High Wind in Montana, December 20, 2018

Area Forecast Discussion
National Weather Service Great Falls MT
931 AM MST Thu Dec 20 2018

.UPDATE...

Gusty winds dominate the weather story for our area today. Forecast
remains accurate, with only minor changes made to temperatures to
better fit observed trends. No further updates will be made, at this
time.
- Fogleman

&&

.SYNOPSIS...

High pressure moves across the Northern Rockies and Montana today
for generally dry conditions. The next Pacific frontal system moves
inland tonight and rapidly east across Montana Friday morning. Snow
will develop tonight over western Montana with a period of snow also
possible across southwest Montana early Friday morning. Strong winds
will accompany this storm system over areas along the east slopes of
the Rockies tonight and portions of central Montana Friday
morning.

&&

.AVIATION...
Updated 1200Z.

VFR conditions prevail through this evening as an upper level ridge
moves across the region. A gradual increase in moisture aloft will
bring broken high level cloud-cover with clouds and precipitation
increasing along the continental divide late this evening. Strong
winds, Mtn wave turbulence and low level wind shear will re-develop
over western portions of North central MT late this afternoon and
evening as the next Pacific storm system moves into the Pacific NW.
The frontal system sweeps east across north-central and SW MT Friday
morning with a period of strong winds possible across central MT and
period of snow and MVFR conditions across SW MT including the KBZN
terminal.  Hoenisch

&&

.PREV DISCUSSION...
/ISSUED 421 AM MST Thu Dec 20 2018/

Today through Saturday...an upper level ridge drifts east across
the region today before the next incoming upper level trough from
the NE Pacific moves inland tonight and very quickly east across
MT Friday. Strengthening SW cross-barrier flow ahead of the trough
and a deepening surface trough to the east of the Rockies will
support strong wind development along the immediate east slopes of
the Rocky Mtn front by late this afternoon and the High Wind
Watch is upgraded to warning with earlier start time there as well
as further east across Glacier county. Models still depict a
period of strong westerly flow as the mid level shortwave and
surface trough/front shift across central MT Friday morning, which
would support some marginal strong wind gusts, especially across
some of the favorable areas for wind enhancement east of Rogers
Pass and NE of the Little Belts in Judith Basin county where a
High Wind Watch has been issued for Friday morning. Snow develops
this evening along the continental divide west of the Rocky Mtn
Front with a period of snow likely to accompany the frontal
passage through SW MT early Friday morning. Generally looking at
about 1-4" of snow accumulation primarily in the Mtns with this
quick moving system. One area of concern however is the Bozeman
area, where the timing of the frontal passage could bring a quick
burst of snow during the Friday AM commute period. Drier
conditions develop in NW flow aloft behind the front Friday
afternoon and continue through Saturday. Temperatures will range
from around 15 degrees above seasonal averages today then cool to
just slightly above average by Saturday. Hoenisch

Saturday night through Thursday...The progressive pattern that we
have been in for the past week or so looks to continue through
the middle of next week. This ongoing pattern of shortwave troughs
followed by shortwave ridges will continue to shift the weather
regimes from wet and windy weather, to mild and dry weather on and
off through next week. An upper level trough over the forecast
area Saturday will track eastward through Saturday night, with
some brief ridging moving over the area during the overnight
hours. By Sunday morning, this ridge of high pressure will
quickly decay as another shortwave trough approaches from the west
and brings another round of precipitation and gusty winds along
with it. As that system dissipates over the area Sunday night,
another series of waves will track across the area Monday morning
through Thursday. There remains some uncertainty as to the track
of these wave and their exact impacts to specific areas given
continued model differences and changing trends. For instance,
previous models were showing an increased likelihood for rain and
snow for the Tuesday into Wednesday timeframe. However, now it is
trending slightly drier and warmer. Models are still showing a
small chance of lingering snow showers as colder air feeds in from
the North/Northwest Tuesday night into Wednesday morning, but
given the trend, confidence is lower than normal.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  33  42  23 /   0   0  10   0
CTB  47  30  39  19 /   0  10  10  10
HLN  45  28  38  19 /   0  30  30   0
BZN  43  24  38  13 /   0  20  70   0
WEY  31  15  30   4 /  10  60 100  10
DLN  41  24  35  10 /   0  30  60   0
HVR  47  31  43  20 /   0   0  20  10
LWT  47  30  40  19 /   0  20  20   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 3 PM this afternoon to 11 AM MST Friday
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

High Wind Watch from late tonight through Friday morning
Cascade...Central and Southern Lewis and Clark...Judith Basin.

High Wind Warning from 8 PM this evening to 11 AM MST Friday
Eastern Glacier.

&&

http://www.weather.gov/greatfalls