FXUS63 KBIS 301004
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
404 AM CST MON NOV 30 2009
.SYNOPSIS...
CURRENTLY...BAND OF MID/HIGH CLOUDS ASSOCIATED WITH MID LEVEL WARM
ADVECTION MOVING ACROSS WESTERN AND CENTRAL ND. CLOUDS MOVING
SOUTHEAST IN THE STRONG NORTHWEST FLOW ALOFT WITH AN UPPER LEVEL
TROUGH OVER THE ROCKIES.
.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT...
USED A BLEND OF THE GFS/SREF/ECMWF FOR THE BASIS OF THE SHORT TERM
FORECAST...WITH DETAILS MAINLY FROM THE GFS. THE NAM WAS A SLOWER
OUTLIER WITH THE CLIPPER SYSTEM PROGGED FOR TUESDAY.
NORTHWEST FLOW ALOFT WILL CONTINUE TODAY AND BECOME MORE ZONAL BY
TONIGHT...THUS ALLOWING ANOTHER MILD DAY ACROSS THE STATE TODAY.
EXPECTING HIGH TEMPERATURES FROM THE LOWER 40S NORTH TO LOWER 50S IN
THE SOUTHWEST.
AN UPPER LEVEL SHORTWAVE IN THE WESTERLIES IS EXPECTED TO BREAK DOWN
THE UPPER RIDGE OVER THE ROCKIES THIS AFTERNOON AND TONIGHT. THE
UPPER SHORTWAVE AND ACCOMPANYING SURFACE LOW IS EXPECTED TO ENTER
NORTHWESTERN NORTH DAKOTA AROUND MIDNIGHT TONIGHT...THEN CROSS THE
NORTHERN PART OF THE STATE AND LIE OVER NORTHERN MINNESOTA BY NOON
TUESDAY. THIS PATH IS MUCH FARTHER SOUTH THAN THAT OF PREVIOUS MODEL
RUNS...AND MANY OF THE SHORT TERM MODELS ARE AGREEING ON A MORE
SOUTHERLY PATH. HOWEVER THE NAM DEPICTS THE CLIPPER SYSTEM MOVING IN
A PATH THAT IS THE FARTHEST SOUTH THAN THE OTHER MODELS. THUS HAVE
PREFERRED THE GFS/SREF/ECMWF AS STATED ABOVE. SINCE THE TRACK OF THE
CLIPPER IS FARTHER SOUTH...HAVE INTRODUCED SOME HIGHER CHANCE
PROBABILITIES OF PRECIPITATION TUESDAY - ESPECIALLY ACROSS NORTHERN
NORTH DAKOTA. THINKING AN INCH OR TWO POSSIBLE ACROSS NORTH CENTRAL
NORTH DAKOTA ON TUESDAY.
THE MODELS INDICATE STRONG NORTHWESTERLY WINDS TO DEVELOP AS THE LOW
AND COLD FRONT MOVE ACROSS THE STATE...BUT NOT AS STRONG AS PREVIOUS
MODEL RUNS. HOWEVER...WINDS MAY STILL REACH ADVISORY CRITERIA OF
SUSTAINED SPEEDS OF 30-40 MPH FOR A FEW HOURS. THE STRONG WINDS AND
POSSIBILITY OF SNOW ACCUMULATIONS WILL MEAN A CHANCE FOR SOME
BLOWING SNOW AS WELL. THUS HAVE MENTIONED BLOWING SNOW TUESDAY
AFTERNOON. COLD ADVECTION BEGINS TUESDAY WITH SOME AREAS SEEING
FALLING TEMPERATURES THROUGHOUT THE DAY. EXPECTING LOW TEMPERATURES
MAINLY IN THE TEENS FOR TUESDAY NIGHT WITH NOT MUCH RECOVERY ON
WEDNESDAY WITH HIGHS MAINLY IN THE 20S AS HIGH PRESSURE SLIDING DOWN
THE EAST SIDE OF THE CANADIAN ROCKIES CONTINUES PUSHING INTO THE
DAKOTAS. LOW TEMPERATURES WEDNESDAY NIGHT WILL LIKELY BE IN THE
SINGLE DIGITS ACROSS WESTERN AND CENTRAL NORTH DAKOTA. THE CONTINUED
NORTHERLY UPPER LEVEL FLOW OVER THE STATE DURING THIS TIME WILL
BRING A CONTINUED CHANCE OF LIGHT SNOW OR FLURRIES THROUGH WEDNESDAY
NIGHT.
TEMPERATURES SHOULD STAY ABOVE NORMAL UNTIL COLD FRONTAL PASSAGE
TUESDAY...THEN FALL TO NEAR SEASONAL AVERAGES FOR TUESDAY NIGHT
THROUGH WEDNESDAY NIGHT AND INTO THE LONG TERM FORECAST PERIOD.
.LONG TERM...THURSDAY THROUGH SUNDAY NIGHT...
A DRASTIC SHIFT IN FLOW PATTERN IS ON THE HORIZON AS METEOROLOGICAL
WINTER BEGINS. AFTER AROUND A MONTH OF MAINLY PROGRESSIVE SPLIT FLOW
ALOFT...MODELS/ENSEMBLES NOW AGREE THAT HIGH LATITUDE BLOCKING WILL
DEVELOP OVER NORTHWESTERN NORTH AMERICA AND NEGATIVE HEIGHT
ANOMALIES WILL RETURN TO SOUTH CENTRAL/SOUTHEASTERN CANADA. AS IS
COMMON WITH PATTERN SHIFTS...THE GUIDANCE SPREAD IS HUGE DURING THE
TRANSITION AS EACH ENSEMBLE MEMBER AND DETERMINISTIC MODEL GETS
THERE DIFFERENTLY.
THE ENVELOPE OF SOLUTIONS HAS LITTLE SPREAD ON THURSDAY...WITH
NORTHERLY FLOW OVER NORTH DAKOTA AND A RIDGE AXIS TO THE WEST. THIS
PATTERN FAVORS BELOW AVERAGE TEMPERATURES FOR THE AREA...SO GRIDDED
TEMPERATURES WERE ADJUSTED DOWNWARD TOWARD THE 18 UTC/30 HPC
GUIDANCE. BY FRIDAY...THE SOLUTION ENVELOPE GROWS CONSIDERABLY. SOME
00 GEFS MEMBERS PROGRESS THE RIDGE AXIS INTO SOUTH CENTRAL NORTH
DAKOTA...SUGGESTING THAT MORE WESTERLY FLOW WITH LOW-LEVEL WARM AIR
ADVECTION COULD FORCE A REBOUND TOWARD AVERAGE TEMPERATURES. THE 00
UTC ECMWF/GFS MAINTAIN H5 TROUGHING OVER THE NORTHERN PLAINS AT THIS
TIME...BUT WITH SUCH LARGE DIFFERENCES IN SOLUTIONS IT IS REASONABLE
TO STAY CLOSE TO CLIMATOLOGY/CONTINUITY.
PRECIPITATION CHANCES ON THURSDAY AND FRIDAY ARE RATHER LOW...BUT IT
IS WORTH MENTIONING THAT THE 00 UTC GFS IS CONSIDERABLY FASTER WITH
A DEEP LOW TRACKING SOUTHEASTERLY THROUGH THE DAKOTAS...AND HAS
ASSOCIATED WARM AIR ADVECTION SNOW IN THE AREA BY FRIDAY MORNING.
THE LAST COUPLE RUNS OF THE ECMWF HAVE DIFFERING OPINIONS...AND
EITHER LACK THE STRONG SURFACE LOW OR ARE OVER A DAY SLOWER WITH THE
SYSTEM. IT SEEMS THAT WITH SUCH STRONG RIDGING AHEAD OF THE LOW THE
SLOWER SOLUTION MAY BE ONTO SOMETHING. STILL...SUCH LARGE
DIFFERENCES JUSTIFY STICKING CLOSE TO CONTINUITY UNTIL SOME FORM OF
A MODEL CONSENSUS DEVELOPS.
REGARDING THE REAL COLD WEATHER...IT APPEARS THAT THE BROAD CYCLONIC
FLOW ACROSS THE NORTHERN TIER WILL FAVOR WELL-BELOW AVERAGE
TEMPERATURES BY EARLY NEXT WEEK. THE MAIN SOURCE OF UNCERTAINTY IS
WITH THE POSSIBLE POSITIVE TILT OF THE TROUGHING. IF THE HIGH
LATITUDE OMEGA BLOCK OVER ALASKA DRAWS LOWER HEIGHTS BENEATH IT ON
ITS SOUTHEAST SIDE THE UPPER LEVEL TROUGH AXIS WOULD BE WEST OF THE
DAKOTAS...FAVORING CLOSER-TO-AVERAGE TEMPERATURES. MUCH WILL DEPEND
ON THE ORIENTATION OF THE TROUGH...BUT IT DOES APPEAR LIKE NEXT WEEK
COULD SET DECEMBER UP TO BE A COLD CONTRAST TO THE PAST MONTH.
&&
.AVIATION...
WESTERLY WINDS AT THE SURFACE ARE DUE TO BECOME SOUTHERLIES IN
ADVANCE OF A DEEPENING LOW PRESSURE SYSTEM PUSHING THROUGH EASTERN
NORTH DAKOTA MONDAY INTO TUESDAY. ASSOCIATED FRONTAL PASSAGE IS
EXPECTED EARLY TUESDAY MORNING WITH ANOTHER SHIFT TO WESTERLY AND
THEN NORTHWESTERLY. WINDS BEHIND THE COLD/OCCLUDED FRONT WILL BE
GUSTY AND TURBULENT...THOUGH LOW LEVEL WIND SHEAR IS NOT
ANTICIPATED. CLOUDS AND PRECIPITATION ISSUES SHOULD BE
MINIMAL...WITH MINOT AND JAMESTOWN BEING THE FAVORITES FOR SOME
MVFR CEILINGS AND SCATTERED SNOW.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS/SHORT TERM...JV
LONG TERM/AVIATION...SCHECK
