Area Forecast Discussion
Issued by NWS Great Falls, MT

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000
FXUS65 KTFX 190340
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
940 PM MDT Fri Aug 18 2017

.UPDATE...

Mid level shortwave is progressing east across NW and N-Central
MT this evening with satellite imagery showing band of mid-level
cloud-cover and embedded wave clouds along it. Main impact this
evening however, continues to be smoke from fires near and west of
the continental divide streaming east across central and SW MT in
enhanced westerly flow ahead of the shortwave. As flow aloft
veers to more west-northwesterly tonight some improvement is
possible over N-central MT, though smoke will probably linger
across SW MT into Saturday morning. Surface frontal boundary and
wind shift to the north currently approaching Calgary AB, should
reach the MT/AB border around 6am, continuing south through
N-central MT Saturday morning. Until then, expect relative
humidity to remain below 30% with some locations still in the
upper teens, and this combined with breezy west winds will
maintain critical fire weather conditions through much of tonight.
Hoenisch

&&

.SYNOPSIS...
Mild and breezy conditions continue overnight as a dry cold front
moves into Northwest Montana. Temperatures trend cooler through
the weekend, but the area will remain dry. Wildfire smoke will
also continue hazy skies through the weekend, especially near the
Continental Divide.

&&

.AVIATION...
Updated 0000z

Mainly VFR conditions are expected through the forecast
period...however...some areas may see MVFR conditions due to
reduced visibility in smoke. Area wild fires may bring reduced
vis and haze at times especially from KGTF to KHLN to KBZN.
Mountain obscuration will also be possible in these areas.
Otherwise expected some high clouds and diminishing winds tonight.
Another VFR day is expected for Saturday. A weak front may shift
the winds to a more north to northwest direction Saturday
morning...continuing into Saturday afternoon. Anglin

.FIRE WEATHER...

The Red Flag Warning remains in effect for all of the TFX fire
weather zones tonight. Critical fire weather conditions have
developed as expected, and are expected to continue tonight
due to low humidity and gusty west winds ahead of a dry cold
front. Active fire behavior is expected overnight in these
conditions. Winds will shift more northwesterly and decrease on
Saturday with less critical afternoon humidity due to the passage
of the cold front.

Additional fire weather highlights are possible again early next
week, as it will remain warm and dry with low humidity and
potentially gusty winds at times.

&&

.PREV DISCUSSION...
/ISSUED 604 PM MDT Fri Aug 18 2017/

Tonight through Sunday...Critical fire weather conditions have
developed this afternoon with low relative humidity and gusty
winds associated with an approaching shortwave trough. Active fire
behavior is expected to continue through the night as detailed
below in the fire weather sub section. Satellite imagery remains
cloud free, except over Glacier county where wave cloud activity
is marking the advancing wave. Expect clouds to increase in
coverage overnight. The cold front passes through the forecast
area early Saturday morning. This will produce cooler temperatures
and higher relative humidity, but gusty northwest winds will
continue to support elevated fire weather concerns. Areas of smoke
will persist in valleys along and near the Continental Divide, and
may even increase in coverage if fires produce more active smoke
plumes. However, smoke should decrease with improving visibility
and air quality in the northwest winds behind the passing front.

Sunday Night through Friday...The next shortwave trough is
expected to cross western Montana Sunday night into Monday
morning. Forecast models indicate little moisture in the lower
portions of the atmosphere. However, there may be adequate
moisture aloft to support areas of thin mid- to high-clouds
through Monday morning. Should these clouds develop, those seeking
to view the eclipse may encounter periods of obscuration at
times. There remains uncertainty in the timing and extent of cloud
coverage associated with this passing wave. An upper level ridge
will traverse the CWA from west to east Monday night through
Wednesday, resulting in continued warm conditions and primarily
dry weather. Our weather may become slightly cooler and more
unsettled next week Thursday and Friday due to an upper-level
trough digging southward and eastward from British Columbia.
Accordingly, the potential of showers and thunderstorms should
increase Thursday and Friday. Low and high temperatures are
expected to be near or slightly above- normal during the period.
The warmest readings will likely occur Tuesday and Wednesday, when
the aforementioned high pressure ridge is firmly overhead. Jaszka

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  90  59  84  51 /   0   0   0   0
CTB  88  54  78  45 /   0   0   0   0
HLN  90  62  88  53 /   0   0   0   0
BZN  88  52  90  49 /   0   0   0   0
WEY  77  43  81  37 /   0   0   0   0
DLN  85  53  88  46 /   0   0   0   0
HVR  92  57  82  51 /   0   0   0   0
LWT  86  56  84  51 /   0   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 6 AM MDT Saturday 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 Saturday Deerlodge/Western
Beaverhead National Forest.

Red Flag Warning from noon to 9 PM MDT Saturday Eastern
Beaverhead National Forest.

&&

$$

weather.gov/greatfalls



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