Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 232105
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
305 PM MDT Sat Sep 23 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 249 PM MDT Sat Sep 23 2017

Northern and Central Wyoming will be on the western part of
a low pressure storm system which will bring snow mainly to the
mountains.  Snowfall of 5 to 10 inches is expected in the
Wind River and Bighorn mountains with3 to 6 inches over the
Absaroka mountains. Areas from 7000 to 5500 feet may see snowfall
of 1 to 2 inches.  West of the continental divide will see
some light snow showers along and near the Continental divide
tapering off to the west with little snowfall in the valleys.
Temperatures will be cold with generally high relative humidity
through Monday.  Some snow will linger over the mountains Sunday
night and Monday with clearing from west to east. Monday morning
will be cold. Monday night and Tuesday will be generally dry
with warming.

.LONG TERM...(Tuesday night through Saturday)
Issued at 249 PM MDT Sat Sep 23 2017

By Tuesday night, the shortwave on the backside of the exiting long
wave trough will be scooting off to the east of us, leaving us in nw
confluent flow and dry conditions. The only main difference in the
models as the ridge begins to build in from the west, is the way the
Euro depicts Wyoming in a col region Tuesday night with the exiting
shortwave over Minnesota farther to the east northeast of us than
the other models depict, with the cut off low over Vegas and the
building ridge over the far western US along with the ridge bulging
northwest from the Southern Plains. The other models still have us
under lingering nw flow, but overall, this really will not make a
difference in the outcome of the forecast. The basic trend for the
remainder of next week will be for warming temps as the ridge
continues to build in from the west, with the high ovhd by next
Saturday. The GFS does have a shortwave sliding southeast in the nw
flow along the front side of the building high Thursday, but it will
be lacking moisture so did not include pops, even in our northeast
zone for Thursday. We should see high temperatures approaching 60 in
many areas on both sides of the divide by Wednesday. By Saturday,
high temperatures will be well up in the 60s east of the divide with
70 in the Big Horn basin. High temps in the western valleys by
Saturday will be in the low 60s. So we have sunny pleasant fall
weather to look forward to beginning Wednesday. This trend goes hand
in hand with the 5 wave ridge moving east across the Western United
States, amplifying as it does, with the exiting long wave trough
deepening over the eastern half of the US during the week next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 249 PM MDT Sat Sep 23 2017

Thick multilayer cloud decks will be encompassing much of the CWA
along and east of a line extending from western Sweetwater County,
north along the west slope of the Wind River mountains, to the
eastern boundary of Yellowstone Park through Sunday. This area will
have extensive areas of IFR/MVFR conditions through 00z Sunday along
with mtn obscn. The terminals west of this area including KRKS,
KBPI, and KPNA with have more variability in the height of the cigs
and vsby during this time frame. However, Northwest WY including
KJAC will have VFR conditions along with occasional MVFR conditions
this afternoon with more frequent MVFR conditions along with LCL IFR
conditions after 00Z Sunday this evening as the trough axis over
Eastern Idaho approaches the area. This vast area of lowered vsby
and cigs will include an extensive area of precip with snow falling
above 5500 feet where vsby will be lowest, along with rain below
5500 feet. These conditions will persist through 00Z Monday.

&&

.FIRE WEATHER...
Issued AT 249 PM MDT Sat Sep 23 2017

Northern and Central Wyoming will be on the western part of
a low pressure storm system which will bring snow mainly to the
mountains.  Snowfall of 5 to 10 inches is expected in the
Wind River and Bighorn mountains with3 to 6 inches over the
Absaroka mountains. Areas from 7000 to 5500 feet may see snowfall
of 1 to 2 inches.  West of the continental divide will see
some light snow showers along and near the Continental divide
tapering off to the west with little snowfall in the valleys.
Temperatures will be cold with generally high relative humidity
through Monday.  Some snow will linger over the mountains Sunday
night and Monday with clearing from west to east. Monday morning
will be cold. Monday night and Tuesday will be generally dry
with warming.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM this evening to 6 PM MDT
Sunday for WYZ008-009-014-015.

&&

$$

SHORT TERM...Baker
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...Baker



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