FXUS65 KGGW 102108
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
208 PM MST THU DEC 10 2009
.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SATURDAY...
THE SHORT TERM WILL BE NOT AS COLD...WITH A FEW PERIODS OF LIGHT
SNOW...AND NO STRONG WINDS.
THE POLAR VORTEX CENTER NOW IN NUNAVUT...ANCHORING THE LARGE
LONG-WAVE TROUGH OVER CANADA AND CONUS...DROPS SOUTH INTO NORTHERN
SASKATCHEWAN TONIGHT. THIS LOW CENTER REMAINS IN PLACE AS THE
WHOLE UPPER TROUGH FLATTENS OUT EAST-WEST AS IT ROTATES. THE MAIN
EFFECT WILL BE TO WITHDRAW THE ARCTIC BOUNDARY BACK NORTH ACROSS
THE INTERNATIONAL BORDER. AT 00Z FRIDAY 850MB TEMPERATURES RANGING
FROM -22*C TO -12*C WILL WARM TO -12*C TO -4*C 24-HOURS LATER. AS
A RESULT SURFACE TEMPERATURES WILL IMPROVE. THE DEGREE OF WARMING
WILL DEPEND OF THE AMOUNT OF MIXING THAT OCCURS. MET GUIDANCE IS
AROUND 10*F DEGREES WARMER THAN MAV GUIDANCE. WITH SNOW ON GROUND
AND LIMITED SUN...THE MAV GUIDANCE SEEMS MORE REASONABLE.
TEMPERATURES WILL BE MUCH WARMER THAN THE LAST SEVERAL DAYS...BUT
WILL STILL REMAIN BELOW NORMAL BY 10*F TO 15*F.
THE LIGHT SNOW NEAR THE ARCTIC BOUNDARY WILL MOVE NORTH AS THE
BOUNDARY MOVES. THEREFORE MOST LIGHT SNOW WILL END AFTER MIDNIGHT
TONIGHT. THE NEXT ROUND OF SNOW WILL BE ASSOCIATED WITH A VERY
WEAK WAVE AND ENHANCED BAND OF 500MB VORTICITY ALONG THE BORDER
WITH CANADA. THE BEST QPF WILL REMAIN IN CANADA BUT A REPEAT OF
LIGHT SNOW FRIDAY NIGHT AND SATURDAY WILL BE CONFINED MOSTLY TO
THE ZONES NORTH OF THE MISSOURI RIVER.
HIGH SURFACE PRESSURE TO THE SOUTHWEST WILL MAINTAIN A STEADY BUT
LIGHT BREEZE FROM THAT DIRECTION TONIGHT AND FRIDAY...ENHANCING
THE SLIGHT WARMING. THE WEAK SHORT-WAVE FRIDAY NIGHT WILL SHIFT
WIND AROUND TO THE NORTH. SATURDAY A DEVELOPING LEE TROUGH WILL
VEER THE WIND AROUND FURTHER TO THE EAST AND SOUTHEAST. NO STRONG
WINDS ARE ANTICIPATED THROUGH THE SHORT TERM. SCT
.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
A POLAR VORTEX OVER NORTHERN CANADA DROPS SOUTHWARD REACHING THE
NORTHERN PRAIRIE PROVINCES LATE THIS WEEKEND. A SHORTWAVE TROUGH
SPINS AROUND THE WESTERN LOBE OF THE UPPER LOW SLAMMING A STRONG
ARCTIC FRONT THROUGH NORTHEAST MONTANA. MODELS ARE STILL
STRUGGLING WITH THE TIMING WHETHER THIS IS A SATURDAY NIGHT/SUNDAY
OR SUNDAY/SUNDAY NIGHT EVENT...BUT THE SOLUTIONS ARE VERY
COLD...MID MINUS 20S CELSIUS AT 850MB...AND TRENDING WETTER. THE
WIND PROFILE IS SUCH THAT A NORTHERLY PUSH OF ARCTIC AIR IS
UNDERCUTTING MOIST WESTERLY FLOW ALOFT CREATING AN OVERRUNNING
SITUATION WITH A BROAD AREA OF IMPLIED VERTICAL ASCENT ALONG AND
BEHIND OF THE LEADING EDGE OF THE FRONTAL ZONE. THIS SCENARIO
SUGGESTS EFFICIENT SNOW GROWTH...WHILE QPF AMOUNTS ARE ONLY A
TENTH OR TWO...SNOW RATIOS WOULD BE RATHER HIGH AND THIS COULD
RESULT IN POSSIBLY TWO TO PERHAPS FIVE INCHES OF SNOW. 850MB WIND
SPEEDS ALSO REACH 25KT...SO A MODESTLY STRONG GUSTY WIND WOULD BE
ACCOMPANY THE SNOW. HOWEVER TO THE CONTRARY...MODELS HAVE BEEN
VERY INCONSISTENT AND THIS WET TREND IS NEW AS IT IS STILL WITHIN
THE REALM OF POSSIBILITIES THAT THE ENERGY COULD SPLIT THE LOCAL
AREA...SO POPS WERE ONLY INCREASED TO THE CHANCE CATEGORY AT THIS
TIME...BUT IF THIS TREND CONTINUES OVER THE NEXT FEW PERIODS A
HEADLINE FOR SNOW AND BLOWING SNOW MAY BECOME NECESSARY. THE POLAR
VORTEX RACES EASTWARD NEXT WEEK WITH UPPER RIDGING SLOWLY BUILDING
OVER THE WEST BY THE MIDDLE AND END OF NEXT WEEK...WITH A SLOW
MODIFYING TREND COMMENCING. AJZ
PREVIOUS LONG TERM DISCUSSION...
POLAR VORTEX OVER CANADA TO REMAIN THE DOMINANT FEATURE SATURDAY
NIGHT THRU MONDAY BEFORE IT FINALLY MOVES FAR ENUF EAST TO ALLOW
SOME UPPER RIDGING AND MILDER AIR TO MOVE IN. REINFORCING SHOT OF
ARCTIC AIR COMES SATURDAY NIGHT OR EARLY SUNDAY MORNING IN THE
FORM OF A COLD FRONT. THAT AIR THEN REMAINS IN PLACE UNDER A
SURFACE HIGH UNTIL A SURFACE TROF MOVES IN MONDAY NIGHT AND BRINGS
MILDER AIR FROM THE SOUTHWEST AS SOME SEMBLANCE OF AN UPPER RIDGE
DEVELOPS OVER THE INTERMOUNTAIN WEST. COULD BE SOME LIGHT
OVERRUNNING SNOW AS THIS WARM FRONT PASSES. BEHIND THAT IT APPEARS
THINGS DRY OUT AND WARM UP INTO THE MIDWEEK PERIOD. THE UPPER
RIDGE TO OUR WEST ON TUESDAY CONTINUES TO TRUNDLE EAST AND IS
EXPECTED TO BE OVER THE AREA BY WEDNESDAY NIGHT OR THURSDAY.
EXTENDED MODELS THO HAVE BEEN QUITE CHANGEABLE OF LATE...THUS
CONFIDENCE IS STILL LOW AT THIS POINT ON THE WARM SOLUTION FOR THE
MIDDLE TO END OF NEXT WEEK. WILL WARM THINGS A BIT BUT STILL PLAY
THINGS CLOSE TO THE VEST BY NOT BEING TOO LIBERAL WITH THE AMOUNT
OF WARMING.
&&
.AVIATION...
VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH FRIDAY WITH
SCATTERED TO BROKEN CLOUD COVER AT OR ABOVE 8K FT. A LIGHT WEST
WIND LESS THAN 10KT THIS EVENING WILL SHIFT TO A SOUTHERLY
DIRECTION LATE TONIGHT. AJZ
&&
.CLIMATE...
0.02 INCHES OF LIQUID PRECIPITATION WAS MEASURED AT GLASGOW AS OF
11 AM THURSDAY DECEMBER 10TH IN THE FORM OF MELTED SNOW. THIS WAS
THE FIRST MEASURABLE PRECIPITATION RECEIVED SINCE OCTOBER 27. THIS
WAS A TOTAL OF 43 DAYS WITHOUT MEASURABLE PRECIPITATION...WHICH
TIED FOR THE 13TH LONGEST PERIOD WITHOUT MEASURABLE PRECIPITATION
ON RECORD...AND THE LONGEST SINCE THE FALL OF 1965 WHEN THERE WERE
49 CONSECUTIVE DAYS WITHOUT MEASURABLE PRECIPITATION. THE LONGEST
DRY PERIOD ON RECORD IS 57 DAYS FROM NOVEMBER 19TH 1932 THROUGH
JANUARY 14TH 1933. AJZ
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
WEATHER.GOV/GLASGOW
