Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 221942 CCA

Area Forecast Discussion...Update
National Weather Service Riverton WY
1014 AM MDT Tue Aug 22 2017

.SHORT TERM...(Today through Thursday night)
Issued at 225 AM MDT Tue Aug 22 2017

Imagery shows an upper ridge/trof pattern across the CONUS from west
to east with a weak cut-off upper low still over cntrl California
coast and the Bermuda High also still intruding across sern/scntrl
USA. WY is currently under weak split flow, with the inflection
point between the nrn branch`s trof to the east and the ridge to the
west over nern WY. Circulation between the upper high and low over
the srn/swrn CONUS is just starting to moving weak monsoonal
moisture towards the FA. The SFC has continuing heat induced low
pressure over the Desert SW with a weak front to the north from srn
OR...east across srn WY and into the cntrl Plains and post frontal
high pressure building into the nwrn CONUS.

Today, post trof passage with nw flow aloft transitioning to upper
ridging and drying once again, expect most clear/sunny (smokey?)
skies with the only moisture/cloud intrusion into the FA coming into
swrn/srn WY with low POP chances across this area in the
afternoon/evening. Wednesday will have the ridge axis directly over
wrn WY with some modest monsoonal flow rotating into and across WY
from the south. Additionally, expect lee side troffing and the
passage of a weak upper level disturbance and front, allowing for
isolated (low elevations and foothills) to widely scattered
(mountains) showers/thunder to blossom in the afternoon and evening
across much of the FA except for the Big Horn Basin and Johnson
county. PWs are forecast to rise above .75 inch for most of the FA
so locally heavy rain...some with terrain tied mountain
storms...small hail and gusty winds will all be possible. Thursday
will have decent moisture/clouds remaining across the FA with
another upper level disturbance moving through WY, pushing a little
stronger front through area later in the afternoon and evening.
Again, high PWs but a little faster moving showers/storms will still
bring some chances for heavy rain in addition to small hail and
gusty wind from the local downpours.

.LONG TERM...(Friday through Monday)
Issued at 225 AM MDT Tue Aug 22 2017

Friday will see another chance of afternoon and evening showers
and thunderstorms over the region. Some storms will have heavy
rain and gusty wind. Saturday looks dry over most of the region.
Isolated showers and storms may occur in the Bighorn mountains and
across Johnson county in the afternoon and evening. Dry weather is
expected on Sunday and Monday. Only very isolated showers or
storms may pop up over the northern mountains in the late
afternoon and early evening Monday. Next Tuesday should see a
return to isolated showers and storms as more mid and high level
moisture returns to the region. Temperatures will be warm to very
warm with 80s to around 90 east of the divide and mid 70s to
lower 80s west of the divide. Wind will remain on the light side
during this period.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday)
Issued at 225 AM MDT Tue Aug 22 2017

Conditions will remain VFR through 12Z/Wed. Moisture to the
southwest of Wyoming will make a gradual return to the southwest
quadrant of the state late today and tonight. Weak convection, limited
by shear and instability, could again occur in extreme southwest Sweetwater
County late this afternoon and early evening. Little chance of impacting KRKS.
Drift smoke from any upstream fires in the Western United States should
have little impact on vsby today. Mid-cloud deck will push north early
Wednesday, but don`t see precipitation with these clouds. Diurnally-driven
west-northwest wind 10-12kts anticipated at KBPI and KPNA between 20Z/this
afternoon and 02Z/Wed. Other terminals to be 10kts or less through much
of the forecast period, with westerly surface flow west of the Continental
Divide and northerly surface flow to the east.


Issued AT 225 AM MDT Tue Aug 22 2017

Fuels at critical levels for most of the low elevation forecast
zones in addition to mountain zones above 8000 feet across western
and central Wyoming. (Please see the Fire Weather Forecast product
for more information). Elevated fire weather concerns continue for
southern and southwestern Wyoming today, mainly due to low RH values
expected by this afternoon along with occasional diurnal mixed out
wind gusts between 15 and 25 mph along and west of the Continental
Divide. Dry conditions continue with minimum RH values dropping into
the mid teens across the lower elevations, lower to mid 20s in the
foothills, and 25 to 35 percent in the mountains. Wednesday and
Thursday will be slightly cooler and more humid overall with
isolated to widely scattered chances for heavy rain producing





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