Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 200528

Area Forecast Discussion
National Weather Service Great Falls MT
1125 PM MDT Thu Oct 19 2017

Aviation Section Updated.


Breezy southwest winds will decrease overnight and shift more
westerly across Central Montana. A frontal boundary moves into the
region Friday bringing a chance for showers, primarily to the
Rocky Mountains and Southwest Montana. Windy conditions look to
persist through the weekend with cooler temperatures expected.


.UPDATE...Winds have diminished and RH values have risen so the
Red Flag Warning has been cancelled. Have updated overnight low
temperatures as well as winds based on short term model consensus
tools. Have also updated sky condition to increase cloud cover as
models are not doing a very good with upper level deck currently
over the region. mpj


Updated 1125Z.

Scattered to broken high cloud-cover will prevail overnight. A cold
front moves through the forecast area by mid-day Friday with winds
shifting to the west and increasing behind the front. Widespread
snow and mountain obscurations expected along the Continental Divide
after 12Z Friday, while isolated to scattered showers accompany
frontal passage through the plains. VFR conditions expected to
prevail at all forecast terminals through the period, except for
brief IFR/MVFR conditions possible in showers. Mountain wave
turbulence and low level wind shear expected to redevelop in favored
locations as west winds increase behind frontal passage. mpj/PN


/ISSUED 556 PM MDT Thu Oct 19 2017/

Tonight through Saturday...High pressure exits the region today with
the next upper trough moving inland over the Pacific coast. The
surface front moves east across Central Montana Friday ushering in a
period of unsettled weather in a much more progressive flow. Chances
of seeing precipitation increase along the Continental Divide and
Southwest Montana, lasting through Saturday. Winds aloft will remain
from the southwest before shifting more westerly Friday. Gusty
surface winds will persist across North-Central MT during the period
with the strongest winds along the Rocky Mtn Front. Expect the
diurnal trend of winds weakening overnight and strengthening during
the day to continue with gusts across the plains reaching the 30 to
40 kt range Saturday. Temperatures return to more seasonal ranges
with highs across the plains in the 50s.

Saturday night through Thursday...The weather pattern will continue
to quickly evolve through the upcoming weekend as the longwave
trough pushes east, leaving behind a quasi-zonal flow aloft. While
normally this would yield benign or near-seasonal weather
conditions, this will not be the case. To the southwest, a strong
upper-level ridge will develop which will lead to steepening
heights/increasing upper-level flow along the northern Rockies. This
will transition into yet another high wind event during the day on
Sunday for most of the CWA, especially along the Rocky Mountain
Front, east across the Plains. While the exact magnitude and of the
event remains uncertain this far out, maximum wind gusts will have
no problem peaking again 35-45mph across the Plains, with the
potential for higher gusts above 50-55mph along ridgetops. Expect
these numbers to be fine tuned as we get closer to the upcoming
weekend. With the upper-level flow set in place, expect gusty
winds to persist into the overnight hours Sunday night and to a
lesser extent into Monday. We will see another cold front swing
through during the day on Monday as a weak disturbance rides the
progressive westerly to northwesterly flow aloft. There may be
enough moisture around to squeeze out a few showers along northern
areas, but coverage will be limited. Temperatures will drop off
again for afternoon highs on Monday thanks to the passing front,
and a developing PacNW surface high draining in cooler air from
the northwest. Much of the same will be expected on Tuesday as the
surface high drifts east across Montana. The good news is with
this surface high in place, winds are not expected to be a
problem. Wednesday, another cold front will dive south from
southern Canada. GFS and ECMWF solutions currently are not in
agreement on timing, which will have a big impact on how warm we
get for afternoon highs on Wednesday. At this time, regardless of
frontal speed, it is likely SW low-level flow will support
adequate downsloping, enough for a relatively warm day before the
front knocks temperatures down yet again Wednesday night. Looking
even further out Thursday and beyond, the pattern stays relatively
inactive with a NW flow in place, temperatures should remain near
seasonal average while staying relatively dry. KLG


GTF  49  56  36  52 /   0  10  20   0
CTB  41  51  33  50 /   0  10  10   0
HLN  42  47  34  52 /   0  20  20  10
BZN  42  55  30  50 /   0  60  30  10
WEY  28  40  22  35 /  10  80  50  20
DLN  40  48  27  46 /   0  50  30  10
HVR  42  59  36  55 /   0  20  30  20
LWT  45  62  33  49 /   0  20  20  10



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