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000
FXUS65 KTFX 181723
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1122 AM MDT Fri Aug 18 2017

...UPDATED AVIATION SECTION...

.UPDATE...
This mornings forecast update includes the mention of some areas
of smoke across central and southwestern areas through noon today.
Still expecting low relative humidity values for northern and
central areas later this afternoon, with a red flag warning in
place from noon today thru early tomorrow morning. Otherwise,
forecast remains on track with no significant changes. KLG

&&

.SYNOPSIS...
The region will be dry and warmer than normal today into tonight
with gusty west winds. A Canadian cold front will then cool
temperatures back below normal with lighter and more northerly
winds for the rest of 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 1722z

Expect mainly VFR conditions for all terminals this afternoon and
evening. Some hazy skies from neighboring wildfires will limit
distance ridge/mountain tops for HLN and BZN, where conditions may
reach MVFR shortly early this afternoon. However, impacts will be
minimal as visibility is expected to slowly increase. Otherwise,
winds will continue to pick up across the entire region due to
mixing with wind directions ranging mostly from the west. Some high-
level clouds will work in overnight, with winds subsiding after
midnight tonight. By early tomorrow morning, a dry cold front will
surge southwards from Canada across with a prominent wind shift
expected for CTB and HVR, and eventually central area terminals by
mid to late morning tomorrow, followed by breezy northerly wind. KLG

&&

.FIRE WEATHER...

The Red Flag Warning remains in effect for all of the TFX fire
weather zones this afternoon and tonight. Critical fire weather
conditions are still expected across much of north central and
southwest Montana this afternoon and evening due to low humidity
and gusty west winds ahead of a Canadian cold front. Winds will
likely to remain gusty for much of tonight ahead of the front
with poor overnight humidity recovery, causing fires to remain
active throughout the night. Winds will shift more northerly and
decrease on Saturday with less critical afternoon humidity due to
the passage of the cold front.

Additionally 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.
Coulston

&&

.PREV DISCUSSION...
/ISSUED 430 AM MDT Fri Aug 18 2017/

Today through Sunday...A high pressure ridge over the area will
be broken down by a broad shortwave trough this afternoon and
tonight, resulting in a dry westerly flow aloft through the
period. Some mid and high cloudiness will pass over the forecast
area with little to no chance for thunderstorms. However, winds
will be of greater concern, at least through tonight. Mid level
westerly winds will increase through tonight and will generally
be translated down to the surface with the passage of a pre-
frontal surface trough. Gusts to between 20 and 30 mph at times
will be common for much of the area, but gusts closer to 40 mph
will be possible along the Rocky Mountain Front. Winds will
decrease and shift more northerly from the north late tonight
through the day on Saturday with the passage of a Canadian cold
front. Again, this will likely not bring showers or
thunderstorms, but temperatures will cool from around 5 degrees
above normal today to around 5 degrees below normal for Saturday
into Sunday. Smoke will also linger across the area, but am only
keeping mention of it in the forecast for areas along the
Continental Divide where reduced visibility is being detected by
automated observing systems.
Coulston

Sunday Night through Friday...A shortwave trough should advance
eastward over the CWA Sunday night into Monday morning, but
models continue to insist a lack of moisture and instability will
prevent showers and thunderstorms from accompanying the
disturbance. Later on Monday, stabilizing high pressure aloft
should begin building-in from the west. Thus, at this point,
decreasing cloud cover and dry weather conditions are still on
tap for the solar eclipse. The aforementioned ridge aloft 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  91  53  83  51 /   0   0   0   0
CTB  86  49  77  46 /   0   0   0   0
HLN  89  57  87  53 /   0   0   0   0
BZN  88  49  86  49 /   0   0   0   0
WEY  78  34  77  34 /   0   0   0   0
DLN  86  48  85  46 /   0   0   0   0
HVR  92  54  80  51 /   0   0   0   0
LWT  87  52  82  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...Deerlodge/Western Beaverhead National Forest...
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.

&&

$$

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