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000
FXUS65 KTFX 010410
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
910 PM MST Sat Nov 30 2013

.UPDATE...Forecast area will remain beneath an unsettled
northwesterly flow aloft overnight. Radar is currently quiet but
moisture will advect into the region by midnight with scattered to
numerous showers developing over the mountains. Current forecast
appears to handle this well and will allow pops, weather and wind
forecast to remain as-is. Temperatures, however, have been slow to
fall and a few locations have even bumped up a few degrees as
downslope westerly winds combine with cloud cover to prevent
cooling. Have updated overnight lows to increase them several
degrees in many locations, especially across Central Montana. mpj

&&

.AVIATION...
UPDATED 0000Z.
Expect VFR conditions through early evening as BKN-OVC mid-level
ceilings (5000-10000 ft) move in across the Rocky Mountains. Leading
edge of moisture from a strong low pressure system near the Gulf of
Alaska expected to arrive later this evening with scattered -RASN
developing mainly along/south of a line from KHLN to KLWT. At the
far end of the TAF period expect ceilings to begin to fall with
showers and terrain obscuration entering the region. West to
southwest winds will generally be light until after 15Z.

&&

.PREV DISCUSSION...
/ISSUED 500 PM MST Sat Nov 30 2013/

Satellite imagery this afternoon reveals the main upper level
features that will be responsible for a major pattern change over
the Northern Rockies and MT next week. This includes a high over
low block near the Aleutians with a deepening upper low over the
Yukon beginning to dig southeastward with a strong upper let and
moisture plume to its south in the Eastern Pacific. The Yukon
upper low will dig south along the BC coast through the next 24
hrs while the Pacific moisture plume and jet nose onshore later
tonight and tomorrow. Clouds will increase across the area tonight
with precipitation increasing along the Continental Divide. Some of
the moisture may spill east of the divide into central central MT
on Sunday, but downslope westerly flow will limit its coverage and
amounts. Winds aloft steadily strengthen through the day Sunday
flow is squeezed between the descending upper low along the west
coast and an upper  level ridge to its southwest. By Saturday
afternoon, expect locally strong winds to develop over western and
central zones in response to the increasing winds aloft and
surface low development to the lee of the Rockies. Strong winds
look to continue through early Monday afternoon. Hoenisch

Monday through Saturday...Primary focus for this period continues to
be centered on the high confidence pattern change toward much colder
temperatures and snowfall potential. Overnight guidance has trended
a bit faster with the cold frontal passage on Monday. Both the
deterministic GFS and EC depict the cold front crossing the
US/Canada border around/shortly after 12z with the arctic air mass
settling in over the entire forecast area by around 06z Tuesday. As
a result...temperatures on Tuesday will likely rise only a few
degrees from the overnight lows. Frigid temps will remain firmly
entrenched through the end of the forecast period with highs
remaining in the single digits for most locations.

As for snowfall outside the watch areas...there is still some
uncertainty with regard to snow accumulation on the plains.
Highest confidence period for snowfall over the plains is from
Monday night into Tuesday morning. Appears at least a couple of
inches will be possible but the potential exists for higher
amounts. Could see a period of gusty winds accompanying the snow
which could result in significant reductions in visibility and
poor travel conditions. Will need to continue to monitor the
latest information and fine tune the forecast for anticipated
impacts. Foltz/Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  35  51  36  42 /  10  30  30  70
CTB  31  45  28  29 /  10  10  30  80
HLN  34  46  38  45 /  20  40  50  70
BZN  28  46  33  46 /  30  30  40  60
WEY  20  32  24  32 /  70  80  80  90
DLN  30  45  35  44 /  20  20  40  50
HVR  30  44  27  36 /  10  30  60  60
LWT  31  49  35  44 /  10  30  50  70

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING until 5 PM MST Tuesday FOR ELEVATIONS ABOVE
5000 FEET FOR Central and Southern Lewis and Clark...Northern
Rocky Mountain Front...Southern Rocky Mountain Front.

HIGH WIND WATCH from Sunday afternoon through Monday morning
Broadwater...Cascade...Central and Southern Lewis and Clark...
Eastern Glacier...Jefferson...Judith Basin...Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

WINTER STORM WATCH from Sunday morning through Tuesday afternoon
FOR ELEVATIONS ABOVE 6500 FEET FOR Beaverhead...Broadwater...
Cascade...Gallatin...Jefferson...Judith Basin...Madison...
Meagher.

&&

$$


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