FXUS63 KBIS 071017
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
400 AM CST MON DEC 7 2009
.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT...
VERY COLD TEMPERATURES CONTINUE TO BE THE MAJOR HIGHLIGHT IN THE
SHORT TERM FORECAST PERIOD. WILL YET AGAIN UTILIZE AN OVERALL MODEL
BLEND AS MOST FEATURES ARE WILL AGREED UPON.
CURRENTLY...POSITIVELY TILTED UPPER LEVEL TROUGH IN PLACE ACROSS THE
NORTHERN CONUS STRETCHING FROM THE PACIFIC NORTHWEST NORTHEAST
TOWARDS THE NORTHERN HUDSON BAY REGION. COLD ARCTIC HIGH PRESSURE
CONTINUES TO SLOWLY PUSH SOUTH TOWARDS THE NORTHERN HIGH PLAINS FROM
THE FRONT RANGE OF THE CANADIAN ROCKIES...BRINGING CONTINUED WEAK
CAA INTO THE NORTHERN PLAINS. SHORT WAVE ENERGY EJECTING INTO THE
DAKOTAS FROM THE BASE OF THE UPPER TROUGH OUT WEST IS RESULTING IN
INCREASING CLOUDS SOUTH TO NORTH OVER THE FORECAST AREA...HELPING TO
KEEP TEMPERATURES WARMER OVER MY SOUTHERN COUNTIES (AROUND ZERO TO
10 ABOVE) WHEN COMPARED TO MY NORTH (5 TO 15 BELOW) WHERE SKIES
REMAIN CLEAR TO SCATTERED.
TEMPERATURES...OUR COLD AIRMASS WILL PERSIST OVER WEST AND CENTRAL
ND THROUGH THE SHORT TERM PERIOD (MON-WED) AS THE COLD CANADIAN SFC
HIGH SLOWLY DRIFTS SOUTH TOWARDS THE NORTH CENTRAL CONUS AND SETTLES
OVER THE REGION TUESDAY/TUESDAY NIGHT. WE THEN WILL SEE A REINFORCED
SHOT OF COLD ARCTIC AIR WEDNESDAY NIGHT AS A POLAR VORTEX DRIFTS
SOUTH INTO/TOWARDS THE CENTRAL CANADIAN PRAIRIE PROVINCES. END
RESULT WILL BE SUBZERO LOWS MONDAY NIGHT AND HIGHS MAINLY IN THE
SINGLE DIGITS ABOVE MONDAY AND TUESDAY. CLOUD COVER WILL BE A MAJOR
FACTOR IN REGARDS TO TEMPERATURES...AND WITH EXPECTED CLEARING
TUESDAY NIGHT IN THE WAKE OF A MID LEVEL TROUGH...TEMPERATURES LOOK
TO DROP OFF TO NEAR 10 BELOW SOUTH AND TO NEAR 20 BELOW ACROSS THE
NORTH. ON WEDNESDAY WE SEE INCREASING CLOUDS WEST TO EAST AS ANOTHER
MID LEVEL TROUGH (ASSOCIATED WITH THE ABOVE MENTIONED POLAR VORTEX)
MOVES INTO THE REGION. SUBZERO HIGHS ARE EXPECTED ACROSS THE NORTH
WHERE NOT MUCH OF A TEMPERATURE RECOVERY IS EXPECTED WITH THE NEAR
20 BELOW MORNING LOWS AND INCREASING CLOUDS CUTTING OFF SOLAR
ENERGY. THE INCREASED CLOUDINESS WED NIGHT IS THEN EXPECTED TO KEEP
LOWS AROUND 5 BELOW TO MAYBE ZERO...HELPING TO KEEP TEMPERATURES
STEADY IF NOT INCREASING FROM WED AFTERNOONS HIGHS.
NORTHWEST WINDS OF 10-20 MPH ARE FORECAST TO ACCOMPANY THE UPPER
TROUGH PASSAGE WED NIGHT...AND WHEN COMBINED WITH SUBZERO
TEMPERATURES THE RESULTANT WIND CHILL TEMPERATURES ARE FORECAST ON
AVERAGE TO RANGE FROM 25 TO 35 BELOW. IF THIS HOLDS TRUE WE WILL
NEED A WIND CHILL ADVISORY OVER MUCH IF NOT ALL OF THE CWA. WILL
CONTINUE TO MONITOR.
PRECIPITATION...OCCASIONAL FLURRIES EXPECTED TO CONTINUE AT LEAST
THROUGH THE DAYTIME HOURS TODAY. WILL MAINTAIN SLIGHT CHANCES FOR
LIGHT SNOW TONIGHT ACROSS MY SOUTHERN COUNTIES AS THE MAIN IMPULSE
FROM THE BASE OF THE TROUGH ACROSS THE PACIFIC NORTHWEST DIGS SOUTH
INTO THE SOUTHWEST CONUS AND STARTS TO EJECT S/WV IMPULSES INTO THE
CENTRAL PLAINS. A MAJOR WINTER STORM WILL THEN DEVELOP ACROSS THE
CENTRAL PLAINS ON TUESDAY...EJECTING NORTHEAST INTO THE WESTERN
GREAT LAKES REGION BY TUESDAY NIGHT. SURFACE HIGH PRESSURE IN PLACE
ACROSS OUR LOCAL REGION WILL KEEP MOST PRECIPITATION OFF TO OUR
SOUTH. HOWEVER...MODELS ARE DEPICTING THE NORTHERN EXTENT OF THE
STORMS PRECIP SHIELD GRAZING MY SOUTHERN COUNTIES...IN ADDITION TO A
NORTHERN STREAM MID LEVEL TROUGH PUSHING ACROSS THE STATE TUESDAY
DAYTIME. WILL MAINTAIN LIGHT SNOW CHANCES FROM THE HIGHWAY 200
CORRIDOR AND POINTS SOUTH...ALTHOUGH THE GREATEST CHANCES WILL BE
ALONG THE SOUTH DAKOTA BORDER AREA (ANY ACCUMULATIONS HERE WILL BE
LIGHT...MAYBE A FEW TENTHS AT BEST IF ANYTHING). PRECIPITATION
CHANCES END BY TUESDAY NIGHT AS THE NORTHERN STREAM TROUGH SWINGS
THROUGH BRINGING CLEARING SKIES.
WILL ALSO EXPAND LIGHT SNOW CHANCES FURTHER EAST FROM WED INTO WED
NIGHT AS THERE MAY BE ENOUGH MID LEVEL SUPPORT WITH THE UPPER TROUGH
TO WARRANT AT LEAST SLIGHT CHANCES FOR NOW.
.LONG TERM...THURSDAY THROUGH MONDAY
THE GFS AND ECMWF START THE LONG TERM PERIOD...THURSDAY...IN VERY
CLOSE AGREEMENT ON BOTH THE SYNOPTIC SCALE AND RESULTING MESOSCALE
DETAILS OVER NORTH DAKOTA. THEN THEY FLIP...AND THEN FLOP.
BY FRIDAY THE GFS HAS AN OPEN WAVE PASSING THROUGH WITH THE AXIS OF
ARCTIC AIR RIGHT OVER THE STATE...WHILE THE EC DELAYS THIS
FEATURE...INTENSIFIES IT...AND HAS WARM ADVECTION FLOODING THE STATE
AHEAD OF IT. THE MODELS THEN ARE COMPLETELY OUT OF SYNC ON INTENSITY
AND TIMING...WITH THE GFS BEGINNING A LONG STRETCH OF H5 RIDGING AND
A WARMING TREND BEGINNING OVER THE WEEKEND AND CONTINUING THROUGH
240 HOURS...WITH TEMPERATURES BACK ABOVE NORMAL BY MONDAY OR
TUESDAY (DECEMBER 14-15). THE EC...ON THE OTHER HAND...BRINGS ITS
POLAR VORTEX THROUGH SOUTHERN CANADA OVER THE WEEKEND...WITH ITS -36
DEGREES C AIR AT H85...BRUSHING NORTH DAKOTA. THIS IS FOLLOWED BY H5
RIDGING AND A WARMING TREND BEGINNING ON ABOUT TUESDAY.
THESE MODEL DIFFERENCES WOULD RESULT IN A SIGNIFICANTLY DIFFERENT
TEMPERATURE FORECAST BEGINNING ON DAY 6 AND CONTINUING PAST THE
FORECAST PERIOD. ONE THING THAT IS AGREED ON...NO SIGNIFICANT
PRECIPITATION THROUGH THE PERIOD.
AS I HAVE NO GOOD REASON TO FOLLOW ONE MODEL OVER THE
OTHER...FORECAST CONTINUITY WAS MAINTAINED...AND IN ADDING THE NEW
DAY 8 FORECAST TO THE GRIDDED DATA (NDFD - NATIONAL DIGITAL FORECAST
DATABASE) I KEPT SUNDAY AND MONDAYS TEMPERATURES THE SAME. THAT
MEANS OPTIMISTIC WITH RESPECT TO THE EC...AND PESSIMISTIC WITH
RESPECT TO THE GFS.
&&
.AVIATION...
A HIGH PRESSURE RIDGE WILL CONTINUE TO BUILD FROM ALBERTA TO
MONTANA...KEEPING NORTH DAKOTA IN A COOL NORTHERLY FLOW.
EXPECT IMPROVEMENT IN VSBYS AS THE HIGH BRINGS MORE STABLE AIR INTO
NORTH DAKOTA THAT DECREASES THE SNOW FLURRIES. LOWER DEW POINT AIR
WORKING IN WILL LIFT PREVAILING CIGS TO VFR...WITH OCCASIONAL
PATCHES OF MVFR CIGS NOT TO BE RULED OUT.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...NH
LONG TERM/AVIATION...JPM
