Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 051147
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
540 AM MDT SAT SEP 5 2015

AVIATION SECTION UPDATED

.DISCUSSION...

TODAY THROUGH MONDAY... AN ELONGATED AND NEARLY STATIONARY CLOSED
UPPER LOW POSITIONED OVER OREGON CONTINUES TO SUPPORT COOL AND
RAINY WEATHER FOR NORTH CENTRAL MONTANA. A COMBINATION OF LOW
LEVEL UPSLOPE FLOW...MID LEVEL WARM ADVECTION...AND DIVERGENCE
PROVIDES FAVORABLE SYNOPTIC FORCING FOR ASCENT. ADDITIONAL NEW
RAINFALL AMOUNTS TODAY AND TONIGHT RANGE FROM AROUND 0.25 INCHES
OVER CENTRAL MT UP TO AROUND ONE INCH ALONG NORTHERN PORTIONS OF
THE ROCKY MOUNTAIN FRONT. SNOW LEVELS ARE EXPECTED TO DROP TO
AROUND 6500 FT MSL WITH 1 TO 3 INCHES OF SNOW ON THE HIGHER ROCKY
MOUNTAIN PEAKS. IMPACTS TO TRAVEL OVER MOUNTAIN PASSES ARE NOT
EXPECTED SO WILL NOT ISSUE A WINTER WEATHER ADVISORY. AREAS OF
RAIN MAY BECOME MORE CONVECTIVE WITH ISOLATED THUNDERSTORMS
SATURDAY AFTERNOON DUE TO STEEPENING LAPSE RATES. MODELS HAVE COME
INTO EXCELLENT AGREEMENT IN ACCELERATING THE TROUGH DEPARTURE AWAY
TO THE NORTHEAST EARLY SUNDAY. FORECAST POPS AND QPF WERE LOWERED
OVER MUCH OF THE SOUTHWEST DUE TO THIS MORE RAPID DEPARTURE. LOW
TEMPERATURES IN HIGHER SOUTHWEST VALLEYS WILL DROP INTO THE 20S ON
SUNDAY AND MONDAY MORNINGS. WEST WINDS AROUND 25 MPH WITH GUSTS TO
35 MPH WILL DEVELOP ACROSS NORTH CENTRAL MONTANA SUNDAY BEHIND THE
DEPARTING WEATHER SYSTEM. FAIR AND DRY CONDITIONS PREVAIL ON
MONDAY AS TEMPERATURES TREND WARMER...BUT STILL BELOW AVERAGE.
NUTTER

MONDAY NIGHT THROUGH SATURDAY. PERIOD BEGINS WITH A MINOR
DISTURBANCE SLIDING SOUTH FROM BC/ALB INTO WESTERN MT AND THE
ROCKY MTN FRONT. ASSOCIATED PRECIPITATION WON`T MAKE IT VERY FAR
INTO THE ADJACENT PLAINS THANKS TO WESTERLY DOWNSLOPE FLOW AND
DISSIPATES ALTOGETHER BY LATE MON NIGHT. GFS AND ECMWF MODELS THAT
YESTERDAY INDICATED DRY CONDITIONS FOR THE REMAINDER OF THE WEEK
NOW SHOWING A MODERATELY STRONG SHORTWAVE TROF MOVING THROUGH THE
NORTHERN HALF OF MT WITH WIDESPREAD LIGHT RAIN ON TUES AFTN/EVE.
MODELS HAVE ALSO DELAYED THE RETURN OF HIGH PRESSURE RIDGING INTO
THE NORTHERN ROCKIES UNTIL THURS, BUT HAVE ALSO EXTENDED THE
RESULTING DRY CONDITIONS THROUGH NEXT WEEKEND. DAILY HIGH
TEMPERATURES WILL REMAIN 8 TO 10 DEGREES COOLER THAN NORMAL
THROUGH WEDNESDAY, THEN STEADILY WARM UNDER THE STRENGTHENING
RIDGE, REACHING MID 70S TO LOW 80S BY SATURDAY. WARANAUSKAS

&&

.AVIATION...

UPDATED 1140Z. MIX OF PRIMARILY MVFR/IFR CONDITIONS DUE TO LOW
CEILINGS AND AREAS OF PATCHY FOG EXPECTED THROUGH THIS MORNING.
BANDS OF MOISTURE ASSOCIATED WITH LARGE LOW PRESSURE SYSTEM ALONG
WA/OR/ID BORDER THIS MORNING WILL GENERATE WIDESPREAD LOW CLOUD
COVER AND SCATTERED -SHRA THROUGH MIDDAY.  AS THE LOW MOVES INTO
WESTERN MT THIS AFTN, ADDITIONAL MOISTURE ARRIVES PRODUCING
WIDESPREAD -RA INTO THIS EVENING.  ISOLATED -TSRA ALSO POSSIBLE FOR
MUCH OF THE DAY AS INSTABILITY INCREASES ON EASTERN FLANK OF THE
SYSTEM.
WARANAUSKAS

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  56  44  61  42 /  70  70  20  10
CTB  49  40  58  41 / 100  60  40  20
HLN  60  41  63  40 /  90  60  20  10
BZN  64  36  63  37 /  50  30  10  10
WEY  56  21  54  22 /  30  20  10   0
DLN  55  33  60  34 /  70  40  10   0
HVR  57  43  61  40 /  80  50  30  20
LWT  63  40  62  37 /  50  70  20  10

&&

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

$$

WEATHER.GOV/GREATFALLS


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