Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211026
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
326 AM 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...

Today through Wednesday...A high pressure ridge aloft will build
over our area today through Wednesday and become unusually-strong.
However, a Pacific weather disturbance traversing this ridge will
cross our region this evening through early Wednesday morning.
Enhanced westerly flow aloft accompanying this disturbance will
contribute to a favorable environment for a downslope windstorm
along/near the Rocky Mountain Front. Thus, issued a high wind
warning for the Rocky Mountain Front and eastern Glacier County from
5 PM this evening until 11 AM MST Wednesday. Winds are expected to
become breezy elsewhere, especially tonight into Wednesday. In
addition, the approach of the aforementioned disturbance will cause
a stationary front along the Rocky Mountain Front and Central MT
mountains to advance northeastward as a warm front in North-Central
MT late this afternoon through early Wednesday morning.

Periods of upslope precipitation are expected along the Continental
Divide and the mountains of Central/Southwest MT. Elsewhere,
scattered rain and/or snow showers are possible late this afternoon
into Wednesday morning, with the approach/passage of the weather
disturbance and/or warm front. In addition, an elevated melting
layer may promote a period of light freezing rain along portions
of the Hi-Line prior to the passage of the warm front. Today`s
highs will be several degrees on either side of normal, while
Wednesday will have above-normal low and high temperatures. In
fact, Wednesday`s highs will be about 15-25 degrees above-normal.

Wednesday night through Thanksgiving...The aforementioned high
pressure ridge aloft will begin to be broken-down by multiple
Pacific weather disturbances during this period. Winds will remain
breezy and additional high wind highlights may be necessary,
especially along the Rocky Mountain Front. Periods of upslope
precipitation will persist along the divide, while the remainder of
the CWA will likely remain dry due to the Chinook effect.
Temperatures will remain abnormally-warm and some record highs may
be challenged on Thanksgiving.
Jaszka

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 0536Z.

A SE`ward-moving disturbance over the area should exit North-Central
and Southwest MT by 12Z/Tue. This disturbance will be accompanied by
scattered pockets of precipitation. Over North-Central MT, mainly
snow is expected, but some freezing drizzle cannot be ruled-out
completely. In Southwest MT, occasional light rain and/or snow is
expected. CIGS and VSBY will tend to be in the VFR to IFR range, but
could occasionally be lower in steadier snow. Conditions will
improve, overall, by around 12Z/Tue as high pressure aloft builds-in
behind the departing disturbance. However, CIGS will lower and
precipitation chances will increase after 00Z/Wed as another Pacific
disturbance nears the Continental Divide by 06Z/Wed. Periods of
mountain obscuration are also expected.
Jaszka

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  44  41  62  48 /  20  20  10  10
CTB  35  34  57  44 /  20  20   0  10
HLN  44  36  55  37 /  10  20  10  10
BZN  43  37  54  35 /  20  30  10  10
WEY  36  30  41  31 /  30  40  40  20
DLN  48  37  56  36 /  20  20  10  10
HVR  32  27  58  41 /   0  20  10  10
LWT  41  38  60  44 /  20  20  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 5 PM this afternoon to 11 AM MST
Wednesday Eastern Glacier...Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

&&

$$

http://www.weather.gov/greatfalls



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