FXUS65 KGGW 292129
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
229 PM MST SUN NOV 29 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH TUESDAY...
A BROAD UPPER LEVEL RIDGE OVER THE WESTERN STATES WILL MAINTAIN
NORTHWEST FLOW ALOFT OVER EASTERN MONTANA TONIGHT. 850MB
TEMPERATURES WHICH WERE AROUND -4*C TO 0*C AT 12Z THIS MORNING
INCREASE TO +2*C TO +6*C OVERNIGHT. MID-TO-HIGH CLOUDS FLOWING
WITH THE UPPER WIND WILL HELP MODERATE MINIMUM TEMPERATURES A
BIT. THE RESULT WILL BE SURFACE LOWS AROUND +10*F ABOVE NORMAL
TONIGHT. BOTH MAV AND MET GUIDANCE PROMOTE FOG POSSIBLE FOR KGGW
AND KOLF. WEAK WIND AND SOME CLEARING COULD GENERATE FOG FOR THESE
AREAS SINCE DEW POINTS WILL BE CLOSE TO TEMPERATURES. INCLUDED
PATCHY FOG FOR LOW AREAS ALONG THE MISSOURI AND MILK RIVERS.
MONDAY...UPPER FLOW BECOMES MORE ZONAL AS THE NEXT SHORT-WAVE
TROUGH MOVES ACROSS THE CANADIAN ROCKIES. HOWEVER THERMAL RIDGING
RESULTS IN 1000MB-500MB THICKNESS HEIGHTS PEAKING TO OVER 550DM.
THIS WAA WILL IMPROVE MAXIMUM SURFACE TEMPERATURES TO OVER +15*F
ABOVE NORMAL.
MONDAY NIGHT AND TUESDAY...THE GFS AND THE NAM BOTH HAVE THE COLD
FRONT POISED JUST NORTH OF THE INTERNATIONAL BORDER AROUND
MIDNIGHT...WHILE A CLOSED SURFACE LOW DEVELOPS OVER SOUTHERN
SASKATCHEWAN WHICH WILL STRENGTHEN THE SURFACE GRADIENT OVER THE
FORECAST AREA INITIATING STRONGER OVERNIGHT WINDS. THE COLD FRONT
DROPS SOUTH OVER THE AREA BEFORE SUNRISE. WIND WILL VEER TO THE
NORTHWEST AND INCREASE TO AROUND 20-30KTS. 12Z 850MB WINDS RANGE
AROUND 35-40KTS AND LINE UP WITH THE SURFACE GRADIENT. 700MB WINDS
WILL BE STRONGER RANGING FROM 45KTS TO 55KTS DEPENDING ON THE
MODEL. AS LAPSE RATES IMPROVE AFTER SUNRISE...AND DEPENDING ON THE
CLOUD COVER...THE UPPER WINDS WILL BEGIN TO MIX TOWARDS THE
SURFACE MORE EFFICIENTLY. THERE IS THE POTENTIAL FOR OCCASIONAL
WIND GUSTS GREATER THAN 50KTS TO DEVELOP BUT SUSTAINED WINDS
SHOULD RANGE AROUND 25-35KTS GUSTING TO 40-50KTS. WITH 850MB WINDS
AT AROUND 35KTS...THERE ARE NO CURRENT PLANS FOR A HIGH WIND WATCH
FOR NOW. WITH 850MB TEMPERATURES DROPPING FURTHER TO AROUND
-10*C...THIS CAA WILL PLUNGE TEMPERATURES ALL THE WAY DOWN TO
NORMAL...WHICH WILL BE QUITE A CHANGE FROM THE DAY BEFORE. AS A
RESULT OF THE COLD FRONT...DYNAMICS DEVELOP OVER THE CENTRAL
REGION CWA GENERATING SOME PRECIPITATION. SOME OF THIS COULD SLIP
INTO OUR SOUTHWESTERN ZONES AFTER MIDNIGHT. HOWEVER THE FRONT
DROPS WELL TO THE SOUTH BY 18Z TAKING THE BEST DYNAMICS WITH IT.
DO NOT EXPECT MUCH PRECIPITATION TO DEVELOP OVER THE LOCAL CWA
WITH THIS STORM. BY 18Z THE UPPER LOW CLOSES OFF AND STACKS UP
OVER THE CLOSED SURFACE LOW IN SOUTHERN MANITOBA. AS A RESULT
THERE WILL BE AN AREA OF WRAP-AROUND MOISTURE NEAR THE LOW CENTER
THAT WILL BACK OVER OUR NORTHEASTERN ZONES IN THE
AFTERNOON...POSSIBLY GENERATING AN AREA OF LIGHT SNOW. SCT
.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...
GOING FORECAST WAS IN GOOD SHAPE AND ONLY MADE MINOR TWEAKS. ONE
WAS MADE TO RAISE TEMPS ON WEDNESDAY MAINLY OVER THE SW ZONES AS
LACK OF SNOWCOVER SHOULD ALLOW THIS AREA TO WARM A BIT MORE THAN
EXPECTED. OTHER CHANGES WERE TO HELP OUT WITH COORDINATION. JAMBA
PREVIOUS DISCUSSION...
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...
PATCHES OF FOG AND/OR LOW CLOUDS MAY RETURN TONIGHT TO AREAS THAT
HAD THEM EARLIER TODAY (GLASGOW AND WOLF POINT). ANY FOG OR LOW
CLOUDS SHOULD BURN OFF QUICKLY MONDAY MORNING. WINDS ARE EXPECTED
TO BE 10 KTS OR LESS INTO MONDAY. JAMBA
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
WEATHER.GOV/GLASGOW
