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000
FXUS65 KTFX 040516
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1015 PM MST Tue Dec 3 2013

.UPDATE...
Updated forecast is out. Widespread heavy snowfall has ended
across the region...as the main storm system pulls into the upper
Midwest. However...a weak upper level disturbance continues to
move southward through the region. This disturbance is producing a
fairly large area of very light snowfall over North Central MT.
(Over Southwest MT...little to no snowfall is expected the rest of
tonight.) Snowfall rates are only near 0.1 inches an hour this
evening...with radar reflectivity generally less than 10dbz. With
the best snow growth potential generally within 1000 feet
AGL...not expecting a good snow producing event from this upper
level disturbance. Thus an additional inch of snowfall is possible
from 8 PM tonight through about 8 AM or so on Wednesday morning.
At this time we will not extended the winter storm warning and no
snow advisory is being issued. Again...other than a passing snow
shower in Southwest MT...most of the Southwest will remain dry
overnight. Overnight lows look on track...but did warm
temperatures up a few degrees in the Cut Bank area...as more
clouds will stay in this region.

The only other change was to add a wind chill advisory for areas
along Highway 2 from Browning to Harlem...as wind chills are
running near 20 below. These wind chills will remain that low
through tonight and tomorrow...and could actually fall to near 30
below on Wednesday afternoon as winds increase a bit. Brusda

&&

.AVIATION...
UPDATED 0514Z.
A deep upper level low pressure trof will remain over the region
through Wednesday night. Cold Canadian air will continue to move
south into central Montana and cause light snow and lowered cigs and
vsbys. Widespread MVFR/IFR conditions will continue into Wednesday
morning. Conditions will slowly improve will most areas returning to
VFR conditions by Wednesday noon.

&&

.PREV DISCUSSION...
/ISSUED 408 PM MST Tue Dec 3 2013/

Tonight through Wednesday Night...Broad upper level low continues to
drift slowly through Southwest Montana. Cyclonic flow around this
low has produced northeasterly flow overrunning colder air
concentrated along and east of the continental divide. This lift
is strongest from around 750 to 650 mb and enhanced locally by
orographic lift on north and east facing slopes. Snowfall amounts
have been light as the snow growth layer is colder than -20C.
Drier air will continue to deepen and a mid-level wind shift to
more northerly will end precipitation overnight. Up to an
additional half to one inch of snow may be possible for central
Montana. At the surface, the rate of pressure rises have slowed,
so anticipate a gradually slackening of winds. Wind chill concerns
have been expressed in the Winter Weather Warning. With both
snowfall and winds decreasing, the forecast package is on track to
routinely expire the Winter Weather highlights at 06Z tonight.
However, areas of light snow flurry activity will persist into mid
day Wednesday and we will continue to monitor for any wind chill
criteria. Temperatures have held nearly steady today and are
expected to drop into the single digits below zero tonight. Nutter

Thursday through Tuesday...See no changes to the basic pattern of
an upper ridge from off the west coast to the Gulf of Alaska and
an upper trough over western or central U.S. at least into the
weekend. The northerly flow aloft over southwest through
north central Montana will keep very cold air over the area at
least into the early part of the weekend. Expect the lower
elevations to remain mostly dry through Saturday with isolated to
scattered snow showers over the mountains. A Canadian weather
system is expected to bring increasing moisture later in the
weekend and have increased the chances of snow but not gone too
high as models differ on timing and placement of the snow. Models
differ with surface features and associated temperatures late in
the weekend and early next week as some guidance develops
downslope winds and moderating temperatures while other guidance
continues cold temperatures and upslope flow. Differences in
forecast temperatures become huge by Tuesday with highs ranging
from the 30s to highs below zero. Since do not have a strong
feeling on which way to go have gone in between the two extremes.
Blank

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  -5   2 -17   1 / 100  40  10  10
CTB  -5   0 -25  -4 / 100  30  10  10
HLN  -4   3 -15   3 /  20  40  10  10
BZN  -9   3 -18   1 /  40  40  20  10
WEY -17   2 -20   2 /  30  20  10  10
DLN  -9   4 -13   4 /  20  20  10  10
HVR  -5   2 -24  -8 / 100  30  10  10
LWT  -7   0 -19  -2 / 100  40  20  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY until 5 PM MST Wednesday Blaine...Eastern
Glacier...Eastern Pondera...Hill...Liberty...Northern Rocky
Mountain Front...Toole.

&&

$$

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