Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 171739

Area Forecast Discussion
National Weather Service Great Falls MT
1115 AM MDT Thu Aug 17 2017

Aviation Section Updated

Updated forecast is out. Isolated thunderstorms will affect areas
around Turner before Noon. Otherwise smoke continues to affect
areas from north of Great Falls southward to the I-90 corridor.
Added smoke for the rest of today...especially with the smoke plume
from the Lolo Peak Fire headed towards the Helena/Boulder/Bozeman
area. Otherwise minor tweaks to temps/rh with the overall forecast
on track. Brusda


Mostly dry and warm conditions can be expected over the entire
region for the next a weak upper level ridge resides
over the region. Afternoon highs will generally be in the 80s
through the middle portions of next week. Areas of smoke will
affect the region as well through the upcoming weekend.


Updated 1740z.
VFR conditions will prevail over the region through the
period...except for areas of smoke. The smoke will affect areas
from just north of Great Falls southward to Bozeman the greatest.
Visibility could be reduced to less than 4 miles at times.
Distant mountains/passes could be obscured at times. Brusda


/ISSUED 515 AM MDT Thu Aug 17 2017/

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


GTF  85  52  91  53 /   0   0   0   0
CTB  83  49  86  50 /   0   0   0   0
HLN  87  53  90  55 /   0   0   0   0
BZN  83  49  88  50 /   0   0   0   0
WEY  75  37  77  38 /   0   0   0   0
DLN  79  47  85  48 /   0   0   0   0
HVR  87  52  92  55 /   0   0   0   0
LWT  82  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 until 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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