FXUS63 KBIS 081000
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
400 AM CST TUE DEC 8 2009
.SHORT TERM...TODAY THROUGH THURSDAY NIGHT...
FORECAST CONCERNS/HIGHLIGHTS IN THE SHORT TERM PERIOD WILL FIRST
FOCUS ON THE INCREASING POTENTIAL FOR LIGHT ACCUMULATING SNOWFALL
ACROSS SOUTHWEST AND SOUTH CENTRAL ND TODAY INTO THIS EVENING. WILL
ALSO FOCUS ON THE COLD TEMPERATURES PERSISTING THROUGH THURSDAY.
MODELS REMAIN IN DECENT AGREEMENT...SO WILL AGAIN USE A GENERAL
BLEND.
CURRENTLY...POSITIVELY TILTED UPPER LEVEL TROUGH STRETCHING FROM THE
SOUTHWEST CONUS NORTHEAST TOWARDS THE HUDSON BAY REGION. A POTENT
SHORT WAVE IS ROUNDING THE BASE OF THE TROUGH OVER SOUTHERN CA AND
WILL EJECT INTO THE CENTRAL ROCKIES LATER THIS MORNING. OTHER S/WV
IMPULSES HAVE EJECTED NORTHEAST INTO THE GREAT PLAINS THIS EARLY
MORNING...TRIGGERING AREAS OF LIGHT SNOW/FLURRIES AS FAR NORTH AS
SOUTHWESTERN/SOUTH CENTRAL ND. BROAD/COLD ARCTIC HIGH PRESSURE HAS
TAKEN UP RESIDENCE OVER SOUTH CENTRAL CANADA AND THE FAR NORTHERN
PLAINS...AND THUS FAR IS KEEPING CLOUDS AND THE LIGHT SNOW CONFINED
TO SOUTHERN ND. RESULTANT TEMPERATURES ARE WARMER ACROSS THE SOUTH
AND BITTER COLD OVER THE NORTH UNDER CLEAR TO PARTLY CLOUDY SKIES.
PRECIPITATION...A MAJOR WINTER STORM WILL DEVELOP ACROSS THE CENTRAL
PLAINS/MIDWEST TODAY INTO TONIGHT AS THE ABOVE MENTIONED MID LEVEL
WAVE EJECTS NORTHEAST TOWARDS THE GREAT LAKES REGION. SURFACE HIGH
PRESSURE WILL REMAIN IN PLACE ALONG THE INTERNATIONAL BORDER AREA
KEEPING THE BRUNT OF THE STORM WELL OFF TO OUR SOUTH.
HOWEVER...MODELS ARE IN AGREEMENT WITH THE NORTHERN EXTENT OF THE
STORMS PRECIP SHIELD GRAZING MY SOUTHERN COUNTIES AND WITH KEEPING
THE SFC HIGH OVER NORTHERN ND THROUGH 00Z. WILL INCREASE SNOW
CHANCES THIS MORNING AND AFTERNOON INTO THE LIKELY RANGE ROUGHLY
ALONG AND SOUTH OF INTERSTATE 94...WITH LOWER POPS CONFINED UP TO
THE HIGHWAY 200 CORRIDOR. HAVE THEN EXTENDED CHANCES FOR LIGHT SNOW
INTO THE EVENING HOURS SOUTH OF THE SFC HIGH MAINLY ACROSS MY FAR
SOUTHWEST...THE SOUTH CENTRAL...AND THE SOUTHEAST (WHERE THE BEST
LINGERING CHANCES SHOULD RESIDE).
WENT WITH SNOW RATIOS AROUND 25:1 AFTER LOOKING AT TEMPS FROM THE
BOUNDARY LAYER UP TO 850MB. THIS RESULTED IN TOTAL SNOWFALL AMOUNTS
FROM AROUND ONE INCH ACROSS MY SOUTHERN COUNTIES...WITH LESSER
AMOUNTS AS YOU PROGRESS NORTH. THERE IS SOME BLSN POTENTIAL ACROSS
THE SOUTHEAST WHERE WINDS WILL INCREASE THIS AFTERNOON/TONIGHT TO
AROUND 15KTS. FOR NOW WILL LEAVE OUT AND PUNT TO THE DAY
SHIFT.
TROUGHINESS PERSISTS ACROSS THE REGION THROUGH THURSDAY AS A POLAR
VORTEX DROPS TOWARDS SOUTH CENTRAL CANADA. THIS PATTERN WILL RESULT
IN INCREASING CLOUDS WEST TO EAST WED DAYTIME AND WARRANTS
MENTIONING SCATTERED FLURRIES AT LEAST INTO THURSDAY AFTERNOON.
TEMPERATURES...OUR COLD AIRMASS WILL PERSIST OVER THE LOCAL REGION
THROUGH THE SHORT TERM PERIOD (TUE-THU) AS THE ABOVE MENTIONED POLAR
VORTEX DROPS SLOWLY SOUTH. RESULT WILL BE CONTINUED SUBZERO
LOWS...AND HIGHS MAINLY FROM THE SINGLE DIGITS BELOW TO THE SINGLE
DIGITS ABOVE. CLOUD COVER WILL OF COURSE BE A MAJOR FACTOR IN
REGARDS TO TEMPERATURES...AND WITH EXPECTED CLEARING TONIGHT IN THE
WAKE OF A MID LEVEL TROUGH...TEMPERATURES LOOK TO DROP OFF TO 10-15
BELOW SOUTH AND TO NEAR 25 BELOW ACROSS THE NORTH.
WILL NEED TO MONITOR FOR POTENTIAL WIND CHILL ADVISORIES THROUGH THE
SHORT TERM PERIOD WITH THESE COLD TEMPS...ESPECIALLY WED NIGHT WHEN
WINDS ARE EXPECTED TO BE AS HIGH AS 10-20 MPH ACROSS MUCH OF THE
CWA.
.LONG TERM...FRIDAY THROUGH MONDAY...
THE FORECAST PROBLEM OF THE DAY CONCERNS THE BITTER TEMPERATURES
MOVING INTO PLACE OVER THE NORTHERN PLAINS. A VERY STRONG OMEGA
BLOCK OVER THE NORTHEAST PACIFIC/NORTHWESTERN NORTH AMERICA SHOULD
SLOWLY WEAKEN AFTER FACILITATING A TREMENDOUS EQUATORWARD PUSH OF
THE POLAR VORTEX CURRENTLY OVER THE NORTHERN CANADIAN MARITIMES. IT
IS THIS SYSTEM THAT IS FORECAST TO REJUVENATE THE ARCTIC AIRMASS
OVER THE NORTHERN PLAINS WITH ITS SUB -20C 850 HPA TEMPERATURES.
AN ASSOCIATED CLIPPER FRONTAL PASSAGE ON SATURDAY SHOULD ALLOW FOR
LOW-LEVEL MIXING AND RESULTANT DOWNWARD MOMENTUM TRANSFER SUFFICIENT
FOR 15-25 MPH WINDS...WHICH WILL DEFINITELY ADD TO THE BITTER COLD
AND CAUSE WIND CHILL TEMPERATURES IN THE -30F TO -45F RANGE. SOME
SNOW IS POSSIBLE ALONG/NEAR THE FRONT...BUT ACCUMULATIONS SHOULD BE
MINIMAL AS MOISTURE IS SCARCE IN THIS ARCTIC AIRMASS.
BY SUNDAY MORNING...THE 00 UTC GFS/ECMWF AGREE THAT A SURFACE HIGH
PRESSURE SYSTEM WILL PASS OVER NORTH DAKOTA. CLEAR SKIES AND CALM
WINDS SHOULD REALLY ALLOW FOR TEMPERATURES TO CRASH AS RADIATION
REALLY GETS GOING.
MODELS/ENSEMBLES SEEM TO LOSE A LOT OF THEIR BAROCLINICITY JUST
AFTER THE FORECAST PERIOD...WITH CONSIDERABLY LARGER SPREAD BY
MONDAY. THERE IS AN ASSORTMENT OF WEAK HIGHS AND LOWS STAMPED ALL
OVER THE HIGH LATITUDES...WITH NEARLY ZONAL WESTERLIES OVER CONUS.
IT SEEMS MORE REASONABLE THAT THE FLOW WILL BECOME PROGRESSIVE AS
THE OMEGA BLOCK BECOMES UNDERCUT BY LOWER HEIGHTS...BUT WILL
CONTINUE TO GENERATE STRONGER LOW PRESSURE SYSTEMS WITH SO MUCH
BAROCLINICITY OVER CONUS.
OVERALL...LOOK FOR WEEKEND LOW TEMPERATURES TO PERHAPS DECREASE IN
FUTURE FORECASTS AS TIMING/POSITION OF THE SURFACE HIGH ARE PINNED
DOWN.
&&
.AVIATION...
A DEVELOPING LOW PRESSURE SYSTEM IN COLORADO IS FORECAST TO SWING
NORTHEASTWARD INTO THE GREAT LAKES BY WEDNESDAY MORNING WHILE
SURFACE HIGH PRESSURE DOMINATES EASTERN MONTANA AND NORTH DAKOTA.
VFR CONDITIONS SHOULD SOON BECOME MVFR WITH OCCASIONAL IFR CEILINGS
AS LIGHT SNOW PUSHES INTO NORTH DAKOTA THIS MORNING. UPSTREAM
VISIBILITIES HAVE REMAINED ABOVE 2 SM...AND THERE IS LITTLE REASON
TO EXPECT THEM TO FALL BELOW THAT.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS/SHORT TERM...NH
LONG TERM/AVIATION...SCHECK
