Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 310457
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1055 PM MDT Thu Oct 30 2014

Updated Aviation

...INCREASING CONFIDENCE IN SIGNIFICANT SNOWFALL FOR PORTIONS OF
NORTH CENTRAL AND SW MT THIS WEEKEND...

.UPDATE...Quiet weather conditions continue this evening as broad
high pressure ridge extends from the Four Corners area well into
northern Alberta/Saskatchewan. Widespread mid- and high-level clouds
cover most of central and southwest MT thanks to extensive Pacific
moisture coming up the west side of the ridge and ahead of a deep
low pressure trof off the PacNW coast, but not expecting any
precipitation tonight from the current cloud cover.  Going forecast
is in good shape, so only made minor adjustments to cloud cover to
better match satellite imagery and reduce temperatures a few degrees
across parts of Liberty/Hill/Blaine counties as hourly temps have
cooled quicker than forecast.
Waranauskas

&&

.DISCUSSION...

Tonight through Friday night...A strong upper ridge over central
Montana this evening will continue shifting east as southwest flow
aloft increases tonight into Friday. There will be moisture in this
flow aloft which will bring cloudiness from time to time but low
levels are expected to continue dry and so do not expect any
precipitation during the period. The only exception to this is there
is a slight chance to chance of showers over the mountains of the
Rocky Mountain Front late Friday night. For Friday have lowered some
high temperatures slightly but still expect at least a few places
will be near record high temperatures.

Saturday through Sunday night...Recent model runs have converged
on the solution that has been offered by the ECMWF model over the
last several days, bringing a closed mid/upper level trough north
across SW and Central MT Saturday night and Sunday, resulting in
widespread/locally moderate-heavy precipitation to the forecast
area. The upper level trough will be over the Great Basin area
Saturday with surface low pressure deepening through the day over
NW WY/SW MT. Showers and possibly a few isolated thunderstorms
will develop over SW MT Saturday afternoon with light
precipitation also developing by late afternoon over the Western
MT Mtns. Precipitation will become widespread Saturday night as
the upper level circulation tracks NE into the State and surface
low pressure tracks NE into eastern MT by Sunday morning. Cooling
aloft will occur in association with the upper level feature while
low level cooling moves south into North Central MT in response to
the surface low development. This will allow snow levels to lower
throughout Saturday night, likely to as low as 3000 feet by Sunday
morning. Heaviest precipitation looks to be focused over areas
along and west of I-15 with 5-10 inches possible at and above pass
levels along the Continental Divide. Snow amounts are trickier
further east and at lower elevations with a transition to snow
occurring over western portions of the North Central MT Plains
earlier than locations further east at some point Saturday night and
in the valleys of SW MT Sunday morning. Timing of this transition
will have a large role in accumulations for the Plains and Valleys
just east of I-15. Will issue a Winter Storm Watch to highlight
potentially hazardous travel over mtn passes as well as possible
accumulating snow at lower elevations Saturday night and Sunday with
further refinements of the Winter Weather Highlight as details
relating to timing of the transition to snow become clearer. Hoenisch

Monday through Thursday...The weekend storm system moves quick,
exiting east Monday, but some lingering precipitation may be seen
over the mountains. High pressure transits over the region Tuesday
night before unsettled westerly flow brings a chance of
precipitation back to the Continental Divide Wednesday which
continues through Thursday. High temperatures will be mostly in the
40s Monday before warming back to near 60 by Thursday.

&&

.AVIATION...
UPDATED 0500Z.
Despite an upper-level ridge that is moving over the region,
upper-level moisture will keep broken mid- and high-level clouds
across the area. Some clearing is expected after 06z, but scattered
to broken high clouds will likely persist through Friday.
East-southeasterly winds will be less than 10 kts tonight, then
shift south-southwest on Friday. The exception is at KHVR where
easterly winds 15 to 20 kts will persist. Overall, VFR conditions
are expected for the next 24 hours. MLV

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  71  39  55 /   0   0   0  10
CTB  35  64  35  50 /   0   0   0  40
HLN  39  67  39  58 /   0   0   0  30
BZN  31  67  32  64 /   0   0   0  20
WEY  26  57  25  53 /   0   0   0  40
DLN  37  67  37  60 /   0   0   0  30
HVR  34  58  34  58 /   0   0   0   0
LWT  38  69  40  62 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday evening
Beaverhead...Broadwater...Cascade...Central and Southern Lewis
and Clark...Chouteau...Eastern Glacier...Eastern Pondera...
Eastern Teton...Gallatin...Hill...Jefferson...Judith Basin...
Liberty...Madison...Meagher...Northern Rocky Mountain Front...
Southern Rocky Mountain Front...Toole.

&&

$$

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