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000
FXUS63 KLSX 190147
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
847 PM CDT SAT MAY 18 2013

.UPDATE...
ISSUED AT 847 PM CDT SAT MAY 18 2013

MAIN CONCERN CONTINUES TO BE POTENTIAL FOR TSRA ALONG-NE OF THE
WRMFNT AS IT PUSHES NEWD OVERNIGHT. WRMFNT CURRENTLY EXTENDS FROM
SERN KS INTO FAR SWRN MO AND N-CNTRL AR. EXAMINATION OF KSGF RAOB
FROM 00Z INDICATES A DECENT ENOUGH CAP CENTERED AROUND BULGE OF
WARM AIR AT H800 WITH A VERY SIZABLE REGION OF CAPE ABOVE...AROUND
4500 J/KG. BUT TO GET ANYTHING GOING...LIFT WILL HAVE TO COME UP
HIGH WITH SPECIAL ATTENTION AT THE H600-700 LAYER. MOISTURE
CONVERGENCE AT THE H600-700 LAYER WILL NOT ARRIVE UNTIL LATE THIS
EVENING FOR CNTRL-SERN MO AND EVEN THEN WILL BE WEAK. SOME
ADDITIONAL LIFT WILL BE PROVIDED BY A VORT MAX THAT WILL SLIDE
THRU CNTRL AND UP INTO NERN MO AND W-CNTRL IL DURING LATE EVENING
AND EARLY OVERNIGHT...AND SO HAVE ESSENTIALLY TIED RAIN CHCS TO
THESE FEATURES...STARTING WITH SLIGHT CHC BUT EDGING HIGHER INTO
LO CHC CATEGORY WITH TIME EITHER FROM THE ENHANCED LIFT FROM THE
VORT MAX OR STRONGER MOISTURE CONVERGENCE. THIS SHOULD ALL EXIT BY
15Z/SUNDAY. WITH PLENTY OF CAPE TO WORK WITH FOR ANY CELLS THAT DO
POP AND MARGINAL SHEAR...CAN SEE HAIL POTENTIAL...ALTHOUGH LIMITED
A BIT BY THE HIGH FRZG LEVELS.

ATTENTION THEN TURNS TOWARDS WHAT SHOULD BE THE FIRST OF A FEW
POTENTIALLY SEVERE EVENTS. SVR TSRA OVER THE PLAINS NOW SHOULD
WEAKEN AND GET DEFLECTED MAINLY TO THE NW...ALTHOUGH MAY GET SOME
ON SUNDAY MORNING THRU NERN-CNTRL MO AND W-CNTRL IL. OUTSIDE OF
THAT...OUR REGION LOOKS PRETTY DEVOID OF ANY LIFT AND SHOULD HAVE
ENOUGH OF A CAP TO PRECLUDE TSRA DEVELOPMENT...ESPECIALLY WITH
DWPTS EXPECTED TO DRY OUT A BIT SUNDAY AFTERNOON AFTER PEAKING IN
THE LO 70S IN SPOTS EARLIER IN THE DAY. AGGRESSIVE STANCE ON MAX
TEMPS LOOKS GOOD.

TES

&&

.SHORT TERM...(THROUGH LATE TONIGHT)
ISSUED AT 312 PM CDT SAT MAY 18 2013

THE PRIMARY CONCERN TONIGHT IS POTENTIAL THUNDERSTORM DEVELOPMENT
NORTH OF A NW-SE ORIENTED WARM FRONT THAT WILL LIFT ACROSS THE CWA
OVERNIGHT. GIVEN THE UNSTABLE AIRMASS IN PLACE OVER THE REGION
/MUCAPES ON THE ORDER OF 2500-3000J/KG AS PER THE RUC...GFS...AND
LOCAL WRF MODELS FOR TONIGHT/ ADDITIONAL WAA AND A VEERING LLJ
COULD CERTAINLY PROVIDE ENOUGH LIFT TO FIRE SOME STORMS DURING THE
LATE OVERNIGHT AND EARLY MORNING HOURS. THE 4KM WRF-NNM AND HRRR
DEVELOP SCATTERED STORMS TONIGHT NORTH OF THE FRONT...PARTICULARLY
THROUGH THE 09Z-12Z TIME FRAME. THUS...HAVE MAINTAINED TRENDS IN
TONIGHT`S FORECAST...INTRODUCING SCHC POPS AFTER MIDNIGHT WITH A
FOCUSED AREA OF CHC POPS MARCHING NORTHWARD THROUGH THE LATE
OVERNIGHT HOURS AND TOWARD DAYBREAK.

OTHERWISE...ANOTHER WARM NIGHT IS AHEAD FOR THE AREA...WITH LOW
TEMPERATURES EXPECTED TO DROP INTO THE MIDDLE 60S FOR SOUTHWEST
ILLINOIS TO UPPER 60S OVER MID MISSOURI AND FOR THE STL METRO AREA.

JP

.LONG TERM...(SUNDAY THROUGH NEXT SATURDAY)
ISSUED AT 312 PM CDT SAT MAY 18 2013

ON SUNDAY...WARM FRONT TO LIFT NORTH OF FORECAST AREA BY
MIDDAY...SO JUST HAVE SLIGHT CHANCE POPS DURING THE MORNING
HOURS...THEN BEST CHANCES OF STORMS IN CENTRAL/NORTHEAST MO...WEST
CENTRAL IL DURING THE AFTERNOON HOURS CLOSER TO THE MAIN WEATHER
SYSTEM. THE ACTIVITY RAMPS UP DURING SUNDAY EVENING AND THE
OVERNIGHT HOURS AS A SHORTWAVE ROTATES AROUND THE UPPER SYSTEM
THROUGH THE FORECAST AREA...THOUGH BEST CHANCES REMAIN OVER
CENTRAL/NORTHEAST MO...WEST CENTRAL IL ON NOSE OF LOW LEVEL JET.
WITH DECENT SHEAR AND INSTABILITY...AS WELL AS LOW LEVEL
MOISTURE...SEVERE STORMS ARE POSSIBLE OVER THIS AREA...WITH THE
MAIN THREAT BEING LARGE HAIL. OTHERWISE...WITH WARM FRONT LIFTING
NORTH OF FORECAST AREA AND 850 TEMPS APPROACHING 20C...WILL SEE
TEMPS WARM UP INTO THE MID TO UPPER 80S. LOWS SUNDAY NIGHT TO
REMAIN MILD...IN THE MID TO UPPER 60S.

ON MONDAY...ACTIVITY TO TAPER OFF A BIT...BEFORE RAMPING BACK UP
LATE MONDAY AFTERNOON AND THROUGH THE OVERNIGHT HOURS WITH NEXT
SIGNIFICANT SHORTWAVE AND ANOTHER ROUND OF SEVERE WEATHER POSSIBLE.
WITH MODELS CONTINUING TO SLOW DOWN THIS SYSTEM...WILL SEE THE
STORMS PERSIST THROUGH WEDNESDAY BEFORE TAPERING OFF AS FRONTAL
BOUNDARY FINALLY MOVES THROUGH. TEMPERATURES TO REMAIN ABOVE NORMAL
THROUGH THE FIRST PART OF THE WORK WEEK...BEFORE COOLING OFF TO NEAR
NORMAL TEMPS IN THE 70S FOR THE LAST HALF OF THE WORK WEEK.

WITH SLOW EXIT OF SYSTEM AND FRONTAL BOUNDARY STALLED OUT JUST SOUTH
OF FORECAST AREA ON THURSDAY...CHANCE POPS OVER SOUTHEAST HALF OF
FORECAST AREA STILL LOOKS GOOD. OTHERWISE...DRY WEATHER EXPECTED
FRIDAY AND SATURDAY.

BYRD

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 639 PM CDT SAT MAY 18 2013

VFR CONDITIONS ARE EXPECTED FOR AT LEAST THE NEXT FEW HOURS WITH
INCREASING UNCERTAINTY AFTER 06Z. AN AREA OF SHOWERS AND
THUNDERSTORMS IS EXPECTED TO DEVELOP OVER PARTS OF MO/IL OVERNIGHT
DUE TO A WARM FRONT LIFTING THROUGH THE AREA IN THE PRESENCE OF AN
UNSTABLE AIR MASS. VCSH LOOKS REASONABLE ATTM DUE TO UNCERTAINTY
REGARDING COVERAGE AND TIMING. SOUTHEASTERLY WINDS WILL BECOME
SOUTHERLY TOMORROW AND GUST TO AROUND 20-25 KTS ON THE WARM SIDE
OF THE FRONT. SCT SHOWERS AND THUNDERSTORMS ARE POSSIBLE NEAR PEAK
HEATING TOMORROW AFTN /ESPECIALLY ALONG ANY OUTFLOW BOUNDARIES
LEFT OVER FROM EARLIER CONVECTION/.

SPECIFICS FOR KSTL...VFR CONDITIONS ARE EXPECTED FOR AT LEAST THE
NEXT FEW HOURS FOLLOWED BY INCREASING UNCERTAINTY AFTER 06Z. AN
AREA OF SHOWERS AND THUNDERSTORMS IS EXPECTED TO DEVELOP OVER
PARTS OF MISSOURI OVERNIGHT DUE TO A WARM FRONT LIFTING THROUGH
THE AREA IN THE PRESENCE OF AN UNSTABLE AIR MASS. THE COVERAGE AND
SOUTHERN EXTENT OF THE OVERNIGHT CONVECTION ARE UNCERTAIN AT THIS
TIME HOWEVER THE VCSH TIMING IN THE PREVIOUS TAF LOOKS REASONABLE.
SOUTHEASTERLY WINDS WILL BECOME SOUTHERLY AND GUST TO AROUND 20
KTS TOMORROW ON THE WARM SIDE OF THE FRONT. SCT SHOWERS AND
THUNDERSTORMS ARE POSSIBLE NEAR PEAK HEATING TOMORROW
AFTERNOON /ESPECIALLY ALONG ANY OUTFLOW BOUNDARIES LEFT OVER FROM
EARLIER CONVECTION/ BUT THE BEST CHC FOR PCPN WILL BE AFTER THE
END OF THE VALID TAF PD.

KANOFSKY

&&

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

$$

WFO LSX