Area Forecast Discussion
Issued by NWS Riverton, WY

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337
FXUS65 KRIW 172045
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
145 PM MST Fri Feb 17 2017

.Short Term...Tonight Through Monday

A series of weak short wave low pressure troughs in southwest
flow aloft will bring periods of snow to the western mountains and
valleys, some rain in the valleys in the afternoons, through the
weekend and early next week. Snowfall is expected to be rather
light with 3 to 6 inches in the mountains every 12 to 24 hours.
Valley areas may see 1 to 3 inches every 12 to 24 hours. Expect
significant breaks in the precipitation between the troughs.
Some areas of rain and snow will move across areas east of
the Continental Divide but overall the west will be windy with
variable clouds and warming.


.Long Term...Monday Night Through Friday

The active period will continue through most of the long term. The
next system looks to move into the west Monday afternoon and
continue into Monday night. There is a bit of warm air initially so
we have some mix of rain and snow in the valleys Monday evening
before colder air moves in and changes everything over to snow for
the later at night. There could be some heavy snow with this system
as well later at night with some upper level support coming from the
left front quadrant of an 110 knot jet passing near the area
although the GFS is a bit more bullish on that idea than the GFS.
The snow looks to taper off but not stop on Tuesday with some
upslope flow continuing. Meanwhile, mainly dry weather should
continue East of the Divide. However, we can not rule out a few
showers across northern areas as the jet max approaches the area.
The big story Monday night will again be the wind. And the wind
threat of wind will be across the normally wind prone areas, a.k.a.
the Lee of the Absarokas, Rock Springs through Natrona County as
well as possibly the Lander Foothills. 700 millibar winds increase
to 50 to 65 knots and with some downward momentum possible from the
right front quadrant of the jet, a high wind event looks to be
decent possibility Monday night into early Tuesday before decreasing
later on Tuesday. Temperatures should continue to be above normal
through the that period with snowmelt continuing for many areas.

The sixty-four thousand dollar question for this period is what
happens with the mid week system. Both the GFS and European are
showing a decent storm developing with some lee cyclogenesis on
Wednesday night and into Thursday and then bombing the storm out as
it moves into the Plains states. However, the models still differ
on the details on what is expected to happen, as expected 5 to 7
days out. For now, what was in continuity still looks fairly
reasonable so we made only minor tweaks at this point. Temperatures
for Wednesday could be tricky though since a lot depends on the
arrival of the precipitation and cold front. This storm should move
out Thursday night with snow gradually tapering off. Another system
may move in on the backside of this storm. However, the models
differ on the strength of it so again, we made few changes to
continuity.

&&

.Aviation.../00Z Issuance/

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

VFR conditions will prevail at the terminal sites through 03Z.
Clouds will be lowering after 00Z with scattered areas of snow
developing by 03Z Saturday in southwest WY. This snow will
spread northward through 12Z Saturday. Areas of MVFR conditions
will occur after 03Z in the southwest, spreading northward
through 12Z Saturday. Expect mountains to become frequently
obscured tonight. Visibility and ceilings should improve after 12Z
Saturday with largely VFR conditions except for possible at KJAC.

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR conditions will prevail at the terminal sites through the
period. Isolated snow showers may develop after 03Z through 12Z
Saturday with dry conditions expected after that.

&&

.Fire Weather...

A series of weak short wave low pressure troughs in southwest
flow aloft will bring periods of snow to the western mountains and
valleys, some rain in the valleys in the afternoons, through the
weekend and early next week. Snowfall is expected to be rather
light with 3 to 6 inches in the mountains every 12 to 24 hours.
Valley areas may see 1 to 3 inches every 12 to 24 hours. Expect
significant breaks in the precipitation between the troughs.
Some areas of rain and snow will move across areas east of
the Continental Divide but overall the west will be windy with
variable clouds and warming. Areas with light winds will
experience poor smoke dispersal through the weekend while windy
areas will have fair to good smoke dispersal in the afternoons.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...C.Baker
LONG TERM...Hattings
AVIATION...Hattings
FIRE WEATHER...C.Baker



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