908 
FXUS63 KLSX 151742
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
1242 PM CDT MON APR 15 2013

.UPDATE...
ISSUED AT 1225 PM CDT MON APR 15 2013

MADE MINOR UPDATES TO ZONES...MAINLY TO REMOVE MORNING WORDING AND
KEEP SCATTERED SHOWERS AND THUNDERSTORMS FOR REST OF
TODAY...MAINLY NORTH OF I-44. ALSO...ADJUSTED HIGHS FOR AREAS THAT
ARE HAVING RAIN...DROPPED A FEW DEGREES.

BYRD
&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 351 AM CDT MON APR 15 2013

THE PRECIPITATION TRENDS TODAY ARE QUITE UNCERTAIN OWING TO THE
LACK OF IDENTIFIABLE LARGE SCALE FORCING AND GENERALLY WEAKLY
RISING HEIGHTS ALOFT. THE SHORT WAVE WHICH HELPED GENERATE A SOLID
NARROW LINE OF CONVECTION ACROSS CENTRAL AND NE MO YESTERDAY
EVENING HAS PASSED TO THE NORTHEAST. AFTER IT BEGAN EXITING...THE
ORGANIZATION AND COVERAGE OF PRECIPITATION AHEAD OF THE COLD FRONT
DRAMATICALLY WANED. BEST I CAN TELL THE CURRENT WEST-EAST BAND OF
MID-LEVEL BASED SHOWERS AND THUNDERSTORMS FROM CENTRAL KS INTO
CENTRAL MO IS ASSOCIATED WITH AN AREA OF MID-LEVEL THETAE
ADVECTION AND A WEAK IMPULSE WITHIN THE WSW FLOW ALOFT. THIS
ACTIVITY IS OCCURING IN THE WAKE OF THE COLD FRONT AND INDICATIONS
ARE THAT IT SHOULD SPREAD TO THE EAST NORTHEAST IN SOME FORM THIS
MORNING. ADDITIONAL LOW-MID LEVEL WAA AND GETS REFOCUSED IN THIS
SAME GENERAL CORRIDOR TO THE NORTH OF THE FRONT FROM CENTRAL MO
INTO WEST CENTRAL IL THIS AFTERNOON. THE FRONT IS NOW FORECAST TO
HAVE LESS SOUTHWARD PENETRATION TODAY AND THIS EVENING...MUCH AS
ANTICIPATED LAST NIGHT OWING TO THE LACK OF RISING PRESSURE BEHIND
IT AND THE NEARLY PARALLEL FLOW ALOFT. MODEL CONSENSUS IS THE
FRONT SHOULD LIE NEAR A LINE FROM NE IL TO THE STL VICINITY INTO
SW MO AT 00Z. SCATTERED THUNDERSTORMS COULD DEVELOP ALONG THE
FRONT DURING THE LATER AFTERNOON INTO THE EVENING AS THE AIR MASS
GETS FAIRLY UNSTABLE AND THERE IS A NARROW REGION OF REDUCED CIN.
DEEP LAYER SHEAR AND INSTABILITY ARE SUFFICIENT THAT SOME OF THE
STORMS COULD BE SEVERE. OF GREATER CONCERN TONIGHT IS THE
POTENTIAL FOR ELEVATED THUNDERSTORMS DEVELOPING THIS EVENING TO
THE NORTH OF THE FRONT. A 30+ SWLY LLJ IS FORECAST TO PROVIDE
IMPRESSIVE LOW LEVEL CONVERGENCE/LIFT AND GIVEN THE DEEP LAYER
SHEAR...I WOULD EXPECT SOME ORGANIZED CLUSTERS OF THUNDERSTORMS IN
A WSW-ENE ZONE FROM CENTRAL INTO EAST CENTRAL MO AND SOUTH CENTRAL
IL WITH LARGE HAIL POTENTIAL.

GLASS

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 351 AM CDT MON APR 15 2013

THE ACTIVE WEATHER PATTERN WILL PERSIST THROUGH THE FIRST PART OF
THIS PERIOD. THE FRONT WILL SINK INTO SOUTHERN MO AND SRN IL LATE
MONDAY NIGHT. ONCE AGAIN ANY THUNDERSTORM THREAT ON TUESDAY AND
TUESDAY NIGHT WILL BE LARGELY TIED TO FRONTAL CONVERGENCE DURING
THE AFTERNOON AND EVENING AND LIFT/WAA/CONVERGENCE IN THE COOL
SECTOR ASSOCIATED WITH A SWLY LLJ. THE WARM SECTOR ACROSS FAR
SOUTHERN MO AND IL WILL BECOME VERY UNSTABLE TUES AFTERNOON AND
SIGNIFICANT ELEVATED INSTABILITY IS FORECAST WELL NORTH INTO THE
COOL AIR LATE TUES AFTERNOON INTO TUESDAY NIGHT WITH MUCAPES
EXCEEDING 1500 J/KG. I THINK ANOTHER EPISODE OF ELEVATED THUNDERSTORMS
WILL OCCUR ON TUESDAY NIGHT AS THE SWLY LLJ PROVIDES GOOD LIFT/CONVERGENCE
ALONG AND NORTH OF THE I-70 CORRIDOR DURING THE EVENING WITH THIS
ZONE SHIFTING NORTHWARD SOME OVERNIGHT. ONCE AGAIN THE MUCAPE
VALUES ARE IMPRESSIVE AND SHEAR IS STOUT SUGGESTING POTENTIAL FOR
ELEVATED HAILERS.

WED/WED NIGHT HAVE THE POTENTIAL TO BE A VERY ACTIVE SEVERE WEATHER 
PERIOD WITH NUMEROUS SEVERE THUNDERSTORMS AND OUTBREAK POTENTIAL. 
THE STALLED FRONT WHICH WAS ACROSS SOUTHERN MO AND IL ON TUESDAY 
WILL LIFT NORTHWARD DURING THE DAY ON WEDNESDAY IN RESPONSE TO
CYCLOGENESIS ACROSS THE PLAINS AND THE NEWD ADVANCING SURFACE LOW.
THERE ARE DIFFERENCES WITH RESPECT TO HOW FAR NORTH THE FRONT WILL
LIFT AND HOW QUICKLY THE PLAINS LOW AND ATTENDANT COLD FRONT WILL
MOVE EASTWARD ON WED AFTERNOON AND NIGHT. THE GFS IS THE SLOWEST
AND ECMWF THE FASTEST WITH THE NAM/SREF SOLUTION FOLLOWED AT THIS
TIME. TO THE NORTH OF THE FRONT THERE MAY BE ONGOING ELEVATED
THUNDERSTORMS IN THE MORNING. AS THE FRONT LIFTS NORTHWARD...A
MOIST WARM SECTOR WILL ADVANCE NORTHWARD BENEATH STEEP MID LEVEL
LAPSE RATES...RESULTING IN VERY UNSTABLE CONDITIONS TO THE SOUTH
OF THE FRONT WITH SBCAPES AOA 2000 J/KG. THE WARM FRONT ITSELF
COULD BE THE FOCUS FOR THUNDERSTORMS AT JUST ABOUT ANYTIME WHILE
THERE IS SOME UNCERTAINTY IN THE AMOUNT OF CAPPING WITHIN THE VERY
UNSTABLE WARM SECTOR DURING THE DAYTIME. DEEP LAYER SHEAR AND
INSTABILITY WOULD FAVOR DISCRETE SUPERCELLS THROUGHOUT THE DAY AND
EVENING ON WEDNESDAY WITH UPSCALE ORGANIZATION INTO A LINE OR
BROKEN LINES WED NIGHT AHEAD OF THE ADVANCING COLD FRONT.

THE FRONT SHOULD EVENTUALLY EXIT TO THE EAST OF THE CWA BY LATE 
THURSDAY WITH MUCH COOLER AIR LATE WEEK INTO THE FIRST PART OF THE 
WEEKEND.

GLASS
&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1242 PM CDT MON APR 15 2013

FRONTAL BOUNDARY REMAINS OVER MIDDLE OF FORECAST AREA EXTENDING
FROM NORTHERN IL TO JUST NORTH OF KSTL TO JUST SOUTH OF KSGF. SO 
SCATTERED SHOWERS AND THUNDERSTORMS TO CONTINUE AFFECTING STL
METRO AREA...BEFORE BRIEFLY DIMINISHING AROUND 22Z...THEN PICKUP
ONCE AGAIN BY 00Z AS NEXT SIGNIFICANT SHORTWAVE MOVES THROUGH. AS
FOR KCOU AND KUIN...ON NORTHERN FRINGES OF ACTIVITY THIS
AFTERNOON...SO JUST HAVE SHOWER/VCSH MENTION THERE..THEN HAVE
SHOWER/VCTS MENTION FOR LATE THIS AFTERNOON THROUGH THIS
EVENING...BEFORE TAPERING OFF MOST LOCATIONS BETWEEN 06Z AND 07Z
TUESDAY. MODEL TIMING/COVERAGE STILL HARD TO PIN DOWN FOR TUESDAY
MORNING...SO JUST HAVE SHOWER/VCTS MENTION BEGINNING 14Z/15Z FOR
SITES ALONG I-70 CORRIDOR. AS FOR CIGS THROUGH THE PERIOD...KUIN
TO REMAIN LOW END VFR...WHILE KCOU AND METRO AREA TAFS TO STAY
MVFR THROUGH MOST OF TAF PERIOD DUE TO LOCATION OF STALLED FRONTAL
BOUNDARY. WINDS TO REMAIN TRICKY AS WELL. NORTH OF FRONT WINDS TO
BE NORTHERLY...WHILE THOSE CLOSE TO BOUNDARY TO SLOWLY VEER TO
THE NORTH BY THIS EVENING...THEN EVENTUALLY TO THE EAST AS
BOUNDARY SETTLES TO THE SOUTH.

SPECIFICS FOR KSTL...FRONTAL BOUNDARY REMAINS OVER MIDDLE OF FORECAST
AREA EXTENDING FROM NORTHERN IL TO JUST NORTH OF KSTL TO JUST
SOUTH OF KSGF. SO SCATTERED SHOWERS AND THUNDERSTORMS TO CONTINUE
AFFECTING STL METRO AREA...BEFORE BRIEFLY DIMINISHING AROUND
22Z...THEN PICKUP ONCE AGAIN BY 00Z AS NEXT SIGNIFICANT SHORTWAVE
MOVES THROUGH. TAPERING OFF OVER METRO AREA BY 07Z TUESDAY. MODEL
TIMING/COVERAGE STILL HARD TO PIN DOWN FOR TUESDAY MORNING...SO
JUST HAVE SHOWER/VCTS MENTION BEGINNING AROUND 15Z FOR METRO AREA. 
AS FOR CIGS THROUGH THE PERIOD...VFR CIGS TO LOWER TO MVFR BY 00Z
AND REMAIN THAT WAY THROUGH REST OF TAF PERIOD DUE TO LOCATION OF
STALLED FRONTAL BOUNDARY. WINDS TO REMAIN TRICKY AS WELL. SOUTH
WINDS TO SLOWLY VEER TO THE NORTH BY 00Z...THEN EVENTUALLY VEER TO
THE EAST AS BOUNDARY SETTLES TO THE SOUTH BY 15Z TUESDAY.

BYRD
&&

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

$$
WFO LSX