Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 210336
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
936 PM MDT SAT AUG 20 2016

.UPDATE...

A broad upper level ridge extends from the Pacific NW across the
Northern Rockies and MT this evening with just some scattered
high level cloud-cover streaming across the region. Dry conditions
with mainly clear skies and light winds will prevail overnight
with no significant changes to previous forecast. Still looking at
additional warming and drying to occur Sunday across the region as
the upper level ridge axis shifts across the forecast area
followed by windy and dry...but slightly cooler conditions Monday
as a dry cold front moves across the region. Hoenisch

&&

.AVIATION...
UPDATED 2320Z

An upper level ridge of high pressure will gradually expand east
across the Northern Rockies and MT tonight through Sunday for a dry
and stable westerly flow aloft. Little or no cloud-cover is
anticipated through the period with just some passing high clouds
tonight. Winds will be relatively light through Sunday morning with
a slight increase in W/SW surface winds Sunday afternoon. VFR
conditions will prevail. Hoenisch

&&

.FIRE WEATHER...
Warm and very dry conditions developing tomorrow will remain in
place on Monday as a strong upper-level low pressure system moves
across southwest Canada. The tight pressure gradient from this
system will produce widespread sustained winds of 15 to 25 mph,
with gusts of 30 to 45 mph (some locations may see gusts in excess
of 50 mph) Monday afternoon and evening, prompting issuance of a
fire weather watch for portions of the Rocky Mtn Front and
adjacent plains. The combination of dry conditions and gusty
winds will extend into central MT as well, but recent rain events
have lowered the overall fire danger there, so we have kept those
locations outside the watch area for the time being. However, with
fine fuels already cured in many locations, residents, travelers,
land/emergency managers and fire crews should be prepared for
near-critical fire conditions east of the watch area through Mon
evening. Waranauskas

&&

.PREV DISCUSSION...
/ISSUED 520 PM MDT SAT AUG 20 2016/
This Afternoon through Sunday Night...High pressure ridging
currently centered along the Pacific Coast will move into and across
the Northern Rockies area through Sunday night. Other than some
passing high clouds streaming into Montana along the eastern
boundary of the ridge this aftn/eve, most locations in our region
will see mostly clear skies over the next 36-48 hours. As the ridge
axis approaches, winds aloft will turn to the west-southwest,
bringing in a much warmer airmass.  As a result, highs tomorrow will
climb into the upper 80s and low 90s across central and southwest MT.
Waranauskas

Monday and Monday night...The impact weather for the period occurs
on Monday as a closed upper level trough crosses the Canadian
Rockies. Surface pressure falls ahead of this system will cause
increasing winds along the Rocky Mountain Front and adjacent plains
early Monday. Strong subsidence along with 700 mb winds around 55kt
could bring wind gusts of 55 to 65 mph to the Rocky Mountain Front
early Monday. The west-southwesterly downslope flow will enhance
drying and bring afternoon relative humidity down to around 15
percent Monday afternoon. For these reasons a fire weather watch is
posted as discussed further in the Fire Weather section. A cold
front will push through the forecast area from northwest to
southeast Monday evening as the upper low moves away as an Alberta
Clipper system. Strong subsidence on the south side of this trough
will inhibit precipitation for most areas through Monday night. PN

Tuesday through Saturday...The upper level low associated with the
Monday cold front will move east on Tuesday. Light precipitation and
low clouds may persist along the Hi-line Tuesday as the system
moves east. The low then broadens into an upper trough with
north/northwest flow aloft prevailing over Montana Wednesday through
Friday. Temperatures during this period are expected to remain
somewhat below seasonal averages for fairly comfortable late-summer
conditions. However, models have trended toward including a slight
chance to chance for showers and thunderstorms across much of the
forecast area during this period so have increased PoPs slightly.
Model solutions diverge significantly late Friday and Saturday with
the GFS digging another shortwave trough into the northern Rockies
for a continued chance of precipitation while the ECMWF builds a
shortwave ridge for dry conditions. For now, have gone with a
blended solution with temperatures warming back near seasonal
averages for Saturday. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  56  89  54  82 /   0   0   0   0
CTB  54  86  53  73 /   0   0   0  10
HLN  54  88  56  83 /   0   0   0   0
BZN  48  87  49  86 /   0   0   0  10
WEY  43  78  41  76 /   0   0   0  10
DLN  48  86  48  83 /   0   0   0   0
HVR  55  90  54  84 /   0   0   0   0
LWT  53  85  54  84 /   0   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Monday afternoon through Monday evening
for MTZ114-116-118.

Fire Weather Watch from Monday afternoon through Monday evening
for MTZ110-111.

&&

$$

weather.gov/greatfalls



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