Area Forecast Discussion
Issued by NWS Great Falls, MT
FXUS65 KTFX 071125
Area Forecast Discussion
National Weather Service Great Falls MT
425 AM MST Wed Dec 7 2016
...AVIATION SECTION UPDATED...
Today through Friday...Northwesterly mid- to upper-level flow and
the arctic surface high pressure ridge should continue to persist
over the CWA through Thursday morning. A shortwave trough embedded
within the flow aloft will move southeastward during the course of
the day today. Lift and limited moisture ahead of this disturbance
should result in nothing more than scattered snow flurries and a
dusting of snow accumulation across the region. By Thursday
afternoon, still expect diffluent southwesterly flow aloft and
associated lift ahead of a low- to midlevel shortwave trough
approaching from the Pac NW to allow surface pressure falls to
commence over the CWA. In addition, model data are now in better
agreement that a surface warm front accompanying the disturbance
will advance northward into Southwest MT and near the I-90
corridor by Thursday evening. This pattern looks favorable for
isentropic lift of the aforementioned southwesterly flow of warm,
moist air to occur over the arctic air mass remaining over most of
the area, ahead of the front. The pattern will set the stage for a
widespread snowfall, especially Thursday night into early Friday
By daybreak Friday, snow looks to become more scattered over the CWA
as the aforementioned disturbance weakens while moving farther
eastward and flow aloft becomes more zonal due to a rather flat
mid- to upper-level high pressure ridge building-in from the Pac
NW. This shift in the flow aloft will cause isentropic lift to end
over our area. Thus, during the day on Friday, upslope flow looks
to become the main trigger for snow. On Friday, the aforementioned
warm front looks to move farther north toward the Central MT
mountains. With southerly surface flow south of the front and
easterly to northeasterly flow ahead of it, places such as the
south aspects of Southwest MT mountains and the north/east
aspects of the Rocky Mountain Front, Little Belts, and Big Snowy
Mountains will likely experience upslope snow showers. Winter
weather highlights may be needed for at least a portion of the CWA
for Thursday into Friday, but will wait for more model guidance
before issuing any highlights.
As for temperatures, low and high temperatures will be about 20 to
35 degrees below normal today through Thursday. Thursday morning
still looks to be the coldest for many places due to mainly clear to
partly cloudy skies. Thus, the wind chill advisory will remain in
effect for the entire CWA through at least noon today and will
likely be extended with the forecast update later this morning. By
Thursday night and Friday, the aforementioned warm front will
cause a more marked variation in temperatures. South of the front,
many places in Southwest MT will have lows in the 5 to 15 degree
range Thursday night and highs in the lower 20`s to mid 30`s for
Friday. North of the front, most places in North-Central MT will
experience lows in the range of 0 to -10 degrees Thursday night
and highs in the single digits or teens on Friday.
Friday Night through Tuesday...An upper level low pressure
shortwave will move over the West Coast Friday night and moisture
ahead of this system will be crossing the Rockies. A surface front
will lay across the zones with the result that the northern zones
will be very cold while the southwest zones will be closer to
normals. The shortwave will cross the Rockies early Saturday and
continue east across the zones. Brisk west winds aloft will keep
the chance of snow mainly over the higher terrain, and especially
along the Divide. The northern tier, especially the northeast
zones, will receive the least accumulation. High pressure will
build Saturday night, the air mass will dry and also begin to
trend warmer. However, the northwest flow aloft will be quite
unsettled and snow showers will remain in the forecast. A
shortwave in Alberta will move southeast Sunday towards the
Dakotas. This will will not bring much change in the chance for
precipitation but it will bring another cold front across the
Canadian border. Temperatures Sunday will again struggle to move
above zero across the Hiline and above single digits across the
central zones. Currently, the coldest air is forecast to slide
east of the zones...but a slight change in position would cause
very cold temperatures over the eastern zones.
Widespread cloud cover will dissipate as high pressure builds over
Central and Southwest Montana. Local MVFR CIGS are expected until
18z with VFR conditions prevailing afterwards. Surface high pressure
will continue to keep surface winds light through Thursday.
.PRELIMINARY POINT TEMPS/POPS...
GTF -1 -12 1 -3 / 10 10 10 50
CTB -2 -15 -4 -9 / 10 10 10 40
HLN 7 -9 14 8 / 10 10 10 50
BZN 8 -10 15 12 / 10 10 10 40
WEY 10 -14 13 9 / 10 10 10 50
DLN 11 -7 16 14 / 10 10 20 50
HVR 0 -11 -1 -4 / 10 10 10 30
LWT -1 -12 4 -1 / 10 10 10 40
Wind Chill Advisory until noon MST today Blaine...Broadwater...
Cascade...Central and Southern Lewis and Clark...Chouteau...
Eastern Teton...Fergus...Hill...Jefferson...Judith Basin...
Meagher...Southern Rocky Mountain Front.
Wind Chill Advisory until noon MST today Eastern Glacier...
Eastern Pondera...Liberty...Northern Rocky Mountain Front...
Wind Chill Advisory until noon MST today Beaverhead...Gallatin...