766
FXUS63 KLSX 191733
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
1233 PM CDT THU JUN 19 2025
KEY MESSAGES
- A PROLONGED PERIOD OF HEAT IS EXPECTED SATURDAY THROUGH AT LEAST
EARLY NEXT WEEK, AND POSSIBLY LONGER. HEAT IMPACTS ARE EXPECTED,
INCLUDING LIKELY SOME SIGNIFICANT IMPACTS, WITH HIGHEST
CONFIDENCE IN THE ST. LOUIS METRO AREA. AN EXTREME HEAT WATCH
HAS BEEN ISSUED FOR THIS AREA COVERING SATURDAY THROUGH TUESDAY.
SHORT TERM
(THROUGH LATE FRIDAY AFTERNOON)
ISSUED AT 338 AM CDT THU JUN 19 2025
WHILE ATTENTION IS SHIFTING TO THE POTENTIAL FOR AN EXTENDED PERIOD
OF IMPACTFUL HEAT OVER THE WEEKEND AND BEYOND, WE STILL HAVE A FEW
THUNDERSTORMS TO CONTEND WITH AS A COLD FRONT PUSHES THROUGH THE
AREA.
AS OF 3 AM, A DISORGANIZED LINE OF THUNDERSTORMS CONTINUED TO
SLOWLY PUSH THROUGH SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS,
LIKELY DUE TO A COMBINATION OF CONVERGENCE ALONG THE FRONT AND
MODEST LINGERING INSTABILITY (500-1000J/KG MLCAPE). THIS ACTIVITY
HAS BEEN RATHER PERSISTENT, BUT HAS NOT SHOWN MUCH IN THE WAY OF
ORGANIZATION OR SEVERE POTENTIAL IN SEVERAL HOURS. HOWEVER, THERE
REMAINS JUST ENOUGH EFFECTIVE SHEAR (30-40KT) AND THE
AFOREMENTIONED INSTABILITY TO SUPPORT A LOW END THREAT OF A STRAY
DAMAGING WIND GUST BEFORE ABOUT 5 AM. AFTERWARDS, THIS ACTIVITY
IS LIKELY TO SINK SOUTH OF THE AREA, AND DRY CONDITIONS ARE
EXPECTED THEREAFTER.
MEANWHILE, A FEW AREAS OF PATCHY FOG HAVE DEVELOP IN THE WAKE OF
THESE SHOWERS, AND THIS MAY EXPAND A BIT THROUGH THE EARLY MORNING.
WE DON'T EXPECT THIS TO BE WIDESPREAD, BUT FOLKS SHOULD BE PREPARED
FOR CHANGING VISIBILITIES OUT ON THE ROADS EARLY THIS MORNING,
MAINLY IN RURAL LOW-LYING AREAS AND RIVER VALLEYS.
AS WE HEAD INTO THE AFTERNOON, DRY AND SEASONABLY WARM CONDITIONS
CAN BE EXPECTED TODAY BEHIND THE COLD FRONT, AND IT IS RECOMMENDED
THAT IF YOU HAVE OUTDOOR ACTIVITIES THAT NEED TO GET DONE, TODAY IS
THE DAY TO DO IT. THAT IS BECAUSE AN EXTENDED PERIOD OF HEAT IS ON
THE WAY FRIDAY ONWARD, AND TODAY IS LIKELY TO BE THE MOST
COMFORTABLE DAY OVER THE NEXT SEVERAL, AND POSSIBLY A WEEK OR MORE.
UNTIL THEN, ENJOY THE AFTERNOON OF MID 80S AND REASONABLY HUMIDITY.
OVERNIGHT, A FEW MORE PATCHES OF RIVER VALLEY FOG WILL ALSO BE
POSSIBLE, BUT CONFIDENCE IS LOW THAT THIS WILL OCCUR OUTSIDE OF A
FEW SPOTS IN THE OZARKS THAT REMAIN SHELTERED FROM SLOWLY INCREASING
SOUTHERLY WINDS.
BRC
LONG TERM
(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 338 AM CDT THU JUN 19 2025
THE PRIMARY FOCUS IN THE EXTENDED FORECAST PERIOD CONTINUES TO BE AN
EXTENDED PERIOD OF HEAT, WHICH WILL FEATURE THE WARMEST CONDITIONS
OF THE YEAR SO FAR BY A SIGNIFICANT MARGIN. AT THIS POINT, HEAT
IMPACTS APPEAR TO BE LIKELY, WITH SOME SIGNIFICANT IMPACTS POSSIBLE.
AS OF NOW, WE HAVE THE HIGHEST CONFIDENCE IN SIGNIFICANT IMPACTS
ACROSS THE ST. LOUIS METRO AREA, WHERE THE URBAN HEAT ISLAND EFFECT
INCREASES THE POTENTIAL CEILING OF TEMPERATURES (AND FLOOR OF LOW
TEMPERATURES).
BY FRIDAY, A LARGE RIDGE OF HIGH PRESSURE IS EXPECTED TO BUILD
ACROSS THE MISSISSIPPI RIVER VALLEY AND EVENTUALLY SPREAD ACROSS THE
ENTIRE EASTERN HALF OF THE U.S. AS THIS OCCURS, SIGNIFICANT
TEMPERATURE ANOMALIES ARE EXPECTED TO DEVELOP AND PERSIST ACROSS A
VERY LARGE AREA, REMAINING IN PLACE FROM FRIDAY THROUGH EARLY NEXT
WEEK, AND POSSIBLY LONGER. THE CORE OF THIS HEAT DOME IS EXPECTED TO
BE LOCATED ACROSS THE UPPER MIDWEST AND GREAT LAKES REGION, WHERE
ENSEMBLE MEAN 850 MB TEMPERATURES AND 500 MB HEIGHT VALUES ARE
CURRENTLY FORECAST TO REACH OR EXCEED THE 99TH PERCENTILE RELATIVE
TO CLIMATOLOGY, AND IN SOME CASES NEAR THE CLIMATOLOGICAL MAXIMUM.
THIS PERSISTS FOR SEVERAL DAYS, WITH THE GREATEST MAGNITUDE BETWEEN
SATURDAY AND MONDAY. LOCALLY THESE ANOMALIES ARE A LITTLE BIT LOWER
THAN THAT, BUT ARE STILL NEAR THE 90TH PERCENTILE FOR MULTIPLE DAYS.
AS SUCH, IT IS A NEAR CERTAINTY THAT WE WILL WARM QUICKLY FRIDAY
ONWARD, WITH AFTERNOON TEMPERATURES LIKELY TO REACH WELL INTO THE
LOW TO MID 90S, AND MAYBE EVEN THE UPPER 90S IN THE ST. LOUIS METRO
AREA, WITH HIGH HUMIDITY THAT KEEPS LOW TEMPERATURES IN THE 70S.
THIS IS EXPECTED TO PERSIST FOR SEVERAL DAYS, WITH HIGHEST
CONFIDENCE BETWEEN SATURDAY AND MONDAY, WHEN PRECIPITATION IS NOT
LIKELY TO PROVIDE RELIEF, AND THE WARMEST TEMPERATURES ALOFT ARE
STILL IN PLACE. THIS MAY ALSO CONTINUE TUESDAY AND WEDNESDAY AS
WELL, ALTHOUGH THERE IS LOWER CONFIDENCE ON THESE DAYS AS THE UPPER
RIDGE SHIFTS SLIGHTLY EASTWARD, AND THE POTENTIAL FOR SHOWERS AND
THUNDERSTORMS GRADUALLY INCREASES.
THAT BEING SAID, WE HAVE HIGH CONFIDENCE OF HEAT INDEX VALUES
REACHING NEAR OR ABOVE 100 DEGREES FOR SEVERAL CONSECUTIVE DAYS, AND
LIKELY TO 105 OR MORE IN THE ST. LOUIS METRO AREA THANKS TO THE
EFFECT OF THE URBAN HEAT ISLAND. CONSIDERING THIS, LOW TEMPERATURES
IN THE MID TO UPPER 70S, THE FACT THAT THIS IS THE FIRST SUCH HEAT
OF THE YEAR, THE ADDED DURATION COMPONENT, AND THE INCREASED
VULNERABILITY IN THE METRO AREA (ESPECIALLY IN AREAS WITH
SIGNIFICANT TORNADO DAMAGE), WE HAVE OPTED TO PULL THE TRIGGER ON AN
EXTREME HEAT WATCH FOR THE ST. LOUIS METRO AREA (AND METRO EAST) FOR
SATURDAY THROUGH TUESDAY. WHILE THE WINDOW MAY ULTIMATELY BE
SHORTENED BY SHOWERS AND THUNDERSTORMS MID WEEK, WE FEEL THAT
CONFIDENCE IS HIGH ENOUGH, AND THE BENEFIT OF EXTRA LEAD TIME IN
THIS CASE IS GREAT ENOUGH, TO ACCEPT THE POTENTIAL RISK OF NOT QUITE
TECHNICALLY MEETING THE DURATION CRITERIA (105 DEGREE HEAT INDEX FOR
4+ DAYS).
IN ADDITION, ADDITIONAL HEADLINES MAY ALSO BE NEEDED IN ADDITIONAL
AREAS OUTSIDE OF THE METRO AREA IN FUTURE FORECASTS, MOST LIKELY IN
THE FORM OF A HEAT ADVISORY. IN THESE AREAS, THE CURRENTLY FORECAST
HEAT INDEX VALUES ARE MORE SUGGESTIVE OF LOWER-END IMPACTS MORE
FITTING OF AN ADVISORY, AND CONFIDENCE IS A BIT TOO LOW IN THOSE
AREAS TO ISSUE A HEADLINE JUST YET. HOWEVER, I WANT TO STRESS THAT
THE ST. LOUIS METRO AREA IS NOT THE ONLY AREA THAT WILL SEE AT LEAST
SOME IMPACTS, JUST THAT THIS IS WHERE WE ARE CURRENTLY MOST
CONFIDENT.
LOOKING AHEAD TO THE MIDDLE AND LATTER HALF OF THE WEEK, WE DO SEE
SLOWLY INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS TUESDAY
ONWARD AS THE UPPER RIDGE FLATTENS A BIT. HOWEVER, CURRENT
PROBABILITIES REMAIN LOW OVERALL (20-30%), AND THE PREVAILING UPPER
FLOW PATTERN IS LIKELY TO CONTINUE TO FEATURE HIGH PRESSURE. AS
SUCH, ABOVE AVERAGE TEMPERATURES ARE MOST LIKELY TO PERSIST THROUGH
THE END OF THE WEEK, AND WHILE WE MAY SEE INTERMITTENT BREAKS FROM
SHOWERS, THERE IS ALSO A LOW CHANCE THAT IMPACTFUL HEAT PERSISTS
BEYOND TUESDAY AS WELL.
BRC
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1225 PM CDT THU JUN 19 2025
DRY, VFR CONDITIONS WILL PERSIST THROUGH THE TAF PERIOD. WINDS
WILL GRADUALLY SLACKEN THIS EVENING BEFORE TURNING SOUTHERLY
FRIDAY MORNING.
MRB
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...EXTREME HEAT WATCH FROM SATURDAY AFTERNOON THROUGH TUESDAY
EVENING FOR JEFFERSON MO-SAINT CHARLES MO-SAINT LOUIS CITY
MO-SAINT LOUIS MO.
IL...EXTREME HEAT WATCH FROM SATURDAY AFTERNOON THROUGH TUESDAY
EVENING FOR JERSEY IL-MADISON IL-MONROE IL-SAINT CLAIR IL.
WFO LSX
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