Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 042211
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
311 PM MST Mon Dec 4 2017

.SHORT TERM...valid for Tue and Wed...

Pesky narrow band of light snow from near Harlowton to Billings
and Fort Smith has been slow to diminish but latest radar trends
suggest it is finally doing so. The combination of departing PV,
building heights from the west and increasing downslope gradients
will result in a dry night across our western lower elevations.

A couple forecast issues to deal with. First in our east. Clipper
dropping out of Saskatchewan will bring a reinforcing cold front
to eastern sections tonight, allowing for a period of mainly light
snow (and we are already seeing echoes on GGW radar upstream).
Then, moist isentropic ascent will overrun the surface cold air
with a favorable dendritic layer to bring another period of mainly
light snow to our far east on Tuesday. In addition, passage of
surface low into the Dakotas will result in increased NW winds. In
fact, latest GFS and EC show near 50 kts of 850mb wind with a
well-mixed boundary layer by Tuesday afternoon. Have raised wind
speeds to show gusts to 50 mph but it is possible that gusts will
exceed this especially on the ridges. A little snow cover may
result in a little stable layer along the surface and this may
keep gusts down a bit. All of that said, have issued a winter
weather advisory for snow and blowing/drifting snow for Fallon and
Carter Counties. Travel will be difficult in these areas
tomorrow. Gusts of 40-50 mph will extend west through Rosebud
County as well.

Now for the west. Aforementioned passage of surface low to our
east and a period of of favorable isallobaric wind will bring
strong west winds to our western foothills late tonight and
Tuesday. Surface gradients and northerly flow aloft not at all
favorable for gap flow, but west winds should be quite strong at
Big Timber and Harlowton. Have raised wind speeds here to bring
gusts in excess of 50 mph. Expect difficult crosswinds on Hwy 191.
With strong/stable surface high with 1040+mb pressures anchored
to our west, will need to keep watch of possible higher gusts.

Gusty W-NW winds will continue through Wednesday as another
clipper drops out of Canada and tight downslope gradients remain
in place. Winds should not be as strong as on Tuesday. We could
also see another shot of light snow to our far east on Wednesday
as another front backs in, increasing baroclinicity.

Temperatures will moderate to the 30s/lower 40s Tuesday, then fall
back to the upper 20s/30s Wednesday. Coldest temps will stay in
our east through the period.

JKL

.LONG TERM...valid for Thu...Fri...Sat...Sun...Mon...

Extended forecast will be fairly quiet across much of our region
with temperatures  above normal and precipitation chances below
normal.

A strong ridge of high pressure will be anchored over the western
coast of the United States on Thursday. There is good agreement
in many of the global models that this ridge will remain in place
through much of the extended forecast. At the mid-levels,
west/northwesterly flow under this ridge will prevail over the
region which should keep temperatures above normal through next
weekend. Forecast also looks fairly dry through the extended
period given the lack of any significant weather systems. The
main forecast concerns through the extended forecast will be
breezy conditions along our mountain foothills. A lee-side trough
just east of the Rocky Mountain will remain through much of the
extended forecast...yielding an elevated pressure gradient along
the mountain foothills. Occasional wind gusts to 40 or 50 mph are
possible through the extended forecast, especially Thursday night
into Friday morning.

Model spread begins to increase by next Tuesday as the ridge
slowly begins to break down. A few shortwave disturbances could
drop south along the eastern side of the ridge bringing much
cooler air into our eastern zones next week. These waves could
also increase precipitation chances for eastern Montana and the
western Dakotas. Dobbs

&&

.AVIATION...

VFR conditions will prevail for most locations except those in
our eastern zones near KMLS/KBHK and south/east of these locations
as snow showers develop after midnight. Widespread MVFR
conditions will develop in these areas along with occasional IFR
restrictions in the heavier snow showers. Snow showers will end by
the late morning hours as the disturbance pushes away. Elsewhere,
gusty west winds will develop tonight along our mountain
foothills with 45 kt gusts possible. Expect these gusts to spread
east after sunrise. Dobbs

&&

.PRELIMINARY POINT TEMP/POPS...

    Tue     Wed     Thu     Fri     Sat     Sun     Mon
-----------------------------------------------------------
BIL 025/041 027/039 027/047 033/052 031/050 029/046 029/046
    11/N    00/N    10/B    00/N    00/U    00/B    01/B
LVM 022/036 022/035 023/042 027/045 027/044 023/041 025/043
    11/N    01/N    10/N    00/N    00/N    00/N    01/B
HDN 025/042 023/039 022/046 028/051 025/050 023/046 025/046
    11/N    10/N    11/B    00/B    00/U    00/B    01/B
MLS 023/039 023/034 020/041 026/045 023/046 024/043 024/040
    43/S    01/N    00/B    00/B    00/U    00/B    02/W
4BQ 022/036 023/034 018/040 028/045 024/047 025/044 025/042
    53/S    11/N    10/E    00/B    00/U    00/B    01/B
BHK 017/033 021/027 015/036 022/039 020/042 021/040 021/037
    47/S    22/S    11/E    00/B    00/U    00/B    12/W
SHR 019/039 021/035 019/043 027/050 025/051 024/046 023/046
    11/N    11/N    11/B    00/B    00/U    00/U    00/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory in effect from 8 PM this evening to 6
      PM MST Tuesday FOR ZONES 33-37.
WY...None.

&&

$$
weather.gov/billings



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