Area Forecast Discussion
Issued by NWS Great Falls, MT

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000
FXUS65 KTFX 170215
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
815 PM MDT Sat Sep 16 2017

.SYNOPSIS...
An upper level trof of low pressure will exit the region
tonight...as a brisk westerly flow develops aloft. Expect a nice day
on Sunday...but gusty west wind will develop Sunday night into
Monday. For Monday afternoon through Thursday...an upper level trof
of low pressure will be over the region...resulting in a chance for
showers and cool temperatures to continue.

&&

.EVENING UPDATE...

The main forecast challenge for tonight is how much will clouds and
wind limit the potential of fog and, for some, the first freezing
temps of the season. Clouds associated with the departing storm
system have stuck around longer than originally anticipated
across SW MT and the updated forecast keeps clouds around longer
in that area over the next few hours. Mid/high clouds associated
with a fast- moving shortwave advancing through the Pac NW at this
time will move over the area later tonight, especially SW MT.
Ultimately, this may keep temps from falling as low as originally
forecast. Although, surface obs to the west indicate these clouds
are mostly higher- level clouds, so the impact to temps shouldn`t
be as great as would be expected with lower clouds. I raised temps
a touch compared to the previous forecast, but I expect many
areas will see near/below freezing temps there. Across central MT,
a lee-side trough should keep the wind up some tonight which I
expect will limit the fog potential, despite the recent precip/wet
ground. Any sheltered areas could see some patchy fog, though.
The wind will be lighter for most SW valleys and I kept a mention
of fog in overnight there. Also, of note, with temps near/below
freezing tonight, patchy black ice is expected on roads where snow
accumulated over the past couple of days. MARTIN

&&

.AVIATION...
Updated 0000Z.
Clouds are generally decreasing over the area, but will linger over
the mountains causing mountain obscuration at times. As drier air
continues to move in, the recent moisture and light winds may
contribute to fog developing late tonight into early Sunday morning.
Have added VCFG with some areas possibly seeing reduced cigs/vis,
especially over central and southwest Montana. High pressure will
yield mainly quiet conditions across the region. MLS

&&

.PREV DISCUSSION...
/ISSUED 610 PM MDT Sat Sep 16 2017/
Tonight through Monday night...The main storm system from the past
few days is exiting the region...as drier air moves in aloft. This
dry air will allow for areas of fog to develop tomorrow morning.
Otherwise...much of Sunday should be a nice day...as we will be
in-between storm systems. On Monday...the next upper level trof
will be approaching the region...with a chance for showers
approaching the region by late in the day. The airmass will be
just unstable enough for an isolated thunderstorm over the far
southwest. Brusda

Tuesday through Saturday...The dominant and strong upper level
disturbance over central Alberta will continue to remain in
control of the Pac NW during the day on Tuesday. This will allow
for a persistent westerly Pacific flow following the passage of
the cold front. Look for light showers, along with relatively cool
temperatures areawide during the daytime on Tuesday with breezy
west winds. By Wednesday, models continue to try and develop a
secondary/embedded shortwave around the large cyclonic flow aloft
across WA/OR/ID. Following this idea, there could very well be an
enhanced opportunity for widespread rainfall areawide on
Wednesday. In addition, a strengthening 700mb jet in response to
this developing trough would yield rather windy conditions during
the afternoon hours. Temperatures will remain on the cool side due
to widespread cloud cover and will likely struggle to reach the
50`s by Wednesday afternoon. This wet and cool pattern will
continue into Thursday and Friday as the aforementioned upper-
level disturbance remains in control, with a persistent westerly
flow aloft across the state. It`s not until next weekend that this
pesky disturbance slowly exits to the east as a strong ridge
builds off the Pac NW coast. By this period, a progressive NW flow
aloft will keep temperatures cool, with off and on rain shower
chances as several weak disturbances advance along the flow across
the state. Still no signs of returning heat in the long range,
with temperatures averaging 10 to 15 degrees below normal for the
majority of the time period. KLG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  35  64  45  64 /   0   0   0  20
CTB  33  65  43  58 /   0   0  10  20
HLN  35  65  42  61 /   0   0   0  40
BZN  33  63  38  64 /   0   0   0  30
WEY  27  54  29  57 /   0   0   0  20
DLN  33  61  37  59 /   0   0   0  40
HVR  35  68  41  71 /   0   0   0  10
LWT  35  64  41  68 /   0   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls



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