Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 180525
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1125 PM MDT TUE MAY 17 2016

.Short Term...Tonight Through Friday

Upper low has dropped steadily southward as expected with the
main circulation over Southern Nevada and another circulation over
East Central Utah. Weak upslope flow is keeping low clouds in
across most of the south half of the area. Any erosion of these
will likely result in a higher strato-cu deck to form. Boundary
layer gradually dries overnight with clouds generally decreasing
and retreating to the mountains. Convection that forms over the
wrn mtns later this afternoon and early evening will all but end
overnight. On Wednesday, we are still seeing more afternoon
instability with more daytime heating and residual moisture,
especially over and near the mountains. Very limited chance east
of the divide. Best chance will probably be Southern Sweetwater
County off the higher terrain and in the usual areas. On Thursday,
our large upper low will move into the Pacific Northwest with the
associated cold front moving into Eastern Idaho/Wrn Wyo border by
late in the afternoon or early evening. Cyclonic nose of the jet
will move into Idaho but models are differing and further north
than yesterday. Still looks like good potential of some stronger
thunderstorms forming over Eastern Idaho and then moving into at
least Northwestern Wyoming late in the afternoon/evening hours. As
the upper low digs into the west, the flow will actually back,
keeping the front near or just west of our area on Friday. We may
actually see some convection forming over the Wasatch and then
racing northward into Swrn Wyo later Friday. Some others may
still form in Eastern Idaho and try to move into our area but more
southerly flow could keep them west of the border. Still worthy of
a chance of showers and some thunderstorms in the west Friday with
anything east of the divide mainly over the mountains and far
north. The main weather east of the divide, especially Thursday
into Friday will be much warmer conditions with increasing south
to southwest wind and increasing snowmelt. Highs by Friday will
likely hit the upper 70s to mid 80s east of the divide with low
rh`s and strong/gusty s to sw wind. Any isold showers/tstms
(mainly near the foothills and north) will have strong wind
potential.

.Long Term...Friday Night through Tuesday

With the center of the large scale trough back over Oregon Friday
night, light to moderate strength showers and thunderstorms are
only expected across western WY, with the activity diminishing
after midnight. Overnight temperatures Friday night will likely be
warmer with southerly flow continuing. As the day progresses
Saturday, the mid levels will slowly destabilize in far western WY
as a tight temperature gradient moves west to east. The
instability will allow moderate strength showers and thunderstorms
across western WY. Southern WY and east of the divide will still
be quite warm with 700mb temps more than 8C. South to SW surface
flow more than 20mph and stronger mid level flow bring up more
moisture from the south/southwest. The center of the trough
doesn`t move much on Saturday, but the models are showing a
southern wave gather up and move into the Great Basin late Sunday
into early Monday, and then through WY on Monday. The movement of
this weak low center should draw the cooler air in the Pacific
Northwest across all of WY on Sunday. As this low center moves
over WY, the GFS leaves it more of an open wave while the ECMWF
wraps it up much more. As a result the ECMWF is much more bullish
with the precipitation on Monday. Have trended the forecast more
toward a GFS solution. Some areas across WY could see moderate to
significant precipitation sometime from late Sunday into Monday.
Snow levels Monday morning should range from about 7500 feet in
western WY to 8000 to 8500 feet in central WY.

Secondary energy from the eastern Pacific moves into the west late
Sunday into Monday as well, keeping a large scale trough over the
western US from Monday into the middle of the week, at least.
700mb temps early in the week are expected to only range from
about -2C in NW WY to +4C in the SE, resulting in below normal
temperatures next week with a chance of showers, primarily in the
western mountains. Differences in model solutions make for sketchy
details at this time.

&&

.AVIATION.../06Z ISSUANCE/

West of the Continental Divide...KBPI/KJAC/KPNA/KRKS Airports

VFR conditions are expected to prevail at the airports through the
period.  Drying will continue with general clearing over the west as
high pressure builds in over the area from the northwest.  With
afternoon heating scattered rain showers are expected to develop
over the higher mountains with a few thunderstorms possible.  Higher
mountains may become obscured locally in heavier showers and
thunderstorms from 19Z - 02Z Thursday.

East of the Continental Divide...KCOD/KCPR/LND/KRIW/KWRL Airports

VFR conditions are expected to prevail at the airports through the
period.  Drying will continue with general clearing over the area as
high pressure builds in from the northwest. With afternoon heating
scattered rain showers are expected to develop over the higher
mountains along the continental divide with a few thunderstorms
possible.  Higher mountains may become obscured locally in heavier
showers and thunderstorms from 19Z - 02Z Thursday.

&&

.FIRE WEATHER...

Fire danger will be low through tonight as green-up and elevated
humidity levels continue across Wyoming. A few showers and/or
perhaps an isolated stray thunderstorm will be possible into this
evening, mainly across the mountains or near a weak surface
boundary across the far south. Otherwise, isolated to scattered
mountain showers and storms along with warmer and drier weather
around for most areas through Thursday. Then, the next spring
system will arrive across western Wyoming Thursday night with good
chances for increased precipitation. East of the divide, the
weather will become quite warm and windy with increased fire
danger as temperatures soar into the mid 70s to mid 80s Friday and
Saturday with min rh`s in the upper teens to lower 20s and strong
south to southwest wind at times.

&&

.RIW Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...Skrbac
LONG TERM...McDonald
AVIATION...C.Baker
FIRE WEATHER...Skrbac



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