Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 210248
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
848 PM MDT Fri Oct 20 2017

.SYNOPSIS...
Breezy west winds will decrease overnight across Central Montana,
as a frontal boundary moving across the region will bring a
chance of scattered showers, primarily to the Rocky Mountains and
Southwest Montana, through tonight. Brief clearing moves in
Saturday ahead of the next system moving in from the west. Expect
winds to increase from the west becoming very strong and gusty
late Saturday. Windy conditions look to persist through late
Sunday with cooler temperatures expected.

&&

.UPDATE...Surface cold front that swept through the region earlier
this evening has moved into Eastern Montana. Behind the front,
winds have diminished faster than anticipated and shower activity
is gradually decreasing as well. Have updated the forecast to
lower wind speeds to be more in keeping with observed and forecast
conditions for the remainder of the night. Have also made some
tweaks to PoPs, weather and sky condition based on short term
model consensus tools, satellite and radar imagery. Remainder of
the forecast package appears to be in good shape and no further
updates are anticipated. mpj

&&

.AVIATION...
Updated 2356Z.

Surface cold front along a line from KHVR to KLWT to KLVM continues
to move eastward this evening. Band of precipitation accompanies
frontal passage with isolated/scattered showers behind the front
gradually diminishing. West winds are gusting 35 to 45 knots behind
the front for an hour or two with sustained winds of 15 to 25 mph
expected to persist overnight and through the day on Saturday. Low-
to mid-level broken/overcast cloud cover persists overnight with
partly cloudy conditions developing on Saturday. VFR conditions are
expected to prevail but brief IFR/MVFR conditions are expected in
precipitation. Mountain obscurations likely through at least 15Z
Saturday. mpj

&&

.PREV DISCUSSION...
/ISSUED 556 PM MDT Fri Oct 20 2017/
Tonight through Sunday...A period of unsettled weather in a much
more progressive flow looks to dominate the weekend. Chances of
seeing precipitation increase along the Continental Divide and
Southwest Montana through Friday night. A period of sun moves in
briefly Saturday before the next push of moisture arrives from the
west later Saturday night. Winds strengthen once again across North-
Central MT Saturday night into Sunday. 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. Temperatures return to more seasonal
ranges with highs across the plains in the 50s.

Sunday night through Thursday...The main concerns during this
period center around wind and the potential for continued elevated
fire weather concerns.

An impressive upper level jet and associated moisture/precip aimed
at the Pacific NW will gradually shift south away from the area
Sunday night, with precip diminishing in the mountains. NW flow
takes over aloft as the upper level trough pushes into the central
US. This is followed by an anomalously strong ridge (for late-
October) TUE/WED which will likely yield a return to above normal
temps (60s/70s at lower elevations) both days. The models are then
in very good agreement in bringing a sharp trough SE out of Canada
later WED into THU. In this transition, another wind event appears
possible late Tuesday night into Wednesday, especially along the
Rocky Mtn Front where a 60-80kt mid-level jet and strong pressure
gradient are forecast to be co-located. Out over the plains, high
wind criteria may not be met, but as has been seen in previous
breezy/windy days, relative humidity values may fall low enough to
warrant elevated to near-critical fire weather concerns. The
shortwave forecast to dive SE out of Canada will likely be
accompanied by a strong northerly jet. Where the models differ is
where the upper jet and coldest air is directed (ie. right over our
area or further east across eastern MT and the Dakotas). Regardless,
the mild temps TUE/WED should quickly be replaced by much colder
temperatures by Thursday...along with some accumulating snow.
Forecast temperatures for next Thu/Fri are well below the
NBM...closer to the 12z GFS MEX forecast. The potential then
exists for yet another wind event late in the week as well.
MARTIN/Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  50  45  62 /  10   0  20  10
CTB  37  47  39  58 /  10  10  20  20
HLN  37  50  41  63 /  10  10  20  20
BZN  31  49  38  62 /  20  10  20  30
WEY  25  33  28  45 /  70  20  60  60
DLN  29  44  36  58 /  10  10  20  20
HVR  41  52  37  64 /  30  20  20  20
LWT  37  48  38  61 /  40   0  20  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 Watch from late Saturday night through Sunday evening
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

$$

weather.gov/greatfalls


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