Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 210435

Area Forecast Discussion
National Weather Service Great Falls MT
1035 PM MDT Sun Aug 20 2017

...Update to Aviation...


Area remains under a weakly cyclonic WNW flow aloft this evening
with subtle shortwave features tracking east across eastern MT as
well as central ID/OR. Widespread high cloud-cover with some
embedded mid-level cloud is accompanying these features this
evening with some partial clearing already moving into NW MT.
Radar showing some very weak returns over portions of N-central MT
this evening, most likely from virga, and cannot rule out a few
sprinkles, but no measurable precipitation is anticipated.



West to northwest flow aloft will continue over the region through
Monday. Precipitation is not expected, but areas of wildfire smoke
will persist. Near-normal temperatures are forecast through Monday.
Tuesday and Wednesday will feature above-normal temperatures as high
pressure aloft builds-in from the Pacific Northwest. Fair weather
will likely persist through mid-week.


Updated 0435Z.

Northwesterly flow aloft continues to bring periods of broken mid-
and upper-level clouds to the forecast area tonight. Models in good
agreement transitioning to few/scattered mid level clouds by 18Z
Monday with widespread VFR conditions prevailing through Monday
night. However, areas of wildfire smoke are still expected to bring
MVFR visibility at times, especially in the valleys of Southwest
Montana and in portions of Central Montana downwind of western
Montana fires. mpj



Fire weather highlights are not anticipated through mid-week, but
cannot be totally ruled-out due to continued warm, dry, and
potentially breezy conditions. Fire weather concerns should
increase on Thursday, when the upper-level ridge collapses over
Montana and a surface cold front spreads gusty winds and
scattered thunderstorms, some dry, over the area.


/ISSUED 535 PM MDT Sun Aug 20 2017/

Tonight through Monday...the H500 shortwave which moved over the
Northern Rockies this morning will continue to slide east into the
Northern High Plains through tonight, all the while as ridging
builds in from the west. High clouds were steadily moving in from
the Pacific Northwest and Intermountain West as of this afternoon,
and are expected to overspread most if not all of North Central and
Southwest Montana by this evening. While these clouds are expected
to be expansive in coverage this evening and somewhat opaque,
current model consensus and BUFKIT soundings show most if not all of
these high clouds departing North Central and Southwest Montana
prior to 15z on Monday. The departure of said cloud cover should
yield sunny to mostly sunny skies for the region, with the only
limiting factor in viewing the much anticipated eclipse being
smoke/hazy from wildfires currently burning over the Intermountain
West, Northern Rockies, and Western Canada. Ridging will continue to
build into the Northern Rockies during the day on Monday, and then
amplify over the region through the day on Tuesday. As this ridge
builds and amplifies into and over the Northern Rockies, high
temperatures will climb significantly. High temperatures by Tuesday
will generally be in the upper 80s to low 90s, which will be
approximately 10 degrees warmer than during the day on Monday. -

Tuesday Night through Sunday...Aforementioned high pressure ridge
aloft will continue to traverse the CWA from west to east Tuesday
night through Wednesday, allowing warming temperatures and primarily
dry weather to persist. Somewhat cooler temperatures, along with
scattered showers and thunderstorms, remain possible on Thursday and
Friday due to an upper-level trough digging southward and eastward
from British Columbia. In addition, a Pacific cold front
accompanying this trough should sweep eastward over the CWA on
Thursday. This system will have a little more moisture to work with
than past fronts as weak monsoonal moisture moves in the region
later Wednesday. The result will be a fair chance of showers and
thunderstorms Thursday afternoon and evening. Precip will then
diminish for Friday. This sharp front may also bring increased winds
starting Wednesday when the disturbance approaches...and continuing
for Thursday into Friday as the front moves through. This will at
least continue elevated fire weather concerns...and have to be
monitored for fire weather highlights. Drier conditions and slightly
warmer temperatures should return next weekend, as another high
pressure ridge aloft builds-in from the south and west. Near to
slightly above-normal low temperatures are expected throughout the
period. High temperatures are forecast to be about 10 degrees above-
normal Wednesday, with some areas seeing highs return in the low to
mid 90s. Highs Thursday through next weekend should be near or
slightly above-normal in the low to mid 80s. Friday should be the
coolest day as our region resides within a post-frontal environment
and beneath the aforementioned trough aloft. Expect highs in the 70s
to low 80s for Friday. Jaszka/Anglin


GTF  50  82  49  90 /   0   0   0   0
CTB  46  79  47  87 /  10   0   0   0
HLN  52  84  49  91 /   0   0   0   0
BZN  47  84  44  90 /   0   0   0   0
WEY  36  76  37  80 /   0   0   0   0
DLN  48  82  46  88 /   0   0   0   0
HVR  50  82  50  89 /   0   0   0   0
LWT  49  80  47  86 /  10   0   0   0



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