061
FXUS63 KLSX 231311
AFDLSX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SAINT LOUIS MO
811 AM CDT SAT OCT 23 2021
UPDATE
ISSUED AT 801 AM CDT SAT OCT 23 2021
12Z REGIONAL SURFACE ANALYSIS DEPICTS A SUBTLE STATIONARY BOUNDARY
ACROSS SOUTHWEST MISSOURI FORMED BY THE ONGOING CONVECTION THERE.
THE HEAVIER DOWNPOURS AND THUNDERSTORMS THERE COULD CAUSE FLOODING
CONCERNS AMIDST PRECIPITABLE WATER VALUES OVER 1.2" (ABOVE THE
90TH CLIMATOLOGICAL PERCENTILE) IN THIS AREA. HOWEVER, THOSE
HIGHER RAIN RATES ARE EXPECTED TO BE CONFINED TO THAT PORTION OF
THE STATE AND NOT ENCROACH THE SOUTHERN COUNTIES OF OUR CWA.
ADDITIONALLY, FLASH FLOOD GUIDANCE SUGGESTS THAT UPWARDS OF 2"/HR
RAIN RATES WILL NEED TO BE REALIZED TO CAUSE CONCERN FOR US.
WITHOUT CONVECTIVE ACTIVITY, THOSE RATES WILL LIKELY NOT BE
REALIZED IN OUR AREA THIS MORNING.
MRB
SHORT TERM
(THROUGH LATE SUNDAY AFTERNOON)
ISSUED AT 330 AM CDT SAT OCT 23 2021
THE MAIN FOCUS FOR THIS PORTION OF THE PERIOD WILL BE SEVERAL ROUNDS
OF CONVECTION, SOME CAPABLE OF HEAVY RAINFALL AND SEVERE WEATHER.
CURRENTLY, A CLUSTER OF SHOWERS AND THUNDERSTORMS IS ONGOING OVER
PORTIONS OF SOUTHWESTERN MISSOURI AT THE NOSE OF A LOW LEVEL JET.
THIS JET IS EXPECTED TO VEER THROUGH THE MORNING INTO THE AFTERNOON,
BRINGING THE FOCUS FOR THESE SHOWERS AND THUNDERSTORMS ACROSS
PORTIONS OF SOUTHEASTERN MISSOURI AND SOUTHWESTERN ILLINOIS. AS THE
JET WEAKENS THROUGH THE DAY, THE INTENSITY AND COVERAGE OF THIS
CONVECTION IS EXPECTED TO WANE, MOSTLY EXITING THE CWA OR
DISSIPATING DURING THE LATE AFTERNOON.
OUR ATTENTION THEN TURNS TO TONIGHT AND EARLY SUNDAY MORNING. AT
THAT TIME, A WARM FRONT WILL LIFT THROUGH THE CWA AS THE LOW LEVEL
JET ONCE AGAIN RAMPS UP AND INTERACTS WITH THE BOUNDARY. THIS WILL
RESULT IN A BAND OF SHOWERS AND THUNDERSTORMS ALONG THE BOUNDARY AS
IT LIFTS NORTHWARD, EVENTUALLY SLOWING AND STALLING ACROSS
NORTHEASTERN MISSOURI AND WEST-CENTRAL ILLINOIS. AT THAT TIME, THERE
WILL BE TWO THREATS TO FOCUS ON: 1) THE POTENTIAL FOR TRAINING
CONVECTION CAPABLE OF HEAVY RAINFALL, AND 2) SEVERE THUNDERSTORMS
CAPABLE OF LARGE HAIL. AS FOR THE HEAVY RAIN THREAT, THE 00Z HREF
MEAN HAS PRECIPITABLE WATER AROUND 1.5", AND WITH CONVECTION EXPECTED
TO TRAIN ALONG THE FRONT, RAINFALL AMOUNTS OF 1-2" WITH LOCALIZED
3"+ ARE POSSIBLE ACROSS NORTHEASTERN MISSOURI AND WEST-CENTRAL
ILLINOIS THROUGH EARLY SUNDAY AFTERNOON. THE DURATION OVER WHICH
THIS RAIN WILL FALL AS WELL AS DRIER SOILS IN THIS PORTION OF THE
CWA ARE EXPECTED TO LIMIT FLOOD POTENTIAL. ALTHOUGH, I CAN'T
COMPLETELY RULE OUT AN ISOLATED INSTANCE OF FLASH FLOODING OR A
SMALLER TRIBUTARY OR TWO RISING TO AROUND FLOOD STAGE. WITH THE
SATURDAY NIGHT/SUNDAY MORNING SEVERE THREAT, ELEVATED CONVECTION
WITH THE FRONT WILL POSE A LARGE HAIL THREAT PRIMARILY ACROSS
NORTHEASTERN MISSOURI AND WEST-CENTRAL ILLINOIS. HOWEVER, THE MAIN
THREAT FOR SEVERE WEATHER WILL BE LATER IN THE DAY ON SUNDAY AS A
SHORTWAVE EJECTS OUT OF THE GREAT PLAINS AND A SURFACE LOW DRAGS
A COLD FRONT TOWARD THE CWA.
THEN, THE ATMOSPHERE WILL BECOME RATHER UNSTABLE, WITH APPROXIMATELY
1,500 TO JUST OVER 2,000 J/KG OF SBCAPE AHEAD OF THE FRONT. THE
VERTICAL WIND PROFILE IS ALSO FORECAST TO BE SUPPORTIVE OF SEVERE
STORMS, WITH ROUGHLY 40-50 KTS OF 0-6KM BULK SHEAR AND LONG, CURVED
HODOGRAPHS PRESENT OVER THE CWA. BY MID AFTERNOON, THE FRONT IS
EXPECTED TO BE IN WESTERN MISSOURI WITH A PRE-FRONTAL TROUGH OVER
CENTRAL MISSOURI. SEVERAL CAMS HAVE DISCRETE CONVECTION ASSOCIATED
WITH THIS TROUGH, WHICH WOULD BE SUPERCELLS CAPABLE OF ALL SEVERE
HAZARDS. GIVEN LOW LCLS (<1,000 M), HIGH EFFECTIVE SRH (>300M2/S2),
AND MLCAPE OF AROUND 1,500 J/KG, TORNADOES ARE OF PARTICULAR CONCERN
WITH THESE EARLIER STORMS. AS THE FRONT ENTERS THE CWA DURING THE
EVENING AND STORMS TRACK FURTHER INTO EASTERN MISSOURI AND WESTERN
ILLINOIS, UPSCALE GROWTH INTO A LINEAR STORM MODE IS EXPECTED,
WITH BOWING SEGMENTS CAPABLE OF PRIMARILY DAMAGING WIND GUSTS AND
TORNADOES. THE SEVERE THREAT IS EXPECTED TO DIMINISH AS STORMS
WEAKEN AND EXIT THE CWA SHORTLY AFTER MIDNIGHT ON MONDAY.
ELMORE
LONG TERM
(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 330 AM CDT SAT OCT 23 2021
THE SHORTWAVE AND SURFACE LOW WILL CONTINUE PUSHING EASTWARD ON
MONDAY. MOISTURE WRAPPING AROUND THE BACKSIDE OF THE LOW WILL
SUSTAIN DENSE CLOUD COVER OVER THE CWA, AND WHEN PAIRED WITH LOW-
LEVEL COLD AIR ADVECTION, WILL KEEP TEMPERATURES ON THE COOL SIDE
OF CLIMATOLOGY FOR MOST LOCATIONS.
THIS COOLER WEATHER WILL BE SHORT LIVED AS AN UPPER-LEVEL RIDGE
BUILDS INTO THE MIDWEST LATE MONDAY INTO TUESDAY. IN TURN, LOW-LEVEL
WINDS WILL SHIFT TO OUT OF THE SOUTH, USHERING IN WARMER AIR AND
RETURNING TEMPERATURES TO NEAR NORMAL VALUES FOR TUESDAY AHEAD OF
OUR NEXT SYSTEM ASSOCIATED WITH A DEEP, UPPER-LEVEL TROUGH.
ENSEMBLE GUIDANCE STILL DIFFERS ON THE PHASING OF THIS TROUGH AND
ITS ASSOCIATED SURFACE SYSTEM AS IT TRAVERSES THE CENTRAL PORTION OF
THE CONUS. DESPITE THESE DIFFERENCES, CONFIDENCE IS HIGH THAT THE
CWA WILL SEE ANOTHER ROUND OF RAIN LATE TUESDAY THROUGH POSSIBLY AS
LONG AS FRIDAY. RAIN WILL NOT BE CONTINUOUS THROUGH THIS ENTIRE
PORTION OF THE PERIOD, BUT A FROPA ON WEDNESDAY AND DEEPENING
SURFACE LOW IN PROXIMITY TO THE CWA WILL LINGER THE CHANCE FOR
SEVERAL ROUNDS OF SHOWERS FOR PORTIONS OF THE REGION.
ELMORE
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 641 AM CDT SAT OCT 23 2021
SEVERAL ROUNDS OF RAIN AND SUB-VFR FLIGHT CONDITIONS ARE EXPECTED TO
IMPACT ALL LOCAL TERMINALS THROUGH THE PERIOD. THIS MORNING, AN AREA
OF SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL SKIM PAST KCOU,
KJEF, KSUS, KSTL, AND KCPS. WHILE THE BEST CHANCE FOR THIS
CONVECTION WILL REMAIN SOUTH OF THESE TERMINALS, I CAN'T RULE OUT A
SHOWER OR TWO PASSING NEAR THE TERMINALS LATER THIS MORNING INTO THE
EARLY AFTERNOON. OF MORE IMPORTANT NOTE WITH THIS AREA OF SHOWERS IS
ONSET OF LOW STRATUS FROM SOUTHWEST TO NORTHEAST ACROSS THE
TERMINALS THROUGH THE LATE MORNING, FINALLY REACHING KUIN BY THIS
EVENING. BY THAT POINT IN THE PERIOD, YET ANOTHER ROUND OF RAIN AND
THUNDERSTORMS IS EXPECTED AT ALL LOCAL TERMINALS. THIS ROUND WILL
HAVE POTENTIALLY GREATER IMPACT THAN THE EARLIER PERIOD SHOWERS, AS
HEAVIER SHOWERS AND THUNDERSTORMS WILL LIKELY REDUCE VISIBILITIES TO
MVFR AND POSSIBLY BRIEF IFR CONDITIONS. HOWEVER, GIVEN THE
UNCERTAINTY IN THE PLACEMENT OF THESE HEAVIER CORES, I'VE LEFT
VISIBILITIES VFR FOR NOW. IFR CEILINGS ARE EXPECTED AT KUIN, KCOU,
AND KJEF LATER IN THE PERIOD, BUT CONFIDENCE IS CURRENTLY HIGH THAT
CEILINGS WILL STAY MVFR AT THE OTHER LOCAL TERMINALS.
ELMORE
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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