FXUS63 KDVN 112102
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
300 PM CST FRI DEC 11 2009

.SYNOPSIS...
QUIET...BUT VERY COLD WEATHER ACROSS THE FORECAST AREA TODAY WITH 
ONLY SOME AC CLOUDS TO MAR THE OTHERWISE BRIGHT SUNSHINE.  
FRESH...VERY WHITE SNOWCOVER ALSO MAKING THINGS VERY BRIGHT OUT 
THERE.  TEMPERATURES HAVE RISEN QUITE WELL TODAY...DESPITE ONLY WEAK 
WARM AIR ADVECTION AT THE SURFACE AND LIGHT WINDS.  ACROSS THE NORTH 
WE ARE WELL INTO THE TEENS...AND 30-35 FAR SOUTH WHERE THERE IS THE 
LEAST SNOW COVER.  AT UPPER LEVELS...DEEP CYCLONIC FLOW CONTINUES 
WITH A DEEP VORTEX OVER CANADA.  THIS HAS SHIFTED EAST...ALLOWING 
WARM AIR ADVECTION TO BE GOING ON ALOFT AT MOST LAYERS.  IN 24 
HOURS...OUR 850MB TEMPERATURE HAS GONE FROM -21 TO -12.  ...LE...

&&

.SHORT TERM...TONIGHT AND SATURDAY.
TONIGHT WILL REMAIN QUIET WITH WARMER TEMPERATURES DUE TO THE 
CONTINUING WARM AIR ADVECTION.  THIS WILL BE OFFSET BY THE LIGHT 
WINDS AND NEARLY CLEAR SKIES PRODUCING GOOD CONDITIONS FOR 
RADIATION.  OVER THE SNOW COVER HAVE GONE BELOW GUIDANCE...BUT HAVE 
KEPT TEMPERATURES NEAR OR JUST BELOW GUIDANCE IN THE SNOW FREE 
AREAS...AND IN THE AREAS WHERE THE SNOWPACK IS NOT SO DEEP ACROSS 
THE SOUTH.  

SATURDAY IS A TRICKY DAY...WITH STRONG WARM MOIST ADVECTION COMING 
UP FROM THE SOUTH...THE LEADING EDGES OF THE SYSTEM THAT WILL AFFECT 
US SATURDAY NIGHT.  LOTS OF WARM AIR MOVES INTO THE AREA ALOFT...BUT 
THE SURFACE TEMPERATURES IN THE SNOWPACK AREA WILL REMAIN BELOW 
FREEZING...THOUGH TEMPERATURES IN THE FAR SOUTH WILL BE ABOVE 
FREEZING.  THIS LEAVES US WITH A MIXTURE OF RAIN...PERHAPS MIXED 
WITH SNOW IN THE FAR SOUTH WHERE THERE WILL BE WARMER SURFACE 
TEMPERATURES...AND A SNOW OR FREEZING RAIN MIXTURE WHERE THE SURFACE 
TEMPERATURES ARE BELOW FREEZING OVER THE SNOWPACK.  FOR NOW HAVE PUT 
THE FREEZING LINE NEAR THE SOUTHERN EDGE OF THE DEEPEST 
SNOWPACK...BUT THIS MAY NEED TO BE SHIFTED AS LATER MODEL RUNS COME 
IN.  MAX TEMPERATURES SHOULD BE IN THE EARLY AFTERNOON BEFORE THE 
PRECIPITATION COMES IN...THEN FALL VERY SLOWLY UNTIL EVENING.  
...LE...

.LONG TERM...SATURDAY NIGHT THROUGH NEXT FRIDAY...
THE PRIMARY CONCERN INITIALLY WILL BE THE PCPN TYPE AND ANY AMOUNTS 
SATURDAY EVENING.  MODELS CONTINUE TO SHOW A STRONG POTENTIAL FOR A 
LIGHT FREEZING RAIN OR FREEZING DRIZZLE EVENT IN THE SOUTH 1/2 TO 
2/3RDS. THE MAGNITUDE WILL LIKELY BE VERY WEAK...BUT POSSIBLY ENOUGH 
TO WARRANT AN ADVISORY FOR SLICK CONDITIONS. IN THE NORTH 1/2...A 
MIX OF SNOW AND LIGHT SLEET APPEARS LIKELY...WITH AMOUNTS GENERALLY 
LESS THAN ONE INCH. TEMPERATURES WILL LIKELY REMAIN RATHER FLAT 
OVERNIGHT...WITH MID 20S NORTH TO LOWER 30S SOUTH. 

SUNDAY THROUGH EARLY MONDAY...WAA CONTINUES...LIKELY AT LEVELS 
ALOFT...WITH A CLOUD LAYER IN BETWEEN.  THIS CREATES A STRONG BUST 
POTENTIAL...AS A SHALLOW INVERSION SETS UP UNDER CLOUDS.  DRIZZLE OR 
FREEZING DRIZZLE WILL BE POSSIBLE AFTER MIDNIGHT SATURDAY NIGHT INTO 
EARLY SUNDAY...AND AGAIN SUNDAY NIGHT INTO MONDAY MORNING. A VERY 
STRONG COLD FRONT IS SET TO ARRIVE MONDAY...WITH HIGHS OCCURRING IN 
ADVANCE OF IT...AND FALLING TEMPS BEHIND IT. MONDAY NIGHT THROUGH AT 
LEAST WEDNESDAY APPEAR VERY COLD AGAIN...WITH AN INCREASINGLY STRONG 
ARCTIC INTRUSION FORECAST. A WAVE OF LOW PRESSURE WHICH WAS FORECAST 
TO BE WELL NORTH OF THE AREA MONDAY IS TRENDING SOUTH...ANY 
FARTHER...AND POPS WILL NEED TO BE RAISED MONDAY AND MONDAY NIGHT 
FOR SNOW.  LOOKING BEYOND...MODERATION LOOKS ON TAP FOR THURSDAY AND 
FRIDAY...WITH A LOW THREAT FOR PCPN.
...ERVIN...

&&

.AVIATION...
VFR CONDITIONS THROUGH THE TAF PERIOD...WITH SOME AC DRIFTING PAST 
THE TAF SITES AROUND 10KFT.  SOUTH-SOUTHWEST WINDS OF LESS THAN 10 
KTS WILL TURN MORE SOUTH TONIGHT.   ...LE...

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

LE/ERVIN