Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 171015

Area Forecast Discussion
National Weather Service Billings MT
315 AM MST Wed Jan 17 2018

.SHORT TERM...valid for Tdy and Thu...

A disturbance riding west to east across southern Canada will
increase westerly winds across the area today, helping to finish
scouring out the cold arctic air from low lying areas this
afternoon. Expect temperatures in the 30s and lower 40s this
afternoon for most locations, with maybe a few sheltered river
valley locations east holding in the upper 20s.

Winds in the western foothills around Livingston and Nye will
increase through the day, becoming strong this evening with gusts
to around 60 mph at times. These strong winds looks to continue
off and on through Thursday night and have issued a Wind Advisory
to cover this.

Thursday will see increasing cloud cover as a strong Pacific trof
moves toward the area. Strong SW-NE oriented jet stream on the
eastern periphery of the trof will park over the western zones
for about 12 hours late Thursday afternoon and Evening producing
strong downslope winds off the Beartooth/Absaroka mountains. In
addition to strong wind gusts these winds will work to inhibit
precipitation overnight despite the increasing moisture and energy
advection. Undercut precipitation guidance significantly due to
this downslope wind regime. Cold front moves through before
sunrise as the jet shifts eastward which will slacken the pressure
gradient allowing gap and downslope winds to weaken and
precipitation chances to increase heading through Friday morning.

Temperatures Thursday will be the warmest of the forecast period.
Have undercut guidance a bit from the 50s for western and central
areas back to the mid-upper 40s for highs based on cloud cover
and snow pack, with 35 to 45 over eastern zones.

Some mountain wave signatures Thursday evening will have to be
watched closely going forward for Beartooth and Bighorn foothills.
Models have 65-75kts of wind cresting the top of these mountain
ranges ahead of the cold front. Chambers

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

Still looking at a period of precipitation for the region Friday
through Fri. night. Models were in generally good agreement for
this system which will feature a strong NE to SW oriented jet over
the area, bringing in a subtropical atmospheric river. Jet
divergence will be confined to the western zones, and accordingly,
the highest precipitation chances will be over the SW mountains
and adjacent foothills. The area will be post-frontal on Fri. and
westerly mid-level flow will keep the airmass from getting too
cold. This flow will also provide downsloping off the mountains
which will keep precipitation chances lower over the plains. For
Friday morning, expect high chances for snow over and near the
western mountains with a chance over the plains. Expect a rain and
snow mix with snow over the mountains Fri. afternoon.
Precipitation will change back to all snow Fri. evening and
diminish from N to S over the area Fri. night.

An inch or 2 of snow is expected in KLVM with 2-3 inches in the
foothills. Around 6 inches is expected in the Beartooths/Absarokas
with lesser amounts over the other mountains. The biggest impact
from this system would be the rain and snow causing slick road
surfaces as the precipitation falls on frozen ground. High
temperatures will be slightly above normal on Friday, then
temperatures will drop below freezing Friday night.

Northern branch of a split trough will cross the area on Saturday
into Sat. night. A slight chance of snow will linger in the
mountains, with a chance of snow over KSHR and the far SE from the
departing energy from Friday`s system. Highs on Saturday will
reach the lower 30s. Brief upper ridging builds in for Sunday for
a mainly dry forecast and windy conditions in the gap flow and
Big Timber areas. Highs will be similar to Saturday`s readings. Models
showed additional Pacific energy and moisture crossing the region
on Monday bringing a slight chance of snow, before a ridge
approaches the area for Tuesday bringing dry conditions. Windy
conditions will continue in the favored western areas on Monday.
Not good model agreement for Wednesday, but blends brought a
slight chance for snow into the central and W. GEFS showed large
temperature spreads for late in the period, and model blends gave
20s and 30s for Monday and teens to 30s for Tuesday and Wednesday.



VFR will prevail over the area today and tonight. Localized
mountain obscurations are possible over the Beartooths/Absarokas
tonight. Expect LLWS over KMLS this morning and again tonight. SW
surface winds in KLVM will increase tonight with gusts of 40 to 50
kt expected late tonight. Arthur



    Tdy Thu     Fri     Sat     Sun     Mon     Tue
BIL 040 030/045 030/040 020/032 015/030 014/030 010/023
    0/N 00/N    34/O    31/B    11/U    02/S    21/N
LVM 041 036/049 031/040 016/032 014/034 017/035 018/034
    0/N 00/N    76/O    42/S    21/N    22/S    32/S
HDN 038 020/042 027/038 017/033 012/030 010/028 005/025
    0/U 00/B    25/O    41/B    11/U    02/S    21/B
MLS 032 020/038 026/037 019/031 011/028 011/024 007/015
    0/U 00/B    23/O    21/B    11/B    02/S    21/B
4BQ 040 022/044 028/039 023/034 014/032 012/028 011/023
    0/U 00/B    13/O    21/B    11/B    02/S    21/B
BHK 040 020/044 026/040 021/035 012/033 010/025 008/016
    0/U 00/B    12/O    21/B    11/B    03/S    21/B
SHR 041 020/046 029/038 019/031 014/030 012/030 012/026
    0/U 00/B    13/O    32/S    21/B    01/B    21/B


MT...Wind Advisory in effect from 6 PM this evening to 6 AM MST
      Friday FOR ZONES 65-66.


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