FXUS65 KGGW 291009
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
309 AM MST SUN NOV 29 2009

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH TUESDAY...
RIDGING TO START MOVING INTO THE FORECAST AREA TODAY CREATING WEST
WINDS WHICH SHOULD BEGIN TO PUSH OUT LOW LEVEL STRATUS AND FOG OUT
OF THE AREA BY MID MORNING. WINDS TURN SOUTHWEST ON MONDAY WITH
APPROACHING RIDGE AXIS AND WAA STREAMING INTO THE AREA AS MONDAYS HIGHS
WILL BE 15 TO 20 DEGREES ABOVE NORMAL. 

THE ANTICIPATED SHORTWAVE TROUGH DIVES SOUTH OUT OF CANADA
TUESDAY. THE GFS CONTINUES TO SHOW GOOD CONSISTENCY WITH THE
TROUGH. FROPA AT THIS POINT LOOKS TO BE NEAR 12Z TUESDAY. THE
FRONT REMAINS DRY AS ONLY SLIGHT CHANCE POPS WERE LEFT IN THE
FORECAST AND DURATION IS QUITE SHORT AS WELL WITH 50 TO 60KT 700MB
WINDS PUSHING THE FRONT THROUGH. NORTHWEST WINDS CONTINUE TO BE
THE MAIN CONCERN WITH THE FRONT WITH 50 KNOTS AT 850MB POSSIBLE.
AT THIS POINT...TIMING OF FROPA DOESNT APPEAR TO BE IN CONJUNCTION
WITH THE BEST MIXING BUT A FEW GUSTS THAT REACH CRITERIA CANT BE
RULED OUT AT THIS POINT AND MODELS HAVE WAFFLED A BIT FROM RUN TO
RUN ON THE STRENGTH OF THE WINDS. CAA FILTERING IN AFTER PASSAGE
WILL ONLY BRING TEMPERATURES BACK DOWN TO NEAR NORMALS FOR THIS TIME
OF YEAR. SHALLENBERGER

.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...
THE DAY TO DAY DETAILS OF THE EXTENDED FORECAST REMAIN MUDDLED IN
UNCERTAINTY. HOWEVER...SOME TRENDS CAN BE GLEANED UPON MOVING
OUTWARD TOWARD A PLANETARY SCALE. OVER THE PAST SEVERAL WEEKS THE
LONGWAVE FLOW OVER NORTH AMERICA HAS BEEN SPLIT WITH A BENIGN
NORTHERN ZONAL BRANCH OVER CANADA AND AN ACTIVE SOUTHERN BRANCH
OVER THE SOUTHERN UNITED STATES. THIS HAS PRODUCED MILD AND DRY
CONDITIONS ACROSS THE NORTHERN HIGH PLAINS AND HAS CONFINED THE
ARCTIC AIR TO THE NORTH POLE AND SIBERIA. A CHANGE IN THE LONGWAVE
PATTERN APPEARS IMMINENT OVER THE NEXT WEEK. GLOBAL OPERATIONAL
MODELS...ECMWF...GFS...AND GEM ALONG WITH ENSEMBLE
GUIDENCE...GEFS...GEM...AND NAEFS SUGGEST A DEEPENING CYCLONE OVER
THE CENTRAL PACIFIC WITH A HIGHLY AMPLIFIED UPPER RIDGE DEVELOPING
OVER THE EAST PACIFIC AND EXTENDING AS FAR NORTH AS ALASKA. A
PATTERN SUCH AS THIS WOULD SHIFT ARCTIC AIR BACK INTO NORTH
AMERICA. WHETHER THE TREND IS TOWARD NEAR TO SLIGHTLY BELOW
AVERAGE TEMPERATURES OR BITTERLY COLD ARCTIC AIR REMAINS IN
QUESTION...BUT AN END TO MILD TEMPERATURES SEEMS LIKELY DURING THE
FIRST WEEK OF DECEMBER.

THE EXTENDED PERIOD BEGINS TUESDAY NIGHT WITH NORTHWEST FLOW ALOFT
IN THE WAKE OF THE VIGOROUS TROUGH FROM TUESDAY WITH MODELS
DEMONSTRATING DECENT AGREEMENT AT THIS POINT. SURFACE HIGH
PRESSURE BUILDS IN FROM THE NORTH WITH TEMPERATURES NEAR SEASONAL
AVERAGES. THIS PATTERN GENERALLY PERSISTS THROUGH THURSDAY BEFORE
SIGNIFICANT MODEL DISAGREEMENT ARISES. THE 00Z GFS AND GEM BRING A
DEEPENING PACIFIC TROUGH THROUGH THE REGION DURING THE FRIDAY
NIGHT/SATURDAY TIMEFRAME. THE GFS TARGETS THE LOCAL AREA WITH SNOW
WHILE THE GEM FOCUSES SNOW OVER THE MOUNTAINS AND GRAZES THE LOCAL
AREA. A RESURGENCE OF POLAR AIR FOLLOWS THIS SYSTEM WITH 850MB
TEMPERATURES FALLING BELOW -10C...WITH ONLY A SLIGHT MODIFICATION
THEREAFTER AS AN UPPER TROUGH PERSISTS OVER THE REGION. THE 00Z
ECMWF HAS A MUCH DIFFERENT SOLUTION AS IT IS MUCH STRONGER WITH
UPPER RIDGING OVER THE INTERMOUNTAIN WEST. NORTHERLY FLOW PERSISTS
LATE IN THE WEEK BEFORE THE RIDGE CRASHES OVER NORTHEAST MONTANA
WITH AN ARCTIC FRONT LOOMING AT THE END OF THE FORECAST PERIOD. AT
THIS POINT THE 00Z GEM SOLUTION IS FAVORED WITH A SLIGHT CHANCE OF
SNOW ADDED FOR FRIDAY NIGHT. IT IS PLAUSIBLE THAT A TROUGH WILL
DROP SOUTH THROUGH THE AREA AS THE AFOREMENTIONED PATTERN CHANGE
BEGINS...BUT PERSISTENCE WOULD ARGUE AGAINST THE STRENGTH OF THE
GFS. AJZ

&&

.AVIATION...
FOG AND LOW CLOUDS PRODUCING LIFR CONDITIONS ALONG AND NORTH OF
THE MILK AND MISSOURI RIVER VALLEYS AT KGGW AND KOLF WILL PERSIST
THROUGH MID MORNING. MID AND HIGH CLOUDS WILL INCREASE AFTER
SUNRISE AND THIS WILL LIKELY SLOW THE DISSIPATION OF FOG AND LOW
CLOUDS. WIND SPEEDS WILL INCREASE TO 10-15KT OUT OF THE WEST
DURING THE AFTERNOON...WHICH SHOULD CLEAR OUT ANY LINGERING LOW
CLOUDS. VFR CONDITIONS WILL PREVAIL AFTERWARD. AJZ

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

WEATHER.GOV/GLASGOW