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000
FXUS63 KLSX 180847
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
347 AM CDT SAT MAY 18 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 325 AM CDT SAT MAY 18 2013

BOTH FOG AND STRATUS HAVE DEVELOPED ACROSS SOUTHEAST MISSOURI AND
SOUTHERN ILLINOIS DURING THE OVERNIGHT HOURS...WITH PATCHY FOG
FURTHER NORTH. ADDITIONAL DEVELOPMENT TO THE NW SHOULD CONTINUE
THROUGH DAYBREAK. AT THIS TIME DENSE FOG IS CONFINED TO THE FAR SRN
CWA AND WILL ISSUE AN ADVISORY FOR THIS REGION UP TO SULLIVAN
THROUGH 14Z. MOST AREAS WILL SEE A DRY DAY WITH WARMER TEMPERATURES
AS THE PLAINS UPPER RIDGE SHIFTS INTO THE MS VALLEY AND LOW LEVEL
WAA GETS UNDERWAY. THE EXCEPTION MIGHT BE IN SOUTH CENTRAL IL
ALONG THE BACKSIDE OF THE RETREATING AND WEAKENING UPPER LOW WHERE
AN ISOLATED DIURNAL SHOWER IS POSSIBLE.

I AM STILL THINKING THERE IS POTENTIAL FOR SCATTERED ELEVATED
THUNDERSTORMS OVERNIGHT TONIGHT. MID LEVEL LAPSE RATES STEEPEN
QUITE A BIT AND THIS COMBINED WITH LOW LEVEL WAA/MOISTURE TRANSPORT
AND CONVERGENCE/LIFT VIA A SWLY LLJ WILL RESULT IN THE THREAT OF
ELEVATED STORMS TO THE NORTH OF A WNW-ESE ORIENTED WARM FRONT
DRAPPED ACROSS SOUTHERN MO. SOME OF THE CONVECTION ALLOWING MODELS
INCLUDING THE NSSL 4KM WRF SUPPORT THIS SCENARIO SHOWING SCATTERED
CONVECTIVE DEVELOPMENT IN A NW-SE ZONE ACROSS EASTERN MO BETWEEN
06-09Z.

GLASS

.LONG TERM...( SUNDAY THROUGH THURSDAY)
ISSUED AT 325 AM CDT SAT MAY 18 2013

AN ACTIVE PERIOD OF WEATHER IS ON TAP FOR THE AREA FROM SUNDAY
THROUGH WEDNESDAY AS A COMPLEX LONG WAVE TROF SLOWLY MIGRATES
THROUGH THE NATIONS MIDSECTION WHILE A SERIES OF SHORT WAVES
EJECT ENEWD THRU THE BASE AND ACROSS PORTIONS OF THE MID/UPPER MS
VALLEY. MULTIPLE SEVERE WEATHER EPISODES ARE POSSIBLE IN THE
SUNDAY NIGHT THROUGH TUESDAY NIGHT TIME FRAME AND UNTIL THE FRONT
FINALLY PUSHES TO THE EAST OF THE CWA LATE WEDNESDAY.

SUNDAY LOOKS LIKE A WARM DAY WITH STRENGTHENING WAA AND H85 TEMPS
RISING TO ABOVE +19 DEGC. THE AFOREMENTIONED WARM FRONT WILL BE
LIFTING NORTHWARD DURING THE DAY AND THE WARM SECTOR SHOULD BECOME
QUITE UNSTABLE BUT LOOKS CAPPED. IN QUESTION IS THE AREA ACROSS NE
MO AND WEST CENTRAL IL WHERE SOME OF THE MODELS WANT TO DEVELOP
DEEP CONVECTION...APPARENTLY TO THE NORTH OF THE RETREATING WARM
FRONT. DEEP LAYER SHEAR AT THIS TIME FRAME IS MORE SUPPORTIVE OF
MULTICELLS CAPABLE OF LARGE HAIL. THE THUNDERSTORM AND SEVERE
WEATHER THREAT WILL RAMP UP ON SUNDAY NIGHT...SPECIFICALLY ACROSS
CENTRAL MO AND INTO NE MO. A SIGNFICANT SHORT WAVE IS FORECAST TO
ROTATE NEWD FROM KS/OK AND INTO IOWA WITH AN ACCOMPANYING MID
LEVEL WIND MAX. THIS WILL STRENGTHEN THE DEEP LAYER SHEAR. AT THIS
TIME I EXPECT THAT SEVERE STORMS ACROSS EASTERN KS AND WESTERN MO
WILL GROW UPSCALE AND SHIFT EASTWARD INTO CENTRAL MO...WEAKING
LATE ACROSS EASTERN MO. CONVECTIVE TRENDS ARE A BIT UNCERTAIN ON
MONDAY MORNING BUT ANY ONGOING STORMS ARE EXPECTED TO DIMINISH AS
LARGE SCALE SUBSIDENCE DOMINATES IN THE WAKE OF THE LIFTING SHORT
WAVE. BY LATE AFTERNOON/EARLY MONDAY EVENING A SURFACE FRONT IS
EXPECTED TO LIE FROM THE SURFACE LOW IN IOWA ACROSS NW MO INTO SE
KS. THE WARM SECTOR AIR MASS WILL BE AT LEAST MODERATELY UNSTABLE
WITH LITTLE CAP IN A BROAD ZONE WHERE WSW DEEP LAYER SHEAR WILL BE
AOA 40 KTS...SUPPORTIVE OF SUPERCELLS. AT THIS TIME EXPECTING
SCATTERED STORMS TO DEVELOP DURING THE LATE AFTERNOON/EARLY
EVENING WITHIN THIS ZONE WITH AN UPSWING IN COVERAGE DURING THE
EVENING AS THE NEXT SHORTWAVE SPREADS LARGE SCALE ASCENT INTO THE
MID MS VALLEY. ONGOING CONVECTION ON TUESDAY MORNING LEADS TO
UNCERTAINTY IN THE DETAILS FOR TUESDAY/TUESDAY NIGHT...BUT THE
GENERAL SYNOPTIC PATTERN OF ANOTHER EJECTING SHORT WAVE AND
ATTENDANT PROGRESSING COLD FRONT ALONG WITH AT LEAST WEAK-MODERATE
INSTABILITY AND DEEP LAYER SHEAR OF 30-40 KTS SUPPORTS POTENTIAL
FOR A CONTINUED SEVERE WEATHER THREAT AND NUMEROUS THUNDERSTORMS.

GLASS

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1137 PM CDT FRI MAY 17 2013

STILL EXPECTING IFR CIGS/VSBYS TO DEVELOP TONIGHT...THO IT SEEMS
LIKE IT`S TAKING A LITTLE LONGER THAN EXPECTED. JUST STARTING TO
SEE SOME VSBYS DROP INTO MVFR RANGE OVER THE PAST HOUR OR SO...AND
KFAM IS NOW DOWN TO 2SM. EXPECT THIS TREND TO CONTINUE...WITH MOST
OF THE AREA EXPERIENCING IFR CIGS/VSBYS BEFORE DAYBREAK SATURDAY
MORNING. LATEST MODEL GUIDANCE HAS BACKED OFF ON THE LOW END...SO
HAVE TWEAKED TAFS TO GO A BIT HIGHER AND DELAY THE ONSET OF IFR
CONDITIONS AS WELL. STILL EXPECTING FLIGHT CONDITIONS TO IMPROVE
TO VFR BY LATE MORNING ACROSS THE AREA.

SPECIFICS FOR KSTL...

STILL EXPECTING IFR CIGS/VSBYS TO DEVELOP AT LAMBERT TONIGHT...THO
IT SEEMS LIKE IT`S TAKING A LITTLE LONGER THAN EXPECTED. JUST
STARTING TO SEE SOME VSBYS DROP INTO MVFR RANGE IN THE STL METRO
AREA OVER THE PAST HOUR OR SO...AND KFAM IS NOW DOWN TO 2SM.
EXPECT THIS TREND TO CONTINUE...WITH THE VSBY DROPPING TO MVFR
BETWEEN 08Z AND 10Z...AND IFR CIGS DEVELOPING A LITTLE LATER AS WELL.
LATEST MODEL GUIDANCE HAS BACKED OFF ON THE LOW END...SO HAVE
TWEAKED THE TAF TO GO A LITTLE HIGHER THAN PREVIOUSLY FORECAST. STILL
EXPECTING FLIGHT CONDITIONS TO IMPROVE TO VFR BY LATE MORNING.

CARNEY

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...DENSE FOG ADVISORY UNTIL 9 AM CDT THIS MORNING FOR IRON MO-
     MADISON MO-REYNOLDS MO-ST. FRANCOIS MO-STE. GENEVIEVE MO.

IL...NONE.
&&

$$

WFO LSX