AREA FORECAST DISCUSSION
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FXUS65 KTFX 240152
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
652 PM MST MON NOV 23 2009
.UPDATE...
UPDATING ZONES TO ADJUST MIN TEMPERATURES OVER NORTH CENTRAL
MONTANA. TEMPERATURES ARE FALLING FAIRLY QUICKLY UNDER THE CLEAR
SKIES. ALSO...STARTING THE HIGH WIND WARNING NOW OVER THE ROCKY
MOUNTAIN FRONT REGION...AS WIND GUSTS ARE GUSTING TO NEAR 60 MPH
AT EAST GLACIER ALREADY. BRUSDA
&&
.AVIATION...
UPDATED 2325Z.
AN UPPER LEVEL HIGH PRESSURE RIDGE WILL KEEP THE AIRMASS DRY
THROUGH THE NIGHT. HOWEVER...A FAST MOVING SHORTWAVE WILL FLATTEN
THE RIDGE BY MIDNIGHT AND BRING STRONG SURFACE WINDS ACROSS THE
NORTHERN ROCKIES AND ADJACENT PLAINS...GUSTS IN EXCESS OF 70 KTS ARE
POSSIBLE NEAR RIDGE TOPS AND FAVORED PASSES BETWEEN 06 AND 18Z. MID
LEVEL CLOUDS ASSOCIATED WITH THIS SHORTWAVE WILL SPREAD ACROSS THE
ZONES BUT VFR CONDITIONS WILL PREVAIL DURING THE NEXT 24 HOURS.
&&
.PREV DISCUSSION...
/ISSUED 430 PM MST MON NOV 23 2009/
TONIGHT THROUGH WEDNESDAY...NORTHWEST FLOW ALOFT WILL SHIFT MORE
WESTERLY TONIGHT AS A WEAK SHORTWAVE HELPS TO FLATTEN A BUILDING
RIDGE OVER THE INTERIOR PACIFIC NORTHWEST. AS WESTERLY FLOW
DEVELOPS...A STRONG PRESSURE GRADIENT IS EXPECTED ALONG THE ROCKY
MOUNTAIN FRONT WHICH WILL ALLOW FOR STRONG DOWNSLOPING WINDS OVER
THE AREA SO HAVE UPGRADED HIGH WIND WATCH TO A HIGH WIND WARNING
BEGINNING LATE TONIGHT THROUGH MIDDAY TUESDAY. AT THIS
TIME...STRONGEST WINDS ARE ANTICIPATED BETWEEN 09Z AND 12Z
TUESDAY WITH WIND GUSTS UP TO 70 MPH. IN ADDITION...LINGERING
MOISTURE AND ENERGY EMBEDDED WITHIN THE FLOW ALOFT WILL KEEP A
CHANCE OF SNOW SHOWERS OVER THE MOUNTAINS WITH A FEW INCHES OF
SNOW POSSIBLE IN THE HIGHER ELEVATIONS. SNOW SHOWERS COMBINED WITH
STRONG WINDS WILL CAUSE AREAS OF BLOWING SNOW AND REDUCED
VISIBILITIES...PARTICULARLY THROUGH FAVORED MOUNTAIN PASSES AND
CANYONS ALONG THE ROCKY MOUNTAIN FRONT. A FEW MOUNTAIN SNOW
SHOWERS ARE ALSO POSSIBLE ACROSS PARTS OF SOUTHWEST MONTANA AS THE
SHORTWAVE MOVES SOUTH HOWEVER LITTLE SNOW ACCUMULATION IS
EXPECTED. EVEN THOUGH DRY CONDITIONS OVERALL ARE EXPECTED ACROSS
THE NORTH-CENTRAL AND CENTRAL PLAINS...UNSETTLED WEST-
NORTHWESTERLY FLOW ALOFT WILL KEEP A SLIGHT CHANCE OF PRECIP IN
THE MOUNTAINS. RIDGE IS EXPECTED TO DOMINATE BY TUESDAY NIGHT WITH
OVERALL DRY CONDITIONS EXPECTED THROUGH WEDNESDAY. TEMPERATURES
WILL ALSO GRADUALLY WARM TO ABOVE AVERAGE BY WEDNESDAY. MLS
WEDNESDAY NIGHT THROUGH MONDAY NIGHT...WEDNESDAY NIGHT AND
THANKSGIVING A STRONG UPPER RIDGE WILL BE OVER THE AREA. THIS
WILL TRANSLATE INTO DRY WEATHER WITH TEMPERATURES ON THANKSGIVING
WELL ABOVE NORMAL. RAISED HIGH TEMPERATURES OVER THE PLAINS INTO
THE UPPER 50S TO LOWER 60S. THE ECMWF AND GFS COMPUTER MODEL RUNS
ARE NOT IN AS GOOD AGREEMENT AS THEY WERE YESTERDAY WITH THE
TIMING OF A WEATHER DISTURBANCE FOR LATER THIS WEEK. THE ECMWF
BRINGS THE DISTURBANCE THROUGH FRIDAY NIGHT WHILE THE GFS BRINGS
IT THROUGH ON SATURDAY. WILL CONTINUE WITH A CHANCE OF SNOW
SHOWERS MAINLY OVER THE WESTERN MOUNTAINS FOR FRIDAY SHOULD THE
FASTER ECMWF PAN OUT. WILL CONTINUE WITH THE IDEA OF SLIGHT
CHANCE TO CHANCE CHANCES OF PRECIPITATION FOR FRIDAY NIGHT AND
SATURDAY ACCOUNTING FOR THE DIFFERENCES IN FORECAST TIMING OF THE
WEATHER DISTURBANCES. BOTH MODELS HAVE THE AREA UNDER A
RELATIVELY DRIER NORTHWEST TO NORTH FLOW ALOFT LATER IN THE
WEEKEND INTO VERY EARLY NEXT WEEK AND THIS WAS WELL ACCOUNTED FOR
IN THE INHERITED CHANCES OF PRECIPITATION WHICH WERE LOWER THAN
THOSE OF FRIDAY NIGHT AND SATURDAY. MONDAY NIGHT SIGNIFICANT
DIFFERENCES BETWEEN THE ECMWF AND GFS MODEL RUNS SHOW UP AS THE
ECMWF HAS A STRONG WEATHER DISTURBANCE APPROACHING THE AREA WHILE
THE GFS HAS A STRONG UPPER RIDGE OVER THE AREA. WITH THESE
DIFFERENCES DECIDED TO GO WITH CHANCES OF PRECIPITATION CLOSE TO
CLIMATOLOGICAL NORMALS. BLANK
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 28 46 28 50 / 0 10 10 0
CTB 29 43 25 48 / 0 10 10 0
HLN 25 43 27 46 / 0 20 10 0
BZN 11 38 20 41 / 0 10 10 0
WEY 8 29 12 34 / 10 20 20 10
DLN 16 37 20 40 / 0 10 10 0
HVR 24 46 19 47 / 0 10 10 0
LWT 24 43 21 46 / 0 20 10 0
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 11 AM MST TUESDAY FOR MTZ009-010-048.
&&
$$
WEATHER.GOV/GREATFALLS
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