Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 080535
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1030 PM MST Wed Dec 7 2016

AVIATION SECTION UPDATED

.UPDATE...

IR satellite imagery shows a stubborn low/mid level stratus deck
remains over parts of central/SW MT (roughly from Great Falls to
Lewistown south through Helena and Bozeman). It is unclear how
quickly these clouds will move out, if at all, as some models keep
the clouds around through the night. This cloud deck appears to
be preventing temperatures from falling as quick beneath it
compared to areas with less cloudcover. Note Cut Bank with less
cloudcover is already down to -12 as of 9pm while Helena and Great
Falls are at 5 and 1, respectively. For this reason, raised
overnight lows beneath the clouds just a bit. Still, a bitterly
cold night is expected areawide. Lastly, added scattered flurries
to parts of central/SW MT beneath the stratus deck where it has
been lightly snowing since this afternoon. However, only dusting
level accumulations, if that, are expected overnight. Martin

&&

.AVIATION...Updated 0530Z.
VFR conditions expected overnight and through Thurs as weak high
pressure ridging moves into central MT. Current area of mid-level
(5000-6000 ft) overcast over KGTF/KHLN/KBZN has shown little change
in areal coverage past several hours.  However, infrared satellite
imagery is showing a few breaks in the cloud deck and a patch of
drier west of the Continental Divide that may make its way into
central MT overnight further decreasing the cloud cover.  So have
kept mention of just scattered clouds for KBZN/KHLN/KGTF for
tomorrow morning, but confidence is only marginal at best on the
that cloud forecast.  Winds will remain light and variable across
the region through Thurs morning.

Have added mention of -SN and mix of VFR/MVFR ceilings for
KBZN/KEKS/KHLN/KGTF on Thurs night as broad plume of moisture from
next Pacific weather system moves into southwest MT and steadily
spreads northward.
Waranauskas

&&

.PREV DISCUSSION...
/ISSUED 430 PM MST Wed Dec 7 2016/

Tonight through Thursday...High pressure aloft will gradually
build northeast into the forecast area during the period. This
will shift the cyclonic northwest flow aloft to a more
anticyclonic westerly flow, which will help clear skies
overnight. As a result, temperatures will fall to their coldest
levels in at least a year, as lows generally fall into the -10F to
-20F. Some mountain valleys with higher snowpack will likely fall
to around -30F. However, the northerly winds across North Central
Montana have generally fallen below 10 mph, so have cancelled the
Wind Chill Advisory. Moisture will gradually increase as the high
pressure ridge builds into the area, bringing mainly high clouds
to the area on Thursday, but a few snow showers will likely move
into the Southwest Montana/Northeast Idaho border area. Warmer air
will start to move into Southwest Montana, pushing highs into the
10 to 15 above range, while cold air will keep highs across North
Central Montana in the single digits above and below zero.
Coulston

Thursday night through Saturday night...A series of Pacific upper
level jet and shortwave impulses will move across the region this
period with bulk of the energy moving near or just south of the
forecast area. First in this series is a weakening wave that
tracks east across SW MT Friday morning. Expect light snow to
spread east across central and southern portions of the forecast
area Thursday night with snow diminishing from west to east as
the wave exists on Friday. As this wave is weakening, higher
precipitation amounts will be found over southern and sw portions
of the forecast area where 1- 3 inches of snow are possible from
roughly Helena south with locally higher amounts up to 4 inches
near the ID border. A second and somewhat stronger wave moves
across the region Friday night through Saturday morning, brining
a second more widespread round of light snow. Much of the
forecast area will see 1-3 inches of additional snow from this
feature with areas near the ID border again seeing the highest
amounts of 3 to 5 inches. Will issue a winter weather advisory to
highlight arrival of snow in SW portions of the forecast area
Thursday evening and beginning over central portions of the
forecast area late Thursday night, though steadier snow
accumulations in northern areas may not occur until the Friday
night wave arrives. Hoenisch

Sunday through Wednesday...The northwest flow aloft will be quite
unsettled and snow showers will remain in the forecast through the
middle of next week. A shortwave in Alberta will move southeast
Sunday towards the Dakotas. This will will not bring much change
in the chance for precipitation but it will bring another cold
front across the Canadian border. Temperatures Sunday will again
struggle to move above zero across the Hiline and above single
digits across the central zones. Currently, the coldest air is
forecast to slide east of the zones...but a slight change in
position would cause very cold temperatures over the eastern
zones. Zelzer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF -14  -4  -8   5 /  10  10  70  50
CTB -18  -4 -11  -4 /  10  10  50  50
HLN -10   7   0  26 /  10  10  80  40
BZN -10  11   6  30 /  10  10  80  40
WEY -21  12   7  28 /  10  20  80  70
DLN  -7  14  10  34 /  10  10  80  30
HVR -14   0  -7   2 /  10  10  20  50
LWT -15   4  -4   9 /  10  10  50  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 11 PM Thursday to 5 PM MST Saturday
Broadwater...Cascade...Central and Southern Lewis and Clark...
Fergus...Jefferson...Judith Basin...Meagher.

Winter Weather Advisory from 5 PM Thursday to 5 PM MST Saturday
Beaverhead...Gallatin...Madison.

&&

$$

weather.gov/greatfalls



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