Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 271941

Area Forecast Discussion
National Weather Service Riverton WY
141 PM MDT Thu Jul 27 2017

.SHORT TERM...This afternoon through Sunday

Synopsis...Upper level ridge begins to shift, in response to a
shortwave trough moving NE toward western WY this afternoon. As
a result, storms coverage will be concentrated over northern and
central portions of the forecast area. Showers may linger through
the overnight hours, as the trough exits over the Dakotas Friday
morning. A flat ridge will be in place over the area Friday and
Saturday, before building again during the day Sunday. A few
minor perturbations may pass over the area through the period,
with the best monsoonal flow somewhat suppressed to the south and

Discussion...Convective activity starting to fire at 18Z over
western portions, in response to the approaching shortwave.
Convection over Johnson and Natrona expected to be isolated for
the next hour or two. Coverage will increase across the north, as
the shortwave passes through and temperatures continue to rise.
Convection expected to be isolated across southern portions,
mainly from storms forming off the Uintas.

Although conditions will be drier through the rest of the period,
dewpoints will remain in the 40s and 50s. Fire danger will also remain
low despite the drier conditions. Convection will be isolated,
with most of the storm activity concentrated over the mountains.

.LONG TERM...Sunday night through Thursday night

It looks like more of the same across the area from Sunday through
Tuesday. Most of the monsoonal moisture will remain to the south of
the area but there will be enough moisture around for isolated to
widely scattered thunderstorms in most areas. It is very difficult
the most numerous storms this far out. And, in addition, with the
slow movement of the storms heavy rain will be a threat. As for
temperatures, look for temperatures close to seasonal averages with
the cloud cover hanging around. With a couple of shortwaves moving
through the area for Sunday night and Monday, these look to be the
two most active days.

The models are now indicating the ridge building a bit further to
the east for Wednesday and especially Thursday. This may lead to a
decrease in the coverage of thunderstorms with less moisture along
with warming temperatures aloft and higher heights. In addition,
with less cloud cover and higher thicknesses, temperatures will again
climb to above normal levels. As a result, we raised high
temperatures for Wednesday and Thursday, especially Thursday. Future
shifts may want to raise them some more if these trends continue.

.AVIATION...00Z Issuance

Showers and thunderstorms will continue into this evening. Locally
heavy rain will occur with stronger storms. This will produce local
MVFR conditions due to reduced visibility. Mountains will be
obscured at times. Showers and storms will be decreasing in coverage
by 06Z with lingering showers over the north through 12Z Thursday.
More showers or thunderstorms will develop on Thursday after 18Z
although coverage will be less than previous days and mainly in and
near the northern mountains around KCOD and possibly KCPR and


Fuels remain at critical levels for most forecast zones east of the
Divide (Please see the Fire Weather Forecast product for more
information). Today, fire danger is low for most mountain
locations and low to moderate for all other lower elevations, as
monsoonal moisture and precipitation chances continue across the
forecast area. Winds will continue to be seasonally light across
the forecast area with the day`s gustiest winds found near
stronger showers or thunderstorms (25 to 35 mph across western
portions of the forecast area...35 to 55 mph east of the Divide
and over southern Wyoming). Today there will be isolated to widely
scattered showers/storms across the lower elevations...with
scattered chances over the mountains. Expect periods of locally
heavy rain, small hail and gusty winds with the stronger showers
and storms. Drier weather and less chances for precipitation
return Friday and continue into Saturday.




LONG TERM...Hattings
FIRE WEATHER...LaVoie is the U.S. government's official web portal to all federal, state and local government web resources and services.