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000
FXUS65 KTFX 231934
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
134 PM MDT Sat Sep 23 2017

.SYNOPSIS...
An upper level low pressure system will slowly move through the
central Rocky Mountains through Sunday, leaving southwest and
central Montana in a cooler and drier part of the system. The
result will be light winds, cool temperatures and clearing skies.
Given the recent precipitation, low level moisture combined with
clear skies may result in areas of fog tonight. Widespread frost
will also develop overnight as temperatures drop to below freezing
in many areas.

&&

.DISCUSSION...
A slow moving upper low will weaken as it moves from the Great Basin
tonight into northwest Wyoming on Monday. Although this pattern
brings little in the way of wind, dynamics, or moisture to
southwest and Central Montana, enough low-level moisture lingers
to produce isolated snow showers over the mountains tonight and
early Sunday. Likewise, a weak surface gradient will result in
light winds. Tonight temperatures will drop to below freezing in
many areas so expect widespread frost to develop. Temperatures
will remain below normal through Monday. Britton

&&

.AVIATION...
Updated 1820z.
Most of the fog and low clouds have largely dissipated with only
lingering patchy fog and low clouds remaining. Skies will begin to
clear somewhat overnight and expect to see some areas of fog and
possibly low clouds here and there, but do not expect aviation
impacts at this time. Britton

&&

.PREV DISCUSSION...
/ISSUED 540 AM MDT Sat Sep 23 2017/
Monday night through Saturday...By the beginning of next week,
models are in good agreement with the development of broad ridging
over the Pac NW, with the slow moving trough over the Northern
Rockies finally deamplifying and moving off to the NE. This will
place us in a NW flow aloft between the exiting trough and
amplifying ridge to the west. As far as day-to-day details, models
slightly differ on the idea of small embedded shortwaves swinging
across the state along the NW flow. Moisture will be modest,
given PWAT anomalies above normal areawide which may be enough to
squeeze out a few isolated showers Tuesday and Wednesday
afternoon. Regardless, the bigger story will be moderating
temperatures. As we get into Thursday, the aforementioned ridge
across the Pac NW will build eastward across a large majority of
Northwest US. This will send temperatures back to near
climatological normal, if not slightly above normal with
widespread temperatures in the 60`s and 70`s by late week for
many, followed by dry conditions. Models begin to display
noticeable discrepancies as we get into next weekend, with the
general idea of the ridge slowly breaking down. EPS and GEFS
guidance suggests continued above normal height anomalies which
would side against any cold/winter weather issues. However due to
low confidence in this time frame, I`ve decided to keep
temperatures near normal next weekend with only slight rain
chances. But this will likely change as models become in better
agreement in the upcoming few days. KLG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  31  56  35  61 /   0   0   0   0
CTB  30  58  33  62 /  10   0   0  10
HLN  34  56  34  60 /  10  10   0   0
BZN  30  51  32  56 /  10  20  10  10
WEY  26  45  26  48 /  10  20  20  20
DLN  28  48  28  53 /  10  10  10  10
HVR  34  59  35  64 /   0   0   0   0
LWT  32  51  34  57 /  10  10  10  10

&&

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

$$

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