FXUS63 KLSX 262118
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
318 PM CST SAT DEC 26 2009
.DISCUSSION...
/316 PM CST SAT DEC 26 2009/
DEEP NEARLY STACKED SYNOPTIC LOW CONTINUED TO BE THE STORY TODAY.
MAIN FCST CHALLENGES FOR THE LAST 24 HRS HAS BEEN HANDLING THE
DISCRETE NATURE OF INDIVIDUAL SNOWBANDS AS THEY PIVOT AND ROTATE
AROUND THE RESPECTIVE LOW PRESSURE CENTER. AS OF 21Z THE DEEP LOW
WAS CENTERED ACRS ERN IA WITH WV IMAGERGY ILLUSTRATING SEVERAL LOBES
OF SHORTWAVE ENERGY ROTATING IN CONCERT WITH THE DEEP LOW WITH ONE
WAVE PRESSING THRU IL/IN AND A SECOND ROTATING SWD FROM THE
DAKOTAS. WSR-88D RADAR RETURNS HIGHLIGHT A BAND OF LIGHT SNOW
STRETCHED ALONG THE I-70 CORRIDOR WITH WIDESPREAD DEVELOPMENT THRU
IL/IN IN ASSOCIATION WITH AFOREMENTIONED SHORTWAVE ENERGY.
CONTINUED OCCLUSION OF THE LOW HAS ALLOWED FOR A MIX OF BOTH MOIST
AND DRY CONDITIONS MAKING A SIGNIFICANT CHALLENGE IN HANDLING TEMPS
FOR TODAY INTO TONIGHT. W-SWLY WINDS WITH GUSTS UP TO 30 MPH HAVE
BEEN THE NORM FOR TODAY AND SHUD CONTINUE TONIGHT.
SHORT-TERM (TONIGHT - MON)...
FOR TONIGHT SNOWBAND IS EXPECTED TO DISSIPATE ALONG THE I-70
CORRIDOR AS BETTER DYNAMICS SHIFT EWD THRU THE SRN GRT LKS RGN.
WILL GO AHEAD AND PUT HIGHER POPS THRU CNTRL MO INTO CNTRL IL IN
ASSOC WITH THE SNOWBAND FOR THE SHORT-TERM INTO MIDNIGHT. FEEL MOSTLY
CLOUDY CONDITIONS WILL LINGER INTO MORNING SO DO NOT ANTICIPATE
TEMPS TONIGHT TO FALL CONSIDERABLY.
MASSIVE NEARLY STACKED LOW PRES WILL CONTINUE TO ROTATE AND WOBBLE
ACRS THE WRN GRT LKS RGN THRU THE EVNG HRS AND SLOWLY LIFT EWD THRU
THE DAY SUN. THIS WILL PROVIDE ONE LAST DAY OF LIGHT SNOW AND
FLURRIES ACRS THE BI-STATE RGN. DETERMINISTIC MDLS IN AGREEMENT OF
ATTENDANT SHORTWAVE ENERGY ROTATING AROUND THE PARENT LOW THRU THE
NRN FCST RGN AROUND 12Z SUN IN TANDEM WITH A MODEST H3 JET STREAK
PROVIDING DIV ALOFT. RESULTANT ENHANCED LIFT...ESP IN THE DENDRITIC
GROWTH ZONE...IN CONCERT WITH MID-LVL FRONTOGENESIS SHUD WARRENT
HIGHER POPS AND ACCUMULATIONS. HAVE INCREASED POPS ACCORDINGLY ACRS
MUCH OF THE BI-STATE RGN. WITH SNOW TO WATER RATIOS ON THE ORDER OF
15:1 TO 20:1 ANTICIPATE ACCUMULATIONS OF 1 TO 2 INCHES ACRS NERN MO
INTO CNTRL IL WITH LIGHTER AMOUNTS SOUTHWARD ENDING ALONG A LINE
STRETCHED FROM CUBA MO TO SPARTA IL.
MAX/MIN TEMPS HAVE BEEN TRICKY TO FCST FOR THE NEXT 24-48 HRS WITH
CONSIDERATIONS SUCH AS 1) CLOUDS AND 2) SNOW COVERED GROUND. HAVE
BLENDED ACCORDINGLY WITH MAV/MET MOS GUIDANCE AND LOWERED TEMPS FOR
SUN IN ANTICIPATION OF LIGHT SNOW ACRS NERN MO AND CNTRL IL.
SUN NGT INTO MON MASSIVE LOW WILL TRANSLATE EWD ACRS THE GRT LAKES
AND BECOME ABSORBED BY A STRONG POLAR VORTEX PRESSING SWD THRU THE
HUDSON BAY RGN. AS THE RESULTANT TROF PRESSES EWD A MODERATE H5
RIDGE OF HIGHER PRESSURE WILL TRAVERSE THRU THE RNG LENDING TO
ANTICIPATED DRIER CONDITIONS. HAVE FLURRIES CONTINUING INTO
MIDNIGHT EAST OF THE MS RVR THEREAFTER SKIES SHUD BEGIN TO CLEAR AND
WINDS WILL DIMINSH INTO MON. TEMPS SHUD MODERATE AROUND THE LOW
30S ON MON FROM OVERNIGHT LOWS.
EXTENDED (MON NGT - SUN)...
MAIN FOCUS FOR THIS FCST PD WILL BE THE CHCS FOR LIGHT SNOW BY
MIDWEEK. DETERMINISTIC MDLS FAIRLY SUCCINCT IN HANDLING UPR LVL
ENERGY ASSOC WITH A DEEP LOW PRES CENTER SOUTH OF THE ALEUTIAN
ISLANDS BIFURCATING SWD AND DEVELOPING A H5 TROF THRU THE SWRN
CONUS. THIS TROF IS ANTICIPATED TO LIFT THRU THE FCST RGN BEGINNING
0Z WED AND LINGERING INTO THE END OF THE WEEK.
BY 0Z WED SFC HIGH PRES WILL BE ON THE WAY OUT AS WINDS VEER SLY.
ANTICIPATE CLOUDS ON THE INCRS AS H5 DIFFLUENT FLOW BEGINS TO SPREAD
ACRS THE RGN. TEMPS ON TUE SHUD REBOUND FROM MID-UPR TEENS INTO THE
MID 30S. MID-LOW LVL CYCLOGENESIS ALONG THE SWRN GULF COAST IN
CONCERT WITH H5 TROF WILL RESULT IN ISENTROPIC UPGLIDE OF A TONGUE
OF HIGHER THETAE AIR NWD THRU THE BI-STATE RGN. EXPECT BETTER
MID-LVL DYNAMICS AND LIFT TO RESIDE ACRS THE SRN FCST AREA. YET
DIFFICULTIES REMAIN AS A SECOND WAVE OF UPR LVL ENERGY WILL DIVE SWD
THRU THE NRN PLAINS BY 0Z THURS PRESSING A SFC COLD FRONT THRU THE
RGN ON THURS. WITH MDLS IN FAIRLY GOOD AGREEMENT OF QPF RGN-WIDE
AND SUFFICIENT MOISTURE PRESENT IN LOW-MID LVLS HAVE BUMPED POPS
INTO CATEGORICAL CHCS ACRS THE ENTIRE FCST AREA. KEPT TEMPS WARM FOR
WED INTO THURS AHEAD OF SFC COLD FRONT FALLING THEREAFTER. WOULD
EXPECT A NON-DIURNAL TREND IN WAKE OF SFC COLD FRONT ON THURS. HAVE
INCLUDED WIND GUSTS THURS IN WAKE OF THE FRONT TO CONTINUE INTO THE
WEEKEND WITH SIGNFICANTLY FALLING SFC DEWPOINTS.
SECOND WAVE WILL ENHANCE THE DEVELOPMENT OF AFOREMENTIONED H5 TROF
ACRS THE ERN CONUS PROMOTING DEEP CYCLOGENESIS OFF THE MID-ATLANTIC
COASTLINE. SUTTLE HINTS EXIST AMONGST MDLS OF AN INVERTED TROF
STRETCHING ACRS THE GRT LKS RGN INTO THE MID-MS VLY. THERE WILL
STILL BE SUFFICIENT UPR LVL ENERGY CYCLOGENETICALLY WRAPPING AROUND
THE H5 LOW SOUTH OF NEW ENGLAND. FEEL STRONG ARCTIC HIGH AND MUCH
DRIER AIR WILL LIMIT POTENTIAL PRECIP THRU THE RGN BY WEEKS END.
HAVE KEPT REMAINDER OF THE FCST DRY AND COLD AS ARCTIC HIGH PRES
SLINKS INTO THE MID-MS VLY THRU THE WEEKEND. EXPECT ANY DIURNAL
SWINGS IN TEMPERATURE TO BE ON THE ORDER OF 10 DEGREES.
SIPPRELL
&&
.AVIATION...
/1125 AM CST SAT DEC 26 2009/
FOR THE 18Z TAFS...
MASSIVE MID-UPPER LEVEL LOW NOW CENTERED ACROSS WISCONSIN AND
ATTENDANT SHORT WAVES ARE KEY ELEMENTS THRU THIS FORECAST PERIOD.
THE FIRST OF THESE SHORT WAVES CURRENTLY EXTENDING THRU NW MO IS
PRODUCING SNOW FROM NE MO INTO CENTRAL MO. CIGS PRIMARILY MVFR AND
VSBYS IN SNOW ARE IFR/MVFR. THE SNOW WILL SPREAD TO THE EAST
IMPACTING KCOU AND KUIN THROUGH MID AFTERNOON THEN TAPER TO
FLURRIES OR NOTHING. SNOW SHOULD MOVE INTO STL AREA IN THE 19-20Z
TIME FRAME AND PERSIST FOR 3H OR SO...THEN TAPER TO FLURRIES AS
WELL. ANOTHER STRONGER SHORT WAVE WILL DROP SEWD ON SUN MORNING
AND BRING A GREATER POTENTIAL FOR ACCUMULATING SNOW AND ONCE
AGAIN DROP VSBYS INTO IFR.
GLASS
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&
$$
WFO LSX
