Area Forecast Discussion
Issued by NWS Great Falls, MT
FXUS65 KTFX 061133
Area Forecast Discussion
National Weather Service Great Falls MT
435 AM MST Tue Dec 6 2016
...AVIATION SECTION UPDATED...
Today through Thursday...Flow aloft will tend northwesterly over our
CWA through Thursday morning as a mid- to upper-level low,
associated with the arctic air mass, meanders over northern and
central SK. A shortwave trough embedded within this flow will move
generally southeastward from southern BC and the Pac NW this morning
to WY by late tomorrow morning. Lift and moisture ahead of this
shortwave will result in the development of scattered snow showers,
mainly over Southwest MT, today into early Wednesday morning.
Behind this disturbance, a few more shortwave troughs embedded
within the northwesterly flow aloft will move over our area later
Wednesday through Thursday morning. However, limited moisture
looks to result in little or no snow accompanying the passages of
these additional disturbances. At the surface, an arctic high
pressure ridge will persist over North-Central and Southwest MT
through Thursday morning. By Thursday afternoon, diffluent
southwesterly flow aloft and associated lift ahead of a low- to
midlevel shortwave trough approaching from the Pac NW should allow
surface pressure falls to commence over the CWA. In addition,
scattered snow showers will likely begin overspreading the area.
In terms of snow amounts, fresh snow accumulations of about 1-4
inches are expected along the Continental Divide and most
Southwest MT mountains today through Thursday, while the plains
and valleys will have little or no snow accumulation.
During the period, temperatures will be about 20-30 degrees below
normal and many locations will have subzero lows this morning
through Thursday morning. In addition, Thursday morning may be the
coldest due to the potential of mainly clear to partly cloudy skies
over most of the CWA. However, record lows are not expected to be
broken, especially this morning and Wednesday morning, due to
extensive cloud cover. As for the current wind chill advisory, will
keep it going as some locations, particularly those along the Rocky
Mountain Front, Bears Paw Mountains, and in Blaine County will have
wind chills reach or dip below the threshold of -20F. Will let the
day shift re-evaluate these highlights for any necessary extensions.
Thursday night through Monday...A high pressure ridge over Central
and Southwest Montana will be flattened Thursday night as a low
pressure trof moves over the West Coast. Moisture ahead of this trof
will cross the Rockies and bring cloudy skies with increased chances
of precipitation. Snow accumulations will mainly be over the western
mountains. Weak high pressure will build again Friday but another
disturbance moving through the flow aloft from the west will
increase the chances of snow again Friday night and Saturday. As
this trof crosses the zones, the associated cold front will bring
another push of cold air into the region. This will keep
temperatures, especially across the northern tier, well below
normals Saturday and Sunday. Weak high pressure will build again
Saturday night and most snow will be limited to higher elevations.
However, another shortwave will be upstream and periods of light
snow will continue Sunday night through the end of the period. Cold
temperatures will continue through the extended forecast period,
especially across the northern half of the forecast area where
temperatures will generally remain 15 to 20 degrees below normals.
Southwest Montana will not be affected as much by the Canadian
air and temperatures will push upwards towards normals.
Cold upper level trough will remain over the region for moist
northwest flow aloft. Occasional flurries and areas of light snow
will cause MVFR/IFR conditions at times. Generally light west to
northwest winds expected to prevail through the forecast period. mpj
.PRELIMINARY POINT TEMPS/POPS...
GTF 1 -14 2 -11 / 10 10 10 10
CTB -1 -14 -1 -15 / 10 10 10 10
HLN 7 -7 11 1 / 10 10 10 10
BZN 14 -11 9 0 / 20 20 10 10
WEY 12 -17 8 -8 / 20 20 10 10
DLN 12 -7 11 -1 / 20 20 10 0
HVR 3 -3 3 -8 / 10 10 10 10
LWT 2 -9 1 -7 / 10 10 10 10
Wind Chill Advisory until 5 PM MST this afternoon Eastern
Glacier...Eastern Pondera...Liberty...Northern Rocky Mountain
Wind Chill Advisory until noon MST today Blaine...Cascade...
Central and Southern Lewis and Clark...Chouteau...Eastern
Teton...Fergus...Hill...Judith Basin...Meagher...Southern Rocky