516 
FXUS63 KLSX 200814
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
314 AM CDT WED MAR 20 2013

.SHORT TERM...(THROUGH LATE THIS AFTERNOON)
ISSUED AT 313 AM CDT WED MAR 20 2013

STILL DEALING WITH SEVERAL WEAK SHORTWAVES/SECONDARY COLD FRONT THAT 
ARE SLIDING SOUTHEAST THROUGH FORECAST AREA TODAY. COLD FRONT HAS 
MOVED THROUGH PITTSFIELD AND MEXICO AS OF 08Z...EXITING FORECAST 
AREA BY 12Z/13Z TIMEFRAME. SC DECK NORTH OF FRONT TO CONTINUE ITS 
TRACK INTO FORECAST AREA WITH A FEW FLURRIES POSSIBLE THIS MORNING 
BEFORE CLOUDS CLEAR OUT FROM NORTH TO SOUTH.  WITH COLDER AIR 
FINALLY FILTERING IN AND WINDS PICKING UP FROM THE NORTHWEST TO 
NORTH AROUND 10 TO 20 MPH...WITH GUSTS TO NEAR 25 MPH AT 
TIMES...TEMPERATURES WILL STRUGGLE TO WARM UP. EXPECT HIGHS ONLY IN 
THE LOW 30S FAR NORTH TO THE LOW 40S FAR SOUTH.

BYRD

&&

.LONG TERM...(TONIGHT THROUGH TUESDAY)
ISSUED AT 313 AM CDT WED MAR 20 2013

(TONIGHT-THURSDAY NIGHT)

00Z RUNS ARE MAINTAINING FAIRLY GOOD AGREEMENT WITH THEIR HANDLING 
OF SYSTEM THAT WILL IMPACT S MO IN THE THURSDAY-THURSDAY NIGHT TIME 
FRAME.  IN PARTICULAR...SOLUTIONS ARE HOLDING STRONG WITH THE IDEA 
THAT THERE WILL BE A VERY SHARP NE EDGE TO THE SIGNIFICANT 
PRECIPITATION SHIELD...WITH THIS GRADIENT PRIMARILY ALONG OUR COMMON 
CWA BORDER WITH SGF AND PAH. 

290K AND 295K SURFACES FROM BOTH THE NAM AND GFS REALLY DO A GREAT 
JOB OF DEPICTING EVOLUTION OF PRECIP AND THIS SHARP GRADIENT.  
NARROW BAND OF STRONG ASCENT WILL OCCUR IN THE BAROCLINIC ZONE FROM 
WESTERN INTO S CENTRAL MO...WITH THE ASCENDING PARCELS THEN SHARPLY 
TURNING SOUTHEAST AS THEY REACH CENTRAL AND SOUTHEAST MISSOURI AND  
ENCOUNTER THE NW MID LEVEL FLOW.  

ATTM...STILL IN THE PROCESS OF COORDINATING THE FORECAST PARTICULARS 
WITH OUR SURROUNDING OFFICES...BUT IN GENERAL THINK THAT GOING 
FORECAST TRENDS LOOK QUITE GOOD AND AM TRYING TO MAINTAIN THAT 
FLAVOR IN THIS MORNINGS UPCOMING FORECAST. WITH THERMAL PROFILE OF 
AMS SUPPORTING ALL FROZEN PRECIP...STILL LOOKS LIKE THE EXTREME 
SOUTHERN TIP OF OUR CWA...SOUTH OF A CUBA-FREDERICKTOWN LINE...COULD 
SEE ACCUMULATIONS IN THE 3-5 INCH RANGE THROUGH THURSDAY NIGHT. 
AMOUNTS SHOULD TAPER OFF QUICKLY NORTH OF THIS LINE...AND DON'T 
EXPECT MUCH IN THE WAY OF ACCUMULATION N OF A JEF-FAM LINE.  WITH 
MAIN EVENT STILL 30+ HOURS AWAY...NO HEADLINES ATTM.   

BAROCLINIC ZONE WILL GRADUALLY LIFT NORTHEAST FRIDAY AND FRIDAY 
NIGHT AS SURFACE RIDGE EXTENDING FROM UPPER MISSSISSIPPI VALLEY INTO 
MID OHIO VALLEY BEGINS TO WEAKEN.  THIS WILL ALSO ALLOW WARM 
ADVECTION REGIME TO SLOWLY WORK NORTHEAST ACROSS THE CWA...
BUT OUTSIDE OF SOUTHEAST MISSOURI DURING THE MORNING THIS ASCENT 
WILL BE MUCH WEAKER THAN WHAT WILL BE OCCURRING OVER SOUTHWEST 
MISSOURI ON THURSDAY/THURSDAY NIGHT.  THIS SHOULD MEAN LOTS OF 
CLOUDINESS THROUGHOUT THE REGION...AND HAVE ALSO ALLOWED LOW POPS TO 
EXPAND NORTH A BIT.  AMS DOES WARM DURING THIS TIME...SO PTYPE WILL 
REMAIN A CHANCE OF RAIN OR SNOW.      

(SATURDAY-TUESDAY)
ALL MEDIUM RANGE OUTPUT CONTINUES TO SUGGEST A FAIRLY POTENT STORM 
SYSTEM WILL BE CUTTING ACROSS THE MID MISSISSIPPI VALLEY LATE 
SATURDAY AND INTO SUNDAY...THE BIG QUESTION IS WHAT WILL BE THE 
EXACT TRACK OF THE STORM.  THE GEM REMAINS THE MOST SOUTHERN 
SOLUTION...WHILE THE OPERATIONAL AND ENSEMBLE GFS AND ECMWF ARE IN 
MUCH BETTER AGREEMENT IN TAKING THE UPPER LOW ACROSS THE NORTHERN 
HALF OF MISSOURI AND INTO NORTHERN OR CENTRAL ILLINOIS BY SUNDAY 
EVENING.  FORECAST OUTPUT STILL HAS A "HMMM" FACTOR FOR WINTER 
WEATHER LOVERS...AS ALMOST ALL OF THEM WOULD SUGGEST THE POTENTIAL 
FOR ACCUMULATING SNOW SOMEWHERE IN THE REGION.  CERTAINLY ANOTHER 
UPWARD TWEEK IN POPS LOOKS APPROPRIATE BUT AT THIS EARLY STAGE STILL 
NOT CERTAIN WHETHER TO HEAD TO THE WARMER OR COLDER SOLUTIONS...AND 
WILL REMAIN FIRMLY IN THE MIDDLE OF THE ROAD FOR NOW.  

SYSTEM SHOULD EXIT BY MONDAY...TAKING MOST OF THE PRECIP THREAT WITH 
IT.  HOWEVER...WITH BROAD TROF REMAINING OVER THE CENTRAL CONUS INTO 
EARLY NEXT WEEK DONT SEE ANY STRONG SIGN OF SPRING-TIME WARMTH IN 
THIS FORECAST PACKAGE.

TRUETT

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1147 PM CDT TUE MAR 19 2013

VFR FCST THRU THE PERIOD. THERE IS A SMALL BATCH OF MVFR CIGS
ACROSS CNTRL AND W CNTRL MO DRIFTING ESE JUST SOUTH OF THE MO
RIVER...WHICH MEANS IT SHOULD MISS KCOU AND THE STL METRO SITES.
THERE IS SOME MID LEVEL CLOUDINESS ASSOC WITH A MID LEVEL
DISTURBANCE FROM WRN MO INTO KS AND NEB THAT WILL MOVE EAST
OVERNIGHT. A COLD FRONT IS ENTERING NTHRN MO AND SHOULD PUSH THRU
THE TAF SITES PRIOR TO 12Z. THERE ARE SCTRD CIGS OF 5-7KFT ALONG
AND JUST BEHIND THE FRONT. WINDS ARE EXPECTED TO PICK UP AS HIGH
PRESSURE BUILDS IN AND THEN DIMINISH NEAR SUNSET.

SPECIFICS FOR KSTL...

COLD FRONT DUE IN AROUND 10Z SHOULD SWING WINDS AROUND TO THE NW
AND THEN PICK UP WITH DAYTIME MIXING. MAX BE A PERIOD OR TWO OF
SOME CIGS NEAR 5KFT IN ASSOC WITH THE FRONT. WINDS WILL DIMINISH
NEAR SUNSET.

2%

&&

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

$$

WFO LSX