Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 010458
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1055 PM MDT Fri Oct 31 2014

Updated Aviation

.UPDATE...
Quiet weather conditions across the region this evening with mostly
clear skies along and west of the Interstate 15 corridor and a
departing swath of mid-level clouds along/east of a Havre-to-
Bozeman line. Not much change expected overnight as we await the
arrival of a potent Pacific weather system that will bring in early
winter conditions beginning Sat eve.  Current forecast still good
for gradually increasing clouds over the Rocky Mtn Front and far
southwest mountains by sunrise, with some spotty valley rain/mtn
snow showers developing there around mid-morning, while rest of the
forecast area remains dry. Only adjustments of note this evening
were to reduce sky cover between now and midnight to better match
current satellite imagery.
Waranauskas

&&

.DISCUSSION...
This Afternoon through Sunday Evening...Warm south-southwesterly
flow at the surface and aloft producing dry and unseasonably warm
conditions this afternoon with high temperatures ranging from the
mid 50s to the low 70s. The pleasant conditions will continue this
evening with no weather impacts expected for any Halloween or
outdoor events.  However, change is on the way beginning tomorrow,
and forecast is still on track for the arrival of early winter
conditions late Sat night through Sun eve. The deep upper-level trof
that will bring the cold temps and snow is currently centered just
off the PacNW coast, with its associated cold front now moving
through western WA/OR.  Forecast models maintained good agreement
and consistency on the upper trof making steady eastward progress
with its leading edge reaching western MT by early Sat morning.  The
surface cold front should cross east of the Continental Divide
around midday Sat and push across the central and southwest MT
during the aftn/early eve. Scattered rain showers are expected
with frontal passage, with a slight chance for a few short-lived
thunderstorms over parts of the southwest counties in the aftn.
Temperatures will fall steadily Sat night, with rain changing over
to snow by early evening in the mountains, but the valleys and
plains will likely stay well above freezing for much of the Sat
overnight period, resulting in mostly rain or rain/snow mix there.

By Sun morning, the colder airmass will settle across the region,
pushing temps close to/slightly below freezing, setting up the
possibility of accumulating snow at the lower elevations.  However,
models continue to focus most of the heaviest precipitation along
the Continental Divide with 6-12 inches of snow expected for the
Rocky Mtn Front and adjacent plains.  Lighter amounts will occur
over the central plains (1-4 inches of snow) and central mtn ranges
(3-6 inches of snow), with the absence of sharply colder air and
relatively warm ground temps still creating some uncertainty as
to whether and how much snow will actually accumulate in the lower
elevations.  For now, the winter storm watch remains in effect for
all counties in the Great Falls forecast area, except for Blaine and
Fergus, beginning at 6pm Sat eve.  The trof axis and surface low
pressure center should move through our region by late Sun aftn,
bringing a gradual end to the snow from west-to-east through Sun eve.
Waranauskas

Sunday Night through Friday...With the weekend storm exiting the
area to the east Sunday night, snow showers will decrease from west
to east across the area. A more progressive westerly flow aloft will
then develop for the workweek, providing a more windy pattern with
precipitation mostly falling in the mountains with passing
disturbances. Models are in good agreement with bringing a shortwave
trough through the area Monday night into Tuesday. As mentioned, the
best chance for precipitation will remain in the mountains,
especially along the Rocky Mountain Front, while potentially strong
west winds spread out over the North Central Montana plains. High
Wind highlights may be needed, especially along the Rocky Mountain
Front. A weak upper level high pressure ridge will build into the
area on Wednesday, bringing the possibility of locally strong winds
to the Rocky Mountain Front once again. Moisture will move through
this weak ridging, which will bring a chance of showers to the
mountains and a lesser chance of showers to the plains. Another
shortwave trough will move through the area on Thursday, again
bringing the potential for strong winds to the Rocky Mountain Front.
However, the GFS (yes) and ECMWF (no) models do not agree on this,
so there is some uncertainty here. The chance for showers will
increase in the wake of this disturbance Thursday night into Friday
as the flow aloft shifts more northwesterly. Temperatures will be
about 5 degrees below normal to begin the week, but they will warm
to between 5 and 10 degrees above normal for Monday night through
Friday due to the persistent westerly downsloping winds.
Coulston

&&

.AVIATION...
UPDATED 0500Z.
Quiet conditions are expected overnight, however mid and upper-level
clouds will increase by Saturday morning as a potent Pacific trough
of low pressure progresses into the Northern Rockies. This trough
will continue to deepen and push a cold front through Montana on
Saturday. This front will cross the Continental Divide early
Saturday afternoon and reach eastern Montana by late Saturday
evening. Surface winds will shift northerly with precipitation
developing from northwest to southeast. Mountains will become
obscured along the Continental Divide by midday Saturday with
showers developing. At most of the terminals, VFR conditions are
expected through 00z Sunday with rain showers developing after 22z.
An isolated thunderstorm is also possible. At KCTB, MVFR conditions
are possible after 20z Saturday as rain begins to mix with snow.
Precipitation will continue to increase in coverage with lowering
cigs/vis after 06z Sunday as a colder airmass moves over
the region. MLV

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  56  31  38 /   0  10 100 100
CTB  34  45  29  38 /   0  20 100 100
HLN  41  61  35  44 /   0  20 100 100
BZN  35  63  33  46 /   0  20  80  80
WEY  26  54  28  36 /   0  50  80  80
DLN  40  61  34  45 /   0  20  90  60
HVR  32  55  33  40 /   0   0  80 100
LWT  41  66  33  41 /   0  10  80 100

&&

.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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