685
FXUS63 KLSX 200717
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
217 AM CDT FRI JUN 20 2025
KEY MESSAGES
- A PROLONGED STRETCH OF DANGEROUS HEAT BEGINS TODAY. A HEAT
ADVISORY TAKES EFFECT AT NOON TODAY AND LASTS THROUGH TUESDAY.
THE MOST INTENSE HEAT WILL OCCUR IN THE ST. LOUIS METROPOLITAN
AREA WHERE AN EXTREME HEAT WATCH IS IN EFFECT FROM NOON SATURDAY
THROUGH TUESDAY.
SHORT TERM
(THROUGH LATE SATURDAY AFTERNOON)
ISSUED AT 213 AM CDT FRI JUN 20 2025
A PROLONGED PERIOD OF DANGEROUS HEAT WILL KICK OFF TODAY AS LOW-
LEVEL RIDGING EXITS TO THE EAST AND SOUTHWEST FLOW IS ESTABLISHED IN
THE AREA. THIS FLOW REGIME WILL ADVECT WARM AIR AND MOISTURE INTO
THE BI-STATE, CATAPULTING NOT ONLY OUR AMBIENT TEMPERATURES BUT OUR
HEAT INDEX VALUES AS WELL. TODAY'S APPARENT TEMPERATURES WILL
ECLIPSE THOSE OF YESTERDAY, WITH MOST OF OUR MISSOURI COUNTIES
REACHING WITHIN +/- 3 DEGREES OF THE CENTURY MARK. THIS IS A FAR CRY
FROM YESTERDAY'S RELATIVELY PLEASANT UPPER 80S. SATURDAY WILL ONLY
BE HOTTER AS HEIGHTS RISE ALOFT AND LOW-LEVEL WARM AIR AND MOISTURE
CONTINUE TO FILTER INTO THE AREA. OUR ILLINOIS COUNTIES ARE FORECAST
TO EXCEED 100 APPARENT TEMPERATURES ON SATURDAY IN ADDITION TO
MISSOURI CALLING FOR A 10+ DEGREE JUMP FROM TODAY'S VALUES. A HEAT
ADVISORY REMAINS IN EFFECT FOR PORTIONS OF CENTRAL AND NORTHEAST
MISSOURI TODAY THROUGH TUESDAY AND HAS BEEN EXPANDED TO INCLUDE THE
REST OF THE FORECAST AREA BEGINNING SATURDAY. THIS CHANGE IS DUE TO
INCREASING CONFIDENCE IN HEAT INDEX VALUES REACHING OR EXCEEDING 100
DEGREES FOR 4 CONSECUTIVE DAYS. AN EXTREME HEAT WATCH REMAINS IN
EFFECT FROM SATURDAY THROUGH TUESDAY FOR THE ST. LOUIS METROPOLITAN
AREA WHERE THE URBAN HEAT ISLAND EFFECT WILL BOOST HEAT INDEX VALUES
TO 105+ DEGREES.
JAJA
LONG TERM
(SATURDAY NIGHT THROUGH THURSDAY)
ISSUED AT 213 AM CDT FRI JUN 20 2025
THE AFOREMENTIONED DANGEROUS HEAT WILL CONTINUE SUNDAY THROUGH AT
LEAST TUESDAY. UPPER LEVEL RIDGING OVER THE AREA WILL ONLY BUILD,
AND SOUTHWESTERLIES WILL REMAIN IN PLACE AS HIGH PRESSURE BUILDS
OVER THE SOUTHEAST/MID-ATLANTIC USA. THIS HOLDING REGIME TAKES ANY
TALK OF RELIEF OUT OF THE QUESTION UNTIL IT BREAKS. HEAT INDEX
VALUES DURING THESE DAYS WILL BE SIMILAR TO PREVIOUSLY DESCRIBED -
AROUND 100 DEGREES WITH THE ST. LOUIS METROPOLITAN AREA CLOSER TO
105 DEGREES. SINCE CLOUD COVER WILL BE SHUNTED OUT OF THE AREA DUE
TO HIGH PRESSURE, THEORETICALLY THE ONLY WAY THESE VALUES WOULD BE
LOWER THAN FORECAST WOULD BE DUE TO BOUNDARY LAYER MIXING. THIS
WOULD LOWER DEWPOINT TEMPERATURES AND KICK OUT SOME OF THE
HUMIDITY. HOWEVER, IT WOULD ALSO RAISE TEMPERATURES, SO UNLESS AN
IMPRESSIVE AMOUNT OF DRY AIR IS MIXED ON ANY GIVEN DAY (WHICH
DOESN'T APPEAR LIKELY), MIXING WILL NOT MAKE MUCH OF A DIFFERENCE.
PART OF WHAT MAKES THIS HEAT SO DANGEROUS IS THE LONGEVITY OF WARM
LOW TEMPERATURES AS WELL AS HOT HIGHS. BETWEEN SUNDAY MORNING AND
TUESDAY MORNING, OUR COOLEST LOW ONLY FALLS TO 72 DEGREES WITH A
DEWPOINT OF 69. HUMID NIGHTS LIKE THESE WILL NOT PROVIDE RELIEF TO
ANY INDIVIDUALS WHO MUST BE OUTSIDE OR TO THOSE WITHOUT AIR
CONDITIONING FOR PROLONGED PERIODS. IT JUST WON'T BE COOL ENOUGH
TO ACHIEVE THAT. THIS IS ESPECIALLY TRUE IN THE ST. LOUIS AREA
WHERE LOWS WILL FALL WITHIN THE 75 TO 80 DEGREE RANGE EACH NIGHT.
WHEN THE HEAT WILL BREAK IS STILL UNCERTAIN. A MID-LEVEL TROUGH
PASSING THROUGH THE NORTHERN ROCKIES/SOUTH CENTRAL CANADA WILL SPUR
A SURFACE CYCLONE AND COLD FRONT MONDAY INTO TUESDAY. MODELS ARE IN
CONSENSUS THAT THIS COLD FRONT WILL BUCKLE NORTH BEFORE PASSING INTO
OUR CWA, BUT HOW FAR IT GETS IS STILL UNCERTAIN. IF WE GET BLOW-OFF
CLOUD COVER OR WARM SECTOR PRECIPITATION, THAT WOULD DENT THE HEAT.
HOWEVER, IT'S NOT CERTAIN THAT'LL HAPPEN. IT DEPENDS ON HOW MUCH THE
MID-LEVEL TROUGH IS ABLE TO ERODE THE RIDGE OVERHEAD. IF THE
TROUGH IS IMPACTFUL, THE HEAT WILL END SOONER. IF THE RIDGE HOLDS
FIRM, DANGEROUS HEAT MAY CONTINUE INTO WEDNESDAY AND POSSIBLY
EVEN THURSDAY FOR SOME OF THE FORECAST AREA.
JAJA
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1044 PM CDT THU JUN 19 2025
CONFIDENCE REMAINS HIGH IN DRY AND VFR FLIGHT CONDITIONS THROUGH
THE TAF PERIOD AT ALL LOCAL TERMINALS. WINDS WILL CONTINUE TO
BECOME SOUTHERLY THROUGH THE MORNING, STRENGTHENING LATER IN THE
MORNING.
ELMORE
CLIMATE
ISSUED AT 1225 PM CDT THU JUN 19 2025
RECORD MAXIMUM TEMPERATURES AT ST. LOUIS, MO (STL), COLUMBIA, MO (COU),
AND QUINCY, IL (UIN) ALONG WITH THE YEAR OF THE RECORD:
| 6/21 | 6/22 | 6/23 | 6/24 | 6/25
--------------------------------------------------------------------
STL | 99 (1988) | 102 (1930) | 101 (1930) | 102 (1988) | 103 (2024)
| | | | |
COU | 98 (1988) | 100 (1988) | 100 (1988) | 103 (1988) | 102 (1988)
| | | | |
UIN | 100 (1988) | 100 (1930) | 100 (1934) | 99 (1988) | 102 (1931)
LSX WATCHES/WARNINGS/ADVISORIES
MO...HEAT ADVISORY FROM NOON SATURDAY TO 9 PM CDT TUESDAY FOR
CRAWFORD MO-FRANKLIN MO-GASCONADE MO-IRON MO-LEWIS MO-
LINCOLN MO-MADISON MO-MARION MO-MONTGOMERY MO-PIKE MO-RALLS
MO-REYNOLDS MO-SAINT FRANCOIS MO-SAINTE GENEVIEVE MO-WARREN
MO-WASHINGTON MO.
EXTREME HEAT WATCH FROM SATURDAY AFTERNOON THROUGH TUESDAY
EVENING FOR JEFFERSON MO-SAINT CHARLES MO-SAINT LOUIS CITY
MO-SAINT LOUIS MO.
HEAT ADVISORY FROM NOON TODAY TO 9 PM CDT TUESDAY FOR AUDRAIN MO-
BOONE MO-CALLAWAY MO-COLE MO-KNOX MO-MONITEAU MO-MONROE MO-
OSAGE MO-SHELBY MO.
IL...HEAT ADVISORY FROM NOON SATURDAY TO 9 PM CDT TUESDAY FOR ADAMS
IL-BOND IL-BROWN IL-CALHOUN IL-CLINTON IL-FAYETTE IL-GREENE
IL-MACOUPIN IL-MARION IL-MONTGOMERY IL-PIKE IL-RANDOLPH IL-
WASHINGTON IL.
EXTREME HEAT WATCH FROM SATURDAY AFTERNOON THROUGH TUESDAY
EVENING FOR JERSEY IL-MADISON IL-MONROE IL-SAINT CLAIR IL.
WFO LSX
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page