Area Forecast Discussion
Issued by NWS Great Falls, MT

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000
FXUS65 KTFX 180429
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
929 PM MST Tue Jan 17 2017

.UPDATE...

Mild and increasingly moist westerly flow aloft continues to
overspread the region this evening as a large Pacific storm system
approaches the west coast. Radar observations show the leading
edge of precipitation ahead of the storm now just reaching the ID
panhandle, on track to reach as far east as the Continental
Divide late tonight or Wednesday morning. High level cloud-cover
will continue to stream east across the region and thicken
overnight. Little change in the winds aloft and pressure gradient
at the surface tonight will result in continued windy conditions
across the Plains, which in combination with the increasing cloud-
cover will limit much in the way of cooling overnight with
temperatures remaining steady in the 30s to low 40s for much of
N-central MT. Winds are also having some impact on temperatures in
some SW MT valley locations including Ennis and Dillon, but cold
pools linger in the Helena and Bozeman areas as well as higher
elevation valleys near the Continental Divide. Hoenisch

&&

.AVIATION...
Updated 0000Z.

VFR conditions expected for most terminals through the forecast
period. One exception will be KHLN where haze may reduce
visibility at times tonight into tomorrow morning. Gusty winds
will diminish only slightly tonight with some low level wind shear
possible at times. Winds may then increase again on
Wednesday...with widespread gusts of 30 to 35 knots expected for
central and northern portions. Increased mid to high level clouds
may also return for Wednesday with increased winds. No
precipitation is expected at area sites. Strong cross mountain
flow could bring mountain wave turbulence at times through the
forecast period. Anglin

&&

.PREV DISCUSSION...
/ISSUED 451 PM MST Tue Jan 17 2017/

Tonight through Thursday...Seasonally mild temperatures and strong
southwest winds will prevail across North-central Montana tonight
through Wednesday. 700 mb winds peak near 60kts over the Northern
Rockies early Wednesday, but models indicate a stable surface
layer will inhibit mixing to the surface. Will continue to monitor
as we expect winds to remain near, but below high-wind criteria.
The valley temperature inversions held once again today for the
southwest, causing persistent air quality concerns. Expect one
more cold night, then cooler temperatures aloft will weaken the
inversion and allow some moderating temperatures in most, but
possibly not all of the southwest valley locations. Pacific
moisture advances up to the west side of the Continental Divide,
producing only a narrow range of snowfall mainly over backcountry
areas through the day on Wednesday. A broad synoptic scale trough
crosses the western U.S. on Thursday. Most of the energy with this
system will split into the central Rockies, spreading chances for
light snow across southwest MT on Thursday. PN

Thursday night through Tuesday...Medium range models continue to be
in good agreement for much of the forecast period but solutions
gradually diverge early next week. Period starts off with a closed
low off the Washington coast merging with a weak trough over the
Great Basin to form a broad upper level trough over the entire
western USA with above normal temperatures across north central
portions of the state returning to more seasonable averages. Core of
energy associated with the upper trough should remain well south of
Montana but occasional disturbances being ejected from the main
trough will bring some chance for precipitation to southwest Montana
and the western mountains. However, expect only a slight chance for
light rain and snow showers across the north central plains. Main
portion of the upper trough drops into the Desert Southwest and
progresses into the southern Great Plains over the weekend.
Shortwave ridging behind this trough will probably remain too weak
to significantly affect temperatures and weather in Montana but
another broad upper trough is expected to develop over the west
coast by early next week. GFS progresses this feature steadily
eastward but the ECMWF holds the trough axis back along the
California coast for an extra 24 hours before beginning eastward
progression. As a result, the ECMWF puts additional precipitation in
southwest Montana on Tuesday while the GFS remains generally dry.
mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  36  47  35  44 /   0  10   0  10
CTB  35  46  31  43 /   0  10   0  10
HLN   8  35  19  34 /   0  10   0  20
BZN   6  36  18  38 /   0  10   0  10
WEY -18  23  14  30 /   0  20  30  30
DLN  17  33  22  35 /   0  10  10  30
HVR  34  46  29  42 /   0   0   0  10
LWT  30  47  30  44 /   0  10   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls


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