Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 040926
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
326 AM MDT FRI SEP 4 2015

.DISCUSSION...

TODAY THROUGH SUNDAY...A CLOSED UPPER LEVEL LOW MOVING SLOWLY
THROUGH THE PACIFIC NORTHWEST WILL MAINTAIN COOL AND RAINY
CONDITIONS OVER MUCH OF THE FORECAST AREA THROUGH THE WEEKEND.
A BAND OF RAIN SHOWERS HAS PERSISTED OVERNIGHT THROUGH EARLY THIS
MORNING FROM SOUTHWEST THROUGH N-CENTRAL MONTANA. THIS IS
ASSOCIATED WITH ISENTROPIC LIFT REALIZED AS A SOUTHERLY 700 MB
FLOW ASCENDS COOLER SURFACE AIR. SHORT TERM GUIDANCE DEPICTS THESE
BANDS OF SHOWERS REASONABLY WELL, SO HAVE CONFIDENCE ON THEIR
SOLUTIONS FOR A DEEPENING EASTERLY UPSLOPE FLOW THAT WILL PRODUCE
STEADY LIGHT RAIN TODAY NORTHWEST OF A LINE FROM HELENA TO HAVRE.
MOST RECENT MODEL GUIDANCE HAS MOVED THE PATH OF THE UPPER LOW
FURTHER NORTH. THE 06Z NAM HAS ACCELERATED A BIT TO COME IN BETTER
AGREEMENT WITH THE PREFERRED GFS/ECMWF SOLUTIONS. THE BIGGEST
FORECAST ADJUSTMENT FORECAST WAS TO REDUCE POPS/QPF OVER SOUTHWEST
MT ON SUNDAY. ANALYTIC SOLUTIONS FOR QUASIGEOSTROPHIC OMEGA
REVEAL STRONG SYNOPTIC ASCENT CONCENTRATED OVER OUR NORTHERN
COUNTIES SATURDAY NIGHT INTO EARLY SUNDAY. CONSEQUENTLY, THE
HIGHEST PRECIPITATION TOTALS MAY EXCEED TWO INCHES THROUGH SUNDAY
ALONG THE ROCKY MOUNTAIN FRONT AND EXTENDING EASTWARD ALONG THE
HILINE. SNOW LEVELS DROP AS LOW AS 6500 FEET EARLY SUNDAY, BUT TOO
LATE TO RESULT IN ANY MORE THAN ABOUT A HALF INCH OF SNOWFALL ON
THE HIGHER PEAKS. NUTTER

.DISCUSSION... SUNDAY NIGHT THROUGH FRIDAY. DEEP UPPER-LEVEL TROF
THAT WILL BRING WIDESPREAD RAINFALL THIS WEEKEND WILL MOVE INTO
ALBERTA/SASKATCHEWAN BY SUNDAY NIGHT. A FEW RESIDUAL SHOWERS WILL BE
POSSIBLE ALONG THE HILINE COUNTIES AND OVER THE ROCKY MTN FRONT AS
THE SYSTEM EXITS, BUT MOST OF OUR REGION WILL REMAIN DRY INTO MON
MORNING.  A WEAK SECONDARY TROF IS FORECAST TO SWING INTO THE
NORTHERN ROCKIES MON AFTN/EVE GENERATING SOME SPOTTY, LIGHT RAIN
SHOWERS MAINLY ALONG/WEST OF THE INTERSTATE 15 CORRIDOR. MODELS ARE
IN GOOD AGREEMENT THAT HIGH PRESSURE RIDGE WILL STEADILY DEVELOP
ALONG THE WEST COAST NEXT WEEK. THE RESULTING WEST-NORTHWEST FLOW
ALOFT OVER MONTANA WILL KEEP CONDITIONS DRY ACROSS THE REGION WITH
GRADUALLY WARMING TEMPERATURES.
WARANAUSKAS

&&

.AVIATION...
UPDATED 2330Z. SOUTHWEST FLOW ALOFT WILL CONTINUE TO
BRING MOISTURE TO THE AREA. SHOWERS WILL BECOME WIDESPREAD OVER
NORTH AND CENTRAL MONTANA OVERNIGHT AND CONTINUE THROUGH FRIDAY. VFR
CONDITIONS PREVAIL WITH AREAS OF MVFR DUE TO LOW CEILINGS AND RAIN.
PERIODS OF IFR CONDITIONS IN FOG ARE POSSIBLE OVERNIGHT AT
KGTF/KCTB. CONDITIONS WILL BECOME INCREASINGLY MVFR AFTER 12Z.
SOUTHWEST MONTANA WILL SEE ONLY SCATTERED SHOWERS WITH VFR
CONDITIONS PREVAILING THERE. MOUNTAINS OBSCURED AT TIMES...WITH IN-
CLOUD ICING AROUND 8KFT MSL.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  46  55  45 /  80  80  80  90
CTB  52  44  51  43 / 100  90  90  90
HLN  59  43  61  42 /  80  80  70  80
BZN  69  44  67  41 /  30  70  60  60
WEY  69  36  64  24 /  20  30  30  50
DLN  62  42  62  35 /  60  70  60  50
HVR  60  47  59  47 /  90  80  60  90
LWT  62  45  60  43 /  30  80  40  80

&&

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

$$

WEATHER.GOV/GREATFALLS


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