FXUS63 KDVN 241036
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
436 AM CST THU DEC 24 2009

.SYNOPSIS...
STRONG SHORTWAVE DIVING S/E FROM SASKATCHEWAN... WHILE POTENT COMPACT
SHORTWAVE WAS MOVING THROUGH WEST CENTRAL TX EARLY THIS AM. 
CWA IN RELATIVE LULL IN PCPN ATTIM WITH MAINLY WAVES OF LIGHT RAIN/DZ
IN CONTINUED WARM/MOIST ADVECTION ON EAST SIDE OF INVERTED SFC
TROUGH EXTENDING THROUGH CENTRAL IA. SFC TEMPS HAVE CLIMBED ABOVE
FREEZING IN FAR N ELIMINATING ICING. MAIN SLUG OF PCPN WITH ACTIVE
CONVECTION EXTENDS FROM TX/LA GULF COAST INTO OH VALLEY WITHIN ZONE
OF STRONG THETA-E ADVECTION AND UPPER DIFFLUENCE.  ..05..

&&

.SHORT TERM...TODAY AND TONIGHT...
SASKATCHEWAN SHORTWAVE AND WEST CENTRAL TX TO PHASE NEAR TO OVER THE
CWA LATE IN THE PD... WITH DEEPENING SFC CYCLONE LIFTING NORTH.
MAIN CHALLENGE REMAINS TRACK WITH IMPACTS ON WX... ESPECIALLY PCPN 
TYPE. 

WAVES OF LIGHT RAIN/DZ WILL CONTINUE THIS AM. RAIN THEN EXPECTED TO
BECOME MOD/HVY LATER TODAY AND TONIGHT WITH STRONG SURGE OF THETA-E
ADVECTION AND FORCING... WITH POTENTIAL FOR ISOLD THUNDER MAINLY 
SOUTHEAST 1/3-1/2. PCPN AMOUNTS OVER NEXT 24 HRS GENERALLY TO RANGE
FROM 0.5 TO 1.5 INCHES. TONIGHT THE CHALLENGE BECOMES PCPN TYPE 
MAINLY IN THE NORTH AND WEST SECTIONS OF CWA. UKMET...ECMWF AND
GEM INDICATE TRACK OF LOW ACROSS FAR SOUTHWEST CWA OR EVEN A LITTLE
NORTHWEST OF THERE INTO SOUTH CENTRAL IA OR NORTH CENTRAL MO.
WARM DRAW AHEAD OF LOW WOULD SUPPORT PCPN REMAINING ALL LIQUID WITH
ONLY SMALL POTENTIAL FOR FZRA EXTREME NW. NAM REMAINS SOMEWHAT
OF AN OUTLIER BEING SLIGHTLY FURTHER S/E WITH LOW OVER WEST CENTRAL
IL NEAR KMQB AT 12Z FRI. THIS WOULD BRING LLVL WINDS MORE FROM 
NORTHEAST OVER FAR NORTHWEST CWA WITH INVERTED TROUGH POSITIONED
IN SOUTHWEST CWA BOTH ALLOWING COLDER AIR DRAW IN FOR CHANGE OVER 
IN PCPN TO MAINLY SLEET AND SNOW NORTHWEST OF KDBQ-KFFL LINE
TOWARD 06Z AND BEYOND. LEANING TOWARD NAM SOLUTION BECAUSE IT HAS
SUPPORT FROM 00Z/24 GFS ENSEMBLE MEMBERS WITH ALL 12 MEMBERS
TIGHTLY CLUSTERED WITH SFC LOW POSITION FROM KMQB-KUIN-KSPI. HAVE
THEREFORE BROUGHT CHANGEOVER TO MAINLY SN/IP IN FAR WEST AFT 06Z.
KEPT WINTER STORM WATCH GOING FOR NOW DUE TO LOW CONFIDENCE ON 
TRACK BUT DID EXPAND SOME MAINLY S/W. NOT ALOT OF CHANGE ON TEMPS
EXPECTED WITH SOME RISE LATE TNGT S/E AHEAD OF APPROACHING LOW. 
..05..

.LONG TERM...CHRISTMAS DAY THROUGH NEXT WEDNESDAY...
FORECAST FOCUS CONTINUES TO BE MAJOR WINTER STORM THAT SEEMS WILL 
NEVER GO AWAY. WILL BE MAKING CHANGES TO HEADLINES AS OPERATIONAL 
MODELS REMAIN ON THE SAME THEME...TAKING RAPIDLY DEEPENING CYCLONE 
OUT OF THE LOWER MS VALLEY AND TRACKING IT TO EASTERN IA. WILL 
RE-ADJUST THE CURRENT WINTER STORM WATCH AND PLACE IT MORE INTO OUR 
WESTERN CWA...DROPPING IT FROM NW IL. THE WATCH WILL BE IN EFFECT 
FROM 06Z FRI TO 12Z SAT.

TREMENDOUS DEEPENING OF THE SURFACE AND UPPER LEVEL LOW OCCURS ON 
CHRISTMAS DAY AND FRIDAY NIGHT. THIS IS A CLASSIC SIGNAL FOR 
PRODUCING HEAVY SNOWS. STRONG LIFT AND STRONG DYNAMIC COOLING SHOULD 
ALLOW FOR RAPID TRANSITION TO SNOW ACROSS ALL OF THE CWA. THE SNOW 
MAY BECOME MODERATE TO HEAVY ESPECIALLY WEST OF THE LOW TRACK. 
PLENTY OF MOISTURE WILL BE WRAPPED INTO THE SYSTEM DESPITE THE 
DEEPER MOISTURE GETTING CUT OFF AS THE CYCLONE OCCLUDES. THE SYSTEM 
GETS SO TIGHTLY WOUND UP THAT IT BECOMES NEARLY STALLED INTO THE 
WEEKEND. THIS WILL KEEP LIGHT SNOWS GOING SATURDAY WITH ONLY CHANCE 
POPS ON SUNDAY. TEMPERATURES WILL BE FALLING FRIDAY WITH COLD 
WEATHER REMAINING RIGHT ON THROUGH NEXT WEEK AND ON INTO JANUARY... 
WITH MOST CLIMATE MODELS SHOWING A WEAKENING EL NINO TREND.

THE MAJORITY OF THE OPERATIONAL MODELS EVENTUALLY SCOOT THE SYSTEM 
INTO THE OH VALLEY ON SUNDAY. THE NAM SEEMS TO BE AN OUTLIER IN 
TAKING LOW NORTHWARD TO MN AND HAS BEEN DISCOUNTED.

MOST OF THE HEAVIER ACCUMULATING SNOWS WILL OCCUR CHRISTMAS DAY WITH 
LIGHTER AMOUNTS CONTINUING INTO SATURDAY. WHEN ITS ALL SAID AND DONE 
EXPECTING ACCUMULATIONS OF AT LEAST 6 TO 8 INCHES IN OUR WESTERN CWA 
...ABOUT 3 TO 4 INCHES FROM NORTHEAST MO THROUGH THE SPINE OF THE MS 
RIVER AND ON INTO NORTHWEST IL...WITH 1 TO 3 INCHES FROM MACOMB TO 
PRINCETON IL. THESE ARE THE TOTALS FOR THE FRIDAY AND SATURDAY 
PERIOD WE ARE COMING UP WITH AT THIS TIME...OF COURSE SUBJECT TO 
REVISION BY LATER SHIFTS IF TRACK OF THE LOW CHANGES. THUS THE 
REASON FOR CONTINUING THE WINTER STORM WATCH AND LETTING DAY SHIFT 
DECIDE ON ANY WARNINGS IF NEEDED. 

LATER SHIFTS MAY NEED TO CONSIDER SNOW CHANCES FOR ABOUT THE MIDDLE 
OF NEXT WEEK AS THE ECMWF HAS SIGNALED THIS FOR THE PAST SEVERAL 
RUNS.    ..HAASE..

&&

.AVIATION...
DENSE FOG AND VLIFR CONDITIONS WILL IMPACT KCID THIS AM. OTHERWISE...
WIDEPSREAD IFR/LIFR CONDITIONS EXPECTED THROUGH TAF CYCLE WITH
PERIODS OF PCPN...MAINLY IN FORM OF RAIN... MODERATE TO HEAVY AT
TIMES LATER TODAY AND TNGT. AFT 06Z POTENTIAL TO SEE RAIN GO 
OVER TO WINTRY MIX OF SN/PL AT KCID. SFC WINDS MAINLY EASTERLY AT
10-20 KTS WITH GUSTS NEAR 25-28 KTS ESPECIALLY LATER TODAY AND TNGT. 
..05..

&&

.HYDROLOGY...
ADDITIONAL PCPN AMOUNTS OF 0.5 TO 1.5 INCHES OF RAIN ON TOP OF
COLD...FROZEN GROUND AND DENSE SNOW-PACK...ESPECIALLY ALONG AND
NORTH OF I-80 CREATE A FAVORABLE ENVIRONMENT OF FLOODING 
ESPECIALLY IN LOW LYING LOCATIONS. FLOODING POTENTIAL ALSO WILL
BE INCREASED IN URBAN AREAS WHERE DRAINAGE INTAKES OBSTRUCTED
BY SNOW AND ICE. ICE JAMS ON RIVERS AND TRIBUTARIES ARE POSSIBLE
DUE TO RISING WATER LEVELS AND MELTING SNOW AND ICE THAT COULD
CREATE SIGNIFICANT FLOODING ALONG AREA RIVERS. A FLOOD WARNING IS
IN EFFECT FOR LAMOINE AT COLMAR WHICH WILL BE GOING ABOVE FLOOD
STAGE IN THE NEXT 12 HRS. FLOOD WATCH IS IN EFFECT UNTIL FRIDAY
MORNING OVER MOST OF THE AREA. ANY RISES ON RIVERS SHOULD BE
REDUCED BY LATER FRI INTO SAT AS MUCH COLDER AIR SETTLES INTO
AREA.  

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...FLOOD WATCH THROUGH LATE TONIGHT FOR JACKSON.

     FLOOD WATCH THROUGH LATE TONIGHT FOR CLINTON-DES MOINES-HENRY IA-
     LEE-LOUISA-MUSCATINE-SCOTT.

     FLOOD WATCH THROUGH THIS EVENING FOR BENTON-BUCHANAN-DELAWARE-
     DUBUQUE-JONES-LINN.

     WINTER STORM WATCH FROM LATE TONIGHT THROUGH LATE FRIDAY NIGHT 
     FOR BENTON-BUCHANAN-CEDAR-DELAWARE-DUBUQUE-IOWA-JEFFERSON-
     JOHNSON-JONES-KEOKUK-LINN-VAN BUREN-WASHINGTON.

     FLOOD WATCH THROUGH THIS EVENING FOR CEDAR-IOWA-JEFFERSON-
     JOHNSON-KEOKUK-VAN BUREN-WASHINGTON.

IL...FLOOD WATCH THROUGH LATE TONIGHT FOR CARROLL-JO DAVIESS-
     STEPHENSON.

     FLOOD WATCH THROUGH LATE TONIGHT FOR BUREAU-HANCOCK-HENDERSON-
     HENRY IL-MCDONOUGH-MERCER-PUTNAM-ROCK ISLAND-WARREN-
     WHITESIDE.

MO...FLOOD WATCH THROUGH LATE TONIGHT FOR CLARK.

     WINTER STORM WATCH FROM LATE TONIGHT THROUGH LATE FRIDAY NIGHT 
     FOR SCOTLAND.

     FLOOD WATCH THROUGH THIS EVENING FOR SCOTLAND.

&&

$$

05/HAASE