FXUS63 KBIS 022131
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
331 PM CST WED DEC 2 2009

.SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT...
FORECAST CONCERNS TODAY INVOLVE SNOW CHANCES. COLD UPPER LOW
CENTERED OVER DEVILS LAKE AT 18Z/NOON WILL DRIFT SOUTH TONIGHT AND
THURSDAY. NAM SOUNDINGS SHOW NEARLY ADIABATIC LAPSE RATES ACROSS
CENTRAL NORTH DAKOTA FROM SURFACE TO 800 MB AND UP TO 100 CAPE
VALUES. LAKE EFFECT MODIFIED CAPE VALUES UP TO 400. I HAVE RAISED
THE CHANCE FOR SNOW ACROSS MUCH OF CENTRAL NORTH DAKOTA TONIGHT
AND THURSDAY. IT WILL BE HARD TO SEPARATE LAKE EFFECTS FROM THE
SYNOPTIC PATTERN BUT LAKE EFFECT MAY ENHANCE SNOW AMOUNTS ACROSS
OLIVER...MORTON AND MERCER COUNTIES TONIGHT AND THURSDAY. WILL ADD
ADDITIONAL SNOW AMOUNTS THERE. ON THURSDAY..LINGERING EFFECTS OF
THE UPPER LOW WILL KEEP SNOW SHOWERS OVER THE REGION...WITH
ADIABATIC LAPSE RATES TO 800 MB AGAIN ON THE NAM SOUNDING. I CAN
ENVISION STREAMS OF LAKE EFFECT SNOWS CONTINUING THURSDAY WITH A
SYNOPTIC VERTICAL MOTION FIELD CONTRIBUTING TO WIDESPREAD SNOW
SHOWERS. BY THURSDAY NIGHT THIS PATTERN WILL DIMINISH AND END AS
UPPER LOW DRIFTS EAST AND WARMING TEMPERATURES ARE SEEN ALOFT.

.LONG TERM...SUNDAY THROUGH WEDNESDAY...
IT REMAINS COLD THROUGH WEDNESDAY. THE LONG TERM BEGINS WITH ONE 
VORTEX WHICH ALREADY ROTATED AROUND FROM HUDSON BAY NOW BECOMES AN 
OPEN WAVE AS IT MOVES OVER THE NORTHERN GREAT LAKES. THIS MAINTAINS 
A BROAD/COLD CYCLONIC FLOW OVER THE CWA SUNDAY AND MONDAY WITH THE 
POTENTIAL FOR SOME SNOWFLURRIES. HOWEVER HAVE KEPT THE FORECAST DRY 
FOR NOW SINCE THE OVERALL THREAT OF MEASURABLE SNOW IS VERY LOW. 

BEYOND MONDAY...WILL NEED TO WATCH A VORTEX WHICH IS CURRENTLY OVER 
THE NORTHERN ARCTIC OCEAN. THIS ARCTIC VORTEX GRADUALLY MOVES EAST 
AND THEN SOUTH INTO CENTRAL CANADA MONDAY/TUESDAY. BOTH THE 12Z GFS 
AND 12Z ECMWF BRING A COLD FRONT THROUGH NORTH DAKOTA WHICH WILL 
REINFORCE THE COLDER AIR FOR TUESDAY AND WEDNESDAY. THE 12Z MODELS 
AND GFS ENSEMBLES ARE IN GOOD AGREEMENT WITH THE LOCATION OF THE 
ARCTIC VORTEX THROUGH THE EXTENDED. IT APPEARS RIGHT NOW THAT OUR 
CWA WILL JUST BE GRAZED WITH THE ARCTIC AIR TUESDAY AND WEDNESDAY. 
THE GFS IS THE COLDEST MODEL WITH H85 TEMPS RANGING FROM -20C SOUTH 
TO -28C NORTH WEDNESDAY. THUS EXPECT HIGH TEMPERATURES TO REMAIN 
BELOW AVERAGE WITH LOW TEMPERATURES ABOUT AVERAGE AT LEAST THROUGH 
WEDNESDAY. HOWEVER THIS SURGE LOOKS SHORT LIVED AS THE GFS AND ECMWF 
SHOW WARM AIR ADVECTION RETURNING FOR THURSDAY AND FRIDAY. 
PRECIPITATION PROSPECTS ALSO LOOK GREATER LATER NEXT WEEK.    
&&

.AVIATION...OCCASIONAL LIGHT SNOW SHOWERS WILL CONTINUE TONIGHT AND 
INTO THURSDAY MORNING BEFORE TAPERING OFF AFTER 18Z THURSDAY. MVFR 
CEILINGS AND VISIBILITIES RANGING BETWEEN 1 AND 3 MILES WILL BE 
COMMON AT THE AERODROMES. VISIBILITY WILL IMPROVE TO VFR AFTER 18Z 
THURSDAY BUT CEILINGS WILL REMAIN MVFR TO LOW VFR. 

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

WAA/KS