Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 131735
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1135 AM MDT Sun Aug 13 2017

.SHORT TERM...Sunday through Tuesday night
Issued at 230 AM MDT Sun Aug 13 2017

Once again, today will be more of the same. We still have a few
thunderstorms to the west and these may make it into southwest
Wyoming before daybreak. Otherwise, expect a day similar to
yesterday with another day of mainly afternoon showers and
thunderstorms and a mix of clouds and sun with more sun in the
morning and more clouds during the afternoon. Temperatures should
be fairly similar to maybe a degree or two cooler than yesterday.

Things could turn a bit more active on Monday. Both the NAM and GFS
show a more potent shortwave approaching northwestern Wyoming late
tonight. With decent moisture in place we added some thunderstorms
to that area late tonight. All areas should have a chance of
thunderstorms with the passage of the shortwave. In addition, the
Storm Prediction Center has some of the area under a marginal
risk. However, there could be a limiting factor. With the wave
moving through in the morning and early afternoon, instability
could be limited somewhat by cloud cover. At this point, the best
chance of stronger storms would be across Johnson County but more
likely across Eastern Wyoming east of the county warning area.
With more cloud cover, temperatures will be a bit cooler. In
addition, with a tighter pressure gradient developing, things
could turn breezier in areas favored by southwesterly flow, mainly
from Rock Springs through Natrona County.

At this point, Tuesday looks similar with more showers and
thunderstorms and locally breezier conditions. The NAM again looks
WAY too cool in some areas with high temperatures so we went
closer to the GFS guidance which looks way more reliable. The
Tuesday storms could be an early show however with most areas
mainly dry by sunset.

.LONG TERM...Wednesday through Sunday
Issued at 230 AM MDT Sun Aug 13 2017

Northwest flow aloft for Wednesday and Wednesday night. Isolated
showers and storms for the north and in Natrona county Wed
afternoon and evening. Dry elsewhere. A weather disturbance moves
through the northwest flow aloft Thursday into Thursday evening.
Again, showers and storms look to occur over the north half with
very isolated activity in the south. Friday and Friday night will
be dry with northwest flow aloft. The GFS and ECMWF models turn
the flow aloft to west on Saturday with limited moisture. Isolated
showers and storms over the northern mountains with dry weather
elsewhere. Next Sunday looks mostly dry east of the divide with
some showers and thunderstorms in the west and far south. ECMWF
model is more bullish than the GFS in the west. Will keep isolated
showers and storms in the west for now. Temperatures will be mild
Wed and Thurs. Then warmer highs Friday through Sunday.

&&

.AVIATION...18Z Issuance
Issued at 230 AM MDT Sun Aug 13 2017

VFR conditions will prevail through the forecast period. An upper
level disturbance moving across WY will trigger widely scattered to
locally scattered showers and thunderstorms again this afternoon
along and west of the Divide...isolated to widely scattered east of
the Divide. Storm and shower coverage will decrease after 02z this
evening. Brief heavy rain, small hail and erratic gusty winds G25-
45kt can be expected at times. Additionally, brief periods of MVFR
in lower VSBY and CIGS will also be possible during periods of
heaviest activity. Mountains will be partially obscured at times
this afternoon and tonight. Another upper level disturbance will
arrive across western and northwestern WY Monday morning with
showers and isolated thunder possible over this area after 10z
Monday morning.

&&

.FIRE WEATHER...
Issued at 230 AM MDT Sun Aug 13 2017

Fire conditions should remain below critical today. Another upper
level disturbance will move across the area and bring another round
of mainly afternoon and evening showers and thunderstorms. However,
most areas should be mainly dry most of the time. Relative humidity
will remain above critical levels with winds light to moderate except
in and around any shower or thunderstorm. Mixing and smoke dispersal
will range from fair in some of the Basins to very good to excellent
across portions of southern Wyoming.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Hattings
LONG TERM...AR
AVIATION...Braun
FIRE WEATHER...Hattings


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