Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 010450
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1050 PM MDT THU APR 30 2015

.DISCUSSION...

MID LEVEL MOISTURE IS PRODUCING A CHINOOK ARCH OVER THE ROCKY
MOUNTAIN FRONT WITH CONTINUED STRONG WESTERLY FLOW ALOFT. THE
FORECAST WAS UPDATED WITH INCREASED SKY COVER IN THIS AREA.
OTHERWISE JUST MINOR ADJUSTMENTS TO ALIGN FORECAST ELEMENTS CLOSER
TO OBSERVED TRENDS THIS EVENING. NUTTER

&&

.AVIATION...
UPDATED 0450Z.

A CHINOOK ARCH WILL RESIDE OVER MUCH OF NORTH CENTRAL MT THRU THE
PERIOD. HOWEVER...VFR CONDITIONS WILL PREVAIL. EXPECT BREEZY WEST TO
NORTHWEST WINDS ONCE AGAIN ON FRIDAY AFTERNOON...WITH WIND SPEEDS
DIMINISHING TOWARDS 02Z SATURDAY. BRUSDA

&&

.PREV DISCUSSION...
/ISSUED 520 PM MDT THU APR 30 2015/

TONIGHT THROUGH SATURDAY...STRONG WESTERLY FLOW ALOFT WILL
CONTINUE AS WILL THE DRY AND STABLE CONDITIONS. MODELS INDICATE A
CHINOOK ARCH WILL LIKELY FORM FRIDAY IN THE LEE OF THE ROCKIES.
TEMPERATURES WILL WARM ABOUT 10 DEGREES FRIDAY. SURFACE
WINDS...WHILE GUSTY DURING THE AFTERNOON...WILL DECREASE AROUND
SUNSET BUT WILL INCREASE AGAIN FRIDAY AFTERNOON. SHORTWAVE ENERGY
WILL MOVE ACROSS SOUTHERN CANADA SATURDAY WITH THE ONLY EFFECT ON
THE AREA WILL BE AN INCREASE IN CLOUDS. TEMPERATURES...WHILE A
LITTLE COOLER SATURDAY...WILL REMAIN ABOVE SEASONAL AVERAGES BOTH
DAYS.

SATURDAY NIGHT THROUGH THURSDAY...MEDIUM RANGE MODELS ARE IN GOOD
AGREEMENT FOR THE LATTER PORTION OF THE WEEKEND THROUGH EARLY NEXT
WEEK. DURING THIS TIME FRAME MODELS ARE SHOWING A BROAD TROUGH
OVER WESTERN PORTIONS OF CANADA WITH GENERALLY WESTERLY FLOW ALOFT
OVER MONTANA. A CANADIAN COLD FRONT ASSOCIATED WITH THIS SYSTEM
WILL BRING COOLER AIR SOUTHWARD INTO THE FORECAST AREA SATURDAY
NIGHT BUT THIS AIRMASS MOVES QUICKLY EASTWARD ON SUNDAY. SHORTWAVE
RIDGING BUILDS OVER THE REGION MONDAY THROUGH TUESDAY FOR WARMER
TEMPERATURES. ISOLATED TO SCATTERED SHOWERS AND A FEW
THUNDERSTORMS WILL BE POSSIBLE OVER SOUTHWEST MONTANA ON MONDAY AS
THE AIRMASS BECOMES SLIGHTLY UNSTABLE. THIS ACTIVITY WILL SPREAD
INTO NORTH CENTRAL MONTANA BY TUESDAY AFTERNOON AS THE FLOW ALOFT
BECOMES SOUTHERLY AHEAD OF AN UPPER LEVEL WAVE EXPECTED TO MOVE
INLAND FROM THE GULF OF ALASKA. MODELS DIFFER IN THE STRENGTH OF
THIS FEATURE WITH THE GFS CLOSING OFF A SIGNIFICANT LOW PRESSURE
SYSTEM OVER THE PACIFIC NORTHWEST AND GREAT BASIN WHILE THE ECMWF
CLOSES OFF A MUCH WEAKER LOW NORTH OF THE CANADIAN BORDER WHILE
SWEEPING AN OPEN WAVE ACROSS THE NORTHERN ROCKIES WEDNESDAY
THROUGH THURSDAY. HAVE ATTEMPTED TO SPLIT THE DIFFERENCE ON TIMING
OF A SURFACE COLD FRONT EXPECTED TO MOVE THROUGH THE REGION AROUND
MID WEEK. HAVE ALSO TRENDED POPS A BIT HIGHER SINCE BOTH MODELS
INDICATE SOME PRECIPITATION BUT HAVE OPTED TO NOT EXCEEDED CHANCE
CATEGORY DUE TO LOW CONFIDENCE. MPJ

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  40  75  47  71 /   0   0   0  10
CTB  37  70  36  62 /   0  10  10  10
HLN  37  75  43  74 /   0   0   0  10
BZN  32  73  37  73 /   0   0   0  10
WEY  26  67  29  68 /   0   0   0  10
DLN  35  74  40  74 /   0   0   0  10
HVR  36  77  42  68 /   0   0  10  10
LWT  38  74  44  71 /   0   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

WEATHER.GOV/GREATFALLS



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