Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 012345
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
545 PM MDT FRI MAY 1 2015

.DISCUSSION...

TONIGHT THROUGH SUNDAY...STRONG WESTERLY FLOW ALOFT WILL CONTINUE.
ENOUGH MOISTURE WITHIN THE FLOW ALOFT CAUSING A CHINOOK ARCH TO
FORM IN THE LEE OF THE ROCKIES. SATELLITE IMAGERY INDICATING THE
ARCH IS BEGINNING TO BREAK DOWN A LITTLE AS THE FLOW SHIFTS EVER
SO SLIGHTLY TO THE NORTHHWEST. PRESSURE GRADIENT CONTINUES TO BE
TIGHTEST ALONG THE NORTHERN ROCKY MOUNTAIN FRONT AND WINDS HAVE
BEEN INCREASING THROUGH THE AFTERNOON. WILL CONTINUE THE HIGH WIND
WARNING AS MODELS INDICATE A STRENGTHENING OF THE WINDS INTO EARLY
EVENING. NORTHWEST FLOW ALOFT SATURDAY WILL CONTINUE GENERALLY DRY
AND STABLE CONDITIONS. THE EXCEPTION WILL BE SOME ISOLATED
SHOWERS OVER THE MOUNTAINS SATURDAY AFTERNOON. A WEAK COLD FRONT
WILL DROP SOUTH OUT OF CANADA SATURDAY NIGHT AND PUSH ACROSS THE
AREA. WINDS WILL SHIFT TO THE NORTHWEST BY LATE AFTERNOON SATURDAY
AND THEN SHIFT TO THE NORTH BY MIDNIGHT. VERY LITTLE MOISTURE WILL
ACCOMPANY THE FRONT AND LITTLE...IF ANY...PRECIPITATION IS
EXPECTED. TEMPERATURES WILL REMAIN IN THE 60S BOTH DAYS WHICH IS
STILL ABOVE SEASONAL AVERAGES.

SUNDAY NIGHT THROUGH FRIDAY...FORECAST MODELS START OFF THE MEDIUM
RANGE PERIOD IN GOOD AGREEMENT BUT DIVERGE SIGNIFICANTLY BY TUESDAY
EVENING. MAIN PROBLEM IN THE FORECAST CONTINUES TO BE THE EVOLUTION
OF AN UPPER LEVEL LOW THAT STARTS OFF THE PERIOD IN THE GULF OF
ALASKA. MODELS DIFFER SIGNIFICANTLY IN THE STRENGTH AND LOCATION OF
THIS FEATURE WITH THE GFS CLOSING OFF A SIGNIFICANT LOW PRESSURE
SYSTEM OVER THE PACIFIC NORTHWEST AT 00Z WEDNESDAY WHILE THE ECMWF
CLOSES OFF A WEAK UPPER LOW IN CENTRAL BRITISH COLUMBIA AND KEEP AN
OPEN WAVE OVER THE PACIFIC NORTHWEST. AS THE WEEK PROGRESSES MODEL
SOLUTIONS TREND EVEN FURTHER APART AS THE GFS MOVES THE CLOSED LOW
SOUTH TO THE CENTRAL CALIFORNIA/NEVADA BORDER REGION AND THE ECMWF
PROGRESSES THE OPEN WAVE EASTWARD THROUGH THE NORTHERN ROCKY
MOUNTAINS. BOTH MODELS INDICATE THAT PRECIPITATION WILL BE SPREAD
INTO MONTANA BUT THE DIFFERENCES IN AMOUNTS/TIMING AND LOCATIONS
CONTINUE TO CREATE A VERY LOW CONFIDENCE FORECAST FOR THE REMAINDER
OF NEXT WEEK. HAVE MADE MAINLY MINOR CHANGES TO THE GOING FORECAST
KEEPING COOL TEMPERATURES AND ISOLATED TO SCATTERED PRECIPITATION AS
THE DOMINANT WEATHER FOR WEDNESDAY THROUGH FRIDAY. IF AND WHEN
MODELS BEGIN TO AGREE ON A SOLUTION I ANTICIPATE THAT MAJOR CHANGES
COULD BE MADE TO THE FORECAST IN ORDER TO CATCH UP WITH WHATEVER
TREND APPEARS MOST LIKELY. MPJ

&&

.AVIATION...
UPDATED 2338Z.
STRONG WEST WINDS ALOFT WILL CONTINUE THROUGH
SATURDAY. SURFACE WINDS WILL DIMINISH THROUGH THE EVENING BUT BECOME
VERY STRONG AND GUSTY AGAIN BY SATURDAY AFTERNOON. THE AIRMASS WILL
REMAIN DRY AND VFR CONDITIONS WILL PREVAIL THROUGH THE NEXT 24 HOURS.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  46  69  33  64 /   0  10  10  10
CTB  36  59  29  61 /   0  10  20  10
HLN  44  73  36  69 /   0  10  10  10
BZN  39  71  33  67 /   0  10  10  10
WEY  29  68  30  66 /   0  10  20  30
DLN  41  72  36  69 /   0  10  10  20
HVR  41  65  32  64 /   0  10  10  10
LWT  45  69  34  63 /   0  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 4 AM MDT SATURDAY FOR MTZ009.

&&

$$

WEATHER.GOV/GREATFALLS


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