Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211001
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
401 AM MDT Wed Jun 21 2017

.SYNOPSIS...

A gradual cooling trend is expected over the next few days as
several cold fronts drop south out of Canada. Each front may bring
a few showers or thunderstorms with it, but mainly across central
Montana. It will be breezy once again this afternoon, and wind
gusts may be briefly enhanced along the Hiline due to nearby
thunderstorms.

&&

.DISCUSSION...

Today through Thursday Night...Yesterday, severe thunderstorms
developed well to our north in Alberta, putting out a well-defined
outflow boundary. This boundary continues to drop south early this
morning and will continue to produce gusty winds of 20-35 mph before
reaching the central mountains where it is unlikely to get past.
Later this afternoon, thunderstorms will likely develop once again
to our north in Alberta, possibly a bit further south than
yesterday. While most of this activity should stay north of the
Border, I added low-end pops along the Hi-line as it is possible a
few of these showers/storms will clip this area. Like yesterday, if
the storms get strong enough, another outflow boundary would likely
drop south through central MT with gusty winds. Given this
possibility, I adjusted the winds for this evening to reflect a
shift out of the N/NW. The strongest wind gusts will likely be along
the Hi-line, especially if any t-storm can move through, with
somewhat lower wind gusts further south.

On Thursday, a cold front will drop south out of Canada, possibly
bringing a few showers with it to central MT. The atmosphere looks
to stay fairly dry, so confidence in showers is somewhat lower and I
kept pops at slight chance/chance. The one area that may see a
better chance of showers is the GNP area where low level upslope
flow may locally enhance lift for a short time. For now, it looks to
be fairly stable Thursday and I opted to leave out any mention of
thunder. An unseasonably strong SFC high then builds in Thursday
night with below normal temps expected under clear skies/light
winds. MARTIN

Friday through Tuesday...MT will remain on the western periphery of
a large scale upper level trough late this week into early this
weekend. Shortwave and upper level jet energy moving through
cyclonic NW flow aloft will support at least a slight chance of
showers Friday and Friday night. Best chance looks to be along the
Northern Rocky Mtn Front/Glacier Park vicinity late Friday as
the next surge of surface high pressure nosing south from AB creates
a period of N/NE upslope flow late Friday, which then translates east
across N-central MT Friday night into Saturday morning. Airmass
dries Saturday and Sunday as the upper trough moves off to the east.
Surface high pressure center drifts east across MT Saturday with
morning low temps around 10 degrees below seasonal averages Saturday
morning and possibly again Sunday morning. Upper ridge amplifying
along the West Coast late this weekend shifts inland and across
region early next week for more significant warming, though this
appears to be brief with the next Pacific trough moving onshore
Tuesday or Wednesday. There is still a great deal of uncertainty by
this point with the inland progression of the trough, but somewhat
cooler conditions with at least a chance for precipitation looks to
develop following the progression of the ridge axis east of the
region. Hoenisch

&&

.AVIATION...
Updated 0450Z.

VFR conditions will continue through at least Wednesday evening. The
westerly flow aloft will strengthen overnight as a disturbance moves
through the area. This will continue partly cloudy skies across the
area with low level wind shear at times over the plains through 12Z.
A few showers are also possible along the Hi-Line as a weak frontal
boundary moves south of the border. Otherwise, breezy westerly winds
over the plains will shift more northerly and become gusty with the
passage of the boundary. Skies will then become mostly clear after
12Z and gusty westerly winds will mix down to the surface once again
after 18Z with a chance of showers and thunderstorms along the Hi-
Line. Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  76  45  69  41 /   0   0  10  20
CTB  71  42  65  40 /  10  20  10  30
HLN  80  48  72  46 /   0   0   0  10
BZN  81  42  72  40 /   0   0   0   0
WEY  78  37  68  34 /   0   0   0   0
DLN  80  43  72  40 /   0   0   0   0
HVR  78  45  69  44 /  20  20  10  20
LWT  74  44  66  40 /  10  10   0  20

&&

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

$$

weather.gov/greatfalls


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