726 
FXUS63 KLSX 270008
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
608 PM CST TUE FEB 26 2013

.SHORT TERM...
ISSUED AT 340 PM CST TUE FEB 26 2013
(TONIGHT - WEDNESDAY)

STACKED LO SYSTEM NOW WOBBLING THRU SRN IL AS IT TRACKS TO THE NE.  
AN OCCLUDED SFC LO EXISTS IMMEDIATELY BELOW JUST TO THE SE OF STL 
CITY...WITH N FLOW ON THE NRN SIDE WHICH COVERS MUCH OF MO AND 
IL...AND W FLOW ON ITS SRN SIDE WHICH COVERS THE FAR SRN PORTIONS OF 
MO AND IL.  RADAR MOSAIC SHOWS TWO AREAS OF PCPN TO THE E...ONE OVER 
CNTRL IL WHICH IS RAIN ON ITS SERN FLANK AND TURNS INTO SNOW AS IT 
SLOWLY PUSHES WWD TOWARDS W-CNTRL IL...AND ANOTHER AREA OF SHRA 
MOVING UP TO THE N FROM THE CAPE GIRARDEAU AREA AND FAR SRN IL.  
MOST OTHER PCPN ACTIVITY EITHER HAS DEGRADED TO --DZ OR IS SCT SHSN 
AND IS NOT GETTING PICKED UP VERY WELL BY RADAR NETWORK DUE TO 
DISTANCE AND WEAKER RETURNS IN GENERAL...BUT SATELLITE SHOWS COOLER 
CLOUD TOPS BUILDING WWD TOWARDS NE-CNTRL MO WHICH WILL ACCOMMODATE 
PCPN-TYPES GOING FROM --DZ/--FZDZ TO SCT SNOW SHOWERS.  SFC TEMPS 
RANGE FROM LO-MID 30S FOR MOST AREAS N AND W OF STL CITY TO NEAR 50F 
IN SALEM IL WHICH WARM BULGE NEAR OCCLUDED SFC FRONT WHICH EXTENDS 
EWD FROM SFC LO. 

TWO AREAS OF PCPN ADDRESSED ABOVE SHOULD BE MAINLY EARLY EVENING 
CONCERNS...AS -SHRA MOVES NWD THRU THE ERN FA IN SWRN IL...WHILE A 
BIT TRICKIER IN CNTRL IL ON WHETHER OR NOT IT WILL IMPACT MUCH OF 
W-CNTRL IL DESPITE WWD MOVEMENT.  THIS IS BECAUSE ENTIRE SYSTEM IS 
LIFTING NE AND WILL SERVE TO RETARD THE WWD MOVEMENT OF THIS PCPN 
AREA WITH TRANSLATIONAL AND ROTATIONAL VECTORS IN NEARLY OPPOSITE 
DIRECTIONS.  BELIEVE COVERAGE THIS AREA AFFECTS WILL BE LIMITED IN 
W-CNTRL IL AND HAVE PLACED LIKELY POPS IN ONLY A SMALL AREA WITH THE 
REST WITH SCT -SHSN EXPECTED WITH PATCHES OF COLDER CLOUD TOPS 
GETTING THROWN BACK INTO THE MIX TO GENERATE ICE IN THE CLOUD NEEDED 
FOR SNOW.  THE REST OF THE AREA WILL LACK THE NEEDED ICE ALOFT AND 
SHOULD JUST SEE --DZ THIS EVENING.

ATTENTION LATER THIS EVENING AND CONTINUING THRU WEDNESDAY THEN 
TURNS TO SNOW CHANCES.  A COMBINATION OF A STRONG SHORTWAVE 
CURRENTLY OVER THE NRN REACHES OF THE LAND OF ENCHANTMENT DIGGING 
INTO THE CNTRL CONUS LONGWAVE TROF OVER OUR AREA AND AN AREA OF 
VORTICITY ROTATING AROUND THE BACKSIDE OF THE CURRENT STORM JUST TO 
OUR SE WILL RESULT IN INCREASING BROADSCALE LIFT BUILDING FROM THE N 
AND W MAINLY AFTER MIDNIGHT...COVERING MUCH OF THE AREA WEDNESDAY 
MORNING AND THEN PULLING AWAY TO THE E...WITH YET ANOTHER 
DISTURBANCE ROTATING AROUND THE BACKSIDE OF THE LO FROM THE N 
WEDNESDAY AFTERNOON TO PROVIDE ADDITIONAL SNOW.  MOISTURE WILL BE 
MORE LIMITED THAN THE LAST SYSTEM AND LIFT WILL BE WEAKER...BUT 
STILL ENOUGH TO RESULT IN LIGHT QPF AMOUNTS OF A TENTH OR TWO FOR 
MOST PLACES SAVE THE FAR SRN FA IN SERN MO.  THIS SHOULD EQUATE TO 
SNOW ACCUMS OF 1-2" FOR MOST PLACES...MAINLY ON NON-ROAD SURFACES 
WHICH SFC TEMPS AT OR JUST ABOVE FREEZING FOR MOST OF THE EVENT WILL 
SHOULD HELP LIMIT WHAT ACCUMULATES THERE.  THE BEST PROBS FOR SNOW 
ACCUM ON ROADS WILL BE WELL TO THE N AND W OF STL METRO WHERE THE 
COLDEST SFC TEMPS WILL BE...AIDED IN PART BY DEEP SNOW PACK. HAVE
ISSUED A SNOW ADVISORY FOR AREAS N AND W OF STL METRO FOR THE
BETTER CHCS TO ACCUMULATE ON ALL SURFACES.

TES

&&

.LONG TERM...
ISSUED AT 350 PM CST TUE FEB 26 2013
(WEDNESDAY NIGHT - NEXT TUESDAY)

LONGWAVE UPPER LEVEL TROF OVER ERN NOAM WILL BE THE RULE FOR MUCH... 
IF NOT THE ENTIRE BREADTH...OF THIS PERIOD AND COULD RESULT IN 
SEVERAL CHANCES FOR SNOW AND WILL ALMOST CERTAINLY RESULT IN AN 
EXTENDED PERIOD OF BELOW AVERAGE TEMPS. 

CONTINUATION OF VORT CENTER ROTATING AROUND THE BACKSIDE OF THIS 
STORM SYSTEM IS EXPECTED AT THE START OF THIS PERIOD WEDNESDAY 
EVENING AND SHOULD RESULT IN FLURRIES OR SCT SNOW SHOWERS...MAINLY 
IN IL.  MORE OF THE SAME FOR THURSDAY THRU EARLY SATURDAY WITH THE 
MOST INTRIGUING OUT OF THESE FRIDAY-FRIDAY NIGHT AS ONE OF A SERIES 
OF STRONG DIGGING SHORTWAVES ATTEMPTS TO CLOSE OFF OVERHEAD DURING 
THIS TIME.  AN EARLIER CLOSING OF THE SYSTEM WILL RESULT IN 
DRAMATICALLY INCREASED PCPN CHCS AND SNOW POTENTIAL...WHILE A 
CLOSING OFF JUST DOWNSTREAM LIKE MOST NWP SOLUTIONS INDICATE ONLY 
SHOW A SMALL CHANCE.  IT WILL BE CLOSE...BUT CURRENTLY SIDING WITH 
THE CONSISTENT MODEL SOLNS WHICH SHOW ONLY A SMALL CHC OF ACCUM SNOW 
WHILE A BETTER CHC FOR FLURRIES. 

FINALLY...MODELS STILL SHOWING A STRONG PAC SHORTWAVE DRIVING SEWD 
THRU THE MID MS VALLEY MONDAY NIGHT-TUESDAY.  MODELS HAVE WARMED UP 
A BIT AND HAVE A MORE OPEN WAVE THAN 24HRS AGO...AND SO SNOW 
POTENTIAL DOES NOT LOOK AS GOOD...BUT STILL WORTH A RAIN/SNOW MIX 
MENTION FOR NOW. 

TEMPS TO BE BELOW AVERAGE THRU THE PERIOD...WITH MODERATION TOWARDS 
NORMAL EXPECTED EARLY NEXT WEEK WITH S-SE FLOW FOR A PERIOD.

TES

&&

.AVIATION...
ISSUED AT 542 PM CST TUE FEB 26 2013

FORECAST PERIOD WILL BE DOMINATED BY CYCLONIC CURVATURE IN THE
WAKE OF VERTICALLY STACKED LOW PRESSURE SYSTEM AS IT PUSHES
NORTHEAST.  AS MENTIONED IN THE SHORT TERM DISCUSSION THE VARIETY
OF DISTURANCES THAT WILL BE IMPACTING AREA SHOULD CONTINUE A
THREAT OF WINTRY PRECIPITATION AT MOST LOCATIONS...UNFORTUNATELY
THERE IS NO CLEAR SIGNAL AS TO SPECIFIC PRECIP TRENDS.
SO...FORECAST FOR THE FIRST FEW HOURS ARE SIMPLY BASED
EXTRAPOLATION OF OBSERVED TRENDS...WITH A GENERAL FORECAST OF IFR
CIGS AND MVFR VSBYS IN LIGHT SNOW LATER TONIGHT AND INTO EARLY
WEDNESDAY MORNING.  

SPECIFICS FOR KSTL...WITH SURFACE LOW PUSHING INTO INDIANA AT THIS
TIME INCREASE IN MIXING SHOULD BRING ABOUT SOME IMPROVEMENT TO
VSBYS AND CIGS OVER THE NEXT FEW HOURS. WHILE CIGS WILL LIKELY
REMAIN IFR...BASED ON UPSTREAM OBS VISIBILITIES SHOULD INCREASE
INTO THE 3-5 MILE RANGE EARLY THIS EVENING.  BASED ONSET OF STEADY
LIGHT SNOW AT 08Z WITH BROAD SCALE ASCENT THAT IS FORECAST INTO
THE AREA AT THAT TIME.

TRUETT

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...WINTER WEATHER ADVISORY UNTIL 6 PM CST WEDNESDAY FOR KNOX MO-
     LEWIS MO-MARION MO-MONROE MO-RALLS MO-SHELBY MO.

     WINTER WEATHER ADVISORY UNTIL NOON CST WEDNESDAY FOR AUDRAIN MO-
     BOONE MO-CALLAWAY MO-COLE MO-GASCONADE MO-LINCOLN MO-
     MONITEAU MO-MONTGOMERY MO-OSAGE MO-PIKE MO-WARREN MO.

IL...WINTER WEATHER ADVISORY UNTIL 6 PM CST WEDNESDAY FOR ADAMS IL-
     BROWN IL-PIKE IL.

     WINTER WEATHER ADVISORY UNTIL NOON CST WEDNESDAY FOR CALHOUN IL.

&&

$$

WFO LSX