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000
FXUS63 KLSX 181805
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
105 PM 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 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1243 PM CDT SAT MAY 18 2013

FOG HAS DISSIPATED ACROSS THE REGION...THOUGH CIGS HAVE BEEN A BIT
SLOW TO RECOVER...PARTICULARLY ACROSS NORTHEAST MO AND OVER THE
OZARKS. LATEST VISIBLE SATELLITE IMAGERY SHOWS AN EXTENSIVE
CUMULUS FIELD DEVELOPING OVER THE MISSISSIPPI VALLEY...THOUGH
EXPECT THE GRADUAL IMPROVEMENT IN CIGS TO CONTINUE THIS
AFTERNOON...WITH JUST SOME SCT VFR CLOUDS EXPECTED.

A NW-SE ORIENTED WARM FRONT WILL SHIFT NORTHWARD ACROSS THE REGION
OVERNIGHT TONIGHT...AND MODELS CONTINUE TO INDICATE THE
DEVELOPMENT OF SOME SHRA/TSRA ALONG AND AHEAD OF THE ADVANCING
WARM FRONT. FOR NOW...HAVE INCLUDED MENTION OF VCSH FOR AREA TAF
SITES DURING THE EARLY MORNING HOURS...AND WILL DEFER TO LATER TAF
ISSUANCES TO FURTHER PIN DOWN TIMING AND/OR MENTION OF TSRA.
OTHERWISE...WINDS WILL REMAIN SOUTHEASTERLY TODAY AND VEER TO
THE SOUTH ON SUNDAY...INCREASING TO ABOUT 10-12KT WITH SOME GUSTS
AS RETURN FLOW SETS IN.

SPECIFICS FOR KSTL...

CIGS ARE EXPECTED TO CONTINUE TO IMPROVE TO SCT VFR THIS
AFTERNOON...WITH LIGHT SOUTHEAST WINDS. OVERNIGHT TONIGHT A WARM
FRONT WILL DRIFT NORTH ACROSS THE AREA...AND MODELS CONTINUE TO
INDICATE SOME SHRA/TSRA DEVELOPMENT ACCOMPANYING THE FRONT. HAVE
CURRENTLY INCLUDED VCSH MENTION FOR KSTL FROM 10-13Z...THOUGH
TIMING WILL LIKELY NEED REFINED IN LATER TAF ISSUANCES...ALONG
WITH POTENTIAL THUNDER MENTION WHEN COVERAGE/INTENSITY BECOMES
MORE CLEAR. WINDS WILL VEER TO THE SOUTH TOMORROW BEHIND THE
ADVANCING WARM FRONT...INCREASING TO 10-12KT AND GUSTING TO
20-22KT BY THE AFTERNOON.

JP

&&

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

$$

WFO LSX