000
FXUS63 KLSX 210849
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
349 AM CDT TUE MAY 21 2013

.SHORT TERM...(THROUGH LATE THIS AFTERNOON)
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...(TUESDAY THROUGH NEXT MONDAY)
ISSUED AT 323 PM CDT MON MAY 20 2013

THE IMPACTS OF THE OVERNIGHT CONVECTION ARE HARD TO GAGE AND WILL
HAVE LARGE RAMIFICATIONS ON THE THUNDERSTORM AND SEVERE THREAT
TUESDAY. ANY ONGOING SHOWERS/THUNDERSTORMS REMNANT FROM OVERNIGHT
ARE LIKELY TO BE LOCATED ACROSS SE MO INTO SW IL DURING THE FIRST
PART OF THE MORNING AND THEN WEAKEN. MODEL GUIDANCE SUGGESTS IT
WILL THEN REMAIN RELATIVELY VOID OF PRECIPITATION WELL INTO MID
AFTERNOON AND THIS SHOULD ALLOW FOR SOME AIR MASS RECOVERY AS
CLOUDS THIN. MID LEVEL LAPSE RATES ARE NOT AS STEEP SO OVERALL
INSTABILITY SHOULD BE LESS THAN THE LAST FEW DAYS...HOWEVER IT SHOULD
BE SUFFICIENT WITH AMPLE DEEP LAYER SHEAR FOR SCATTERED ORGANIZED
THUNDERSTORMS DEVELOPING DURING THE LATER PART OF THE AFTERNOON...RAMPING
UP IN COVERAGE DURING THE EARLY EVENING AS LARGE SCALE ASCENT INCREASES
IN ASSOCIATION WITH A SHORT WAVE ROTATING NEWD FROM EASTERN OK
REGION. ANY RESIDUAL BOUNDARIES WILL PROVIDE FURTHER FOCUS AND
ENHANCE THE SEVERE THREAT. THE LARGE SCALE TROF AND ATTENDANT COLD
FRONT WILL FINALLY MOVE ACROSS THE AREA TUESDAY NIGHT...PASSING
EAST OF THE CWA BY EARLY WEDNESDAY MORNING. DRIER AIR AND COOLER
AIR WILL OVERSPREAD THE AREA ON WEDNESDAY IN THE WAKE OF THE FRONT
AND A SECONDARY COLD FRONT ON WEDNESDAY NIGHT WILL USHER EVEN
COOLER AIR AND HIGH PRESSURE INTO THE AREA.

THE PATTERN WILL BE DOMINATED BY WEAK NW FLOW ON THE BACKSIDE OF
THE UPPER TROF AND LOOKS DRY THURSDAY NIGHT-FRIDAY...THEREAFTER
RETURN FLOW AND WEAK DISTURBANCES PASSING THRU THE PLAINS UPPER
RIDGE AND INTO THE MID/UPPER MS VALLEY WILL BRING A RE-NEWED
CHANCE OF THUNDERSTORMS....ESPECIALLY THE NRN HALF OF THE CWA.
WARMER TEMPERATURES WILL ALSO ACCOMPANY THE RETURN FLOW.

GLASS

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1241 AM CDT TUE MAY 21 2013

ACTIVE/MOST INTENSE CONVECTION HAS BEEN RIDING OUTFLOW BOUNDARY
OVER THE LAST FEW HOURS...AND IS NOW IN THE PROCESS OF EXITING OUR
CWA. HAVE CONTINUED SHOWERS IN THE WAKE OF THE MOST INTENSE
CONVECTION FOR SEVERAL MORE HOURS IN STL AREA AS ELEVATED PRECIP
CONTINUES TO PERCOLATE OVER S CENTRAL MO AND MOVE NE.  ITS
CERTAINLY POSSIBLE THAT RESDIUAL INSTABILITY AND INCREASING
SOUTHERLY FLOW OVERNIGHT COULD REFIRE ELEVATED CONVECTION...BUT
FOR THE TIME BEING HAVE HELD STORMS OUT OF ALL TAFS FOR THE
REMAINDER OF THE OVERNIGHT HOURS. TAFS FOR THE REMAINDER OF THE
NIGHT WILL GENERALLY TREND TO VFR WITH CIGS AOA 8KFT...BUT WILL
CERTAINLY NEED TO WATCH FOR THE DEVELOPMENT OF SOME STRATUS
DURING THE PREDAWN HOURS. HAVE NOT MADE ANY SIGNIFICANT CHANGES
TO TUESDAYS TRENDS...WITH THE REINTRODUCTION OF TSRA BY EARLY/MID
AFTERNOON.

SPECIFICS FOR KSTL...CIGS AOA 8KFT SHOULD BE THE RULE DURING THE
PREDAWN HOURS...WITH A FEW LINGERING SHOWERS STILL POSSIBLE
THROUGH 08Z. SHOULD SEE A BIT OF CU FORM BY MID MORNING...FOLLOWED
BY A THREAT OF THUNDERSTORMS BY MID AFTERNOON.

TRUETT

&&

.PRELIMINARY POINT TEMPS/POPS...
SAINT LOUIS     85  62  79  57 /  70  80  20  10
QUINCY          80  58  72  54 /  40  40  20  10
COLUMBIA        80  56  73  54 /  40  40  10  10
JEFFERSON CITY  81  58  75  55 /  50  50  10  10
SALEM           84  64  79  57 /  70  80  40  10
FARMINGTON      81  61  78  56 /  70  80  20  10

&&

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

$$

WFO LSX