Area Forecast Discussion
Issued by NWS Riverton, WY

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687
FXUS65 KRIW 172059
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
259 PM MDT Thu May 17 2018

.SHORT TERM...This evening through Sunday
Issued at 258 PM MDT Thu May 17 2018

A large Pacific low pressure trough over the northern Rockies
and Great Basin spreading moisture and instability across
western, northern and central Wyoming will continue to produce
showers and thunderstorms with small hail, strong gusty winds and
local heavy rain tonight through Friday. Temperatures will cool
with increasing relative humidity. Showers and isolated
thunderstorms spreading east will linger into Saturday then
decrease as the trough moves east and high pressure moves in from
the west. Enough heating is expected to keep some showers over the
west and north on Sunday.

.LONG TERM...Sunday night through Thursday
Issued at 258 PM MDT Thu May 17 2018

The area will be between storm systems Sunday night and Monday with
one system exiting east across the Plains, and the next Pacific
upper low digging down the California coast. Some weaker
disturbances in southwest flow aloft will interact with slight
instability and some moisture provided by return flow around surface
high pressure over the Plains, resulting in isolate to scattered
afternoon/evening thunderstorms across mainly the south and west on
Sunday, and across most of the area on Monday.

The Pacific upper low will lift northeast across the Great Basin
Tuesday and Wednesday, and across Wyoming Wednesday night and
Thursday.  Low level easterly flow will bring in more abundant
moisture from the Plains to the east slopes of the Divide both days,
so we will likely see some stronger storms with heavy rain potential
across the area.  This system mostly be north and east of the area
by Thursday evening; surface trough axis should be over the High
Plains Thursday afternoon-evening with stronger, more organized
convection along and east of this axis.

&&

.AVIATION...For the 18Z TAFS through 18Z Friday afternoon
Issued at 258 PM MDT Thu May 17 2018

VFR will prevail at all terminals through 12Z/Fri. Convection is
already on the increase but should not impact any terminals until
around 21Z today with the best coverage across the north and
central. KJAC and KCOD the most likely terminals for thunderstorms
with KRKS the least likely. Temperature-dew point spreads favor no
more than 30-40 mph outflow wind gusts east of the Divide.
Thunderstorms should diminish by 05Z/Fri, but lingering showers are
anticipated through at least 08Z/Fri across the northwest.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued AT 258 PM MDT Thu May 17 2018

A large Pacific low pressure trough over the northern Rockies
and Great Basin spreading moisture and instability across
western, northern and central Wyoming will continue to produce
showers and thunderstorms with small hail, strong gusty winds and
local heavy rain tonight through Friday. Temperatures will cool
with increasing relative humidity. Showers and isolated
thunderstorms spreading east will linger into Saturday then
decrease as the trough moves east and high pressure moves in from
the west. Enough heating is expected to keep some showers over the
west and north on Sunday.  Mixing heights will lower Friday
and Saturday with general good smoke dispersal in the afternoons.
Areas with lower clouds and heavier precipitation will have poor
smoke dispersal.

&&

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

$$

SHORT TERM...Baker
LONG TERM...Hulme
AVIATION...Hulme
FIRE WEATHER...Baker



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