FXUS63 KDVN 072146
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
346 PM CST MON DEC 7 2009
.SYNOPSIS...
BROAD MID LEVEL SWLY FETCH OVER THE SRN HALF OF THE U.S. ORIGINATING
IN A DEEP MID LEVEL TROF FROM THE NRN ROCKIES THROUGH NRN CA. THE
MORNING H8 ANALYSIS SHOWED A LOW OVER NRN IL WITH TROF/COLD FRONT
EXTENDING SW THROUGH WRN OK AND NRN TX. AN IMPRESSIVE TEMP GRADIENT
WAS LOCATED OVER TX PANHANDLE WITH -13C AT KAMA AND +9C AT KMAF.
AHEAD OF THE FRONT GULF MOISTURE WAS ALREADY ON SHORE WITH H8
DEWPOINTS OF 8-10C OVER LA AND SE TX. THE LOW PRESSURE THAT BROUGHT
THE -SN TO THE AREA LAST NIGHT HAS MOVED OFF TO THE NE WITH ITS
ATTENDANT COLD FRONT OVER THE OHIO VALLEY.
&&
.SHORT TERM...TONIGHT AND TUESDAY...
THE STORM SYSTEM FOR LATE TONIGHT INTO TUESDAY STILL LOOKS ON
TRACK WITH REASONABLE AGREEMENT AMONG THE MODELS AS THE STORM
DEVELOPS OVER THE SRN PLAINS TONIGHT AND STARTS TO HEAD NE
TUESDAY. GULF MOISTURE ALREADY ONSHORE IN TX/LA WILL BE PULLED
NORTH IN BROAD REGION ISENTROPIC LIFT. COLD AIR WITH THIS SYSTEM
IS IN PLACE AT THE ONSET WITH MODELS KEEPING THE H8 0C LINE SOUTH
OF THE CWFA UNTIL LATE AFTERNOON WHEN IT LIFTS N INTO WCNTRL IL.
USING THE GARCIA METHOD AND A MODERATE AMOUNT OF ISENTROPIC
FORCING WITH 2-3G/KG MIXING RATIOS DURING THE DAY...SUPPORTS
AROUND 2 INCHES OF SNOW NE TO POSSIBLE 5 INCHES SW 6PM TUESDAY.
THIS WILL SUPPORT STARTING OFF A WINTER STORM WARNING AROUND 12Z
IN THE SW AND AT 18Z OVER THE REST OF THE AREA. FOR TEMPS TONIGHT
ALLOWED FOR JUST A FEW DEGREES OF COOLING WITH LIGHT WINDS AND
OVERCAST SKIES HIGHS TUESDAY SHOULD STAY THE UPPER 20S NW WITH WAA
PUSHING TEMPS IN THE SE INTO THE MID 30S. ...DLF...
.LONG TERM...TUESDAY NIGHT THROUGH NEXT MONDAY...
MAIN FOCUS IS ON WINTER STORM/POSSIBLE BLIZZARD THAT WILL BE
ON-GOING TUESDAY NIGHT. WITH 12Z SHORT TERM MODELS COMING INTO
BETTER AGREEMENT...BULK OF FORECAST ON TRACK WITH PREVIOUS THINKING
AND MAIN CHANGES TODAY WERE TO UPGRADE FROM WATCH TO WARNING FOR THE
ENTIRE AREA. TOTAL SNOW AMOUNTS STILL IN THE BALLPARK OF WIDESPREAD
10 TO 12 INCHES...LOCALLY HIGHER...OVER ENTIRE CWFA ALONG AND NW OF
A FFL THROUGH MLI TO SQI. AREAS TO S AND SE WILL HAVE RANGE OF 5 TO
10 FROM SE TO NW. VERY STRONG AND NEARLY BOMBING SURFACE LOW...
TAKING NEARLY IDEAL CLIMATOLOGICAL PATH FOR LOCAL WINTER STORM
CONDITIONS FROM NW OF STL TO SOUTHERN TIP OF LAKE MI...WILL RESULT
IN VERY WINDY CONDITIONS TUE NIGHT AND WED. SUSTAINED 25 TO 30KT
WINDS WITH MUCH HIGHER GUSTS...FALLING SNOW...AND EXPECTED FRESH DEEP
SNOW COVER MAY THEN PRODUCE BLIZZARD CONDITIONS.
12Z GFS HAS SHIFTED THE TRACK OF THE SURFACE LOW CLOSER TO THE MORE
CONSISTENT ECMWF AND HAVE USED A BLEND FOR THIS FORECAST. STRONGEST
UPPER FORCING OVERLAYS THE ISENTROPIC LIFT TUE NIGHT WITH STEEP MID
LEVEL LAPSE RATES OVER THE SE SUPPORTING THUNDERSNOW THERE EARLY.
GARCIA METHOD SUPPORTS OVERNIGHT TOTALS OF 6 TO 8 INCHES...PRIMARILY
BEFORE 3 AM WHEN THE BULK OF MODERATE TO HEAVY SNOW WILL HAVE
SHIFTED EAST. STRENGTHENING SYSTEM AND VERY TIGHT SURFACE PRESSURE
GRADIENT WILL RAMP WINDS UP TO 25 TO 35 KT RANGE WITH GUSTS OF 45
KTS OR HIGHER LIKELY WELL INTO WED.
WITH HIGH CONFIDENCE IN THE ONSET OF WINTER STORM CONDITIONS...AND
BLIZZARD CONDITIONS STILL AT LEAST 24 HOURS OUT...HAVE OPTED TO
UPGRADE THE CURRENT WATCHES TO WINTER STORM WARNINGS FOR THE SNOW
ACCUMULATIONS AND BLOWING SNOW FOR TUE THROUGH WED AFTERNOON.
BLIZZARD CONDITIONS STILL A HIGH PROBABILITY...AND HAVE GONE WITH
A BLIZZARD WATCH ON TOP OF THE CURRENT WINTER STORM WARNING FOR
LATE TUE NIGHT INTO WED IN EASTERN IA...NE MO AND FAR NW IL WHERE
BLIZZARD CONDITIONS MOST LIKELY TO BE APPROACHED. THIS IS THE SAME
AREA COVERED IN THE INITIAL BLIZZARD WATCH ISSUED THIS MORNING...
BUT DO NOT EXPECT BLIZZARD CRITERIA TO BE MET UNTIL WELL INTO THE
STORM.
COLD CONDITIONS FOLLOW LATE THIS WEEK UNDER BROAD UPPER
TROUGH...THEN SLOW WARMING WITH LOW PROBABILITY FOR LIGHT WINTER
PRECIP ESPECIALLY SOUTH OF THE AREA FOLLOWS OVER THE WEEKEND AS
FLOW BECOMES MORE ZONAL.
..SHEETS..
&&
.AVIATION...
VFR TO ISOLD IFR CONDITIONS DUE CIGS AND VSBYS LATE THIS AFTERNOON
WILL IMPROVE TO VFR FOR A AWHILE BTWN 00Z AND 06Z. CONDITIONS WILL
START DETERIORATING AGAIN AFTER 06Z AS A WINTER STORM ORGANIZES OVER
THE SRN PLAINS. LIGHT TO MODERATE SNOW WILL SPREAD OVER ALL TAF
SITES BETWEEN 09Z AND 18Z DROPPING CONDITIONS INTO THE LOWER END OF
MVFR AND IFR RANGE DURING THE MORNING. LIGHT NWLY WINDS WILL TURN
TO THE NE AFTER 06Z. ...DLF...
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...WINTER STORM WARNING FROM 6 AM TUESDAY TO 6 PM CST WEDNESDAY 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 WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY
AFTERNOON 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 STORM WARNING FROM 6 AM TUESDAY TO 6 PM CST WEDNESDAY FOR
BUREAU-CARROLL-HANCOCK-HENDERSON-HENRY IL-JO DAVIESS-
MCDONOUGH-MERCER-PUTNAM-ROCK ISLAND-STEPHENSON-WARREN-
WHITESIDE.
BLIZZARD WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY
AFTERNOON FOR CARROLL-JO DAVIESS-ROCK ISLAND-STEPHENSON.
MO...WINTER STORM WARNING FROM 6 AM TUESDAY TO 6 PM CST WEDNESDAY FOR
CLARK-SCOTLAND.
BLIZZARD WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY
AFTERNOON FOR CLARK-SCOTLAND.
&&
$$
SHEETS/DLF
