Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 212151
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
251 PM MST Tue Nov 21 2017

.SYNOPSIS...

A front draped across the Rocky Mountain Front and Central MT
mountains will advance northeastward as a warm front late this
afternoon through early Wednesday morning. In addition, a Pacific
weather disturbance will traverse the region this evening through
Wednesday morning. The result will be mixed precipitation across
the region and strong downslope winds along and near the Rocky
Mountain Front this evening into Wednesday morning. The rest of
Wednesday will feature breezy winds, very mild temperatures, and
dry weather over most of the region.

&&

.DISCUSSION...

Tonight through Thanksgiving Day...Warm front is starting to lift
across the region bringing increased cloud cover and warming
temperatures. Models indicate precipitation is still possible
along and ahead of this front this evening into tomorrow morning.
Areas along the Hi-Line that are slow to warm may see freezing
rain at times with precipitation from this warm front, while most
other areas will see rain or higher elevation snow. Meanwhile an
strengthening jet and weak disturbance in a flattening ridge will
increase southwesterly winds this evening into Wednesday morning.
Low end High Wind Warning criteria may still be met across the
Rocky Mountain Front and adjacent high plains. Thus have left the
High Wind Warning as is. Warm frontal precip will generally
diminish overnight tonight. Wednesday will see chances for rain
and snow linger across the western mountains and portions of the
southwest, while breezy and mainly dry conditions will be found
elsewhere. Thanksgiving Day will also be mainly dry conditions to
start, although rain and high elevation snow may linger across the
Rocky Mountain Front perhaps impacting those traveling across
Marias Pass. An approaching trough and cold front will also
sharpen the pressure gradient on Thursday, bringing the potential
for very strong winds. With 700 mb winds approaching 70 knots,
most areas across the central and northern portion of the CWA may
see High Wind Criteria. A watch may be needed after the current
warning expires tomorrow morning. With all this wind will come
warming temperatures. Wednesday will see highs in the 50s to near
60 while Thursday sees potentially record setting highs in the
60s. Anglin

Thursday night through Tuesday...An amplified but progressive flow
pattern persists across the region late this week into early next
week with general upper level ridging over the western US,
occasionally broken down by passing upper troughs Thursday night and
again Mon/Tues of next week. Upper trough passing through the region
Thursday night will be accompanied by strong mid level flow aloft
along with a NW to SE Pacific frontal passage. Strong wind potential
will exist across much of the forecast area Thursday night as a
fairly large area of 60-80kt winds at 700MB spreads east across
north-central and SW MT with some recent model data suggesting a
belt of 80kt+ winds possible within this layer over north-central
MT. This combined with the shortwave and frontal passage creates a
favorable setup for strong winds to impact a fairly large portion of
the forecast area Thursday night, including southwest MT (vs
strongest winds typically confined to areas only along the east
slopes of the Rockies). Precipitation will also increase Thursday
night along the continental divide with a period of precipitation
likely to accompany the frontal passage through central and SW MT
Thursday night. Snow levels initially above pass levels will lower
with the frontal passage Thursday night, but may not lower all the
way to valley bottoms. Cooler but still above average temperatures
follow on Friday with upper level ridging building over the region
through the weekend for temperatures warming back to well above
seasonal averages again by Sunday. The next Pacific trough and
associated cold front are expected to sweep east across the area on
Monday with some model spread yet with regard to timing and depth of
this wave. In any case, a period of stronger winds and at least
scattered precipitation will accompany the passage of this
system on Monday followed by cooler conditions.
Hoenisch

&&

.AVIATION...
Updated 1800Z.

Patchy fog and low ceilings may linger across the KCTB area this
morning into the early afternoon...producing some LIFR to IFR
conditions. VFR conditions will be found across the remainder of
the area through the mid afternoon hours. A warm front will then
bring increase clouds and chances for rain showers later this
afternoon through the evening hours. Most sites could see at least
a brief rain shower...possibly bringing some MVFR conditions at
times. The colder sites may also see snow or freezing rain mix in
at times...mainly from about KGTF northward to KHVR. Precip
chances diminish tonight. Westerly winds will then increase for
most sites for Wednesday...with some low MVFR to IFR morning
clouds possible across the KHLN area. Anglin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  59  48  64 /  30  10  10  10
CTB  32  54  43  61 /  20  10  10  20
HLN  38  53  36  59 /  20  10  10  10
BZN  38  52  35  57 /  30  20  10  10
WEY  32  41  32  43 /  40  40  20  20
DLN  38  56  37  57 /  20  20  10  10
HVR  25  56  41  66 /  20  10  10   0
LWT  37  59  45  65 /  20  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 11 AM MST Wednesday Eastern Glacier...
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

$$

http://www.weather.gov/greatfalls



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