328
FXUS63 KLSX 131926
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
226 PM CDT THU AUG 13 2020
SHORT TERM
(THROUGH LATE FRIDAY NIGHT)
ISSUED AT 226 PM CDT THU AUG 13 2020
SLOW MOVING THUNDERSTORMS CONTINUE DEVELOP ALONG THE STATIONARY
FRONT DRAPED FROM CENTRAL NORTH DAKOTA THROUGH CENTRAL IOWA INTO
EASTERN MISSOURI AND SOUTHERN ILLINOIS. DRIVEN BY DAY TIME HEATING
AND A MID-LEVEL LOW AND ASSOCIATED DISTURBANCE THAT RETROGRADED
OVERNIGHT INTO EASTERN MISSOURI AND SOUTHWEST ILLINOIS, THESE STORMS
WILL LARGELY LINGER WHERE THEY FORM. FLASH FLOOD CONTINUES TO BE A
CONCERN AS LONG AS THESE SHOWERS AND THUNDERSTORMS PERSIST ACROSS
THE AREA, PRODUCING PRODIGIOUS RAINFALL AMOUNTS ACROSS PORTIONS OF
SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS THANKS TO 1.5-2" OF
AVAILABLE PRECIPITABLE WATER.
CONVECTION AND SKY COVER IS EXPECTED TO DECAY WITH NIGHTFALL,
LEAVING MOIST CONDITIONS BEHIND. PATCHY FOG WILL BE POSSIBLE DURING
THE EARLY HOURS OF THE MORNING TOMORROW IN AREAS WHERE THE SKY IS
ABLE TO CLEAR SUFFICIENTLY OVERNIGHT. ANY FOG THAT DEVELOPS WILL
DISSIPATE TOMORROW MORNING ONCE THE SUN COMES UP AND DAYTIME MIXING
COMMENCES.
OVERNIGHT AND INTO FRIDAY THE MID-LEVEL LOW CREEPS SLOWLY EASTWARD,
CENTERING THE BEST LIFT OVER SOUTHEAST MISSOURI AND SOUTHWEST
ILLINOIS. AS DAY TIME HEATING KICKS INTO GEAR ON FRIDAY, BLOSSOMING
SHOWERS WILL BE ABLE TO TAP INTO THE 1500-2500 J/KG OF MUCAPE AND 1-
1.5" OF PRECIPITABLE WATER TO GENERATE ANOTHER DAY OF SLOW MOVING
THUNDERSTORMS PRODUCING LOCALIZED HEAVY RAINFALL OVER SOUTHEAST
MISSOURI AND SOUTHWEST ILLINOIS. SHOWERS AND THUNDERSTORMS WILL DIE
OFF WITH THE LOSS OF DAY TIME HEATING AND THE MOVEMENT OF THE MID-
LEVEL LOW AND ASSOCIATED VORTICITY MAXIMA OUT OF THE IMMEDIATE AREA
FRIDAY EVENING.
WITH CONDITIONS ACROSS THE AREA LARGELY UNCHANGED BETWEEN WEDNESDAY
AND FRIDAY, WE CAN EXPECT TEMPERATURES TO BE FAIRLY CONSISTENT WITH
HIGHS IN THE MID TO UPPER 80S AND LOWS IN THE MID 60S TO LOW 70S.
MRM
LONG TERM
(SATURDAY THROUGH NEXT THURSDAY)
ISSUED AT 226 PM CDT THU AUG 13 2020
A LOW-LEVEL COLD FRONT WILL MOVE THROUGH THE REGION SATURDAY
AFTERNOON. SREF PROBABILITIES AND OPERATIONAL MODELS INDICATE
INSTABILITIES BETWEEN 1000-2000 J/KG ARE LIKELY WITH OPERATIONAL
MODELS INDICATING AROUND 20 KTS OF 0-6 KM BULK SHEAR AHEAD OF AND
ALONG THE FRONT. BUT A LACK OF DEEP MOISTURE CONVERGENCE ALONG THE
FRONT WILL GREATLY LIMIT PRECIPITATION CHANCES, SO HAVE KEPT THE NBM
FORECAST OF SCATTERED SHOWERS AND THUNDERSTORMS DURING THE DAY
SATURDAY.
A HIGH PRESSURE SYSTEM WILL BUILD IN BEHIND THE FRONT, LINGERING
THROUGH THE END OF THE PERIOD AND HELPING TO KEEP THE EXTENDED
PERIOD LARGELY DRY. OPERATIONAL AND ENSEMBLE GUIDANCE ALL POINT TO
THE LINGERING SURFACE HIGH AND PERSISTENT NORTHERLY FLOW KEEPING THE
AREA IN BELOW NORMAL TEMPERATURES THROUGH THE END OF THE PERIOD. THE
CIPS ANALOGS FROM ST. LOUIS UNIVERSITY POINT TO BELOW NORMAL
TEMPERATURES STICKING AROUND UNTIL THE END OF NEXT WEEK.
MRM
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1205 PM CDT THU AUG 13 2020
SLOW MOVING THUNDERSTORMS HAVE FORMED ALONG A STATIONARY FRONT
DRAPED THROUGH THE EASTERN HALF OF MISSOURI LATE THIS MORNING.
MORE STORMS ARE ANTICIPATED TO FORM ALONG THIS BOUNDARY AND ARE
EXPECTED TO IMPACT THE ST. LOUIS METRO TERMINALS, INCLUDING KSTL.
UNCERTAINTY STILL EXISTS AS TO WHERE INDIVIDUAL THUNDERSTORMS WILL SET
UP, HOWEVER CONFIDENCE IS HIGH THAT WHERE THUNDERSTORMS FORM,
HEAVY RAIN WILL REDUCE VISIBILITIES TO IFR FLIGHT CONDITIONS AND
COULD PRODUCE FLASH FLOODING. GIVEN THIS, HAVE INCLUDED HEAVY
THUNDERSTORMS AND 3SM IN A TEMPO GROUP FOR THE STL METRO
TERMINALS, INCLUDING KSTL.
KUIN AND KCOU CAN EXPECT VFR FLIGHT CONDITIONS THIS AFTERNOON AND
OVERNIGHT BEFORE THE POTENTIAL FOR FOG FORMATION TOMORROW MORNING.
FOG IS LIKELY ACROSS THE AREA, PARTICULARLY THOSE THAT HAVE SEEN
SIGNIFICANT RAINFALL IN THE PAST COUPLE OF DAYS. HAVE INCLUDED
MVFR FOG AT KCOU AND KUIN WHERE HEAVY RAIN HAS NOT FALLEN
RECENTLY, AND IFR FOG AT KSUS AND KCPS, WHICH ARE MORE MOIST AND
MORE SUSCEPTIBLE TO FOG DEVELOPMENT. HAVE NOT INCLUDED FOG IN THE
KSTL TAF YET, AS IT TENDS TO DEVELOP FOG LATER THAN THE OTHER
TERMINALS, BUT WILL REEVALUATE AS NEEDED.
MRM
LSX WATCHES/WARNINGS/ADVISORIES
MO...FLASH FLOOD WATCH UNTIL 7 PM CDT THIS EVENING FOR CRAWFORD MO-
FRANKLIN MO-IRON MO-JEFFERSON MO-LINCOLN MO-MADISON MO-
REYNOLDS MO-SAINT CHARLES MO-SAINT FRANCOIS MO-SAINT LOUIS
CITY MO-SAINT LOUIS MO-SAINTE GENEVIEVE MO-WARREN MO-
WASHINGTON MO.
IL...FLASH FLOOD WATCH UNTIL 7 PM CDT THIS EVENING FOR BOND IL-
CALHOUN IL-CLINTON IL-FAYETTE IL-GREENE IL-JERSEY IL-
MACOUPIN IL-MADISON IL-MARION IL-MONROE IL-MONTGOMERY IL-
RANDOLPH IL-SAINT CLAIR IL-WASHINGTON IL.
WFO LSX
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