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000
FXUS63 KLSX 142024
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
324 PM CDT TUE MAY 14 2013

.SHORT TERM...(THROUGH LATE TONIGHT)
ISSUED AT 320 PM CDT TUE MAY 14 2013

THE UNSEASONABLY WARM CONDITIONS WE WERE EXPECTING FOR THE LAST FEW
DAYS HAVE BEEN ON THE MARK TODAY WITH TEMPERATURES MORE TYPICAL OF
LATE JUNE/EARLY JULY. ST LOUIS HAS SET A RECORD SO FAR AT 92 DEGREES
AND THERE ARE STILL A FEW MORE HOURS OF HEATING TO GO. AS DISCUSSED
THE LAST FEW DAYS AS WELL...THE MODEL DEW POINT FORECASTS WERE WAY
OVERDONE. A MILD AND GENERALLY CLOUD-FREE NIGHT IS ON TAP AS LOW
LEVEL SOUTHWESTERLY FLOW PERSISTS.

GLASS

.LONG TERM...(WEDNESDAY THROUGH NEXT TUESDAY)
ISSUED AT 320 PM CDT TUE MAY 14 2013

THERE ARE SEVERAL FEATURES TO WATCH OUT FOR IN THE WED-THURS PERIOD
THAT WE HAVE BEEN DISCUSSING...FIRST THE ELONGATED SRN STREAM LOW
PRESSURE TROF CENTERED THROUGH EL PASO AND THE COLD FRONT NOW
STRETCHING FROM MINNESOTA THRU NW IOWA INTO NEBRASKA. THE GUIDANCE
IS IN PRETTY DECENT AGREEMENT WITH THE EAST-WEST FRONT BRINGING THE
FRONT INTO NRN MO-CENTRAL IL ON THURSDAY WHILE THE SRN STREAM
LOW/TROF RESULTS IN INCREASING MOISTURE. THE SURFACE DEW POINTS
ALONG/AHEAD OF THE FRONT STILL APPEAR TO BE OVERDONE GIVEN OBSERVATIONS
TODAY AND LOW LEVEL TRAJECTORIES FOR THE NEXT 24 HOURS. RATHER
THAN DEW POINTS IN THE UPPER 60S...LOWER 60S SEEMS MORE REALISTIC
WHICH WOULD YIELD MODERATE INSTABILITY WITH SBCAPES IN THE
2000-2500 J/KG RANGE RATHER THAT 3500+ AT PEAK AFTERNOON HEATING.
AT THIS TIME EXPECTING SCATTERED SHOWERS AND THUNDERSTORMS TO
DEVELOP IN THE ZONE ALONG/AHEAD OF THE FRONT IN RESPONSE TO
FRONTAL CONVERGENCE. I EXPECT THE COVERAGE OF STORMS TO DECREASE
AWAY FROM THE FRONTAL ZONE AND THINK THE MODELS ARE A BIT OVERDONE
WITH QPF EXTENT OWING TO THE OVERDONE INSTABILITY. I HAVE ALSO
GONE ON THE WARM SIDE OF GUIDANCE FOR HIGHS THINKING THERE WILL BE
QUITE A BIT OF SUN THROUGH THE FIRST HALF OF THE DAY.

THE HIGHEST POPS REMAIN IN THE VICINITY OF THE BOUNDARY WED NIGHT
INTO THURSDAY GIVEN IT IS THE PRIMARY FOCUS...BUT SCATTERED
ACTIVITY COULD OCCUR JUST ABOUT ANYWHERE GIVEN THE MIGRATING
SOUTHERN STREAM UPPER LOW/TROF. THE BOUNDARY ACTUALLY WAVERS NORTH
OF THE AREA BY THURSDAY AFTERNOON AND THE SOUTHERN STREAM UPPER
TROF WILL PASS TO THE EAST OF THE CWA AS WELL. THIS SHOULD RESULT
IN A DECREASING PROBABILITY OF CONVECTION LATE THURS/THURSDAY
NIGHT. ANOTHER WEAK LOW AMPLITUDE SHORT WAVE WILL TRACK ACROSS THE
TOP OF THE UPPER RIDGE ACROSS NORTHERN MO INTO WEST CENTRAL IL
FRIDAY/FRIDAY NIGHT BRINGING A BETTER CHANCE OF SHOWERS AND
THUNDERSTORMS TO NORTHERN SECTIONS OF THE CWA. IN THE WAKE OF THIS
FEATURE...HEIGHTS RISE ALOFT AS THE UPPER RIDGING INTENSIFIES ON
SATURDAY BRINGING WARMER TEMPERATURES. BEGINNING ON SUNDAY WE WILL
BEGING TO COME UNDER THE INFLUENCE OF A PROGRESSIVE UPPER TROF.
THE MODELS DIFFER ON THE STRUCTURE OF THE TROF WITH THE ECMWF
SHOWING MORE POSITIVE TILT. THESE VARIANCES IMPACT THE EASTWARD
COLD FRONT POSITION/MOVEMENT AND THE ASSOCIATED THUNDERSTORM
PROBABILTY...LONGEVITY AND ANY SEVERE WEATHER THREAT. CURRENT
INDICATIONS ARE THE THREAT OF SHOWERS AND THUNDERSTORMS SHOULD
RAMP UP CONSIDERABLY SUNDAY NIGHT INTO MONDAY.

GLASS

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1222 PM CDT TUE MAY 14 2013

GUSTY SOUTHWEST WINDS THIS AFTERNOON WILL TAPER OFF AFTER SUNSET
THIS EVENING...THOUGH DO NOT EXPECT MUCH CHANGE IN THE SUSTAINED
WIND SPEEDS ACROSS THE TAF SITES. CLEAR SKIES TONIGHT WILL GIVE
WAY TO INCREASING UPPER AND MID LEVEL VFR CLOUDS BEGINNING ON
WEDNESDAY MORNING AHEAD OF AN APPROACHING SYSTEM. WINDS WILL REMAIN
SOUTHWESTERLY THROUGH THE FORECAST PERIOD...THOUGH KUIN WILL SEE
WINDS VEER TO A MORE WESTERLY DIRECTION AS A FRONTAL BOUNDARY
DRIFTS SOUTHWARD INTO NORTHERN MISSOURI WEDNESDAY MORNING/EARLY
AFTERNOON.

SPECIFICS FOR KSTL...
GUSTY SOUTHWEST WINDS WILL CONTINUE THIS AFTERNOON BEFORE
DIMINISHING AFTER SUNSET THIS EVENING. DO NOT EXPECT MUCH CHANGE
IN SUSTAINED WIND SPEED TO OCCUR DUE TO PERSISTENT RETURN FLOW
ENTRENCHED OVER THE REGION. VFR CONDITIONS WILL PREVAIL THROUGH
THE TAF PERIOD...THOUGH DO EXPECT INCREASING UPPER AND MID LEVEL
CLOUDS BY WEDNESDAY MORNING. THE MAIN QUESTION REVOLVES AROUND
POTENTIAL SHRA/TSRA ON WEDNESDAY AFTERNOON/EVENING AS A FRONTAL
BOUNDARY MOVES INTO NORTHERN MISSOURI...THOUGH TO CURRENT MODEL
VARIANCES...HAVE KEPT KSTL DRY FOR NOW AND WILL DEFER PRECIP
MENTION TO LATER TAF ISSUANCES.

JP

&&

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

$$

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