Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 180444
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1044 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 06Z TAFS through 06Z Friday night)
Issued at 1041 PM MDT Thu May 17 2018

VFR conditions expected overnight except for possible localized MVFR
across western WY with weak showers before 09Z/Fri.  Generally light
surface wind expect, with gradually turning to the north east of the
divide and KRKS by 15Z/Fri. MVFR ceilings moving into Big Horn Basin
with VCSH between 15Z-18Z/Fri as weak front moves southward.
Scattered thunderstorms expected to develop between 18Z-21Z across
central and southern WY as northerly flow strengthens east of the
divide and runs up against southerly flow in southern WY.  By 00Z-
02Z/Sat widespread rain showers expected across central and southern
WY, especially in upslope areas like vicinity KLND and KCPR. Heavier
precipitation moves to SE WY after 06Z/Sat.  Mountains to be
generally obscured after 00Z/Sat, and VFR/MVFR mix could also see
localized IFR conditions near and around heavier precipitation
Friday evening.

&&

.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...McDonald
FIRE WEATHER...Baker



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