FXUS63 KGID 062340
AFDGID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
535 PM CST SUN DEC 6 2009

.AVIATION...00Z KGRI TAF...SNOW...AS DEPICTED ON RADAR AND IN 
SURFACE OBSERVATIONS...CONTINUES AT GRI AT ISSUANCE. RADAR TRENDS 
INDICATE BACK EDGE OF HEAVIER SNOW BAND APPROACHING FROM THE 
SOUTHWEST AND SHOULD MOVE THROUGH BEFORE 02Z. LIGHT SNOW EXPECTED TO 
CONTINUE FOR A FEW HOURS AFTER THAT...THEN END. IFR CONDITIONS FOR 
THE FIRST FEW HOURS WITH THE HEAVY SNOW...THEN IMPROVING TO MVFR 
CEILINGS AS THE SNOW LETS UP. MVFR CEILINGS EXPECTED THRU THE 
DURATION OF THE TAF...OTHERWISE NO VISIBILITY RESTRICTIONS OR 
SIGNIFICANT WIND CONDITIONS EXPECTED THRU 00Z. 

&&

.SHORT TERM...CURRENT SNOW WILL CONTINUE INTO MID EVENING AS MID
LEVEL WAVE CROSSES THE REGION. FOCUS THEN TURNS TOWARDS SYSTEM
BEGINNING MONDAY NIGHT.

.MEDIUM RANGE...00Z TUESDAY THROUGH 00Z THURSDAY.  THIS PERIOD 
FOCUSES ON UPCOMING WINTER STORM. LOOKING AT THE LATEST MODEL RUNS 
IT APPEARS LIKE A SIGNIFICANT WINTER STORM IS STILL IN STORE FOR 
MUCH OF OUR CWA.  STARTING WITH THE BIG PICTURE...A POSITIVE TILTED 
UPPER LEVEL WAVE LOOKS TO BE SITUATED FROM WESTERN MONTANA TO NW 
CALIFORNIA AT 00Z TUESDAY. THE WAVE IS EXPECTED TO EJECT ACROSS THE 
ROCKIES DURING THE DAY TUESDAY AND PUSH THROUGH OUR REGION TUESDAY 
NIGHT EVENTUALLY BECOMING NEGATIVELY TILTED.  BROAD SCALE SYNOPTIC 
LIFT EXPECTED AHEAD OF THIS SYSTEM AND IS NOTED ON UPPER LEVEL 
Q-VECTOR PLOTS. 

WARM ADVECTION NOTED ON THE 290K ISENTROPIC SURFACE WILL BEGIN IN 
EARNEST AHEAD OF THE MAIN WAVE STARTING BETWEEN 00 AND 06Z TUESDAY. 
THE WARM ADVECTION LOOKS TO CONTINUE FOR A PROLONGED PERIOD OF 
TIME...ABOUT 24 HOURS.  CLOSER EXAMINATION OF THE PRESSURE SURFACE 
AND WINDS SHOW THE BEST LIFT SHOULD BE DURING THE DAYTIME HOURS ON 
TUESDAY. MIXING RATIOS DURING THAT TIME VARY FROM 2 TO 2.5 GM/KG IN 
THE NORTH TO 2.5 TO 3 IN THE SOUTHERN CWA.

SUBTLE DIFFERENCES NOTED BETWEEN THE MODELS AS THE 500 OPEN WAVE 
MOVES THROUGH BUT OVERALL QUITE SIMILAR.  MODELS SIMILAR IN 700 MB 
TRACK TAKING IT EAST ALONG THE NE/KS STATE LINE ON TUESDAY. LATEST 
GFS TAKES THE SURFACE LOW FROM COLORADO BY 18Z TUESDAY TO CENTRAL 
MISSOURI 12 HOURS LATER. MODELS DEEPEN THIS SURFACE LOW PRETTY GOOD 
WHICH WILL ADD ANOTHER FACTOR TO THE WHOLE STORM SYSTEM...THAT BEING 
STRONG NORTHWEST WINDS TUESDAY NIGHT INTO WEDNESDAY MORNING.

FORECAST SOUNDINGS SHOW THAT THIS SHOULD BE A SNOW EVENT ACROSS THE 
ENTIRE CWA WITH TEMP PROFILE WELL BELOW ZERO THROUGHOUT THE COLUMN. 
BEST MOISTURE PREDICTED IN THE SOUTH WITH PRECIPITABLE WATER VALUES 
RANGING FROM 0.5 TO 0.6 INCHES IN THE SOUTH AND 0.35 IN THE NORTH. 
FORECAST SOUNDINGS ALSO POINT TO GOOD COOLING IN THE COLUMN AFTER 
ABOUT 21Z TUESDAY WHICH WILL INFLUENCE LIQUID TO SNOW RATIO.  A 
CHECK OF THE COBB METHOD FROM THE LATEST MODELS WOULD SHOW A 10 OR 
15 TO 1 RATIO EARLIER IN THE EVENT...AND THEN CLOSER TO 15 OR 20 TO 
1 LATER AS THE ATMOSPHERE COOLS.

SO WHAT IT BOILS DOWN TO IS HOW MUCH SNOW AND WIND WE MIGHT GET AND 
WHEN WILL IT START AND FINISH.  STILL LOOKS LIKE THE TIME FRAME OF 
LATE MONDAY NIGHT INTO TUESDAY NIGHT IS ON TRACK WITH THE HEAVIER 
SNOW MOST LIKELY TUESDAY AFTERNOON INTO EARLY EVENING. AS FAR AS 
LOCATION...BELIEVE THE SOUTHEAST CWA SHOULD GET THE MOST WITH THE NW 
THE LEAST. HOWEVER ANY DEVIATION IN THE STORM TRACK COULD AFFECT 
THAT. 

LOOKING AT A CROSS SECTION PLOT SHOWS PLENTY OF MOISTURE...MID LEVEL 
FRONTOGENETICAL FORCING...SOME NEG EPV...DECENT LIFT AS SEEN BY THE 
OMEGA VALUES...AND THAT LIFT WILL BE FAIRLY STRONG THROUGH THE 
DENDRITIC LAYER.  WHAT THIS TELLS ME IS THAT SIGNIFICANT SNOWS ARE 
QUITE LIKELY. WILL NOT PIN DOWN LOCATION AS IT IS STILL TOO FAR 
OUT...BUT WE LOOK TO BE UNDER THE GUN AT THIS TIME.  ONE CONCERN I 
DO HAVE IS JUST HOW WIDE THE HEAVY...GREAT THAN SIX INCHES...SWATH 
OF SNOW IS BEING PREDICTED BY THE MODELS. GFS HAS AN AREA OVER 200 
MILES WIDE WHICH SEEMS A BIT EXCESSIVE.

.LONG TERM...0Z THURSDAY THROUGH SUNDAY. QUIET WEATHER IN STORE AS
EARLY WEEK STORM SYSTEMS EXITS THE PLAINS. WE WILL REMAIN UNDER A
BROAD NORTHWEST FLOW SO IT WILL STAY COOL...ESPECIALLY IF WE END
UP WITH A DECENT SNOW COVER.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...WINTER WEATHER ADVISORY UNTIL 9 PM CST THIS EVENING FOR 
     NEZ039>041-046>049-060>064-072>077-082>087.

     WINTER STORM WATCH FROM LATE MONDAY NIGHT THROUGH LATE TUESDAY 
     NIGHT FOR NEZ039>041-046>049-060>064-072>077-082>087.

KS...WINTER WEATHER ADVISORY UNTIL 9 PM CST THIS EVENING FOR 
     KSZ005>007-017>019.

     WINTER STORM WATCH FROM LATE MONDAY NIGHT THROUGH LATE TUESDAY 
     NIGHT FOR KSZ005>007-017>019.

&&

$$

EWALD/KISNER/EDDY