Winter Storm in Wyoming, March 25 to 26, 2018

Area Forecast Discussion
National Weather Service Billings MT
850 PM MDT Sun Mar 25 2018

.UPDATE...

Current forecast is in reasonably good shape overall. Did make a
few additional minor changes to the PoPs/weather. Convective snow
showers continue to fire around Livingston and along the
foothills, so increased pops in those areas. Still do not expected
exceptional snow accumulation, but a quick inch or so on grassy
surfaces is possible. AAG

&&

.SHORT TERM...valid for Mon and Tue...

Upper low spinning through southern Idaho with very cold aloft and
disturbance ejecting from base of the low into northeast Great
Basin inducing cooling cloud tops over western Wyoming. This area
of lift will overspread northern Wyoming and southeast Montana
this evening bringing a round of moderate to heavy snow with the
focus along the Montana Wyoming border. Current advisories and
warnings look on track for this system with areas along and north
of the Yellowstone River only seeing snow showers from the colder
air aloft where dynamics is weaker. By late Monday afternoon snow
winds down and shifts into the Dakotas. Will be below normal
temperatures on Monday due to clouds and upslope surface flow
limiting mixing.

Monday night is in between weather systems and falling pressure
over Alberta turns surface flow southwesterly which improves
mixing so should not be as cold as tonight. Shortwave moves from
BC to Saskatchewan and an associated Pacific front moves through
the area Tuesday afternoon. This will trigger a few showers but
better period of precipitation develops later Tuesday night as a
polar front drops into the area and another shortwave in northwest
flow aloft passes the area. This system has slowed up a bit so
the best accumulating snow looks to be very late Tuesday night
into Wednesday morning. Temperatures on Tuesday will definitely be
the warmest this week with the better mixing though some areas in
southeast Montana will see below normal temperatures due to fresh
snowfall. borsum

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

Northwest flow aloft on Wednesday in the wake of the wave on
Tuesday persists into Thursday before it starts to trend westerly
on Friday. However...increasing northerly flow over northern
Alberta is going to open the door to a shot of bitter arctic air
towards the region by Friday persisting into the weekend.

The unsettled northwest flow will have shower activity after
Wednesday morning and Thursday but precipitation amounts should
not be significant. Temperatures will have a chance to be near
normal but that depends on where a surface trough sets up and
timing of showers which will be partially diurnal in nature and
will shut off heating early in the afternoon. Southeast Montana
should see less showers but snow cover will hold temperatures
colder.

The change on Friday is going to be a major story though timing is
uncertain. All long term models are looking at arctic air surging
back into the forecast with the westerly flow aloft having a
chance to overrun the cold air with moisture. This means prolonged
accumulating snow and temperatures 30 degrees below normal are
possible. Cold air may stick around into early April though
precipitation will taper off. borsum

&&

.AVIATION...

A rain/snow mix along the Montana/Wyoming border will intensify
tonight and spread east. IFR conditions will become widespread IFR
to LIFR this evening for southern portions of southeast Montana
and northern Wyoming. KSHR will be the most impacted site. Expect
improving conditions after midday Monday. For the rest of the
area, expect mainly VFR conditions through the night. A few snow
showers are expected and could briefly turn conditions to IFR from
KBIL to KLVM through midnight. borsum/TWH

&&

.PRELIMINARY POINT TEMP/POPS...

    Mon     Tue     Wed     Thu     Fri     Sat     Sun
-----------------------------------------------------------
BIL 026/045 029/051 034/046 029/044 028/043 023/040 017/037
    42/S    11/N    45/W    43/W    33/O    32/W    22/W
LVM 023/042 028/050 034/049 030/048 030/049 026/044 020/041
    41/B    12/W    55/W    32/W    33/O    43/W    33/W
HDN 024/040 022/047 032/044 027/044 025/043 021/040 014/038
    43/O    11/B    55/W    53/W    33/O    32/W    23/W
MLS 025/037 022/045 031/041 025/039 023/036 017/033 011/032
    24/O    12/W    33/W    23/W    23/O    32/E    22/W
4BQ 026/037 020/043 031/042 025/041 023/041 019/038 013/035
    69/O    11/U    53/W    33/W    32/O    32/W    13/W
BHK 025/036 023/044 030/038 022/036 020/033 013/031 009/029
    24/O    11/U    33/W    23/J    23/S    32/E    13/J
SHR 024/037 020/048 030/045 026/045 026/047 023/042 017/039
    88/O    11/U    55/W    33/W    32/O    33/W    22/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory in effect until 6 PM MDT Monday FOR
      ZONES 36-38-58.
     Winter Storm Warning in effect until 6 PM MDT Monday FOR ZONE
      37.
WY...Winter Weather Advisory in effect until 6 PM MDT Monday FOR
      ZONE 98.
     Winter Storm Warning in effect until 6 PM MDT Monday FOR ZONE
      99.

&&

weather.gov/billings