Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 201537

Area Forecast Discussion
National Weather Service Great Falls MT
937 AM MDT Wed Sep 20 2017


Moist westerly flow aloft will continue to bring clouds and
showers western and southwest Montana. While breezy conditions
and continued cool temperatures...along with isolated showers are
expected over the plains. This pattern is expected to continue
tonight through Thursday. A larger disturbance may then bring
widespread rain and mountain snow on Friday.


.UPDATE...Surface low pressure system in central Saskatchewan &
Manitoba continues to deepen this morning but is expected to eject
eastward this afternoon. Main impact of this system for Montana is
increasingly gusty downslope winds along the Rocky Mountain Front
and over the adjacent plains. Moist westerly flow aloft will bring
widespread rain and mountain snow to the western mountains but
only isolated/scattered showers are expected over the plains.
Updated forecast mainly to adjust PoP/QPF and weather border
changes by neighboring offices. Also increased winds a bit to be
more in keeping with observations and forecast trends. mpj


Updated 1100z.

Upper level trough/low centered over AB/BC will maintain fast and
unsettled westerly flow aloft across the northern Rockies and MT
with several embedded disturbances passing east across SW MT through
early Thursday. Showers will primarily affect western and SW MT with
drier conditions prevailing across the plains. Occasional MVFR
conditions can be expected at SW MT terminals along with mountain
obscurement. CC


/ISSUED 500 AM MDT Wed Sep 20 2017/

Today through Friday...Upper level low to our north and large
trough to our west will continue to bring a cool and somewhat
active pattern through the short term. Today strong westerly flow
will bring breezy conditions to much of the area. A push of
moisture ahead of a trough looks to bring increased chances for
showers and mountain snow today mainly across the west and south.
Snow levels throughout the day should remain above 7000 feet.
Downsloping flow will keep the plains generally dry...with lowered
RH values...although an isolated shower is still possible. The
energy with this system splits on Thursday...with a large upper
low in Canada and a large trough over our region. The result will
be still cool temperatures and scattered rain and mountain snow
showers. With the split of energy...shower coverage may not be as
widespread as initially thought earlier this week. Snow levels for
Thursday may lower to 6000 feet with some minor to moderate
accumulations possible in the mountains. The attention for the
biggest impacts still remains for Thursday night through Friday.
Models still indicate a cutoff low develops across ID...perhaps
bringing widespread rain showers and snow generally above 5000 as low as 4000 feet...during this time period. Most
areas look to see a chance of precipitation...with the best
chances coming from about Great Falls to Lewistown and south.
Light to moderate...with some isolated heavy...higher elevation
snow is possible with this feature...especially across the
southern half of the CWA. This will continue to be monitored for
any winter weather highlights. Temperatures will continue to be
below normal today and Thursday...with well below normal
temperatures expected for Friday. Most areas Friday morning may
see low temperatures dip into the 30s. Anglin

Saturday through Wednesday...Significant model discrepancies remain
in the evolution of the upper level pattern this weekend into early
Monday. The sensible weather impacts of these discrepancies between
the models lies with coverage of shower activity and cloud cover,
especially for Saturday. Nevertheless, we can say with high
confidence that the pattern will slowly trend toward normal
temperatures with mostly dry conditions by the middle of next week,
with upper-level northwesterly flow building ahead of robust upper
ridging moving onshore the PacNW. CC


GTF  56  36  54  35 /  20  20  10  30
CTB  53  32  50  32 /  10  10  30  30
HLN  56  33  53  36 /  40  30  20  50
BZN  54  35  50  35 /  40  50  20  70
WEY  44  29  39  27 /  70  80  70  70
DLN  53  31  45  31 /  40  30  30  60
HVR  61  36  57  36 /  10  10  10  10
LWT  55  36  52  34 /  30  30  10  50



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