FXUS63 KDVN 152123
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
322 PM CST TUE DEC 15 2009

.SYNOPSIS...
HIGH PRESSURE WAS CENTERED OVER SOUTHEAST NE/SOUTHWEST IA THIS AFTN 
AND PROVIDING REGION WITH WALL TO WALL SUNSHINE... AND ALLOWS 
US TO SEE EXTENT OF SNOW COVER VIA VISIBLE SATL WHICH SHOWS BULK OF
SNOW COVER NORTHWEST OF KBRL-KVYS AXIS. THUS... DESPITE ABUNDANT
SOLAR INSOLATION TEMPS STRUGGLING OVER SNOW PACK WITH SINGLE DIGITS
IN NW 1/3RD WHERE SNOW COVER DEEPEST... WHILE TEMPS AROUND 20 DEGS
FAR SOUTH IN BARREN GROUND. UPPER PATTERN FEATURES TROUGH IN THE EAST
AND FLATTENING RIDGE OUT WEST.           ..05..

&&

.SHORT TERM...TONIGHT AND WEDNESDAY...
ONLY CONCERN IS ON TEMPS WITH EXTENT OF MID/HIGH CLOUDINESS HAVING
IMPACT. MODELS IN GOOD AGREEMENT ON SLIDING HIGH E/SE AND ACROSS
SOUTH TNGT WITH RIDGE AXIS GENERALLY BISECTING CWA BY 12Z. 
CLEAR SKIES ALONG WITH DECREASING WINDS TO ALLOW FOR RAPID DROP IN 
TEMPS THIS EVE...ESPECIALLY OVER SNOW PACK. EXTENT OF MID/HIGH 
CLOUDINESS AND TIMING OF PASSING RIDGE AXIS TO PLAY SIGNIFICANT ROLE
ON MINS TNGT. GENERAL SUGGESTIONS ARE THAT LIGHT SOUTHERLY WINDS 
DEVELOP IN THE WEST LATE TNGT AS RIDGE PASSES ACROSS THE MISSISSIPPI
RVR. THIS IN COMBINATION WITH SOME MID/HIGH CLOUDINESS ATTENDANT TO 
ELEVATED WARM ADVECTION AHEAD OF ALBERTA SHORTWAVE DIVING SEWD THROUGH
UPPER MIDWEST MAY BE ENOUGH TO SEE SOME RECOVERY ON TEMPS OUT WEST. 
IF HIGH CLOUDINESS THICK AS SUGGESTED BY FEW OF THE MODELS THEN 
COULD BE ENOUGH TO SLOW DROP AND SEE TEMPS STEADY ELSEWHERE. WITH 
RAPID DROP ON TEMPS THIS EVE AND ALREADY READINGS IN SINGLE DIGITS 
NW HAVE LOWERED MINS SEVERAL DEGS OVER THE SNOWPACK AND UNDERCUT COLDEST
GUIDANCE BY 1-2 CATS. BOTTOM LINE AS CLOUDS GO.. SO GO TEMPS. LESS
CLOUDINESS AND WINDS NEAR CALM FOR GOOD DURATION THEN LIKELY COLDER 
OVER SNOW PACK. CONCERNS REVEALED IN VERIFICATION OF LOWS THIS AM 
BENEATH SFC RIDGE AXIS IN SD WHERE COUPLE SITES DIPPED DOWN TO -13 
WITH ONLY 2-3 INCHES SNOW DEPTH... WITH NW CWA HAVING DEEPER SNOW DEPTH.
WHILE RUC 2M TEMPS OF -15 TO -18 IN THE NORTH LIKELY TOO COLD GIVEN
THAT MODEL TEMPS ARE RUNNING 3-5 DEGS TOO COLD AT 20Z... NOT UNREASONABLE
TO BE DOUBLE DIGITS BELOW ZERO. 
  
SFC HIGH SLIDES EAST ON WEDNESDAY ALLOWING SOUTHERLY WINDS TO DEVELOP.
THIS ALONG WITH AMPLE SUNSHINE SHOULD RESULT IN WARMER TEMPS...
CHALLENGE BEING WITH HOW WARM. VERIFICATION THIS AFTN ON BACKSIDE OF
SFC RIDGE OVER NE SUPPORTS CUTTING BACK FEW DEGS ON MAXES OVER THE
SNOW PACK... AND WENT CLOSE TO GUIDANCE BLEND IN SNOW BARREN AREAS IN
THE FAR SOUTH.   ..05..

.LONG TERM...WEDNESDAY NIGHT THROUGH NEXT TUESDAY...QUIET WX WILL BE 
SEEN WEDNESDAY NIGHT/THURSDAY AS THE ARCTIC HIGH EXITS THE REGION. 
RETURN FLOW ON THE BACKSIDE OF THE HIGH WILL ALLOW TEMPERATURES TO 
MODERATE CLOSER TO NORMAL. UNCERTAINTY THEN ENTERS THE PICTURE WITH 
THE NEXT SYSTEM.

MODELS BRING A WEAK SYSTEM THROUGH THE AREA THURSDAY NIGHT/FRIDAY. 
THIS SYSTEM IS A HYBRID BETWEEN A CLIPPER SYSTEM AND A COLORADO LOW. 
WRF/GFS ARE THE ONLY MODELS THAT HAVE AN INVERTED TROF. ALL OTHER 
MODELS HAVE A WEAK LOW EITHER PASSING THROUGH THE SOUTHERN 
CWFA...ECMWF... OR SOUTH OF THE CWFA...UKMET/GEM. MOISTURE WILL 
INITIALLY GO INTO RE-SATURATING THE ATMOSPHERE AND HOW LONG THAT 
WILL TAKE IS A QUESTION. BETTER FORCING/ISENTROPIC LIFT IS ACROSS 
THE NORTHERN CWFA PER ECMWF/UKMET WHILE THE GEM IS JUST SOUTH OF THE 
CWFA. GFS HAS STRONG FORCING/LIFT ACROSS THE SOUTHERN CWFA BUT NO 
SFC LOW. SO...WILL GO DRY THURSDAY NIGHT FIGURING SATURATION NEEDS 
TO TAKE PLACE WITH SCHC POPS FOR FRIDAY. PRECIP COULD LINGER INTO 
FRIDAY EVENING SO CONTINUED WITH SCHC POPS.

SATURDAY ON BECOMES MORE UNCERTAIN. OVERALL LARGE SCALE PATTERN HAS 
NEGATIVE AMO CHARACTERISTICS TO IT. A POLAR LOW RETROGRADES ROUGHLY 
ACROSS HUDSON BAY ALL WEEK AND THEN TURNS SOUTH FOR THE WEEKEND. THE 
SOUTHWARD TURN OF THE POLAR LOW INDICATES THAT A DUMP OF ARCTIC AIR 
IS COMING TO THE EASTERN CONUS. THE MOST EFFICIENT WAY TO DO THIS 
WOULD BE WITH A CLIPPER SYSTEM. INDEED...EVERY GLOBAL MODEL TO 
VARYING DEGREES SUGGESTS A CLIPPER SYSTEM LATE IN THE WEEKEND WITH 
THE POLAR LOW ROTATING ACROSS THE GREAT LAKES.

AHEAD OF ALL THIS IS A RESPECTABLE SHORTWAVE MOVING THROUGH ON 
SATURDAY. NOT SURE IF ENOUGH MOISTURE WILL BE AVAILABLE BUT 
CONTINUED THE SCHC POPS FOR SATURDAY. WENT DRY SATURDAY NIGHT BUT 
CONFIDENCE IS NOT THAT HIGH. TIMING OF THE CLIPPER SYSTEM WITH THE 
ARCTIC AIR IS UNCERTAIN. THUS WENT WITH SCHC POPS FOR SUNDAY BUT I 
COULD EASILY SEE THE NEED FOR CHC POPS.

WENT DRY FROM SUNDAY NIGHT ON BUT I HAVE RESERVATIONS ABOUT DOING 
SO. WITH THE POLAR LOW ROTATING THROUGH THE GREAT LAKES SUNDAY NIGHT 
THROUGH MONDAY THERE WILL BE NUMEROUS VORT MAXES/WEAK SHORTWAVES IN 
THE FLOW. ANY ONE OF THESE COULD PRODUCE FLURRIES OR SHSN. LIKEWISE 
...TEMPERATURES WILL BE DEPENDENT UPON CLOUD COVER. ANY BREAKS IN 
CLOUD COVER WILL ALLOW TEMPERATURES TO PLUMMET SO THERE IS 
CONSIDERABLE UNCERTAINTY IN MAX/MIN TEMPERATURES NEXT WEEKEND AND 
EARLY NEXT WEEK.
..08..

&&

.AVIATION...
VFR CONDITIONS WILL BE FOUND THROUGH 16/18Z. SOME MID/HIGH CLOUDS WILL
OVERSPREAD REGION LATER TNGT THROUGH WED AM. NORTHWEST WINDS 6-11 KTS
WILL BECOME LIGHT AND VARIABLE THIS EVE AND MUCH OF TNGT WITH RIDGE 
AXIS OVERHEAD... THEN WINDS BECOME SOUTHERLY WED AM AS RIDGE AXIS 
SLIDES OFF TO THE EAST.  ..05..

&&

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

&&

$$

05/08