FXUS63 KBIS 302121
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
321 PM CST MON NOV 30 2009
.SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT...
CURRENTLY...DEEP NORTHWEST FLOW RESIDES ALOFT...A RESULT OF THE
WESTERLIES DESCENDING FROM RIDGING TO THE WEST INTO TROUGHING OVER
THE EASTERN CONUS. WESTERLY TO SOUTHWESTERLY SURFACE WINDS HAVE
GENERATED SOME GOOD WARM ADVECTION TODAY AND BROUGHT TEMPERATURES UP
TO THE HIGH 40S AND EVEN LOW 50S IN SOME PARTS OF THE CWA.
MODELS REMAIN IN DECENT AGREEMENT FOR THE SHORT TERM PERIOD...THUS
WILL CONTINUE TO USE A GENERAL BLEND FOR THE FORECAST. MAJOR
FORECAST CONCERNS ARE THE SNOW AND WIND ASSOCIATED WITH A CLIPPER
SYSTEM THAT IS FORECAST TO IMPACT THE HIGH PLAINS ON TUESDAY.
NORTHWEST FLOW TURNS MORE WESTERLY TONIGHT AS A SHORTWAVE FROM THE
GULF OF ALASKA BREAKS DOWN THE RIDGING TO THE WEST AND APPROACHES
THE FORECAST AREA. THE RESULTING CLIPPER SYSTEM AND ITS ASSOCIATED
COLD FRONT THEN CROSS INTO THE NORTHWEST CORNER OF THE STATE BY
TUESDAY MORNING...THEN PASS OVER THE RED RIVER VALLEY AND INTO MN BY
MIDDAY. EXPECT TEMPERATURES TO DROP DRAMATICALLY AFTER FRONTAL
PASSAGE.THE MODELS HAVE MOVED THE SYSTEM FARTHER SOUTH THAN
PREVIOUS RUNS...THUS THE CHANCES FOR WRAP AROUND PRECIP TO IMPACT
THE CWA HAVE INCREASED...ESPECIALLY ALONG MY NORTHERN AND
NORTHEASTERN COUNTIES. WHILE HEAVY SNOW SHOULD REMAIN TO THE NORTH
AND NORTHEAST OF OUR CWA...EXPECT OUR MORE IMPACTED AREAS TO
RECEIVE 1 OR 2 INCHES OF SNOW BY TUESDAY NIGHT. GUIDANCE HAS ALSO
SUGGESTED A TIGHT PRESSURE GRADIENT ON THE WESTERN SIDE OF THE LOW
THAT COULD RESULT IN SOME VERY GUSTY WINDS OF 30 TO 40 MPH BEHIND
THE COLD FRONT. THEREFORE...WILL ISSUE A WINTER WEATHER ADVISORY FOR
THE NORTH CENTRAL TIER OF COUNTIES AND A WIND ADVISORY FOR THE
REMAINDER OF WEST AND CENTRAL NORTH DAKOTA.
ALTHOUGH THE CLIPPER SHOULD BE WELL OUT OF OUR AREA BY WEDNESDAY
MORNING...THE AXIS OF THE UPPER LEVEL TROUGH SHOULD STILL BE SLOWLY
MOVING OVER THE NORTHERN PLAINS AND ONLY BEGINNING TO EXIT THE
REGION ON THURSDAY. THEREFORE...AMPLE CLOUDS AND RESIDUAL SNOW
SHOWERS ARE LIKELY TO REMAIN IN THE STATE AS WELL...WITH FURTHER
LIGHT ACCUMULATIONS POSSIBLE THROUGH MIDDAY THURSDAY. STRONG
NORTHERN FLOW ALOFT AND AT THE SURFACE SHOULD KEEP TEMPERATURES
AROUND SEASONAL NORMALS FOR THE REMAINDER OF THE PERIOD.
.LONG TERM...FRIDAY THROUGH MONDAY
PROBLEMS WITH THE FORECAST DURING THIS PERIOD DEAL WITH THE
COLD PATTERN AND ANY CHANCES FOR PRECIPITATION.
THE MODELS CONTINUE TO INDICATE A COLDER PATTERN FOR THE
NORTHERN PLAINS ON FRIDAY AS A CLOSED UPPER LOW SITS OVER
THE GREAT LAKES REGION WHICH EXTENDS INTO THE NORTHERN PLAINS.
THE GFS AND ECMWF MODELS ARE IN AGREEMENT TO START BUT THE
DIFFERENCES BETWEEN THE TWO SHOW UP FOR FRIDAY NIGHT INTO
SATURDAY AS THE COLD UPPER LOW SLOWLY DEPARTS THE GREAT LAKES
AREA.
NEW SHORTWAVE ENERGY IN THE FLOW DEVELOPS OVER MONTANA
AND SOUTHERN SASKATCHEWAN AS PER THE GFS BUT THE ECMWF IS
WEAKER SHOWING A MINOR RIPPLE AT BEST MOVING INTO THE FORECAST
AREA. THE MAIN DIFFERENCE BETWEEN THE MODELS IS THAT THE ECMWF
CLOSES OFF AN UPPER LOW OF THE PACIFIC NW STATES WHILE THE GFS
MAINTAINS A VIGOROUS SHORTWAVE THAT HEADS TOWARDS THE REGION
FOR SATURDAY. IF THE GFS IS RIGHT THEN THERE WOULD BE A CHANCE
FOR SNOW AS A NEW CLIPPER PASSES SOUTH OF THE STATE BY
SATURDAY. OTHERWISE THE REGION WOULD REMAIN DRY BUT COLD IF
THE ECMWF SOLUTION IS RIGHT. THUS HAVE KEPT IT DRY FOR NOW
DUE TO THE DISAGREEMENT AND IT IS A FEW DAYS OUT. IN ANY
CASE IT WILL REMAIN COLD THROUGH MONDAY.
&&
.AVIATION...
NO WEATHER PROBLEMS ACROSS THE FORECAST AREA THIS EVENING AND
TONIGHT. MAINLY VFR CONDITIONS AND SOME HIGH THIN CIRRUS. HOWEVER
BY TUESDAY A CLIPPER SYSTEM WILL PASS FROM NEAR WILLISTON TO MINOT
AND BRING A COLD FRONT THROUGH THAT WILL SWITCH THE WINDS TO THE
NORTHWEST ACROSS THE CWA. THE FAR NORTHERN AREAS MAY SEE SOME
WIDELY SCATTERED SNOW SHOWERS IN MVFR CONDITIONS.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 6 AM CST /5 AM MST/ TO 9 PM CST /8 PM MST/
TUESDAY FOR NDZ001-009-010-017>023-025-031>037-040>048-050-051.
WINTER WEATHER ADVISORY FROM 6 AM TO 9 PM CST TUESDAY FOR
NDZ002>005-011>013.
&&
$$
WAA/BPN/VJ
