FXUS63 KLSX 082100
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
300 PM CST TUE DEC 8 2009
.DISCUSSION...
/300 PM CST TUE DEC 8 2009/
FOCUS CONTINUES TO BE IMPENDING WINTER STORM INCLUDING WIND. THERE
IS GOOD AGREEMENT WITH THE MODELS OVER THE NEXT 24-36 HOURS WITH THE
TRACK OF THE STORM KEEPING THE FAR NWRN PART OF THE CWA ON THE SRN
PERIPHERY OF THE HEAVIEST SNOW PATH TONIGHT. PRECIPITATION OVER
NERN MO/W CNTRL IL HAS TURNED OVER TO MAINLY RAIN CURRENTLY WITH
SOME AREAS RECEIVING LIGHT FREEZING RAIN OR SLEET WITH LITTLE IN THE
WAY OF GLAZE REPORTED. FORECAST SOUNDINGS SUGGEST THAT THIS WILL
BE THE CASE INTO THE EARLY EVENING BEFORE RAPIDLY COOLING OCCURS
IN THE LOWER ATMOSPHERE. BY THIS TIME...THERE WILL BE DECENT
ASCENT CAUSED BY THE APPROACHING TROUGH/ASSOCIATED MID LEVEL
FRONTOGENESIS AS THE PRECIPITATION TO TURN BACKS TO SNOW OVER THE
WARNING/ADVISORY AREA...WITH A BRIEF PERIOD OF MODERATE TO HEAVY
SNOW. FARTHER SOUTH...THE CHANGEOVER WILL BE LATER IN THE EVENING
OR OVERNIGHT BASED ON FORECAST SOUNDINGS. THIS CHANGE OVER WILL BE
OCCURRING ABOUT THE SAME TIME THE SYSTEM IS MOVING OUT SO LITTLE
IF ANY ACCUMULATION OF SNOW STILL LOOKS RIGHT SOUTH OF A JEFFERSON
CITY TO PITTSFIELD.
BIGGEST CHANGE TO FORECAST IS THAT WE HAVE EXTENDED THE WINTER STORM
WARNING/WINTER WEATHER ADVISORY THROUGH TOMORROW ALONG WITH ISSUING
A WIND ADVSORY FROM 3 AM - 6 PM WEDNESDAY FOR THE REST OF THE CWA
BECAUSE OF THE EXPECTED GRADIENT WINDS. WEST TO NORTHWEST WINDS AT
20 TO 30 MPH WITH SOME GUSTS OVER 40 MPH WILL CAUSE REDUCED
VISIBILITIES WHERE THERE IS FRESH SNOW COVER. PRECIPITATION WILL
RAPIDLY TAPER TO FLURRIES AS TROUGH EXITS QUICKLY TO THE EAST.
STILL EXPECT FALLING TEMPS THROUGHOUT THE DAY WITH WIND CHILLS
FALLING BELOW ZERO IN THE NORTHWESTERN COUNTIES BY LATE IN THE
AFTERNOON.
MID-RANGE (0Z THURS - 12Z WED)...
LOW PRES WILL CONTINUE TO DEEPEN AS IT LIFTS THRU THE NERN CONUS WED
NGT INTO THURS. CONSEQUENTLY STRONG W-NWLY WINDS SUSTAINED AROUND 20
MPH AND GUSTING AROUND 35 MPH WILL IMPACT PORTIONS OF THE FA AS
LOW-LVL LAPSE RATES WILL BE FAIRLY STEEP ALLOWING FOR SUFFICIENT
MIXING OF THE BOUNDARY LYR. IN ADDITION A VERY COLD AIR MASS...WHICH
SHOULD AID IN THE STEEPENING OF LOW-LVL LAPSE RATES...WILL MOVE SEWD
ACROSS THE FA WITH H85 TEMPS -12-16C. AM CONFIDENT A STRATUS DECK
WILL HOLD THRU WED EVENING...SLOWLY DISSIPATING THURS MORNING
EASTWARD WITH DRIER AIR ENTRAINING FROM THE WEST. WITH WINDS AND
EFFECTIVE MIXING OF THE BOUNDARY LAYER HAVE BUMPED PREVIOUSLY
FORECASTED THURS LOWS DOWN A DEGREE OR TWO RANGING FROM THE SINGLE
DIGITS FOR LOCATIONS IN NERN MO AND W-CNTRL IL...WITH TEENS
SURROUNDING THE STL METRO REGION AND TO THE SOUTHEAST. DO NOT EXPECT
ANY PRECIP BEYOND 0Z THURS THRU THE END OF THE WEEK.
FROM THURS INTO FRI MORNING SFC HIGH WILL BE IN CONTROL WITH CLEAR
SKIES AND WINDS TURNING SWLY. GUSTY WINDS WILL STILL BE THE NORM
INTO MIDDAY THURS WEAKENING INTO AFTERNOON. THE COLD AIR MASS WILL
REMAIN ENTRENCHED ACROSS THE REGION INTO FRI MORNING. EXPECT AN
AVERAGE 15 DEGREE REBOUND FOR THURS HIGHS RANGING FROM THE UPPER
TEENS INTO THE MID 20S...FALLING INTO THE LOW-MID TEENS FOR FRI
LOWS.
A MORE SUBTROPICAL PATTERN EXHIBITS IN THE UPR LVL FLOW PATTERN INTO
THE WEEKEND AS A SERIES OF WEAK DISTURBANCES EMINATE FROM THE CNTRL
PACIFIC. THE FIRST DISTURBANCE ASSOCIATED WITH AN UPR LVL VORT MAX
ADVECTS THRU THE BI-STATE REGION SAT INTO SUN...WITH A SECOND
DISTURBANCE NOT FAR BEHIND IN THE SRN ROCKIES. ANTICIPATE AN
INCREASE IN MID-UPR LVL MOISTURE AND INCREASING CLOUDS FROM THE
SOUTHWEST AS THE TWO SYSTEMS MOVE EWD. WITH FOCUS UPON THE FIRST
SYSTEM LOW LVLS SHOULD BE DEVOID OF MOISTURE AND EXPECT ANY
RESULTANT FALLING PRECIP TO HAVE DIFFICULTY IN REACHING THE
GROUND...IN ADDITION TO BETTER QVECT FORCING SOUTHEAST OF THE FA.
CONFIDENCE IS LOW FOR POSSIBLE PRECIP THUS HAVE GONE WITH SLGT CHCS
FOR A MIXTURE OF RAIN AND SNOW ON SAT. NEVERTHELESS DO BELIEVE
CLOUDS WILL LINGER SAT THRU SUN AIDED BY A NOCTURNAL INVERSION AND
LIMITED VERTICAL MIXING...AND WITH SFC SLY FLOW WARMER CONDITIONS
SHOULD PREVAIL. HAVE THUS WARMED BOTH SAT AND SUN MORNING LOWS BY
SEVERAL DEGREES.
INTO THE BEGINNING OF NEXT WEEK MDL SOLNS DIVERGE WITH REGARDS TO
TIMING AND PLACEMENT OF THE SECOND DISTURBANCE. A STRONG RIDGE OF
SFC HIGH PRESSURE IS EXPECTED TO BUILD SEWD FROM THE NRN PLAINS INTO
THE SRN GREAT LAKES. A SFC COLD FRONT ALONG AND AHEAD OF THE RIDGE
WILL ACT AS THE FOCUS FOR POTENTIAL WET WX THRU THE FA...BUT THERE
IS A LOT OF UNCERTAINTY AS TO THE OUTCOME. ECMWF SUGGESTIVE OF A
DRIER SOLN COMPARITIVELY WITH THE GFS...WHICH IS MORE ROBUST AND
DEEPENS A SYSTEM EWD OUT OF THE ROCKIES THRU TUE MORN. THUS HAVE
BLENDED THE ECMWF AND GFSENS FOR NEXT WEEK...AND HAVE GONE WITH SLGT
CHCS OF A MIX OF RAIN AND SNOW FOR SUN NGT INTO MON FOR NOW...WILL
EVALUATE WITH LATER RUNS AND WHEN UPR LVL FEATURES ARE BETTER SAMPLED.
BRITT/SIPPRELL
&&
.AVIATION...
/1132 AM CST TUE DEC 8 2009/
FOR THE 18Z TAFS...TEMPS HAVE RISEN ABOVE FREEZING AT ALL TAF SITES
AS OF 17Z...SO PCPN IN THE FORM OF LIGHT RAIN/DRIZZLE AT THIS TIME.
AS NEXT ROUND OF PCPN TRACKS NORTHEAST ACROSS AREA THIS AFTERNOON...
CIGS TO REMAIN AT OR LOWER TO IFR AND REMAIN THERE TIL EARLY
WEDNESDAY MORNING...WHEN THEY WILL LIFT TO MVFR AS SYSTEM PULLS
AWAY. AS FOR PCPN TYPE...KUIN WILL SEE RAIN...MIXED WITH SLEET OR
SNOW AT TIMES...THEN CHANGE OVER TO ALL SNOW BY 06Z. AT KCOU...ALL
RAIN TIL 05Z...THEN CHANGE OVER TO SNOW...AND AT KSUS/KSTL ALL LIGHT
RAIN/DRIZZLE TIL 08Z/09Z WHEN IT CHANGES OVER TO LIGHT SNOW. WINDS
ARE THE OTHER MAJOR FACTOR FOR THE TAFS...PERSIST FROM THE EAST TIL
SYSTEM BEGINS TO LIFT OUT THIS EVENING...THEN SWITCH TO THE
SOUTH...SOUTHWEST THEN WEST AND INCREASE. EXPECT 20 TO 25 KTS
SUSTAINED WITH HIGHER GUSTS DURING THE DAY TOMORROW.
BYRD
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...WIND ADVISORY FROM 3 AM TO 6 PM CST WEDNESDAY FOR AUDRAIN-BOONE-
CALLAWAY-COLE-CRAWFORD-FRANKLIN-GASCONADE-IRON-JEFFERSON-
LINCOLN-MADISON-MONITEAU-MONTGOMERY-OSAGE-PIKE-REYNOLDS-ST.
CHARLES-ST. FRANCOIS-ST. LOUIS-ST. LOUIS CITY-STE.
GENEVIEVE-WARREN-WASHINGTON.
WINTER STORM WARNING UNTIL 6 PM CST WEDNESDAY FOR KNOX-LEWIS-
MARION-SHELBY.
WINTER WEATHER ADVISORY UNTIL 6 PM CST WEDNESDAY FOR MONROE-
RALLS.
IL...WIND ADVISORY FROM 3 AM TO 6 PM CST WEDNESDAY FOR BOND IL-
CALHOUN IL-CLINTON IL-FAYETTE IL-GREENE IL-JERSEY IL-
MACOUPIN IL-MADISON IL-MARION IL-MONROE IL-MONTGOMERY IL-
RANDOLPH IL-ST. CLAIR IL-WASHINGTON IL.
WINTER STORM WARNING UNTIL 6 PM CST WEDNESDAY FOR ADAMS IL.
WINTER WEATHER ADVISORY UNTIL 6 PM CST WEDNESDAY FOR BROWN IL-
PIKE IL.
&&
$$
WFO LSX
