FXUS63 KDVN 032138 CCA
AFDDVN

AREA FORECAST DISCUSSION...CORRECTED TYPOS IN LONG TERM
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
325 PM CST THU DEC 3 2009

.SYNOPSIS...
AN UPPER LOW...EMBEDDED IN A LONGWAVE TROUGH AXIS FROM HUDSON BAY TO 
THE 4 CORNERS REGION...WAS CENTERED OVER FAR N CENTRAL IA THIS 
AFTERNOON. STEEP MID LEVEL LAPSE RATES AND FORCING FROM THIS 
DEFORMATION ZONE WAS RESULTING IN BANDS OF SNOW SHOWERS OVER MAINLY 
THE NORTHERN HALF OF THE LOCAL FORECAST AREA. AT THE SURFACE...19Z 
ANALYSIS INDICATED A LOW PRESSURE TROUGH EXTENDED WEST FROM NRN 
LOWER MI ACROSS SOUTHERN WI AND ALONG THE IA/MN BORDER. A LOW 
LEVEL DRY SLOT ASSOCIATED WITH A WEAK MID LEVEL VORT IN THE SW FLOW 
AHEAD OF THE TROUGH...RESULTED IN WIDESPREAD CLEARING IN THE CLOUD 
COVER OVER MUCH OF THE CWFA THIS MORNING...WITH SUNSHINE ENHANCING 
THE SNOW SHOWERS ALONG THE SOUTHERN PERIMETER OF THE RETREATING LOW 
CLOUDS.

&&

.SHORT TERM...TONIGHT AND FRI...
PRIMARY CONCERN IS SNOW AMOUNTS LATE THIS AFTERNOON AND EVENING. 
MOST WIDESPREAD SNOW SHOWERS HAVE BEEN CONFINED TO UNDER AND EAST OF 
THE UPPER LOW TRACK ACROSS NRN AND NE IA...SOUTHERN MN AND SOUTHERN 
WI. 12Z ANALYSIS HAD 100M HT FALLS AT H5 OVER EASTERN WI... 
SUPPORTING SHORT TERM MODELS DEPICTION OF THE UPPER LOW ROTATING 
NEARLY DUE EAST TONIGHT THROUGH THE BASE OF THE UPPER TROUGH. THIS 
RESULTS IN THE AXIS OF STRONG LOW TO MID LEVEL FORCING/OMEGA AND 6 
TO 7 DEG C/KM MID LEVEL LAPSE RATES BRUSHING THE HIGHWAY 20 CORRIDOR 
AND NORTHWARD ESPECIALLY THIS EVENING. ANOTHER SEPARATE AREA OF MORE 
DIURNAL DRIVEN SNOW SHOWERS OVER CENTRAL IA THIS AFTERNOON WAS MORE 
CLOSELY TIED TO A POCKET OF VERY STEEP H8 TO H7 LAPSE RATES...WHICH 
ALSO ARE SHOWN TO TRANSLATE E-NE ACROSS E CENTRAL IA THIS EVENING. 

OF THE 12Z MODELS...ONLY THE WRF 4KM HAD CORRECT PLACEMENT OF NARROW 
SNOW BANDS THAT IMPACTED NRN IA INTO E CENTRAL IA THIS MORNING. THIS 
DEPICTS SIMILAR BANDS DEVELOPING EASTWARD OVER MUCH OF THE CWFA 
NORTH OF I-80 THIS EVENING. 12Z MODELS HAVE MORE GENERAL WIDESPREAD 
QPF OVER E CENTRAL IA INTO FAR NW IL PRIMARILY BETWEEN 00Z AND 06Z 
AS UPPER LOW PUSHES THROUGH. BEST LOW LEVEL CONVERGENCE ALONG THE 
SLOW MOVING SURFACE TO 925MB TROUGH AXIS REMAINS IN THE FAR 
NORTH...AND THIS IS THE AREA OF GREATEST CONCERN. BASED ON STORM 
HISTORY...WIDESPREAD 1 TO 2 INCHES LOOKS LIKELY IN THE AREA OF 
PRIMARY FORCING WHICH IS GREATEST JUST NORTH OF THE CWFA. BIGGEST 
CONCERN IS THE POTENTIAL FOR SMALLER MESOSCALE CONVECTIVE BANDS THAT 
COULD PRODUCE BURSTS OF HEAVIER SNOW AMOUNTS THAT COULD EXCEED 3 
INCHES IF THEY BECOME STATIONARY OR SLOW MOVING. FOR NOW...WILL HOLD 
OFF ON AN ADVISORY AND EXPECT 1 TO 3 INCHES PRIMARILY NORTH OF 
HIGHWAY 20 CORRIDOR...ESPECIALLY FROM DBQ TO FREEPORT. LOCAL SNOW 
ACCUMULATIONS UP TO 1 INCH WILL BE POSSIBLE AS FAR SOUTH AS I-80 
WHERE DIURNALLY ENHANCED SNOW SHOWERS WILL ROTATE THROUGH LATE THIS 
AFTERNOON AND EVENING. 

OTHERWISE...REST OF TONIGHT AND FRI REMAIN CONSIDERABLY COLDER THAN 
RECENT WEEKS. KEPT FRI HIGHS WELL BELOW NORMAL IN THE UPPER 20S TO 
LOWER 30S AS CLOUDS HANG ON UNDER THE LONGWAVE UPPER TROUGH AND 
THERMAL TROUGH AT H8 OVER THE AREA..
..SHEETS.. 

.LONG TERM...FRIDAY NIGHT THROUGH NEXT THURSDAY...
AN ACTIVE PERIOD IS STILL BEING ADVERTISED AS MEDIUM RANGE MODELS 
CONTINUE TO SHOW SLUG OF ARCTIC AIR ADVANCING SWD THROUGH 
WRN/CNTRL CANADA... AND EVENTUALLY FROM THE NRN ROCKIES THROUGH
THE UPPER MIDWEST LATE IN THE WEEKEND INTO MIDDLE OF NEXT
WEEK. AS RESULT... IMPRESSIVE BAROCLINIC ZONE WILL DEVELOP AND 
REORIENT ITSELF FROM SW TO NE... TO MORE W TO E WITH RESULTANT 
SEMI-ZONAL FLOW. THIS WILL PUT REGION IN OR NEAR STORM TRACK AND 
JET... AND IN THE CROSS HAIRS FOR A COUPLE OF STORM SYSTEMS WITH 
ACCUMULATING SNOW... WITH THE POTENTIAL FOR SIGNIFICANT SYSTEM TO
IMPACT AREA BY MID WEEK.  

FRI NGT... WINDS BACK TO SOUTH IN RESPONSE TO DEVELOPING LOW 
OVER THE PLAINS. ENSUING WARM ADVECTION IN CONCERT WITH 
DEPARTING SHORTWAVE AND INCREASING SUBSIDENCE SHOULD RESULT IN 
CLEARING SKIES. LOCAL MIN TEMP TECHNIQUE SUPPORTS POTENTIAL 
FOR LOWS AS COLD AS 10-14F IN COLD DRAINAGE SITES NORTH... BUT 
DESPITE CLEARING BANKING ON ENOUGH OF SLY WIND TO MAINTAIN BL
MIXING TO SIDE WITH GUIDANCE BLEND ON LOWS. 

SAT-SAT NGT...MAINTAIN SLY WINDS AHEAD OF FRONTAL ZONE WHICH LAYS
OUT FROM GREAT LAKES TO CENTRAL PLAINS. THE SLY WINDS WILL
BRING WARMING TREND... BUT CHALLENGE WILL BE WITH HOW WARM TO GO
AS SUGGESTIONS OF THICK HIGH CLOUDINESS MUCH OF DAY... WHICH CAN
BE SIGNIFICANT INHIBITOR ON WARMING POTENTIAL THIS TIME OF YR. 
NUDGED UP MINS FEW DEGS SAT NGT WITH SLY WINDS AND BL MIXING IN
PRE-FRONTAL ENVIRONMENT. 

SUN-MON...INITIAL BOUT OF ENERGY SHOWN TO EJECT FROM WESTERN 
TROUGH AND RIPPLE ALONG BAROCLINIC ZONE BRINGING SOME ACCUMULATING
SNOW MAINLY SUN NGT INTO EARLY MON. HAVE INCREASED POPS SUN NGT 
AND LEFT SMALL POPS FOR NOW ON MON... BUT THIS WILL NEED TO BE 
REFINED AS TRACK/TIMING BECOME BETTER DEFINED. PRELIM THOUGHTS ARE
GIVEN MAGNITUDE OF THERMAL GRADIENT AND FORCING WITH AID OF LEFT 
EXIT REGION OF 100+ KT H3 JET POTENTIAL FAIRLY WIDESPREAD AMOUNTS
AROUND AN INCH WITH BAND OF 3-4 INCHES POSSIBLE. WOULDN/T BE 
SURPRISED THOUGH TO SEE MODELS TREND A LITTLE WETTER WITH SYSTEM 
NEXT 24 HRS. 

MON NGT-TUE...APPEARS TO BE BREAK IN ACTION BEFORE MAIN ENERGY 
EJECTS OUT. LOWERED TEMPS DURING PD BUT MAY NEED FURTHER 
LOWERING ESPECIALLY WITH NEGATIVE FEEDBACK FROM ANY SNOW COVER. 

TUE NGT-THU...STILL A LOT OF UNCERTAINTY ON STRENGTH AND TRACK OF
ENERGY AS IT EJECTS OUT. TODAYS ECMWF HAS TRENDED TOWARD UKMET
IN SHOWING MORE PHASED SOLUTION AND HENCE STRONGER SYSTEM... THOUGH
ECMWF INDICATES MORE PHASING AND FURTHER WEST AND IS MUCH 
STRONGER... SLOWER AND FURTHEST NW WITH POTENT/DEEP H5 SHORTWAVE 
TROUGH OVER IA 12Z WED WITH SIGNIFICANT SNOW ACCUMS FAIRLY 
WIDESPREAD. MEANWHILE... UK AND GFS FAIRLY CLOSE AND WEAKER AT
144 HRS OR 12Z WED WITH PHASING SHOWN NEAR TO SOUTH OF AREA AND
LOW WORKING UP THROUGH OH VALLEY PUTTING AREA ON NORTHERN EDGE OF 
SIGNIFICANT PCPN SHIELD. GIVEN THE STRENGTH OF BAROCLINIC ZONE AND 
ENERGY FEELING IS STRONGER/SLOWER AND FURTHER NW SOLUTION OF ECMWF 
MAY BE MORE CORRECT. FOR NOW HAVE INCREASED POPS TUE NGT AND 
INTRODUCED SLIGHT CHC POPS AREA WIDE ON WED... AND AWAIT BETTER 
AGREEMENT NEXT COUPLE OF DAYS... THOUGH WOULDN/T BE SURPRISED IF 
WILL BE NEEDING TO RAISE POPS AND EXTEND THEM THROUGH WED NGT. BEARS 
CLOSE WATCHING IN THE COMING DAYS AS POTENTIAL FOR FIRST MAJOR STORM 
WITH SIGNIFICANT ACCUMS PER MAGNITUDE OF JET...BAROCLINIC ZONE AND 
ENERGY... WITH CHALLENGE OF TIMING AND LOCATION. AT THE END OF PD 
AND IMMEDIATELY BEYOND THE CHALLENGE WILL BE WITH TEMPS AS MEDIUM 
RANGE MODELS SHOW CHUNK OF ARCTIC AIR SPILLING SWD BEHIND SYSTEM... 
JUST QUESTIONS ON MAGNITUDE AND SWD EXTENT WHICH TIED TO STRENGTH OF 
DEPARTING SYSTEM. 
..MCCLURE..

&&

.AVIATION...
UPPER LEVEL LOW PRESSURE MOVING ACROSS EASTERN IA AND NW IL WILL 
SPREAD WIDESPREAD LIGHT SNOW AND BANDS OF HEAVIER SNOW SHOWERS EAST 
ACROSS THE CID AND DBQ TERMINALS FROM LATE AFTERNOON THROUGH 
MIDNIGHT. THESE WILL DROP BOTH VISIBILITIES AND CIGS INTO IFR RANGE 
FOR SHORT PERIODS. MLI AND BRL WILL HAVE MORE WIDELY SCATTERED SNOW 
SHOWERS WITH MVFR CIGS AND VERY BRIEF IFR VISIBILITIES BEFORE 03Z. 
AFTER MIDNIGHT...MVFR CIGS SHOULD IMPROVE TO VFR WITH THESE 4 TO 6 
KFT CIGS LINGERING THROUGH FRI MORNING. WEST WINDS FROM 12 TO 20 KTS 
ARE EXPECTED TO DIMINISH AND LOSE GUSTS AFTER 7 PM.  
..SHEETS..

&&

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

&&

$$

SHEETS/MCCLURE