Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 211858
Area Forecast Discussion
National Weather Service Riverton WY
1258 PM MDT Fri Oct 21 2016
.SHORT TERM...Friday through Sunday night
All in all not a lot of concerns today as a ridge of high pressure
will bring largely tranquil weather to the area through the weekend.
But as always, there are a couple of flies in the ointment.
Today looks like a mainly quiet day. With flow turning more
westerly and more sunshine today, temperatures will warm when
compared to yesterday, about 5 to 10 degrees when compared to
Thursday. Tonight, a shortwave will move across the state. The NAM
is showing some 50 knot wind barbs late tonight and Saturday
near the Absarokas which could mean some gusty winds around that
area. However, the GFS is not nearly as bullish and keeps them in
the 30 to 35 knot range. In addition, the threat of strong winds
would be limited mainly to areas around Clark, where impacts would
be limited and this seams to happen every other day this time of
year. As a result, we will not issue any high wind highlights.
Dry weather is expected to continue into Saturday as well. With the
tighter pressure gradient with southwest flow, winds will become
gusty through the southwestern wind corridor. With warm temperatures
and low humidity, fire danger may become elevated in areas which
still have critical fuels. At this time, conditions look marginal
for critical fire conditions. As a result, we will hold off on any
highlights for now and let the day shift take a closer look.
Sunday looks mainly dry as well. Temperatures will cool a few
degrees but still remain above normal. With the less wind, fire
danger should decrease somewhat as well. The models do show a system
moving toward the area from the southwest and increasing moisture.
However, any showers that do develop would be very late at night
Sunday and be restricted to far southern Wyoming. There could be
some increasing high clouds across the area however.
.LONG TERM...Monday through Friday
Models are in decent agreement through much of the extended with longwave
troughs on each Coast with ridging of varying intensities in between
them. Confidence through Wednesday is moderate, but quickly goes
down late next week as models struggle if any energy in the
northern stream in Canada is able to dig into the northern U.S.
Thursday/Friday sending a back door cold front into the area.
Monday and Monday night, models continue to show some moisture
pushing north/northeast into the area in the southwest flow ahead
of a distinct mid-level wave pushing across the Central Rockies
Monday night. This combined with some weak right entrance region
should result in mountain snow/valley rain showers over the west
and south. Some of this activity could spill east of the Divide
mainly in the Wind River Basin and Natrona County. Precipitation
amounts are expected to be on the light side.
By Tuesday, a fairly strong upper jet pushes into the northern
Great Basin/Intermountain West with some left exit region dynamics
overspreading western Wyoming. Also a fairly moist southwest flow
will be present which will keep chances of mountain snow/valley
rain ongoing mainly across the far west. Again precipitation
amounts are expected to be light.
By late Tuesday night into Wednesday, a drying trend is expected
as the area transitions to the anti-cyclonic side of the jet and
ridging takes hold again. Will have some slight pop across the
After Wednesday, models have been struggling on how much energy
would be ejected east out of the longwave trough across the
Northern Rockies, as well as how much energy would be able to
slide south out of Canada. Some ensemble members suggest a
backdoor cold front with some Canadian air could impact the area
late next week. Have gone with consensus with little or no
precipitation with continued above average temps, but again
confidence is low due to model run to run variability.
While widespread VFR conditions are expected through the TAF
period, concerns continue relating to wind across the area.
Downsloping winds over the mountains will leave areas of LLWS,
with the opportunity for increased turbulence. LLWS has been
included at KCOD and KLND...with the threat weakening over KJAC
after 13z Saturday. Gusty surface wind will also be expected over
the wind corridor between KRKS and KCPR through much of the TAF
period...with generally light wind otherwise.
Today will be a dry day across the area with warmer temperatures. A
southwesterly breeze will develop from Rock Springs through Natrona
County. Relative humidity will fall into the teens at times today.
However, critical fire conditions are not expected today since winds
should not reach critical levels. Mixing and smoke dispersal will be
generally fair to poor. Elevated fire danger is possible tomorrow in
Natrona County with a combination of warm temperatures, low humidity
and a gusty southwest wind.