Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 240539
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1039 PM MST Tue Jan 23 2018

.SHORT TERM...(This evening through Friday)
Issued at 235 PM MST Tue Jan 23 2018

Shortwave ridge move in over the next 24-36 hours with steepening
low level inversions for the basins/valleys and increasing
foothill/mtn temps tonight and Wednesday. Weak ripple with
associated upglide in the nw corner this evening will bring a brief
bout of light snow/flurries, otherwise, I dry and quiet period
through Wednesday night. Besides the inversions, we`ll have to worry
about increasing wind potential. The Cody Foothills are starting to
show a gap flow potential tonight with potential for some 45-55 mph
winds in the favored gap flow areas south of Clark along the highway
and just south of Cody. Added in some wind in these areas and will
likely issue an sps for gusty cross-wind potential. The wind
corridor will also see increasing wind later tonight into Wednesday
morning. The winds really get going then as the H7 winds back to sw
and increase to 50kts or so later Wednesday evening through much of
the day Thursday. Will issue a high wind watch for the two wind
corridor zones form Jeffrey City to Casper from 06z Thursday through
00z Friday. The approaching trough arrives in the west Thursday with
the front pushing east across the area through the day. This front
will help mix the basins out and bring a bout of strong west wind
with fropa (and potentially ahead of it). A quick shot of snow will
spread into the west Thursday morning and all but end by Thursday
evening. Amounts look to be sub-advisory for most if not the entire
area. Could be some 3-4 inch or so amounts around the favored Star
Valley locations but overall looks like a 1 to 3 inch type event for
most areas. The mountains will get a quick shot of 2 to 5 inches. As
the cold front blasts across the I80 corridor Thursday afternoon and
early evening, there will likely be a quick shot of snow to go with
the strong to high winds which may cause a few hours of travel
issues. Another system follows right behind this one with another
round of snow out west on Friday (and into the medium range period
but more on that below). Snowfall amounts of 3 to 6 inches in the
mountains and 1 to 3 inches across the lower elevations are a
reasonable expectation during the day Friday with more into the
weekend.

.LONG TERM...(Friday night through Tuesday)
Issued at 235 PM MST Tue Jan 23 2018

We could see some heavy snow showers with the Pacific cold front
early Friday evening, especially in the far northwest where negative
lifted indices are progged. Once we are in the cooler air, steadier
snowfall will occur in the far west later Saturday night once
isentropic lift gets underway. The troughpa will occur around 12Z
Saturday. The Euro is the outlier and the fastest model with the
troughpa occurring in the Great Plains at 12Z Sat. The Canadian is
the most amplified with timing somewhat similar to the GFS, although
the GFS brings the trough through in pieces. In any event, this
trough should blanket the far west with substantial snowfall totals
by Saturday evening given the broad area of isentropic lift expected
there after the fropa. The GFS has bulls eyes of an inch and a third
of precip in some areas with this weather system in the far west.
Areas east of the divide will remain mainly dry. Behind the exiting
trough, periods of light snow will continue over the far west
through Sunday morning as a direct feed off the Pacific from the
west northwest continues behind the trough axis. Then by Sunday
afternoon, warming and drying will take place as the next ridge
builds in from the west along with the jet stream shifting to the
north of the area. Sunday should also turn out to be quite windy
along the east slope of the Divide as well as along the southern
wind wind corridor with h7 winds increasing to 50 knots out of the
west. These winds will help usher in milder air. Temperatures will
warm up to the 40s east of the divide in areas that mix out Monday
and Tuesday. The next upstream Pacific trough will deliver more
snowfall to the far west later Monday night into Tuesday with the
Canadian, again, the most amplified with this trough. With the low
attempting to close off over the Southern Great Basin, we could see
another major snow over the CWA.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1038 PM MST Tue Jan 23 2018

West of the Continental Divide...KJAC, KBPI, KPNA and KRKS

Some morning fog could occur across the western valleys as well as
some ceilings between 035-080 FT AGL Wednesday morning.
Otherwise, VFR conditions with sct-bkn high clouds will occur.
Also some LLWS will be present at times especially Wednesday
night.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

The main concern will be windy west to southwest wind and/or LLWS at
area terminals through the period. The exception will be in the
central basins where winds will be light. Otherwise, expect VFR
conditions with sct-bkn high clouds.

&&

.FIRE WEATHER...
Issued AT 235 PM MST Tue Jan 23 2018

Winds will be on the increase across the Jeffrey City to Casper area
later tonight and continue quite windy the next couple days. The
mountains and foothill areas will see warming temperatures and the
potential of gusty winds at times. The basin/valley inversions will
hold into Thursday morning before weakening as a cold front blasts
across the area Thursday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Wednesday evening through Thursday
afternoon for WYZ019-020.

&&

$$

SHORT TERM...Skrbac
LONG TERM...Lipson
AVIATION...Murrell
FIRE WEATHER...Skrbac


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