499
FXUS63 KLSX 182305
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
605 PM CDT SAT APR 18 2026
KEY MESSAGES
- SOME LOCATIONS WILL REACH THE MID 30S TONIGHT WITH LESS THAN A
50% CHANCE FOR PATCHY FROST SUNDAY MORNING. VEGETATION THAT IS
ELEVATED OFF THE GROUND WILL BE MORE SUSCEPTIBLE TO FROST.
- A NOTABLE WARMUP BEGINS ON TUESDAY LASTING UNTIL AT LEAST
THURSDAY, WHEN TEMPERATURES ARE EXPECTED TO BE 10 DEGREES ABOVE
AVERAGE.
- A PERIOD OF DRY WEATHER IS FORECAST UNTIL AT LEAST TUESDAY NIGHT
WHEN THERE IS A LOW (20%) FOR LIGHT RAIN. A BETTER CHANCE FOR
SHOWERS AND THUNDERSTORMS RETURNS THURSDAY NIGHT INTO FRIDAY.
SHORT TERM
(THROUGH LATE SUNDAY NIGHT)
ISSUED AT 251 PM CDT SAT APR 18 2026
REINFORCING LOW/MID-LEVEL CAA BEHIND LAST NIGHT'S FROPA HAS RESULTED
IN TEMPERATURES ABOUT 15 DEGREES BELOW AVERAGE WITH AFTERNOON HIGHS
GENERALLY IN THE 50S ACROSS THE ENTIRE AREA. ADDITIONALLY, CLOUD
COVER HAS BEEN SLOWER TO CLEAR S OF I-44 IN MO AND I-70 IN IL, WHICH
HAS ALSO LIMITED DAYTIME HEATING ACROSS THAT PART OF THE AREA.
SURFACE ANALYSIS REVEALS A SURFACE HIGH PUSHING EASTWARD NEAR THE
OKLAHOMA PANHANDLE WITH HIGH-RES GUIDANCE SETTLING THIS HIGH JUST TO
THE SOUTH OVERNIGHT. THIS WILL LEAD TO LIGHT WESTERLY WINDS AND A
CLEAR NIGHT ALLOWING FOR EFFICIENT RADIATIONAL COOLING, ESPECIALLY
FOR LOW-LYING AREAS THAT ARE MORE SHELTERED FROM WINDS. GIVEN THE
SETUP DESCRIBED ABOVE, THE COLDEST TEMPERATURES TONIGHT ARE FORECAST
TO BE IN THE MID 30S FOR LOCATIONS ACROSS NORTHEAST MO/WEST-CENTRAL
IL ALONG WITH LOW-LYING/RIVER VALLEY LOCATIONS. IN THESE AREAS,
PATCHY FROST IS POSSIBLE, BUT SHOULD BE LIMITED TO MOSTLY ELEVATED
AND EXPOSED VEGETATION. THE REASON FOR THIS BEING WARM GROUND
TEMPERATURES (2" SOIL TEMPS IN THE 60S/70S) AND SATURATED SOILS
(RESULTING IN SLOWER TEMPERATURE CHANGE OF THE SOIL) HELPING TO KEEP
THE NEAR SURFACE AIR SLIGHTLY WARMER. FURTHERMORE, WITH THE SURFACE
HIGH ACROSS SOUTHERN MO, LIGHT WESTERLY WINDS ARE FORECAST TO BE
STRONGEST (3-7MPH) OVERNIGHT ACROSS NORTHERN MO/WEST-CENTRAL IL,
WHICH WILL WORK TO LIMIT FROST FORMATION AS WELL.
AFTER A CHILLY START IN THE MORNING, A QUICK WARMUP WILL ENSUE ON
SUNDAY THANKS TO WEAK LOW-LEVEL WESTERLY WAA AND ABUNDANT SOLAR
INSOLATION UNDER A MOSTLY SUNNY MID-APRIL SKY. AS A RESULT,
AFTERNOON TEMPERATURES ARE FORECAST TO REACH THE 60S AREAWIDE,
LEADING TO HIGHS ABOUT 10 DEGREES WARMER THAN TODAY. BY SUNDAY
EVENING, A SURFACE HIGH SLIDES SOUTHWARD OUT OF CANADA INTO THE
MIDWEST, PLACING THE AREA WITHIN LIGHT NORTHEASTERLY FLOW. THAT,
COUPLED WITH A MOSTLY CLEAR SKY OVERNIGHT WILL ONCE AGAIN LEAD TO A
RATHER CHILLY NIGHT WITH LOWS FORECAST IN THE MID/UPPER 30S NORTH OF
I-70 AND LOWER 40S SOUTH.
PEINE
LONG TERM
(MONDAY THROUGH NEXT SATURDAY)
ISSUED AT 251 PM CDT SAT APR 18 2026
AT THE START OF THE EXTENDED, THE MID-LEVEL LARGE-SCALE PATTERN
CONSISTS OF TROUGHING OFF THE WEST COAST, BROAD RIDGING ACROSS THE
INTERMOUNTAIN WEST, AND TROUGHING OVER THE EASTERN U.S., PLACING OUR
AREA UNDER NORTHWESTERLY FLOW ALOFT. LONG-RANGE DETERMINISTIC
GUIDANCE UNVEILS A WEAK MID-LEVEL SHORTWAVE, WITHIN THE
NORTHWESTERLY FLOW, MOVING ACROSS THE AREA TUESDAY NIGHT. AHEAD OF
THIS WAVE, SOUTHERLY FLOW ADVECTING GULF MOISTURE INTO THE REGION
WILL BE LIMITED TO ONLY THE LOW-LEVELS. AS A RESULT, MOISTURE RETURN
REMAINS WEAK AHEAD OF THE ARRIVAL OF BETTER LOW/MID-LEVEL FORCING,
OWING TO VERY LOW CHANCES FOR LIGHT RAIN. CURRENTLY, THE LREF
INDICATES AROUND ONLY A 20% FOR MEASURABLE PRECIPITATION TUESDAY
NIGHT INTO WEDNESDAY. AS THE MID-LEVEL RIDGE AXIS CLOSES IN ON THE
AREA WEDNESDAY, HEIGHT RISES ALOFT SHOULD ALLOW FOR CONTINUED WARM
AND DRY CONDITIONS. BY THURSDAY, LONG-RANGE GUIDANCE IS IN GOOD
CONSENSUS THAT A LONGWAVE TROUGH WILL BE POSITIONED NEAR THE
INTERMOUNTAIN WEST AND SLOWLY APPROACHING OUR AREA. THE RESULT FOR
US WILL BE THE RETURN OF DEEP SOUTHWESTERLY FLOW THAT WILL LEAD TO
ABUNDANT WARM/MOIST ADVECTION AND THE RETURN OF SHOWER AND
THUNDERSTORM CHANCES AS EARLY AS THURSDAY NIGHT.
AS FOR TEMPERATURES, THE WEEK WILL START OFF RATHER CHILLY MONDAY
MORNING WITH SOUTHERLY LOW-LEVEL FLOW COMMENCING MID/LATE DAY ON
MONDAY, RESULTING IN TEMPERATURES REBOUNDING NICELY. BY THE
AFTERNOON, MOST OF THE AREA SHOULD BE NEAR THE MID/UPPER 60S WITH
THE WARMEST (LOW 70S) ACROSS THE OZARKS. LOW-LEVEL SOUTHERLY FLOW IS
FORECAST TO CONTINUE TUESDAY THROUGH FRIDAY, RESULTING IN HIGHS
REACHING THE 70S/80S EACH AFTERNOON/EVENING. CONFIDENCE IS HIGH IN
THE CONTINUANCE OF SLIGHTLY ABOVE AVERAGE TEMPERATURES TUESDAY INTO
THURSDAY AS LREF TEMPERATURES IQR SPREADS ARE ONLY AROUND 3 DEGREES
AND CENTERED ON TEMPERATURES 5-10 DEGREES ABOVE AVERAGE. IQR SPREADS
INCREASE SUBSTANTIALLY ON FRIDAY TO 10+ DEGREES INDICATING A
POTENTIAL FRONT NEARBY. SLIGHTLY BELOW NORMAL TEMPERATURES MAY
RETURN NEXT SATURDAY AS TEMPERATURE IQRS BECOME CENTERED ON
TEMPERATURES 10 DEGREES BELOW AVERAGE.
PEINE
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 602 PM CDT SAT APR 18 2026
DRY AND VFR FLIGHT CONDITIONS WILL PREVAIL THROUGH THE REMAINDER
OF THE TAF PERIOD. WINDS WILL BECOME CALM AND VARIABLE OVERNIGHT
AT MOST TERMINALS AS A SURFACE HIGH PASSES THROUGH SOUTHERN
MISSOURI. THE EXCEPTION IS AT KCOU AND KUIN WHERE WINDS WILL
REMAIN RELATIVELY ELEVATED, AROUND 6 KTS. WINDS WILL PICK UP FROM
THE SOUTHWEST SUNDAY AND GUSTS WILL RETURN DURING THE LATE
MORNING.
DELIA
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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