AREA FORECAST DISCUSSION

 
 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.
 
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