Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 190431
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1030 PM MDT Tue Jul 18 2017

...Aviation Section Updated...

.UPDATE...

Little later of an update tonight waiting for high resolution
models for tonight`s convective threat. SPC Meso Analysis show
quite nicely a mid to upper level wave will attempt to ride over
the ridge late this evening into the overnight hours. Abundant
shear and favorable jet dynamics may be enough to produce a few
showers and thunderstorms. This wave is however lacking
instability. SFC cape is almost non-existent...and this
disturbance will have to tap into some sort of elevated unstable
layer...possibly with the help of a low to mid level jet. All
things considered...made some minor adjustments for this wave with
thunderstorms possible from about Lewis and Clark county eastward
to Fergus county. Lightning and gusty winds will be the main
threat. Little rainfall is expected except for maybe Fergus County
area where perhaps an isolated storm drops up to a tenth of an
inch. The threat for hail is also small. Anglin

&&

.SYNOPSIS...
An upper level ridge will be over the region for the next few
days...resulting in very warm afternoon temperatures through
Thursday. Additionally, there will be a slight chance for a
passing thunderstorm. Some of the stronger storms could produce
gusty winds.

&&

.AVIATION...
Updated 0430Z.

VFR conditions are expected to prevail throughout the 1906/2006 TAF
period across all of Southwest and North Central Montana. Isolated
showers and thunderstorms have developed late this evening across
Central Montana, with areal coverage being generally spotty in
nature. However, do expect areal coverage of the aforementioned
showers and storms to increase to scattered across Central Montana.
With this increase in areal coverage, felt confident enough to
insert VCSH at KGTF. Biggest concern with any shower/storm that
approaches the KGTF terminal will be gusty and erratic winds given
the deep inverted-v profiles from this evenings 00Z KTFX sounding.
Otherwise, current thinking is for showers and storms to stay north
of KHLN and KLWT, and south of the KCTB and KHVR terminals. - Moldan

&&

.FIRE WEATHER...
Main concern for fire weather will be isolated thunderstorms
tonight and again Wednesday night. Lightning and storms that
produce little rainfall will be the main threat. Additionally,
surface winds will increase on Friday to become breezy/wind at
times over the Northern Plains. Brusda

&&

.PREV DISCUSSION...
/ISSUED 550 PM MDT Tue Jul 18 2017/
Tonight through Thursday...Main concern the next two days will be
the chances for isolated thunderstorms later tonight and again on
Wednesday night. The storms tonight will likely develop after 9 PM
and then move from west to east across Central MT...mainly along a
line from around Lincoln to north of Lewistown. On Wednesday
night...the storms should be further north...mainly along the
Highway 2 corridor. The main threat from any storms will be gusty
winds and lightning. Afternoon temperatures will remain about 5 to
10 degrees above normal over the next few days. Brusda

Thursday evening through Tuesday...Long range guidance continues to
remain on track as a short wave trough quickly swings across the US-
Canadian border to the north. At the surface, a strong cold front
will push through the area with increasing west-northwesterly winds
off the Divide. By Friday and Friday afternoon, given a strong post-
frontal environment, along with sufficient 700mb wind speeds
yielding 45kt or greater due to the passing trough to the north and
a well mixed boundary layer, gusty winds will likely develop in the
afternoon and evening hours. Winds are more likely to become gusty
along the Hi-line where winds could sustain 20-25 mph at times, with
gusts up to 30 and maybe higher. Additionally, gusty winds combined
with very dry conditions will likely lead to the possibility of fire
danger, especially for northern areas. More details will become
clear as we get closer to the later part of the week. By the weekend
and into next week, the models are still not on the same page about
the evolution of the upper air pattern and will keep the mention of
slightly above-normal temperatures with a slight chance of isolated
showers or storms in the afternoon. KLG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  90  57  90 /  30  10  10  10
CTB  49  85  53  83 /   0   0  20  10
HLN  59  89  59  88 /  20   0   0   0
BZN  52  88  52  88 /   0   0   0   0
WEY  48  80  44  78 /   0   0   0  10
DLN  52  87  52  86 /   0   0   0   0
HVR  56  90  57  91 /  10  10  10  20
LWT  56  87  57  88 /  20  10  10  10

&&

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

$$

weather.gov/greatfalls


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