Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 271742

1041 AM MST Tue Jan 27 2015

No changes needed to current forecast. One more day of very mild
temperatures and generally light winds over the plains. Sub-tropical
moisture plume still on track to impact southwest Montana later
tonight and Wednesday with some light snow.


Expect mainly VFR conditions. Exception is over far southwest
Montana where moisture will increase with snow and areas of mountain
obscurement developing mainly south of a KBZN to KDLN line. North of
that line, to a KHLN to WSS line, expect scattered snow in the
mountains with isolated rain/snow in the valleys. There will be a
threat of brief MVFR conditions should temperatures cool enough that
precipitation ends up being snow. Over central and northern Montana,
expect ceilings generally above 14000 ft with a few snow showers
possible over the mountains of the Rocky Mountain Front after


.PREV DISCUSSION...Issued 354 AM MST Tue Jan 27 2015

Update to morning forecast...Areas of freezing fog have developed in
the Centennial Valley of Beaverhead County and in the West
Yellowstone area. Have therefore added this to the forecast. Call to
West Yellowstone Police indicated that there was fog there, but it
was not significantly dense, so am not anticipating a need for a
Dense/Freezing Fog Advisory at this time. It should dissipate later
this morning after the sun rises and warms the valleys.

Today through Thursday...The upper level ridge of high pressure
that has kept the area dry and mild over the last couple of days
will begin to shift east of the area today. However, it will
linger long enough for another dry and unseasonably warm day, with
breezy westerly winds over the plains of central Montana. Despite
high cloudiness passing overhead, temperatures should warm to
about 15 to 20 degrees above normal for most areas, causing near
record high temperatures once again. An upper level trough of low
pressure will be the next feature to impact the area. It will move
across the far western United States today and through the
northern and central Rockies tonight into Wednesday morning.
However, the main energy with this trough will remain more so over
the central Rockies, bringing precipitation mainly to the western
Montana mountains and to southwest Montana. Light measurable snow
is generally expected for far southwest Montana, with 1 to 2
inches expected in the valleys along the Idaho and Wyoming borders
(including West Yellowstone) and 3 to 5 inches in the mountains.
Amounts are low enough that a Winter Weather Advisory is not
needed at this time. The main impact to the plains of north
central Montana will be to shift the breezy winds more northerly
with the passage of a weak Canadian cold front. As the trough
exits the area on Wednesday, winds will decrease and precipitation
will generally diminish and the upper ridge will rebuild over the
Pacific coast states for Wednesday into Thursday. The resulting
northwesterly flow aloft over the area will cool temperatures back
closer to normal, but they will remain about 5 to 10 degrees above
seasonal averages. Another weak disturbance in the flow will then
bring a slight chance of mountain snow to the area on Thursday.

Thursday night through Monday...Models are in agreement in
forecasting a return to colder and snowier conditions over the
weekend. The period will start off quiet with dry conditions and
relatively light downslope winds over the plains. A cold air mass
will spread southeast Friday night into Saturday and will be
accompanied by snow. The ECMWF model run is faster with the cold
air mass and snow than the GFS model run. Temperatures on the order
of 40 degrees in the early evening on Friday will fall to the
upper teens to lower 20s by early Saturday morning with
temperatures not recovering to freezing except over far southwest
Montana Saturday afternoon. Snow accumulations could range from 1
to 3 inches. Then another surge of cold air and snow will spread
south Sunday and Sunday night with the ECMWF model run again
faster than the GFS model run with the snow and cold. This latter
surge could bring an additional 1 to 3 inches of snow
accumulation. Note that timing of the snow and snow accumulations
will likely change over the course of the next few days. The
previous run of the GFS model started to moderate temperatures and
go drier early next week but the very latest run of the GFS is
more in line with the ECMWF which keeps most of the area in cold
air with periods of light snow. Blank


GTF  62  39  47  28 /   0  10  10   0
CTB  60  36  45  25 /   0  10  10   0
HLN  53  33  46  24 /   0  20  10   0
BZN  50  32  45  22 /   0  50  30  10
WEY  41  25  38  15 /  20  80  50  10
DLN  56  35  49  26 /   0  40  20  10
HVR  52  34  42  24 /   0  10  10   0
LWT  59  35  40  23 /   0  10  10   0




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