SUSCEPTIBLE TO CONVECTIVE POTENTIAL AS
THE ACTIVE STORM TRACK TO THE NORTH SHIFTS SOUTH AND WESTWARD WITH
THE REORIENTATION OF THE UPPER LEVEL RIDGE OVER THE INTERMOUNTAIN
WEST. GLOBAL GUIDANCE SHOWS THE COLD FRONT EXTENDING WEST/EAST IN
THE VICINITY OF THE MISSOURI/IOWA TUESDAY AFTERNOON WITH AN
APPROACHING UPPER LEVEL SHORTWAVE. EVEN IF PRECIPITATION DOESN'T PAN
OUT UNTIL LATER IN THE DAY, CLOUD COVER STREAMING OFF THUNDERSTORMS
COULD CURB THE POTENTIAL FOR WARMER HIGHER TEMPERATURES. THIS IS
ALSO WHERE LREF TEMPERATURES SPREADS (5-8 DEGREES) ARE GREATEST
ACROSS THE REGION, RESULTING IN LESS CONFIDENCE THAN AREAS TO THE
SOUTH.
THERE IS GREATER CONFIDENCE IN THE COLD FRONT MAKING IT INTO THE
AREA LATE TUESDAY INTO WEDNESDAY WITH BETTER CHANCES FOR SHOWERS AND
THUNDERSTORMS THROUGH THE MIDWEEK PERIOD, BRINGING COOLER (NEAR
NORMAL) TEMPERATURES FOR THE LATER HALF OF THE WEEK. SPREAD THEN
BEGINS TO INCREASE AGAIN LATER NEXT WEEK AS AN ADDITIONAL
REINFORCING FRONT APPROACHES WITH TIMING/PLACEMENT LESS CERTAIN.
GENERALLY SPEAKING, IT LOOKS LIKE COOLER WEATHER IS FAVORED ONCE THE
INITIAL FRONT MOVES THROUGH WEDNESDAY.
MAPLES
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 614 AM CDT SAT AUG 16 2025
HIGH PRESSURE OVER THE REGION WILL KEEP THE ACTIVE STORM TRACK TO
THE NORTH/NORTHEAST WITH HIGH CLOUDS STREAMING OVERHEAD FROM TIME
TO TIME. AN ISOLATED SHOWER OR THUNDERSTORM CANNOT BE ENTIRELY
RULED THIS AFTERNOON, BUT CHANCES ARE VERY LIMITED. ANY MID-LEVEL
CLOUD DEVELOPMENT SHOULD REMAIN VFR WITH VFR PERSISTING THROUGH
THE PERIOD.
MAPLES
LSX WATCHES/WARNINGS/ADVISORIES
MO...HEAT ADVISORY UNTIL 8 PM CDT MONDAY FOR AUDRAIN MO-BOONE MO-
CALLAWAY MO-COLE MO-CRAWFORD MO-FRANKLIN MO-GASCONADE MO-
IRON MO-JEFFERSON MO-KNOX MO-LEWIS MO-LINCOLN MO-MADISON MO-
MARION MO-MONITEAU MO-MONROE MO-MONTGOMERY MO-OSAGE MO-PIKE
MO-RALLS MO-REYNOLDS MO-SAINT CHARLES MO-SAINT FRANCOIS MO-
SAINT LOUIS CITY MO-SAINT LOUIS MO-SAINTE GENEVIEVE MO-
SHELBY MO-WARREN MO-WASHINGTON MO.
IL...HEAT ADVISORY UNTIL 8 PM CDT MONDAY FOR ADAMS IL-BOND IL-BROWN
IL-CALHOUN IL-CLINTON IL-FAYETTE IL-GREENE IL-JERSEY IL-
MACOUPIN IL-MADISON IL-MARION IL-MONROE IL-MONTGOMERY IL-
PIKE IL-RANDOLPH IL-SAINT CLAIR IL-WASHINGTON IL.
WFO LSX
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