Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211141
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
400 AM MDT Sat Oct 21 2017

Aviation Section Updated.

.SYNOPSIS...

Clouds thin today as high pressure moves over the region. Rain and
mountain snow returns tonight through Sunday generally along and
west of the Continental Divide. Potentially damaging winds also
develop overnight, peaking in strength Sunday afternoon.

&&

.DISCUSSION...

Tonight through Monday...Cool and breezy conditions prevail today
under clearing skies due to post-wave subsidence. A new surge of
moisture arrives later this evening through Sunday, with rain and
mountain snow developing up to and along the Continental Divide
before spreading further across southwest Montana. Snowfall
amounts of 3-6" are possible over remote areas of the Northern
Rockies, but snow levels actually rise through this event from
around 5 to 8 kft. An unseasonably strong jet stream noses across
North-central MT, resulting in a period of potentially damaging
wind gusts on Sunday afternoon. The strongest winds will be
along the Rocky Mtn Front with gusts into the 70kt range possible.
Across the plains winds 30 to 40kt with gusts into the 50kt range
are possible Sunday afternoon. PN

Monday night through Friday...The main concerns during this
period are a possible wind event for portions of Central Montana
WED, then the potential of sharply colder temps and accumulating
snow WED night/Thursday.

The period starts with an anomalously strong ridge (for this time of
year) building into the western US. Under mostly sunny skies and,
for some, a downsloping SW wind, this should allow temps to warm
into the 60s/70s at lower elevations TUE/WED (although, increasing
clouds may tend to keep it not as mild along the Hi-line by WED).
The breezy/mild conditions may also lead to elevated fire concerns.

Those increasing clouds will signal what is expected to be a potent
shortwave moving over the ridge and crashing into the Northern
Rockies/Northern High Plains late Wednesday/Thursday. This wave
has origins over the Bering Sea and it should be noted that the
models continue to struggle this far out with its track/evolution
and associated impacts. The forecast, then, puts a bit more weight
on the previous forecast to avoid drastic changes one way or the
other. Ahead of the shortwave, another wind event will be
possible, especially portions of Central MT. This is then followed
by a strong cold front. It should be noted that the potential
exists for a fairly drastic temp change from WED to THU in the
wake of the front (possibly a 20-30 degree drop). This system will
also be accompanied by at least some rain/snow, but how much and
how impactful the snow is will very much depend on how quickly the
system moves through. MARTIN

&&

.AVIATION...
Updated 1135Z.

VFR conditions prevail as overnight cloud cover continues to erode.
The next system upstream brings increasing clouds and producing
mountain obscurations southwest Montana Saturday evening. West winds
increase early Sunday morning, with LLWS and mountain wave
turbulence likely over the region. PN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  45  59  45 /  10  10  10  10
CTB  49  41  55  40 /  10  20  20  10
HLN  51  44  59  43 /  10  20  20  20
BZN  50  42  59  42 /  10  20  30  20
WEY  33  31  43  31 /  50  70  60  60
DLN  45  40  56  39 /  10  20  20  20
HVR  53  40  61  40 /  40  30  20  10
LWT  49  40  60  40 /  10  20  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Sunday morning through Sunday evening
Blaine...Cascade...Chouteau...Eastern Glacier...Eastern
Pondera...Eastern Teton...Fergus...Hill...Judith Basin...
Liberty...Meagher...Toole.

High Wind Watch from Sunday morning through Sunday evening
Central and Southern Lewis and Clark.

High Wind Warning from midnight tonight to 10 PM MDT Sunday
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

$$

weather.gov/greatfalls



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