Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 171535
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
935 AM MDT Tue Oct 17 2017

.UPDATE...
No major updates to the forecast this morning. Expect windy
conditions to strengthen across the plains mid afternoon into the
evening before subsiding a bit overnight. Relative humidity will
be fairly low this afternoon as well and thus a fire weather
statement remains in effect for much of Central Montana.

&&

.SYNOPSIS...

Strong an potentially damaging winds will develop this morning along
the Rocky Mountain Front and spread east across much of north
central Montana this afternoon and evening as a low pressure system
moves east across Alberta. Warmer than average temperatures today
will cool slightly on Wednesday with an increase in winds and
temperatures expected again Thursday as the next in series of fast
moving Pacific weather system moves into the region.

&&

.AVIATION...
Updated 1113z.

VFR conditions are expected to continue for all terminals this
morning, as well as throughout the day today. Latest satellite
imagery this morning shows some mountain cloud activity developing
along and east of the Divide across CTB eastward to HVR. But by far,
the main concern today will be widespread strong winds this morning,
increasing throughout the afternoon and evening hours. It is likely
that winds will average sustained 20-30kts at times, especially for
GTF, CTB, HVR and LWT with peak gusts anywhere in that time frame
between 40-50kts or greater. Wind directions will likely range
between 220 and 240 during this event, which will fortunately limit
any significant crosswind issues for most terminals. Regardless,
sufficient boundary layer mixing will support the transfer of
intense winds aloft to the surface which will lead to moderate to
strong turbulence, especially for central and northern parts of the
area through the evening today. Some slight moderation in winds are
possible overnight but will likely continue gusty with wind
directions unchanging. KLG

&&

.FIRE WEATHER...

Strong winds today will combine with low humidity and mild
afternoon temperatures to create critical fire weather conditions
across much of north-central Montana. Afternoon humidity will
likely fall to 15-25% across much of north-central MT, aided by
downslope westerly winds with afternoon temperatures about 10-15
degrees above seasonal averages. Fire danger is greatest in
grassland/fine fuels with strong winds today into this evening.
Winds in excess of 60 mph may also create power line
arching/damage, further increasing the risk for fire starts late
this afternoon and evening as strongest winds pass through the
region. Hoenisch

&&

.PREV DISCUSSION...
/ISSUED 513 AM MDT Tue Oct 17 2017/

Today through Wednesday...First in a series of upper level troughs
is moving onto the BC coast early this morning with surface low
pressure expected to deepen in central AB this afternoon as the
trough progresses inland. Models have trended towards stronger and
more rapid deepening of the surface low across AB/SK later today and
tonight, giving additional support for a widespread strong wind event
across much of north central MT as a belt of strong winds aloft sags
southward into the region. Strong winds still look to initially be
limited to areas near the Rocky Mtn front and portions of Glacier
County through early this afternoon then spread east across north
central MT late this afternoon and evening with the passage of a cold
front and surface low pressure rises. with H7 winds still progged to
reach 80-90kts across Glacier County this afternoon and favorable
ridgetop wind/temp profiles, potential for isolated gusts of 90-100
mph exists for favored locations along the east slopes of the
Northern Rocky Mtn Front and Lewis Range with gusts 70-80 mph
possible from areas near Choteau northeast to the Sweet Grass
Hills. Further south and east, strong winds will primarily be
driven my mixing of the strong winds aloft late in the day as well
as the passage of the surface front in the evening and with gusts
up to 65 mph possible and locally higher where terrain, including
the Highwoods, little belts and Bears Paw Mtns may amplify the
winds some. Winds aloft subside somewhat tonight through Wednesday
and pressure gradient relaxes. Winds aloft increase again
Wednesday night into Thursday as the next Pacific trough reaches
the coast, also backing the flow to more southwesterly. After
some slight cooling on Wednesday, temperatures will warm again
Thursday under the increasing SW flow aloft with potential
increasing again for strong winds for areas along the Rocky Mtn
Front. Hoenisch

Thursday night through Tuesday...By late week, we begin to see a
swift change in the weather pattern as a quick moving cold front
passes through the area on Friday. This will introduce increasing
clouds and spotty rain shower chances. Following the cold front
passage with be much cooler temperatures as afternoon highs will
range 15 to 25 degrees cooler than on Thursday. While the better
coverage of precipitation will likely be confided to central and
southwestern areas, some higher elevations in these areas may likely
see snowfall accumulations as freezing levels drop into Friday night
and Saturday morning.  This system will quickly depart Saturday
afternoon leaving behind clearing skies during the day with highs
remaining near average. However, by Sunday the upper air pattern
begins to change yet again thanks to the development of a strong
upper ridge across the southwestern US. The associated effect across
the northern Rockies will be the development of a strong upper-level
jet thanks to increasing/steepening heights aloft which will lead to
yet another potential high wind event beginning early Sunday and
lasting into the afternoon hours. While it is a bit early to get
specific with details, model guidance remains in good agreement that
another high wind event will bring widespread strong winds,
especially along the Divide and extending east into the Plains.
Since models have been struggling with wind gusts this far along in
the forecast, I have adjusted winds to reflect a more realistic
potential given the confidence of the upper-air pattern. Stay tuned
for updates. As we move into next week, the pattern is not expected
to change much with a progressively NW flow continuing on the
northern periphery of the west coast ridge. Temperatures wont warm
much because of this, but will likely range around to slightly above
normal while generally staying dry. KLG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  73  42  63  50 /   0  10   0   0
CTB  66  34  58  44 /   0  10   0  10
HLN  71  41  66  45 /   0   0   0  10
BZN  71  39  68  40 /   0   0   0   0
WEY  55  27  53  28 /   0   0   0   0
DLN  68  38  64  38 /   0   0   0   0
HVR  74  36  61  44 /   0   0   0  10
LWT  72  39  63  45 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until midnight MDT tonight Cascade...Central
and Southern Lewis and Clark...Chouteau...Eastern Pondera...
Eastern Teton...Hill...Judith Basin...Liberty...Toole.

Red Flag Warning until 7 PM MDT this evening Central and Eastern
Lewis and Clark National Forest Areas...Chouteau and Fergus
Counties...Eastern Glacier/Toole/Central/Eastern
Pondera/Liberty...Hill and Blaine Counties...Lewis and Clark
National Forest Rocky Mountain District-Rocky Mountain Front.

High Wind Warning until 4 AM MDT Wednesday Blaine...Fergus.

High Wind Warning until midnight MDT tonight Eastern Glacier...
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

$$

weather.gov/greatfalls



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