Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 312247
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
354 PM MDT MON AUG 31 2015

.UPDATE...

THE HIGH WIND WARNING IS CANCELLED. WIND GUSTS HAVE DROPPED BELOW 40
MPH IN ZONES 09-10 EXCEPT AT THE ISOLATED DEEP CREEK RAWS. WILL
CONTINUE TO MONITOR FOR MOUNTAIN WAVE INDUCED HIGH WINDS IN THIS
AREA AGAIN TUESDAY MORNING. PN

.DISCUSSION...

TONIGHT THROUGH WEDNESDAY...STRONG WESTERLY FLOW OVER THE NORTHERN
ROCKIES COUPLED WITH AN INVERSION JUST ABOVE RIDGETOPS HAS
MAINTAINED A MOUNTAIN WAVE SIGNATURE TODAY. HIGH WINDS OVER
GLACIER AND WESTERN PONDERA COUNTY WILL WEAKEN EARLY THIS EVENING
AS LOWER LEVELS WARM AND WEAKEN THE INVERSION. A HIGH WIND WARNING
WAS ISSUED THIS MORNING IN RESPONSE TO OBSERVED HIGH WINDS AND
WILL CONTINUE TO MONITOR. THE MOUNTAIN WAVE ACTIVITY RETURNS EARLY
TUESDAY THOUGH CONFINED TO A NARROW ZONE ALONG THE ROCKY MOUNTAIN
FRONT. AGAIN WILL HAVE TO MONITOR WINDS CLOSELY FOR HIGH WIND
CRITERIA EARLY TUESDAY ESPECIALLY AS A MINOR SHORTWAVE ZIPS
THROUGH THE FLOW AROUND 12-15Z. TEMPERATURES TREND WARMER TUESDAY
AFTERNOON WITH A VERY DRY AIRMASS ARRIVING ON A MORE SOUTHWESTERLY
FLOW. HAVE ISSUED A RED FLAG WARNING FOR FIRE ZONE 112 TUESDAY
AFTERNOON FOR WINDS AND LOW HUMIDITY. FIRE WEATHER CONCERNS MAY
EXTEND TO ADJACENT AREAS BUT THERE IS LESS CONFIDENCE THAT BOTH
WINDS AND RH WILL REACH CRITICAL FIRE WEATHER CRITERIA. CLOUDS,
MOISTURE AND CHANCES FOR PRECIPITATION INCREASE ON WEDNESDAY AS A
SERIES OF DISTURBANCES BEGIN TO EJECT FROM A BROAD UPPER LEVEL
TROUGH OVER THE PACIFIC NORTHWEST. PN

WEDNESDAY NIGHT THROUGH MONDAY...AN UPPER LEVEL LOW PRESSURE TROF
WILL BE OVER THE PACIFIC NORTHWEST WEDNESDAY NIGHT. THE ASSOCIATED
COLD FRONT WILL CROSS THE NORTHERN ROCKIES AS EARLY AS WEDNESDAY
EVENING AND MOVE THROUGH CENTRAL MONTANA BY THURSDAY MORNING.
PRECIPITATION AMOUNTS WITH FRONTAL PASSAGE WILL GENERALLY BE ON
THE LOW SIDE. A SHORTWAVE MOVING THROUGH THE TROF WILL MOVE OVER
THE IDAHO PANHANDLE THURSDAY EVENING AND THE CHANCE FOR HEAVIER
PRECIP WILL INCREASE, ESPECIALLY OVER THE SOUTHWEST ZONES WHERE
THE AIRMASS WILL BE SLIGHTLY UNSTABLE. A SECOND SHORTWAVE WILL
MOVE INTO THE PACIFIC NORTHWEST BY FRIDAY MORNING AND THIS WILL
BROADEN AND KEEP THE TROF OVER THE WESTERN US. THIS SHORTWAVE WILL
APPROACH THE ROCKIES FRIDAY AFTERNOON AND EVENING. WEAK
INSTABILITY WILL DEVELOP MAINLY OVER THE WESTERN MOUNTAINS AND
SOUTHWEST MONTANA FRIDAY AND SATURDAY AFTERNOONS ALONG WITH A
CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS. SOME TIMING ISSUES
BETWEEN THE ECMWF AND GFS BEGIN TO DEVELOP FRIDAY NIGHT AS THE
ECMWF DEEPENS AND CLOSES THE LOW OVER WASHINGTON/OREGON AND THE
GFS CONTINUES WITH AN OPEN WAVE. THE APPROACH OF THE TROF WILL
KEEP A THREAT OF RAIN ACROSS MUCH OF CENTRAL AND SOUTHWEST MONTANA
SATURDAY AND SATURDAY NIGHT. THE AIR MASS WILL BECOME VERY MOIST
AND GOOD PRECIPITATION AMOUNTS SHOULD BE ASSOCIATED WITH THIS
SYSTEM. THE DIFFERENCES IN THE MODELS CONTINUE AS THE GFS MOVES
THE TROF EAST OF THE ZONES LATE SATURDAY NIGHT AND SUNDAY...WHICH
WOULD BUILD HIGH PRESSURE AND WARM AND DRY THE AIR MASS. HOWEVER,
THE ECMWF KEEPS THE LOW OVER SOUTHERN IDAHO SATURDAY NIGHT AND
SLOWLY MOVES IT INTO CENTRAL MONTANA BY MONDAY. WITH THESE
DIFFERENCES, CONFIDENCE IN POPS AND FORECASTED TEMPS IS RATHER LOW
DURING THE SATURDAY TO MONDAY PERIOD. ZELZER

&&

.AVIATION...UPDATED 1740Z.

VFR CONDITIONS ARE EXPECTED WITH ANY CEILINGS RESTRICTED TO ABOVE
15000 FT. GUSTY WINDS WILL CONTINUE OVER THE PLAINS THEN DIMINISH
THIS EVENING. LOCAL WIND GUSTS NEAR 50 KTS WILL OCCUR OVER THE NW
PLAINS INTO EARLY THIS AFTERNOON. CONFIDENCE IS LOW AS TO WHETHER
THERE WILL BE ANY VISIBILITY RESTRICTIONS DUE TO SMOKE DURING THE
PERIOD AND HAVE OPTED TO KEEP VISIBILITIES IN THE VFR CATEGORY FOR
NOW.

&&

.FIRE WEATHER...NEW RED FLAG WARNING NOW IN EFFECT FOR FIRE ZONE 112
FOR NOON TO 9 PM TUESDAY.  CURRENT BREEZY TO GUSTY WINDS WILL
CONTINUE THROUGH EARLY THIS EVENING THEN SUBSIDE DURING THE
OVERNIGHT HOURS. GUSTY WINDS RETURN TO THE ROCKY MTN FRONT AND
ADJACENT PLAINS IN GLACIER/TOOLE/LIBERTY COUNTIES TOMORROW WHICH
WILL COMBINE WITH AFTERNOON HUMIDITY VALUES AGAIN DROPPING INTO THE
15-20 PERCENT RANGE. LOW HUMIDITY WILL ALSO DEVELOP OVER MUCH OF
CENTRAL MT BUT WIND SPEEDS SHOULD REMAIN BELOW CRITICAL FIRE WEATHER
CRITERIA.
WARANAUSKAS

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  53  83  53  79 /   0   0   0  10
CTB  50  77  51  70 /   0   0   0  10
HLN  46  84  49  80 /   0   0   0  10
BZN  45  84  49  85 /   0   0   0  20
WEY  33  76  39  75 /   0   0   0  10
DLN  44  83  49  81 /   0   0   0  10
HVR  50  83  51  80 /   0   0  10   0
LWT  49  83  55  83 /   0   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING FROM NOON TO 9 PM MDT TUESDAY FOR MTZ112.

&&

$$

WEATHER.GOV/GREATFALLS



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