FXUS63 KBIS 111007
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
407 AM CST FRI DEC 11 2009

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT...

WIND CHILLS HAVE BEEN RUNNING 15 TO 25 BELOW THIS MORNING...JUST
ABOVE WIND CHILL CRITERIA WITH WINDS OF 5 TO 10 MPH IN GENERAL.
WINDS WILL REMAIN LIGHT THROUGH THE MORNING AND...ALTHOUGH TEMPS
WILL FALL...WIND CHILLS WILL REMAIN MARGINAL FOR AN ADVISORY.
CONSEQUENTLY...WILL END THE ADVISORY WITH THE MORNING ISSUANCE.  
LOOKS LIKE SOME WARM ADVECTION/ISENTROPIC LIFTING WILL DEVELOP
THIS AFTERNOON AS AN UPPER LEVEL LOW OVER NORTHERN SASKATCHEWAN
BEGINS TO MOVE SOUTH TURNING THE UPPER LEVEL FLOW OVER THE STATE
TO THE WEST. SHOULD SEE WARMER TEMPERATURES TODAY AND
SATURDAY...LIKELY AROUND 10 DEGREES WARMER THAN THURSDAY...BUT
HIGHS WILL STILL BE WELL BELOW NORMAL. SOME LIGHT SNOW POSSIBLE
ACROSS THE NORTH TONIGHT...GRADUALLY EXTENDING ACROSS THE FORECAST
AREA BY SUNDAY AND EXTENDING INTO SUNDAY NIGHT AS THE UPPER LEVEL
SHORT WAVE DIGS SOUTH INTO THE AREA. BEST CHANCE OF PRECIP FOR THE
SHORT TERM LIKELY SUNDAY NIGHT AS THE SHORT WAVE MOVES INTO
SOUTHERN ALBERTA PUSHING A SURFACE LOW ACROSS THE CENTRAL US.
EVEN WITH COLD AIR OVER THE FORECAST AREA COULD SEE ENOUGH LIFTING
OVER THE COLD DOME TO GENERATE LIGHT ACCUMULATIONS ALONG THE
SOUTH DAKOTA BORDER.

.LONG TERM...MONDAY THROUGH FRIDAY...

THE MAIN FORECAST CHALLENGE THIS PERIOD IS WITH TEMPERATURES...BOTH 
HOW COLD THEY WILL GET AND HOW LONG THEY WILL REMAIN BELOW AVERAGE. 
MODELS ARE GENERALLY IN AGREEMENT WITH MAJOR FEATURES...SO GRIDDED 
FORECASTS UTILIZED A BLEND OF CONTINUITY AND 00 UTC GFS/ECMWF. 

THE 00 UTC GFS/GEM GLOBAL ARE SLIGHTLY FASTER THAN THE 00 UTC 
ECMWF...BUT THE EXACT TIMING OF SHORTWAVES IN THE LONG TERM IS 
ALWAYS A SOURCE OF LARGE UNCERTAINTY. SO...IT APPEARS THAT AT SOME 
POINT ON MONDAY THERE WILL BE LIGHT TO MODERATE SNOW OUT WEST AND A 
FRIGID ARCTIC SURFACE HIGH PRESSURE QUICKLY FOLLOWS PASSAGE OF THE 
MIDDLE LEVEL TROUGH AXIS. SNOW-COVERED GROUND...00 UTC GFS/ECMWF 850 
HPA TEMPERATURES PUSHING -30C AND A 1040+ HPA SURFACE HIGH SHOULD 
SET THE STAGE FOR TREMENDOUS RADIATION AND SOME LOW TEMPERATURES IN 
THE -30S F. THE BEST AREA FOR THIS LOOKS TO BE OVER WESTERN NORTH 
DAKOTA BASED ON A MEAN SURFACE HIGH POSITION...BUT THAT COULD EASILY 
CHANGE AS THE FORECAST IS REFINED. FOR THIS REASON...THE GRIDDED 
FORECAST ONLY ADVERTISES TEMPERATURES IN THE -20F RANGE. LOOK FOR 
THAT TO DECREASE AS UNCERTAINTY DECREASES WITH TIME. 

FOLLOWING THAT FRIGID TUESDAY MORNING...MODELS/ENSEMBLES UNIFORMLY 
DISSOLVE HIGH LATITUDE BLOCKING AND ADVERTISE PROGRESSIVE FLOW OVER 
THE CONUS. CONFIDENCE IS LOW WITH THIS SOLUTION...SINCE RECENT 
SOLUTIONS PUSHING TEMPERATURES BACK TOWARD AVERAGE HAVE VERIFIED 
RATHER POORLY. FOR THE SAKE OF HONORING CONTINUITY AND 
UNCERTAINTY...LATE PERIOD TEMPERATURES ARE NEAR AVERAGE. 

IT IS WORTH NOTING THAT EVEN WITH THE PROGRESSIVE FLOW AROUND A 
POSITIVE PACIFIC NORTH AMERICAN FLOW PATTERN IN PLACE...00 UTC GEFS 
MEMBERS/GEM GLOBAL/GFS/ECMWF SOLUTIONS ALL FAIL TO ALLOW MIDDLE 
LEVEL CYCLONIC FLOW TO PASS EAST OF THE DAKOTAS. THIS SCENARIO 
GENERALLY PREVENTS A WARM UP TO ABOVE AVERAGE TEMPERATURES...SINCE 
WE USUALLY EXPERIENCE VERY LITTLE WARM AIR ADVECTION WITHOUT PASSAGE 
OF THE MIDDLE/UPPER LEVEL RIDGE AXIS.

&&

.AVIATION...

A WEAK ALBERTA CLIPPER IS FORECAST TO SWEEP THROUGH NORTH DAKOTA 
FRIDAY AFTERNOON...BUT CONDITIONS SHOULD REMAIN VFR THROUGH THE 
PERIOD. THE NEXT REASONABLE CHANCE OF DESCENDING CEILINGS/MVFR 
CONDITIONS IS ON SATURDAY EVENING NEAR WILLISTON AS A CHANCE FOR 
LIGHT SNOW PRECEDES THE NEXT LOW PRESSURE SYSTEM. 

&&

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

$$

SHORT TERM...TSW
LONG TERM/AVIATION...SCHECK