Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 270928

Area Forecast Discussion
National Weather Service Great Falls MT
328 AM MDT Thu Oct 27 2016


Today through Saturday...Upper level ridge extending from the
4-corners region north thru MT will amplify today for additional
warming with afternoon temperatures reaching values around 15
degrees above seasonal averages. Significant amounts of mid-high
level moisture continue to stream over the ridge axis this morning
with some thinning of the clouds-cover likely this afternoon,
especially across southern portions of the forecast area.
Shortwave energy ejecting out of the upper trough in the eastern
Pacific will lift into the Northern Rockies tonight with
relatively weak surface low pressure developing to the lee of the
US/Canadian Rockies. This will bring increasing SW winds to the
forecast area later today and tonight with strongest gusts (40-60
mph) likely along the immediate Rocky Mtn Front. As the shortwave
energy crosses the northern Rockies tonight and low pressure
shifts east across MT, showers will become widespread along and
west of the Continental divide with a few showers also moving east
across central and SW MT Thursday evening as a weak frontal
boundary moves across the region. On Friday, cooler air will begin
to wrap in from the north behind the departing surface low, while
the weak frontal boundary hangs up over SW MT. Next wave ejecting
out of the base of the Pacific trough moves up into he Great
Basin Friday and across SE ID/NW WY Friday night. This will focus
an area of widespread precipitation across areas near the ID/WY
border with a sharp cutoff in precipitation likely for areas north
of I90. Transient upper level ridging then drifts across the
region on Saturday for generally dry conditions early with
increasing clouds again late Saturday ahead of the next Pacific
disturbance moving onshore. Hoenisch

Saturday Night through Thursday...Clouds increase once again from
the west Saturday night as a shortwave ridge axis moves downstream.
Weak warm advection will lift areas of rain into the Northern
Rockies early Sunday. Precipitation continues but shifts further
south and spreads across southwest Montana on Sunday as a jet streak
intensifies in a moist southwest flow aloft. The center of a
significant Pacific trough moves inland across the central west
coast Sunday night, and continues across the central Rockies on
Monday. Periods of rain will accompany the passage of this system,
continuing to affect mainly central and southwest Montana. Snow
levels lower to around 5500 feet over the Northern Rockies, to
around 7000 feet for Southwest MT by Monday evening with snow
possible on area passes.

Monday evening...Halloween: Areas of rain early Monday afternoon
should taper and move east on Monday evening. However, showers may
linger in some areas. Temperatures on Monday evening should be in
the lower to mid 40s for most plains and valley locations.

Tuesday through Thursday...Model solutions diverge through this
period but generally indicate a drier split flow pattern over the
northern Rockies. PN


.AVIATION...Updated 0447Z.

Moist southwest flow aloft continues overnight with widespread mid-
to high-level ceilings prevailing. Breezy to windy conditions will
develop along the east slopes of the Rocky Mountains by 18Z Thursday
with some risk for turbulence aloft near and east of the Rockies.
Weak disturbance in the flow aloft will bring increasing low- to mid-
level ceilings by 00Z Friday with isolated/scattered showers and
widespread obscurations developing over the western mountains. mpj


GTF  70  41  54  37 /  10  20  10  10
CTB  63  34  50  32 /  10  20  10  10
HLN  69  38  55  36 /  10  20  20  20
BZN  70  42  56  38 /   0  20  40  60
WEY  58  34  49  34 /  10  50  70  80
DLN  69  40  55  38 /   0  30  40  60
HVR  67  38  51  33 /  10  20  10  10
LWT  69  40  53  36 /   0  10  20  30



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