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afdbyz

Area forecast discussion...updated
National Weather Service Billings Montana
936 am MDT Wed Oct 18 2017

Update...

In the wake of a cold front passage last night, winds will be
generally lighter today with temperatures a touch cooler.
Downslope gradients will start to strengthen over the western
foothills this afternoon allowing temperatures to warm into the
lower 70s there with highs in the 60s across eastern areas. Have
adjusted the temperatures, sky cover, and winds to current
trends. Otherwise, the rest of the forecast remains on track and
the previous forecast discussion and updated aviation discussion
are below. Stp

&&

Short term...valid for tdy and Thu...

Strong shortwave was ripping across south central Canada. This
system produced 60+mph winds at Livingston, with gusts over 70mph
at Nye, as it produced a strong Lee surface trough. This system
also produced strong winds over northern Montana Tuesday afternoon
and night, with mild temperatures and low humidities over
southern Montana Tuesday. A cold front was now pushing across
northern Montana and will rush through eastern part of the state
this morning. This front will produce gusty northwest winds, but
the strongest surface pressure rises were over northeast Montana,
so not expecting highlight type of winds as the front comes
through, but will be breezy over the southeast this morning. This
front will have the biggest impact on the east for winds, but will
serve to decrease winds at Livingston and Nye.

Humidities were impressively low for this time of year as some
readings were still in the upper teens. As winds decrease,
humidities will rise. Will likely cancel the red flag warning a
bit early as the main fire weather threat was subsiding. Will also
cancel the Wind Advisory and High Wind Warning in place as
surface pressure gradient relaxes this morning. The cooling effect
of the front will be greatest over the east, as high temperatures
will be held down to the lower 60s. Downslope gradients will kick
back in over western and southern zones during the afternoon and
allow high temperatures to reach around 70.

A Lee trough forms once again tonight for increasing winds from
Livingston to Nye. Gradient does not look nearly as tight as the
gradient was yesterday. Guidance and local tools keep winds below
advisory criteria. Winds should increase tonight, but will keep
them below levels needed for a highlight. The flow backs for
Thursday and this will increase downslope warming and cause
temperatures to rise back into the mid to upper 70s for most
locations. Winds will be a little stronger on Thursday with
strengthening 850mb winds of 20-25kts and mixing. Winds should
remain below advisory criteria at Livingston, but will still gust
40-45mph nonetheless. Twh

Long term...valid for Fri...Sat...sun...Mon...Tue...

Extended forecast looking decidedly more active with each model
run. Wind will continue to be the biggest concern through the bulk
of the period. Changes to forecast centered around increasing
pops and precip coverage, and increasing wind values.

The cold front on tap for Friday appears to have sped up, so pre-
frontal warmup looks fairly limited in most locations, with
eastern most zones having best chance of reaching 70s ahead of the
front. Showers and isolated thunder will cross the area with the
frontal passage and through the afternoon. Strong and gusty northwest winds
will accompany frontal passage. Showers will clear out by Saturday morning
while cooler conditions and stronger mid-level winds move in
during the afternoon.

Westerly flow aloft continues to strengthen through Sunday
morning which will strengthen a Lee-side trough east of the Rocky
Mountain front. This will tighten the pressure gradient across our
foothill regions and when combined with 700mb flow nearing
60-70kts. This could result in very strong winds at the surface,
especially in those areas most prone across the region. While not
as strong, windy conditions will spread east through the rest of
Montana into the Dakotas during the day. Continued to trend winds
upward as does continue to look quite windy. That said, am a bit
apprehensive about inherent lift across the region. Think that
timing will be everything with winds Sunday. A weak disturbance
comes into the region Sunday afternoon/evening and increases rain
chances through Monday evening. Conditions will clear Monday
night, and upper level ridging will build back into the region
through the remainder of the period. Aag

&&

Aviation...

Current wind gusts along the foothills of 20 to 30 kts will pick
up through the late morning and reach 35 to 45 kts this afternoon
and evening. Expect these strong winds along the foothills to
continue through the taf period impacting klvm. Off the foothills,
southwest winds around 10 to 20 kts are expected through the taf.
Kshr will see lighter winds in the Lee-side of the bighorns and
remain mostly light and variable through the taf period. Dobbs

&&

Preliminary point temp/pops...

Tdy Thu Fri Sat sun Mon Tue
-------------------------------------------------------
bil 070 047/076 048/060 037/056 042/063 045/062 040/064
0/b 00/u 03/T 21/u 21/north 22/west 11/u
lvm 071 045/077 047/056 033/052 044/061 044/060 040/061
0/north 00/north 05/T 41/north 32/west 33/west 11/north
hdn 069 042/078 044/066 036/058 038/065 041/063 036/065
0/u 00/u 03/T 31/u 22/west 23/west 21/u
mls 066 041/077 043/068 038/058 037/064 042/061 035/062
0/u 00/u 01/b 30/north 12/west 22/west 11/u
4bq 066 041/078 042/073 038/057 036/065 041/060 034/062
0/u 00/u 01/u 20/north 02/west 23/west 21/u
bhk 062 038/079 040/074 038/055 034/062 040/058 034/059
0/north 00/u 00/u 22/west 02/west 22/west 11/b
shr 069 038/079 040/073 033/055 032/064 039/061 034/064
0/u 00/u 02/T 30/b 11/north 22/west 21/u

&&

Byz watches/warnings/advisories...
Montana...Fire Weather Watch in effect from Thursday morning through
Thursday evening for zone 117.
Wyoming...none.

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