000
FXUS63 KLSX 211743
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
1243 PM CDT TUE MAY 21 2013

.UPDATE...
ISSUED AT 1243 PM CDT TUE MAY 21 2013

BACKED OFF ON POPS A LITTLE FOR THIS AFTERNOON...ESPECIALLY OVER
NORTHERN/CENTRAL MO AS ATMOSPHERE IS STRUGGLING TO DESTABILIZE.
BECAUSE OF THIS...SPC HAS PUSHED SLIGHT RISK JUST SOUTH OF
FORECAST AREA...BUT COULD STILL SEE ISOLATED STRONG TO SEVERE
STORMS LATE THIS AFTERNOON AND EVENING. AS FOR HIGHS...MADE MINOR
ADJUSTMENTS...WILL BE IN THE UPPER 70S TO LOW 80S.

BYRD
&&

.SHORT TERM...(THROUGH TONIGHT)
ISSUED AT 348 AM CDT TUE MAY 21 2013

FOCUS THRU THIS PERIOD WILL BE TSRA CHANCES.

SFC ANALYSIS AT 07Z DEPICTS THE EFFECTIVE SFC BNDY ACROSS WRN IA
INTO NWRN MO...THEN EXTENDING SWWD INTO ERN KS. BELIEVE THIS IS SOME
SORT OF PRE-FRONTAL TROF/DRY LINE AS IT APPEARS THE ACTUAL SFC FNT
IS STILL ACROSS ERN NEB INTO WRN KS. THIS TROF/DRY LINE SHUD MOVE
EWD RATHER SLOWLY TODAY.

A NUMBER OF QUESTIONS REMAIN ABOUT TODAY GIVEN THE SPREAD AMONG MDL
SOLNS. EXPECT ONGOING PRECIP TO GRADUALLY MOVE EWD OUT OF THE CWA
LATER THIS MORNING. BELIEVE ISOD TO SCT TSRA WILL DEVELOP THIS
AFTERNOON ALONG THE TROF/DRY LINE. SETUP TODAY DOES NOT APPEAR AS
FAVORABLE FOR SEVERE WEATHER TODAY COMPARED TO YESTERDAY.
HOWEVER...BELIEVE THE GFS/NAM ARE UNDERPLAYING THE EVENT TODAY AND
TONIGHT FOR THE CWA.

MDLS PROG CONVECTION OVER ARKLATEX REGION THIS AFTERNOON/EVE LIFTING
NEWD TONIGHT INTO THE CWA. THIS TSRA WILL BE DRIVEN BY A VORT MAX
CURRENTLY OVER NRN NM/SRN CO REGION. MDLS TO SOME DEGREE...EXCEPT
FOR THE NAM...DEVELOP A SFC WAVE ALONG THE SFC TROF TONIGHT. THIS
LOW SHUD TRAVEL NEWD ALONG THE SFC TROF. THE ECMWF/LOCAL WRF HAVE A
MORE NWRN SOLN AND THIS SEEMS REASONABLE AS THESE MDLS HAVE A FAIRLY
GOOD HANDLE CURRENTLY ON THE STRENGTH OF THIS SYSTEM. IF THIS SOLN
VERIFIES...THIS LOW WILL PROVIDE ENHANCED SHEAR AS WELL AS ALLOW
STEEPER LAPSE RATES TO ADVECT INTO THE AREA. GIVEN PROGD HODOGRAPHS
AND TIMING...BELIEVE TSRA WILL BE LINEAR BY THE TIME THEY ENTER THE
CWA.

IF THIS NRN SOLN IS CORRECT...THE DAY SHIFT MAY NEED TO CONSIDER A
FLASH FLOOD WATCH FOR ERN PORTIONS OF THE CWA.

AS FOR TEMPS...TRENDED AOA WARMEST MOS FOR TODAY AND COOLER FOR
TONIGHT AS THE ACTUAL CDFNT FINALLY MOVES THRU THE AREA.

TILLY

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 440 AM CDT TUE MAY 21 2013

FOCUS STARTS TO SHIFT TO TEMPS AS PRECIP FINALLY MOVES E OF THE
AREA.

WITH FOCUS ON TODAY AND TONIGHT...ONLY MINOR CHANGES WERE MADE TO
THE PREV FORECAST AS MUCH OF IT STILL APPEARS TO BE ON TRACK. MDLS
ARE IN REMARKABLY GOOD AGREEMENT THRU THE PERIOD WRT MASS FIELDS.

UNCERTAINTY REMAINS FOR TEMPS ON WED/THURS. MDLS SUGGEST TEMPS
WILL STRUGGLE TO REACH 70S. HOWEVER...GIVEN THAT IT IS MAY...IF
ANY SUN MANAGES TO MAKE IT THRU THE CLOUDS...WUD BE SURPRISED IF
TEMPS DID NOT AT LEAST BRIEFLY REACH UPPER 70S OR INTO THE LOWER
80S. WITH UPPER RIDGE BUILDING INTO THE AREA ON SAT AND
BEYOND...TEMP FORECAST BECOMES MORE QUESTIONABLE WITH DIFFERING
SOLNS AT THE SFC. FOR NOW...MADE ONLY MINOR CHANGES...BUT BELIEVE
A TREND TWD THE GFS MAY BE NEEDED WITH A WARMER AND DRIER SOLN.

TILLY
&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1243 PM CDT TUE MAY 21 2013

DIURNAL CU AND CIRRUS SHIELD TO PERSIST OVER TAF SITES TODAY AHEAD
OF COLD FRONT. TIMING AND COVERAGE OF STORM DEVELOPMENT IS STILL
HARD TO PIN DOWN FOR LATE THIS AFTERNOON AND TONIGHT AS ATMOSPHERE
IS STRUGGLING TO DESTABILIZE. FEEL THAT KCOU SHOULD REMAIN DRY.
OTHERWISE...SOME STORMS POSSIBLE OVER METRO AREA AFTER 22Z AND
LINGER OVER AREA THROUGH DAYBREAK ON WEDNESDAY. AS FOR KUIN...THEY
WILL BE ON NORTHERN FRINGES OF ACTIVITY AFTER 05Z...TAPERING OFF
BY 10Z. OTHERWISE...SOUTHWEST WINDS TO DIMINISH TOWARDS
SUNSET...VEERING TO THE WEST BEHIND THE FRONTAL BOUNDARY EARLY
WEDNESDAY. THE WINDS WILL PICKUP TO NEAR 15KTS BY MID MORNING ON WEDNESDAY.

SPECIFICS FOR KSTL...DIURNAL CU AND CIRRUS SHIELD TO PERSIST OVER
METRO SITES TODAY AHEAD OF COLD FRONT. TIMING AND COVERAGE OF STORM
DEVELOPMENT IS STILL HARD TO PIN DOWN FOR LATE THIS AFTERNOON AND
TONIGHT AS ATMOSPHERE IS STRUGGLING TO DESTABILIZE. SOME STORMS
POSSIBLE OVER METRO AREA AFTER 22Z AND LINGER OVER AREA THROUGH
11Z WEDNESDAY. OTHERWISE...SOUTHWEST WINDS TO DIMINISH TOWARDS
SUNSET...VEERING TO THE WEST BEHIND THE FRONTAL BOUNDARY BY 11Z
WEDNESDAY. THE WINDS WILL PICKUP TO NEAR 15KTS BY 17Z WEDNESDAY.

BYRD
&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&

$$
WFO LSX