FXUS63 KDVN 092103
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
303 PM CST WED DEC 9 2009

.DISCUSSION...
.SHORT TERM...TONIGHT AND THURSDAY...
LATEST ANALYSIS WAS INDICATING A H975 MB SUPER LOW MIGRATING
NORTHEASTWARD ACRS LK HURON ATTM. INTENSE PRESSURE GRADIENT
STARTING TO RELAX JUST TO THE WEST OF THE DVN CWA BUT STILL VERY
TIGHT TO BE A STRONG WIND DRIVER WELL INTO THE EVENING. A
SECONDARY UPPER LOW/VORT THAT THE MODELS NOT REALLY PICKING UP ON
WELL WAS NOTED PIVOTING AROUND THE MAIN UPPER LOW RIGHT OVER IOWA
AND WAS PRODUCING MODERATE TO LOCALLY HEAVY SNOW THIS AFTERNOON
ACRS CENTRAL INTO EASTERN IA. THUS THE WINDS PRODUCING SIGNIFICANT BLOWING
SNOW/WHITE OUT CONDITIONS AND LINGERING FALLING SNOW SEVERELY REDUCING
VSBYS THIS EVENING SUPPORT THE ONGOING HEADLINES THROUGH 00Z...BUT
WILL THE TRANSITION ALL HEADLINES INTO A CATCH-ALL WINTER WEATHER
ADVISORY FOR THE ENTIRE CWA TO INCLUDE LINGERING BLOWING AND
DRIFTING SNOW THROUGH THE EVENING...AND THEN WIND CHILLS DROPPING
INTO THE ADVISORY CATEGORY AFTER 06Z ESPECIALLY ALONG AND NORTH OF
I80. WITH A LATER NIGHT CLEAR OUT OF CLOUDS...SFC TEMPS MAY DROP
EVEN COLDER THAN THE SUB-GUIDANCE VALUES ALREADY ADVERTISED. BUT
THIS WOULD ALSO FOSTER SOME SFC WIND DECOUPLE DECREASE IN SPEED TO
MAKE UP FOR THE COLDER TEMPS THUS THE FCST WIND CHILL VALUES OF
-20 TO -25 SHOULD BE GOOD IN MOST CASES.

ON THURSDAY...EVEN WITH AMPLE SUNSHINE TEMPS WILL STRUGGLE TO GET
OUT OF THE SINGLE DIGITS ABOVE ZERO AFTER A VERY COLD START
ESPECIALLY OVER THE SIGNIFICANT SNOW PACK AREAS. WILL UNDERCUT EVEN
THE COOLEST OF GUIDANCE HIGH TEMPS FOR THU. WIND CHILLS WILL NOT
IMPROVE ABOVE ADVISORY CRITERIA UNTIL 17Z TO 18Z AT THE EARLIEST.
THUS THE WINTER WX ADVISORY EXTENDED THROUGH 18Z THU FOR THIS
LINGERING PARAMETER. WOULD NOT BE SURPRISED WITH MID MORNING
MIXING TO START DRIVING WINDS AGAIN OF 15-25 MPH IN STILL RATHER
TIGHT LLVL PRESSURE GRADIENT AND START UP THE DRIFTING MACHINE
AGAIN.     ..12..

.LONG TERM...THURSDAY NIGHT THROUGH NEXT WEDNESDAY...
THE LONG TERM REMAINS RELATIVELY QUIET AND COLD THROUGH 
FRIDAY...THEN BECOME SOMEWHAT MORE ACTIVE INTO THE WEEKEND.  WITH 
DEEP SNOW OVER THE NORTHERN 1/2 TO 2/3RDS...TEMPS WILL STRUGGLE TO 
REACH GUIDANCE VALUES UNTIL SATURDAY AND POSSIBLY BEYOND.  THIS 
REQUIRES LITTLE EDITING OF THE PREVIOUS FORECAST...BUT I HAVE MADE 
SOME UPWARD ADJUSTMENT IN THE WEEKEND THROUGH MONDAY AS MODELS 
CONTINUE TO INDICATE ZONAL FLOW WITH A SHORT WAVE COMING ACROSS 
AROUND SUNDAY. WHILE THE ECMWF AND UKMET SHOW THIS WAVE MOVING OVER 
OR JUST NORTH OF THE CWA...I AM CONCERNED THAT THIS IS TOO FAR NORTH 
GIVEN THE SNOW PACK.  A MORE LIKELY POSITION OF THE LOW PRESSURE 
TRACK MAY BE OVER NORTHERN MO INTO SOUTHERN MICHIGAN WHERE LOW LEVEL 
BAROCLINICITY CAN FOCUS.  EITHER WAY...PTYPE MAY BE A MIX...FREEZING 
RAIN OR SNOW.  FOR NOW...WILL LEAVE IT ALL SNOW FOR SIMPLICITY.  
BEYOND THIS SYSTEM...MODELS BRING ANOTHER HIGH PRESSURE DOWN OVER 
THE CWA DURING THE EARLY WEEK.  SINCE SNOW SHOULD STILL BE ON THE 
GROUND...THIS MAY RESULT IN VERY COLD TEMPERATURES ONCE AGAIN.

..ERVIN..

&&

.AVIATION...
SECONDARY ROUND OF MODERATE TO LOCALLY HEAVY FALLING SNOW UNDER
SECONDARY UPPER DISTURBANCE WILL COMBINE WITH ONGOING BLOWING SNOW
TO KEEP VSBYS IN THE IFR TO EVEN LIFR REALM THROUGH AT LEAST 01Z
AT MOST TERMINALS. BLOWING SNOW REDUCING VSBYS OF 1-3SM FROM 01Z THROUGH
04Z THU BEFORE IMPROVEMENT EXPECTED TO VFR. LLVL CLOUDS SHOULD
CLEAR OUT AFTER 06Z AND MAY ALLOW GUSTY WEST WINDS TO SUBSIDE INTO
THE 10-15 KT RANGE. EXPECT WEST TO SOUTHWEST WINDS TO GUST AGAIN
AFTER 15Z UP TO 25 MPH WITH MORNING MIXING AS PRESSURE GRADIENT
STILL RATHER TIGHT THROUGH EARLY AFTERNOON.     ..12..
 
&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO NOON CST 
     THURSDAY FOR BENTON-BUCHANAN-CEDAR-CLINTON-DELAWARE-DES 
     MOINES-DUBUQUE-HENRY IA-IOWA-JACKSON-JEFFERSON-JOHNSON-
     JONES-KEOKUK-LEE-LINN-LOUISA-MUSCATINE-SCOTT-VAN BUREN-
     WASHINGTON.

     BLIZZARD WARNING UNTIL 6 PM CST THIS EVENING FOR BENTON-BUCHANAN-
     CEDAR-CLINTON-DELAWARE-DES MOINES-DUBUQUE-HENRY IA-IOWA-
     JACKSON-JEFFERSON-JOHNSON-JONES-KEOKUK-LEE-LINN-LOUISA-
     MUSCATINE-SCOTT-VAN BUREN-WASHINGTON.

IL...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO NOON CST 
     THURSDAY FOR BUREAU-CARROLL-HANCOCK-HENDERSON-HENRY IL-JO 
     DAVIESS-MCDONOUGH-MERCER-PUTNAM-ROCK ISLAND-STEPHENSON-
     WARREN-WHITESIDE.

     BLIZZARD WARNING UNTIL 6 PM CST THIS EVENING FOR CARROLL-JO 
     DAVIESS-ROCK ISLAND-STEPHENSON.

     WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR BUREAU-
     HANCOCK-HENDERSON-HENRY IL-MCDONOUGH-MERCER-PUTNAM-WARREN-
     WHITESIDE.

MO...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO NOON CST 
     THURSDAY FOR CLARK-SCOTLAND.

     BLIZZARD WARNING UNTIL 6 PM CST THIS EVENING FOR CLARK-SCOTLAND.

&&

$$

12/ERVIN