Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 171116

Area Forecast Discussion
National Weather Service Great Falls MT
515 AM MDT Thu Aug 17 2017


Mostly dry and, at times, breezy conditions will continue to be the
main themes through the upcoming weekend. Temperatures will be near
to slightly above normal. For those looking ahead to the solar
eclipse on Monday, much of the area looks to have mostly sunny
skies. However, there may be a bit more in the way of clouds across
parts of Southwest Montana, so stay tuned.



Today through Saturday...

The main concern over the next several days is fire weather. For a
detailed discussion regarding fire weather concerns, please see the
fire weather section below.

Breezy northwest winds will develop by this afternoon, especially
across the plains today, in the wake of a dry frontal passage this
morning. This combined with continued dry conditions will lead to
elevated to critical fire weather conditions. Breezy westerly
downslope flow then develops across the region for Friday while
transient upper ridging moves overhead, which will result in
seasonably warm and very dry conditions across the region.
Significantly impactful winds are not expected, but they will be
high enough to cause impacts/concerns for the fire community.

Over the weekend, the models continue to advertise yet another
strong cold front dropping south out of Canada. The trend has been
for this front to come in earlier, possibly as early as Friday
night. However, it should quickly return north as a warm front, with
any cooldown being very brief. CC/Martin

Saturday night through Wednesday night...

Main forecast concerns in the long term are precipitation
chances/cloud cover prior to and during the eclipse, followed by
warming and drying conditions into the middle of the week as an
upper level ridge builds in and amplifies over the Northern
Rockies and Northern High Plains.

Zonal flow Saturday night will persist into the early afternoon
hours on Sunday, before a weak H500 disturbance traverses the
Northern Rockies through the late-afternoon/evening hours. This
disturbance will primarily be dry in nature, however, a few showers
and thunderstorms can not be ruled out across far Southwestern
Montana during the late-afternoon/evening hours on Sunday as weak
synoptic scale lift overspreads the region. This biggest impact that
this disturbance will have on the region (especially across
Southwest Montana) will be an increase in high clouds. This cloud
cover is expected to move east during the overnight hours and
away from Southwest and North Central Montana however, as upper
level ridging builds into the Northern Rockies, giving way to
mostly sunny to partly sunny skies for the morning and early
afternoon hours on Monday. The other and potentially biggest
question that how much smoke overspreads the region
from wildfires burning over the Northern Rockies and Western
Canada on Monday? Given relatively weak west to northwest flow in
the mid-to-upper levels, believe that there is a pretty good
chance that skies will be hazy, especially across Southwest
Montana where the flow will be the weakest (and least likely to
disperse the smoke). The aforementioned ridge is then expected to
amplify across the Northern Rockies into the middle of next week,
which will push high temperatures well above normal, limit
precipitation chances, and bring afternoon relative humidity
values to near critical values. - Moldan


Updated 1115z.

Mainly VFR conditions are expected throughout the forecast
period...though smoke from wildfires to the west may cause some
minor visibility issues through 15-18z before improving somewhat as
the upper flow begins to become more northwesterly. What few clouds
are moving across the region will move off to the east by late
afternoon, with mostly clear skies thereafter (with the possible
exception of some smoke). Gusty northwesterly breezes will impact
especially then plains terminals in the afternoon, with winds
becoming lighter and more variable in the evening before increasing
slowly again from the southwest overnight. CC



The weather pattern over the next few days very much seems to
favor elevated to, at times, critical fire weather conditions.

In the wake of a dry cold frontal passage this morning, RH will
likely come up some, especially compared to Wednesday, but will still
remain at or below critical levels in the mid- to high teens. In
addition, a breezy northwest wind is likely with gusts as high as
25 to 30 mph at times. This has resulted in continued Red Flag
Warnings for our eastern districts (113, 115, and 117) for this
afternoon into early evening.

Critical fire weather concerns look to become more widespread
Friday due to much warmer temperatures (upper 80s to lower 90s) and
much lower humidity values along with increased downslope
westerly winds. Thus, with fairly high confidence we have decided
to go ahead and issue a Red Flag Warning for all of our fire
weather zones from early Friday afternoon into mid-evening.

The threat on Saturday looks a bit more conditional depending on
the timing of a cold front forecast to move through. Models have
trended earlier with the front and lower on the winds Saturday,
but we will continue to monitor trends closely. Of note,
overnight RH recoveries are expected to be poor to moderate for
many areas over the next few nights. MARTIN


GTF  84  52  91  53 /   0   0   0   0
CTB  80  49  86  50 /   0   0   0   0
HLN  85  53  90  55 /   0   0   0   0
BZN  82  49  88  50 /   0   0   0   0
WEY  76  37  77  38 /   0   0   0   0
DLN  80  47  85  48 /   0   0   0   0
HVR  85  52  92  55 /   0   0   0   0
LWT  80  51  88  54 /   0   0   0   0


Red Flag Warning from noon to 9 PM MDT Friday Central and
Eastern Lewis and Clark National Forest Areas...Chouteau and
Fergus Counties...Eastern Glacier/Toole/Central/Eastern
Pondera/Liberty...Helena and Townsend Ranger Districts of the
Helena National Forest...Hill and Blaine Counties...Lewis and
Clark National Forest Rocky Mountain District-Rocky Mountain
Front...Lincoln Ranger District of the Helena National Forest.

Red Flag Warning from noon today to 9 PM MDT this evening
Central and Eastern Lewis and Clark National Forest Areas...
Chouteau and Fergus Counties...Hill and Blaine Counties.


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