National Weather Service Raw Text Product

365 
FXUS63 KLSX 061758
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
1158 AM CST THU DEC 6 2012

.UPDATE...
ISSUED AT 1146 AM CST THU DEC 6 2012

QUICK UPDATE FOR CLOUD TRENDS THROUGH THIS AFTERNOON AND FOR
TEMPERATURES. INCREASED SKY COVER GRIDS A BIT INTO MOSTLY CLOUDY
RANGE AREAWIDE THROUGH THE AFTERNOON AS COMBINATION OF MID/HIGH
LEVEL CLOUDINESS ADVECTING FROM THE WEST AND INCREASING LOW-LEVEL
CLOUDS/MOISTURE FROM THE GULF ARE ENCROACHING ON THE CWFA. ALSO
TWEAKED TEMPERATURES A BIT...LOWERING HIGHS A FEW DEGREES OVER
PORTIONS OF CENTRAL AND NORTHEAST MISSOURI WHERE LOOKING AT
UPSTREAM SKY COVER...THESE AREAS LOOK TO STAY OVERCAST ALL DAY.

GOSSELIN

&&

.SHORT TERM...
ISSUED AT 257 AM CST THU DEC 6 2012
(TODAY)

SURFACE RIDGE HAS MOVED OFF TO THE EAST ALLOWING LIGHT SOUTHERLY 
WINDS TO RETURN TO THE REGION TODAY. HOWEVER...HIGH CLOUDS CONTINUE 
TO STREAM ACROSS AREA AHEAD OF NEXT WEATHER SYSTEM. DESPITE THE 
CLOUDS AND TIME OF YEAR...STILL EXPECT WELL ABOVE NORMAL HIGHS TODAY 
IN THE MID 50S TO NEAR 60.

BYRD

&&

.LONG TERM...
ISSUED AT 257 AM CST THU DEC 6 2012
(TONIGHT-SATURDAY)

PRECIPITATION CHANCES REMAIN THE PRIMARY FOCUS HEADING INTO THE END 
OF THE WEEK AS FRONTAL BOUNDARY DRIFTS SOUTH ACROSS THE REGION. 
NAM FORECAST FOR PLACEMENT OF THE FRONT IS CONSISTENTLY NORTH OF
ALL OTHER SOLUTIONS...AND DUE TO THIS HAVE LEANED FORECAST
SPECIFICS FOR SENSIBLE WEATHER TOWARDS THE MORE SWD SOLUTIONS OF
THE GFS...GEM...ECMWF...AND SREF. 

THIS FRONT WILL OOZE ACROSS N SECTIONS OF THE CWA TONIGHT...AND THEN 
INTO S PORTIONS ON FRIDAY.  INITIALLY...PRECIP MAY STRUGGLE TO FORM 
IN SPITE OF RELATIVELY GOOD MOISTURE ADVECTION INTO THE 
BOUNDARY...BUT AS UPPER LEVEL SHORTWAVE APPROACHES LATER TONIGHT AND 
FRIDAY THE INCREASED UVV SHOULD LEAD AT LEAST A CHANCE OF SHOWERS 
FOR THE ENTIRE CWA.  HIGHEST POPS TONIGHT...50%...WILL BE OVER N 
PARTS OF THE CWA WHERE SHORTWAVE WILL MAKE ITS IMPACT FIRST. POPS
WILL REMAIN IN THE CHANCE CAT FOR THE ENTIRE AREA ON
FRIDAY...HIGHEST IN THE FAR EAST WHERE SHORTWAVE ENERGY AND LOW
LEVEL FORCING WILL BE SOMEWHAT MAXIMIZED.

IT NOW LOOKS LIKE THERE WILL BE A LULL IN THE PRECIP OVER MUCH OF 
THE AREA FRIDAY NIGHT AND SATURDAY AS FIRST SHORTWAVE EXITS AND 
KICKS THE FRONTAL BOUNDARY INTO THE OHIO VALLEY.  I HAVE MAINTAINED 
SOME LOW CHANCE POPS OVER S SECTIONS OF THE CWA AS SHORT RANGE 
MODELS STILL SUGGEST SOME SHORTWAVE ENERGY THAT COULD INTERACT WITH 
THE STALLED BAROCLINIC ZONE ALONG THE MO/AR BORDER.  

(SUNDAY-THURSDAY)
EACH RUN OF THE MEDIUM RANGE SOLUTIONS SEEM TO BE COMING INTO BETTER 
CONSENSUS WITH THE STORM SYSTEM OF INTEREST FOR THIS WEEKEND.  ALL 
00Z SOLUTIONS ARE NOW INDICATING THAT THE UPPER DYNAMICS WILL SWING 
THROUGH THE MID MISSISSIPPI VALLEY AS POSITIVELY TILTED UPPER TROF...
WITH A SLIGHTLY FASTER EWD PROGRESSION. WHILE A WEAK SURFACE WAVE COULD
FORM ALONG THE FRONT AS IT LIFTS BACK NORTH ON SUNDAY MORNING
MODELS ARE CERTAINLY INDICATING THAT ANY SIGNIFICANT
CYCLOGENESIS...AND DEFORMATION ZONE PRECIP WHICH WOULD PRODUCED
SIGNIFICANT SNOWFALL...WILL BE WELL TO OUR N. BOTH THE GFS AND
ECMWF HAVE 850MB LOW DEVELOPING ALONG THE INTENSIFYING THERMAL
GRADIENT OVER THE UPPER GREAT LAKES BY MIDDAY SUNDAY. 
SO...WHILE THE SYSTEM WILL LIKELY PRODUCE SOME SNOW IN OUR AREA
AS COLD AIR ENTERS THE BACK SIDE OF THE STORM SYSTEM...THE
SIGNIFICANT PRECIP WILL LIKELY BE WINDING DOWN AS THE AMS COOLS
ENOUGH TO CHANGE THE RAIN OVER TO SNOW. SO...PERIOD OF TIME WITH
SNOWFALL OF ANY INTENSITY WILL BE QUITE BRIEF.

CYCLOGENESIS WILL COMMENCE SATURDAY NIGHT OVER THE PLAINS WITH THE 
APPROACH OF THE UPPER TROF. RESULTANT INCREASE SOUTHERLY FLOW IN OUR 
AREA SHOULD LEAD TO BROAD AREA OF OVERRUNNING SHOWERS N OF THE 
STALLED FRONTAL BOUNDARY ACROSS N AR THAT WILL IMPACT OUR MOST OF
THE CWA ON SATURDAY NIGHT.

A LITERAL INTERPRETATION OF THE FASTER 00Z GUIDANCE WOULD SUGGEST 
THAT THE BULK OF THE PRECIP WITH THIS SYSTEM WOULD ALREADY BE 
EXITING OUR AREA ON SUNDAY MORNING.  HOWEVER..SINCE THIS IS STILL 4 
DAYS AWAY...AND WITH UPPER TROF STILL WELL TO THE WEST BY MIDDAY 
SUNDAY...WILL CONTINUE WITH HIGH CHANCE AND LOW LIKELY POPS FOR MUCH 
OF THE AREA...WITH THE HIGHEST POPS IN SE PARTS OF THE CWA.
LIKEWISE...THE FASTER SOLUTIONS ALSO SUGGEST THAT THE COLD AIR IN 
THE WAKE OF THE SURFACE SYSTEM WILL BE MAKING A STRONG SOUTHWARD 
SURGE BY AFTERNOON.  THERMAL PROFILE OF THE LATEST GUIDANCE SUGGESTS 
THAT THIS MAY BE ABLE TO CAUSE ANY LINGERING RAIN OVER NW PARTS OF 
OUR CWA TO BECOME MIXED WITH OR CHANGE TO SNOW DURING THE 
AFTERNOON...WITH THE CHANGEOVER OCCURRING IN THE LIGHT RAIN ACROSS 
THE REST OF THE AREA ON SUNDAY NIGHT.

ONE THING APPEARS TO BE CERTAIN...AMS CHANGE BEHIND THIS SYSTEM IS 
GOING TO BE SHOCKING ESPECIALLY COMPARED TO WHAT WE'VE EXPERIENCED 
SO FAR THIS DECEMBER.  WHILE THIS STORM STILL DOESN'T TAP THE 
BRUTALLY COLD AIR OVER NORTHERN CANADA AND ALASKA...ON MONDAY 
MORNING TEMPS IN THE 20S AND 30S ON MONDAY MORNING AND GUSTY 
NORTHWEST WINDS ARE GOING TO BE QUITE A CHANGE.  BY MONDAY...ANY 
LINGERING PRECIP IN THE MID MISSISSIPPI VALLEY SHOULD BE LIMITED TO 
FLURRIES.

TUE AND WED SHOULD REMAIN DRY AS THE CENTRAL U.S. WILL BE BETWEEN 
WEATHER SYSTEMS.  HIGH PRESSURE IN THE WAKE OF MONDAYS SYSTEM WILL 
KEEP TUESDAYS TEMPERATURES BELOW NORMAL...SOME MODERATION IS 
EXPECTED BY WEDNESDAY AS SOUTHERLY FLOW RETURNS TO THE AREA. 
  
TRUETT

&&

.AVIATION...
ISSUED AT 1146 AM CST THU DEC 6 2012

MAIN CONCERN FOR THE VALID TAF PERIOD IS LOW STRATUS/FOG AND ITS
IMPACT ON CELINGS AND VISIBILITIES. VFR CONDITIONS ARE EXPECTED
AT ALL TAF SITES THROUGH MIDDLE OF THIS AFTERNOON. AN APPROACHING
WEAK COLD FRONT WILL YIELD LIGHT/VARIABLE WINDS BEGINNING TONIGHT
WITH INCREASING LOW-LEVEL MOISTURE POOLING AHEAD OF THIS BOUNDARY.
CURRENTLY...AM EXPECTING CEILINGS TO LOWER INTO THE MVFR RANGE
VERY LATE THIS AFTERNOON OR EARLY EVENING WITH CEILINGS GRADUALLY
LOWERING THROUGHOUT THE NIGHT. LOWERED CEILINGS TO THE LOW-END
MVFR RANGE/1000 FEET OVERNIGHT WITH LOWERING VISBYS IN BR AS WELL.
LATEST NWP GUIDANCE SUGGESTS IFR CEILINGS/VISBYS IN BR/FG
BEGINNING OVERNIGHT TONIGHT BUT HELD OFF FOR NOW DUE TO LOW
CONFIDENCE. WITH THE FRONT BECOMING STATIONARY OVER CENTRAL
MISSOURI THROUGH CENTRAL ILLINOIS...EXPECT CONDITIONS TO
MARGINALLY IMPROVE AT BEST WITH LIGHT/VARIABLE SFC WINDS
CONTINUING THROUGH THE VALID TAF PERIOD.

SPECIFICS FOR KSTL...

MAIN CONCERN FOR THE VALID TAF PERIOD IS LOW STRATUS/FOG AND ITS
IMPACT ON CELINGS AND VISIBILITIES AT THE SITE. VFR CONDITIONS ARE
EXPECTED THROUGH THE MIDDLE OF THIS AFTERNOON. AN APPROACHING WEAK
COLD FRONT WILL YIELD LIGHT/VARIABLE WINDS BEGINNING TONIGHT WITH
INCREASING LOW-LEVEL MOISTURE POOLING AHEAD OF THIS BOUNDARY.
CURRENTLY...AM EXPECTING CEILINGS TO LOWER INTO THE MVFR RANGE
VERY LATE THIS AFTERNOON WITH CEILINGS GRADUALLY LOWERING
THROUGHOUT THE NIGHT. LOWERED CEILINGS TO THE LOW-END MVFR
RANGE/1000 FEET OVERNIGHT AND THROUGH TOMORROW WITH LOWERING
VISBYS IN BR AS WELL. LATEST NWP GUIDANCE SUGGESTS IFR
CEILINGS/VISBYS IN BR/FG BEGINNING OVERNIGHT TONIGHT BUT HELD OFF
FOR NOW DUE TO LOW CONFIDENCE. WITH THE FRONT BECOMING STATIONARY OVER CENTRAL
MISSOURI THROUGH CENTRAL ILLINOIS...EXPECT CONDITIONS TO
MARGINALLY IMPROVE AT BEST AT LAMBERT WITH LIGHT/VARIABLE SFC
WINDS CONTINUING THROUGH THE VALID TAF PERIOD.

GOSSELIN

&&

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

$$

WFO LSX