Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 222335
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
535 PM MDT Thu Oct 22 2020

.SHORT TERM...This evening through Friday night
Issued at 103 PM MDT Thu Oct 22 2020

The bulk of the snowfall is shifting southeast toward the
southeast portion of the CWA, congruent with the back edge of the
thick stratiform cloud feature as seen on the visible loop that is
casting a shadow on the lower clouds just to the north. This is a
reflection of the exiting QG forcing associated with the
shortwave trough and surface cold front that has made its way all
the way down to Sweetwater County, as the upper jet shifts south.
The back edge of the bulk of the snowfall appears to be making its
way across southeast Sweetwater and southeast Natrona counties at
the moment. Three hourly surface pressure rises of around 8mb
resulted in some wind gusts of 40 to 50 mph in several areas after
the fropa as a tight thermal ribbon shifted south. This front is
being driven by a surface 1041mb high. Winds will continue to
diminish, as the high builds in through this evening and strong
subsidence follows behind from the west following the exiting
shortwave.

Many areas will see the coldest temperatures of the season so far
this season with lows in the single digits and teens.

For Friday, expect mostly sunny but cold conditions as high
temperatures struggle to rise above freezing, with highs generally
relegated to remain 20 degrees milder than the lows Friday morning,
given the lack of mixing.

Another cold night expected one Friday night with lows in the teens
and some single digits. The next stronger approaching shortwave will
deliver more accumulating snow to the far north and west central
portions of the CWA as the flow tightens from the west and becomes
increasingly difluent, a mid level circulation develops over YNP,
and an area of isentropic lift shifts south over this area from
Montana.

.LONG TERM...Saturday through Wednesday
Issued at 1204 PM MDT Thu Oct 22 2020

Expect snow for the start of Saturday across northern portions of
the CWA. The snow is forecasted to spread southward through the
day. Temperatures may be a bit of a challenge on Saturday, as
areas south of the front and the snow may be relatively mild
before falling sharply later in the day and at night. Snowfall
amounts will be heaviest over northwestern portions, with over a
foot of snow expected in the mountains. Areas east of the Divide
will generally receive 1 to 3 inches, as most of the snow will not
start until midday or late in the afternoon. The Cody Foothills,
northern Johnson County and the Upper Wind River Basin near Dubois
could receive 3 to 5 inches.

By Sunday morning, almost every location can expect low
temperatures in the single digits (or even below zero in a few
locations). Temperatures are not forecasted to rebound much during
the day, with highs in the teens and 20s. Many temperature
records are expected to be easily broken for both lows and minimum
highs. In fact, some of the high temperatures may be within a few
degrees of the record lows for the same location. Scattered snow
showers will be concentrated over southern portions Sunday
morning, gradually ending through the afternoon as the system digs
southward over the Four Corners. With the very cold temperatures
on Sunday and then clearing conditions, expect lows Monday morning
to be even colder with widespread below zero readings. Once
again, many temperatures records should be easily broken.

After a frigid start to Monday, a warming trend is expected for the
remainder of the period along with dry conditions. Temperatures are
still projected to be quite cold for Monday after a very cold start
and a northerly wind. Highs are still not expected to be get above
freezing.  For Tuesday and Wednesday, expect the highs to gain about
roughly 10 degrees each day and approaching close to climo by the
end of the period.

&&

.AVIATION...For the 00Z TAFS through 00Z Saturday

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

Snow will continue to decline this evening, but MVFR conditions are
still possible through around 05Z with VFR conditions returning.
Winds will quickly drop off after sunset and remain fairly light
through the day Friday.

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals

VFR conditions are expected at all terminals. Winds will become
light after sunset, continuing through the rest of the TAF
period.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued AT 103 PM MDT Thu Oct 22 2020

Light snow will continue in central Wyoming this evening, but will
be on the decline. Precipitation should be done by midnight. Light
winds return overnight and continue into the day Friday.

A second cold front and a stronger cold surge arrives on Saturday,
with highs Sunday struggling to reach 20 degrees. Temperatures
remain well below freezing through at least Tuesday. Snow looks to
be fairly widespread with this weekend system, but most of the
activity will be in the northwest and across the north.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM MDT this evening for
WYZ008>010.

&&

$$

SHORT TERM...Lipson
LONG TERM...Clayton
AVIATION...Hulme
FIRE WEATHER...Hulme



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