Winter Weather Advisory 7, NWS St. Louis, MO

Bond County, IL, Calhoun County, IL, Clinton County, IL, Fayette County, IL, Greene County, IL, Jersey County, IL, Macoupin County, IL, Madison County, IL, Marion County, IL, Monroe County, IL, Montgomery County, IL, Randolph County, IL, Saint Clair County, IL, Washington County, IL, Audrain County, MO, Boone County, MO, Callaway County, MO, City of Saint Louis, MO, Cole County, MO, Crawford County, MO, Franklin County, MO, Gasconade County, MO, Iron County, MO, Jefferson County, MO, Lincoln County, MO, Madison County, MO, Moniteau County, MO, Montgomery County, MO, Osage County, MO, Pike County, MO, Reynolds County, MO, Saint Charles County, MO, Saint Francois County, MO, Saint Louis County, MO, Sainte Genevieve County, MO, Warren County, MO, Washington County, MO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
310 AM CST THU DEC 6 2007

.DISCUSSION...
WHAT A DIFFERENCE A DAY MAKES...THE MODELS COLLECTIVELY HAVE COME TO
A MORE SOUTHERN AND COLDER SOLUTION FOR THE PRECIPITATION EVENT THIS
AFTERNOON AND TONIGHT. SNOW AND WINTER WEATHER ADVISORIES HAVE
BEEN POSTED.

SHORTWAVE MOVING FROM THE CENTRAL ROCKIES NORTHEAST INTO THE
PLAINS WILL INITIATE STRONG WARM AIR ADVECTION ACROSS THE CENTER
OF THE NATION TODAY AND TONIGHT. A LARGE SHIELD OF PRECIPITATION
WILL MOVE EAST FROM THE PLAINS AND ACROSS THE FORECAST AREA THIS
AFTERNOON AND THIS EVENING. TEMPERATURE PROFILES SUGGEST THAT
LOCATION NORTH OF A MEXICO...MISSOURI TO LITCHFIELD ILLINOIS LINE
WILL SEE ALL SNOW...WITH A SNOW AND SLEET MIX ALONG THE INTERSTATE
70 CORRIDOR...AND A RAIN...SLEET MIX FUTHER SOUTH ACROSS THE
EASTERN OZARKS...SOUTHEAST MISSOURI...AND SOUTHERN ILLINOIS.

USING A 10 TO 1 RATIO FOR SNOWFALL...EXPECT TOTAL SNOW ACCUMULATION
TO BE BETWEEN 2 AND 4 INCHES ACROSS NORTHEAST MISSOURI AND WEST
CENTRAL ILLINOIS...WITH LESSER AMOUNTS FURTHER SOUTH WHERE SLEET AND
RAIN WILL MIX IN WITH THE SNOW.

DONT EXPECT PRECIPITATION TO REACH CENTRAL AND NORTHEAST MISSOURI
UNTIL THE AFTERNOON AND THE ST. LOUIS METRO AREA AND POINTS EAST
WILL PROBABLY HAVE TO WAIT UNTIL LATE THIS AFTERNOON OR EARLY THIS
EVENING BEFORE SATURATION OF THE ATMOSPHER OCCURS.

COLD FRONT MOVES SOUTH ACROSS THE REGION ON FRIDAY AND BECOMES
QUASI-STATIONARY FROM TEXAS THROUGH ARKANSAS TO TENNESSEE RIVER
VALLEY THIS WEEKEND. MEDIUM RANGE GUIDANCE CONTINUES ITS COLDER
TREND AS MODELS LOCK ONTO THE STRENGTH AND DEPTH OF COLD AIR THAT
WILL BE BUILDING SOUTH INTO THE MIDWEST. LOWERED TEMPERATURES TOWARD
LATEST GUIDANCE CONSENSUS...THUS BRINGING THE THREAT OF ICE FURTHER
SOUTH SATURDAY NIGHT/SUNDAY. WILL NEED TO WATCH THIS TREND...AS
SIGNIFICANT AMOUNT OF QPF IS FORECAST TO OCCUR SATURDAY NIGHT AND
SUNDAY...OWING TO THE POSSIBILITY OF ICE ACCUMULATION.

CVKING

&&

.AVIATION...
FOR THE 06Z TAFS...TWO MAIN ITEMS OF CONCERN FOR THE VALID TAF
PERIOD...ONE EARLY AND THE OTHER LATE. THE EARLY ITEM OF CONERN IS
LOW SC CLOUDS AND THEIR UNWILLINGNESS TO DEPART FROM THE AREA.
PART OF THE REASON WHY IS THAT THE STEERING WINDS AT CLOUD LEVEL
HAVE DIMINISHED TO 5KTS OR LESS WITH THE SFC HI PRES BUILT INTO
THE AREA...AND TO ADD COMPLEXITY TO THE SITUATION...THESE WINDS AT
CLOUD LEVEL WILL VEER TO THE SELY LATE TONIGHT. LOOK FOR CLOUDS TO
EVENTUALLY CLEAR OUT OF KSTL/KSUS AND MOVE BACK INTO KUIN LATE
TONIGHT...CLEAR OUT OF KCOU EARLY THURSDAY MORNING...AND CLEAR
KUIN LATER THURSDAY MORNING. THE OTHER ITEM WILL BE LATER IN THE
TAF PERIOD...WITH THE APPROACHING SYSTEM FROM THE W. CLOUDS WILL
OVERSPREAD THE AREA LATE TONIGHT AND THEN THICKEN AND LOWER
THROUGHOUT THURSDAY. MODELS SEEM TO BE IN DECENT AGREEMENT ON
BRINGING BELOW VFR CIGS AND PCPN INTO THE FA FROM W TO E BETWEEN
18Z AND 00Z. PCPN-TYPES ARE GENERALLY AGREED UPON TO BE
PREDOMINANTLY SNOW IN THE NRN FA AND A MIX IN THE I-70
CORRIDOR...ALTHOUGH RECENT MODEL RUNS ARE COLDER AND POINT TO MORE
OF A SNOW EVENT AND HAVE ADJUSTED ACCORDINGLY. OTRW..SELY SFC WNDS
WILL DEVELOP ON THURSDAY AS HI PRES PULLS AWAY BUT WILL STRUGGLE
TO GET MUCH HIGHER THAN 12KTS.

TES

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...SNOW ADVISORY FROM NOON TODAY TO MIDNIGHT CST TONIGHT FOR
     AUDRAIN-KNOX-LEWIS-LINCOLN-MARION-MONROE-PIKE-RALLS-SHELBY.

     WINTER WEATHER ADVISORY FROM NOON TODAY TO MIDNIGHT CST TONIGHT
     FOR BOONE-CALLAWAY-COLE-FRANKLIN-GASCONADE-MONITEAU-
     MONTGOMERY-OSAGE-WARREN.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT CST
     TONIGHT FOR JEFFERSON-ST. CHARLES-ST. LOUIS-ST. LOUIS CITY.

IL...SNOW ADVISORY FROM NOON TODAY TO MIDNIGHT CST TONIGHT FOR ADAMS
     IL-BROWN IL-CALHOUN IL-PIKE IL.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT CST
     TONIGHT FOR BOND IL-CLINTON IL-FAYETTE IL-MADISON IL-MARION
     IL-MONROE IL-ST. CLAIR IL-WASHINGTON IL.

     SNOW ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT CST TONIGHT FOR
     GREENE IL-JERSEY IL-MACOUPIN IL-MONTGOMERY IL.

&&

WFO LSX