High Wind Watch 7, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1125 AM MDT FRI SEP 25 2009

...UPDATE TO AVIATION...

.UPDATE...WEAK WAVE MOVING THROUGH THE AREA WILL BRING COOLER
TEMPERATURES TODAY WITH JUST A FEW HIGH CLOUDS MOVING OVER THE
AREA. GOING FORECAST HAS THIS WELL IN HAND. HOWEVER...HAVE UPDATED
GRIDS AND TEXT PRODUCTS TO BUMP UP WIND SPEEDS FOR SATURDAY
AFTERNOON AND EVENING...ESPECIALLY IN SOUTHWEST MONTANA. EXPECT
THAT GUSTY MID LEVEL WINDS WILL MIX TO THE SURFACE ACROSS A BROAD
SWATH OF THE FORECAST AREA WITH WIND SPEEDS AVERAGING OUT ABOVE
GUIDANCE AND PREVIOUS FORECAST PACKAGE VALUES. ANTICIPATE THAT
FIRE WEATHER WATCH WILL BE UPGRADED TO A RED FLAG WARNING WITH THE
AFTERNOON PACKAGE. WILL ALSO BE TAKING A CLOSE LOOK AT THE
POSSIBILITY OF ISSUING A HIGH WIND WATCH OR WARNING FOR PORTIONS
OF THE ROCKY MOUNTAIN FRONT...ALTHOUGH THIS IS NOT A CERTAINTY.
MPJ

&&

.AVIATION...
UPDATED 1725Z.
VFR CONDITIONS WILL CONTINUE ACROSS NORTH CENTRAL...CENTRAL...AND
SOUTHWEST MONTANA THROUGH AT LEAST 18Z SATURDAY. HIGH PRESSURE ALOFT
WILL KEEP SKIES MOSTLY CLEAR THROUGH MOST OF THE PERIOD. NORTHWEST
WINDS BEHIND A WEAK COLD FRONT TODAY WILL BECOME MORE SOUTHERLY
OVERNIGHT AS A SURFACE TROUGH DEVELOPS TO THE LEE OF THE ROCKIES. A
BROAD SHORTWAVE TROUGH WITH AN ASSOCIATED WEAK CANADIAN COLD FRONT
WILL APPROACH THE AREA FROM THE NORTHWEST OVERNIGHT INTO SATURDAY
MORNING. THIS WILL STRENGTHEN THE WESTERLY FLOW ALOFT AND BRING
INCREASING HIGH CLOUDINESS TO THE AREA...AND THE BREEZY WESTERLY
WINDS WILL MIX DOWN TO THE SURFACE AHEAD OF THE COLD FRONT AFTER
10Z.  COULSTON

&&

.FIRE WEATHER...
A WEATHER SYSTEM WILL BREAK DOWN THE UPPER LEVEL RIDGE OF HIGH
PRESSURE OVER THE REGION ON SATURDAY. THIS WILL BRING A
SIGNIFICANT INCREASE IN WINDS ALOFT WITH VERY WINDY CONDITIONS
OVER A GOOD PORTION OF NORTHERN AND CENTRAL MONTANA SATURDAY
AFTERNOON AND EVENING BEFORE A STRONGER COLD FRONT ARRIVES
SATURDAY NIGHT. THE VERY WARM AND DRY CONDITIONS COMBINED WITH
POTENTIALLY STRONG WINDS WILL LIKELY CREATE CRITICAL FIRE WEATHER
CONDITIONS...SO WILL CONTINUE FIRE WEATHER WATCH FOR SATURDAY
AFTERNOON AND EVENING. MPJ/HOENISCH

&&

.PREV DISCUSSION...
/ISSUED 515 AM MDT FRI SEP 25 2009/

TODAY THROUGH SUNDAY...DRY AND WARMER THAN AVERAGE TEMPERATURES WILL
CONTINUE ACROSS THE AREA DESPITE THE ARRIVAL OF AN UPPER-LEVEL WAVE
OF LOW PRESSURE THIS AFTERNOON.  VERY LITTLE MOISTURE IS ASSOCIATED
WITH THIS SYSTEM...HOWEVER WINDS WILL SHIFT TOWARDS A MORE
NORTHWESTERLY DIRECTION AND TEMPERATURES WILL FALL CLOSER TOWARDS
AVERAGE.  BY FRIDAY NIGHT...CORE OF THE JET STREAM WILL CROSS INTO
NORTHERN MONTANA CAUSING WESTERLY WINDS ALOFT TO INCREASE ACROSS THE
FORECAST AREA ON SATURDAY IN ADDITION TO FLATTENING THE UPPER-LEVEL
RIDGE. WINDS WILL BE QUITE GUSTY ACROSS THE NORTH-CENTRAL PLAINS AND
FAVORED MOUNTAIN PASSES OVER THE NORTHWESTERN PORTION OF THE
FORECAST AREA...HOWEVER DO NOT FEEL THE NEED FOR ANY HIGH WIND
HIGHLIGHTS AT THIS TIME. WARM TEMPERATURES ARE EXPECTED AGAIN FOR
SATURDAY AND WITH STRONG MID-LEVEL WINDS AND LOWERING RH VALUES HAVE
CONTINUED FIRE WEATHER WATCH AS DESCRIBED BELOW. BY SUNDAY...WE WILL
BEGIN TO SEE SIGNS OF CHANGE AS MUCH COOLER CANADIAN AIR BEGINS TO
PUSH SOUTHWARD IN THE WAKE OF A WEAK COLD FRONT. THE FRONT IS
EXPECTED TO SNEAK THROUGH CENTRAL AND EASTERN PORTIONS OF THE
FORECAST AREA ON SUNDAY...HOWEVER THERE IS LITTLE MOISTURE
ASSOCIATED WITH IT SO HAVE CONTINUED WITH A DRY FORECAST AND HIGH
TEMPERATURES AROUND SEASONAL LEVELS. MLS

SUNDAY NIGHT THROUGH WEDNESDAY...MIDTERM FORECAST PERIOD WILL START
OUT FAIRLY QUIET BUT BECOME QUITE ACTIVE EARLY NEXT WEEK.  UPPER
LEVEL RIDGE AXIS MOVES THRU CENTRAL MT LATE SUN/EARLY MON AND WELL
INTO ERN MT BY MON EVE...PRODUCING DRY CONDITIONS WITH TEMPERATURES
WELL ABOVE NORMAL ON MON AFTN.  AS THE RIDGE SLIDES
DOWNSTREAM...FOCUS SHIFTS TO DEEP COLD UPPER LEVEL TROF COMING
ASHORE ALONG THE WA/OR COAST.  GFS AND EUROPEAN MODELS IN REASONABLY
GOOD AGREEMENT ON THE PROGRESSION OF THE SYSTEM INTO THE NRN ROCKIES
ON TUES BUT BEGIN TO SEE MARKED TIMING AND PRECIPITATION COVERAGE
DIFFERENCES WITH GFS PUSHING THE SYSTEM MORE QUICKLY EASTWARD AND
GENERATING PRECIP THAT IS MORE SPOTTY THAN THE CURRENT EUROPEAN
MODEL SOLUTION.  DESPITE THOSE DIFFERENCES...THE MODELS STRONGLY
CONCUR ON ONE KEY POINT...THAT SIGNIFICANTLY COLDER AIR WILL ARRIVE
ABOUT MIDDAY TUES WHEN A SHARP COLD FRONT AND ACCOMPANYING PACIFIC
MOISTURE FIELD PLUNGES SOUTHWARD ACROSS THE STATE.  THE FRONT WILL
HELP CREATE ENHANCED INSTABILITY AND RAPID LOWERING OF SNOW
LEVELS...LEADING TO A BROAD MIX OF PRECIP TYPES FROM RAINSHOWERS AND
THUNDERSTORMS AHEAD OF THE FRONT TO RAIN/SNOW MIX BELOW 5000 FT AND
WIDESPREAD SNOWSHOWERS OVER HIGHER TERRAIN BEHIND THE FRONT FROM
TUES AFTN THRU MIDDAY WED.  TOO EARLY TO MAKE A CALL ON
ACCUMULATIONS BUT A FEW INCHES AT ELEVATIONS ABOVE 6000 FT ARE
CERTAINLY POSSIBLE.  TEMPERATURES WILL NOSEDIVE AS THE FRONT PASSES
THROUGH THE REGION WITH HIGHS ONLY IN THE MID 40S TO LOW 50S BY
WED. WARANAUSKAS

THURSDAY THROUGH FRIDAY...MODELS ARE IN ROUGH AGREEMENT DURING THIS
PERIOD. HOWEVER...THE GFS IS FASTER BY ABOUT 12 TO 24 HOURS IN
MOVING A DEEP UPPER LEVEL LOW PRESSURE FROM SOUTHERN WYOMING EAST
INTO THE MIDWEST. A BLENDED SOLUTION WOULD MOVE THE TROUGH AXIS EAST
OF THE REGION THURSDAY AFTERNOON OR EVENING. AS THE TROUGH MOVES
EAST...PRECIPITATION WILL DIMINISH OVER MANY AREAS AS WEAK RIDGING
MOVES INTO WESTERN MONTANA. DISTURBANCES QUICKLY FLATTEN THE RIDGE
LEAVING A PROBLEMATIC NORTHWESTELY FLOW ALOFT...FOR AN UNSETTLED
PERIOD. DOWNSLOPE WINDS SHOULD KEEP THE PRECIPITATION IN CHECK WITH
ONLY A SLIGHT CHANCE OF SNOW...RAIN OR MIXED SHOWERS. SNOW LEVEL
WILL BOTTOM OUT EARLY THURSDAY AT 3000 TO 4000 FEET. BEHIND THE
RIDGE TEMPERATURES WILL BEGIN TO GRADUALLY MODERATE WITH SNOW LEVELS
BEGINNING TO RISE.  EK

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  77  51  82  43 /   0   0   0  10
CTB  77  47  78  36 /   0   0   0  10
HLN  82  49  84  47 /   0   0   0  10
BZN  85  44  88  43 /   0   0   0  10
WEY  78  28  76  31 /   0   0   0   0
DLN  82  45  81  43 /   0   0   0   0
HVR  80  45  83  40 /   0   0   0  10
LWT  76  47  82  42 /   0   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM SATURDAY AFTERNOON THROUGH SATURDAY
EVENING FOR MTZ112>118.

&&

SHORT TERM...MPJ
LONG TERM...WARANAUSKAS/EK
AVIATION...COULSTON

WEATHER.GOV/GREATFALLS

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