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