Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 242058
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
258 PM MDT Sat Oct 24 2020

.DISCUSSION...

Tonight through Sunday night...

Snow will gradually diminish from the northwest to southeast
tonight into Sunday as forcing decreases and the upper trough
drops south and east of the area. Additional accumulations of 1
to 3 inches will be common tonight into Sunday, with slightly
higher amounts along the Bighorn Mountains. Blowing and drifting
snow will diminish into the evening as well. Record cold
temperatures can be expected tonight with lows in the single
digits above and below zero, and again Sunday night with many
locations going below zero. Highs on Sunday will be in the teens
for most places, a good 40 degrees below normal for October 25th.

The next weather threat after this storm moves out will be blowing
snow in the west. Surface pressure falls on the plains and cold
high pressure over Yellowstone Park will create a strong SW/W
pressure gradient over the foothills. Gap winds in the Livingston
and Big Timber vicinities may increase and reach 30 to 35 mph
with gusts over 50 mph late Sunday night into Monday. This could
lead to significant blowing and drifting of snow impacting travel.
We will be monitoring this situation closely. STP

Monday through Saturday...

Main concerns for early in the period will be gusty winds central
and W with blowing snow. Dry NNW flow will be over the area on
Monday and will be followed by anticyclonic flow through
Wednesday. Upper ridge will move over the region Thursday, then
Friday the model clusters varied from showing a ridge to SW flow.
Mean flow was zonal, and on Saturday, the clusters had a mean
weak ridge over the area. This upper pattern supported lee
troughing, with gusty winds in the gap areas occasionally
spreading into the central zones.

Time-lagged wind graphs for KLVM showed possible sub-advisory
winds through the period, with possible Advisory winds Tue.
through Wednesday. Big Timber was highlighted on the time-lagged
graphics for gusty winds Monday and Mon. night, and was also gusty
on the EC ensemble wind gust graph for Tuesday. The above graphs
also showed possible gusty winds in Harlowton through Tue.
evening. NAEFS had gusty winds over the central zones at 850 mb on
Tue., and the EC Extreme Forecast Index chart showed anomalously
high winds central and W Mon. and Tuesday. Based on the above, and
the orientation of the pressure gradient, have kept sub-advisory
to Advisory winds in the KLVM/Nye areas Mon. through Tue. night,
and have gone with Warning strength winds in Big Timber late Mon.
night into Tuesday. Gradient did not support strong winds in
Harlowton. Went with increasingly gusty winds in the central zones
through Tue. night as well. Also had definite blowing snow from
KLVM-Big Timber and over Nye during windiest periods. Otherwise
had patchy to areas of blowing snow central and W through Tue.
morning. Temps will then be in the 40s which should end threat of
blowing snow.

NBM brought a slight chance of snow to the SW Mountains Fri.
night, otherwise forecast was dry. NBM also showed possible record
cold high temps on Monday, otherwise majority of the period will
be in the 40s to lower 50s. Arthur

&&

.AVIATION...

Snow will continue across the area into the evening, gradually
tapering off from northwest to southeast overnight into Sunday.
Expect MVFR to IFR conditions with localized LIFR with the snow.
Northerly winds with gusts of 25 to 30 kts, will continue to cause
some blowing and drifting snow into the evening, before gradually
decreasing tonight. Mountain obscurations will continue. STP

&&

.PRELIMINARY POINT TEMP/POPS...

    Sun     Mon     Tue     Wed     Thu     Fri     Sat
-----------------------------------------------------------
BIL 004/014 902/026 016/039 029/042 029/044 032/049 032/048
    +2/S    00/Q    01/Q    11/B    10/B    00/B    11/B
LVM 902/014 905/036 018/047 026/050 029/052 030/054 029/052
    51/B    00/Q    01/Q    11/B    10/B    11/B    11/B
HDN 005/016 907/027 011/041 024/042 025/045 027/050 028/050
    +2/S    00/U    01/B    11/B    10/B    00/B    11/B
MLS 005/016 904/026 012/040 026/042 024/046 027/051 030/048
    71/B    00/U    01/B    11/B    00/B    00/B    00/B
4BQ 008/015 904/026 011/042 026/043 025/046 029/052 030/049
    +3/S    00/U    00/B    11/B    00/B    00/B    00/B
BHK 003/016 903/025 012/039 026/040 023/044 028/050 029/047
    71/E    00/U    01/B    11/B    00/B    00/U    00/U
SHR 004/015 907/032 009/045 024/047 025/052 028/056 028/052
    +5/S    00/U    00/B    11/B    10/U    00/U    11/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning in effect until noon MDT Sunday FOR
      ZONES 29>31-34-40-42-56>58-63-65-66-138-141-169>173-228-235.
     Winter Weather Advisory in effect until noon MDT Sunday FOR
      ZONES 32-33-36-37-139.
     Winter Weather Advisory in effect until 6 AM MDT Sunday FOR
      ZONE 64.
     Winter Storm Warning in effect until 9 AM MDT Sunday FOR
      ZONES 67-68.
WY...Winter Storm Warning in effect until noon MDT Sunday FOR ZONE
      199.
     Winter Weather Advisory in effect until noon MDT Sunday FOR
      ZONE 198.

&&

$$
weather.gov/billings


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