Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 260800
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
200 AM MDT Thu Apr 26 2018

.SHORT TERM...Today through Saturday night

A few showers continue to trek southeastward east of the Divide
this morning. Most of this is expected to exit the forecast area
by 12Z, but a few showers could still be lingering over Natrona
County. After a chilly start across the area this morning, a
massive ridge will build over much of the Intermountain West. This
ridge will slowly progress eastward today and Friday, as a cut
off low moves onshore during the day Friday. Moisture from this
system could begin to impact western portions Friday night, but
will increase by Saturday afternoon. Scattered showers with
isolated thunderstorms will mainly stay confined west of the
Divide. The models continue to slow this system, so this activity
could get shifted into the next forecast period. Elevated fire
danger will return across southern portions and the Wind River
Basin today and across all but far western portions Friday and
Saturday. Winds will generally be light today and Friday however.
Gusty south to southwest winds, with very warm temperatures, will
return across the area Saturday.


.LONG TERM...Sunday through Thursday

Overview...A Pacific cold front will push across the area on Sunday.
Windy and dry conditions will prevail across much of southern and
central Wyoming, increasing the risk of rapid spread of any new fire
starts.  A few strong thunderstorms are possible ahead of the front
across northeast Johnson County Sunday afternoon and evening. Cooler
and unsettled conditions will then linger across the area Monday
through Wednesday.

Discussion...Cutoff low off the northern California coast early this
morning will get kicked onto the west coast Saturday before
lifting/fragmenting into strong downstream ridge over the Rockies-
Plains on Sunday.  Overall model trends have been slower with upper
low`s progression across the Intermountain West and associated cold
front`s progression across Wyoming, and this morning`s ECMWF has the
cold front just moving across the Divide around midday Sunday.  Vort
lobe lifting north across Idaho Sunday should keep heavier
precipitation west of the border across Idaho and western Montana
with scattered mountain snow and valley rain showers across western
Wyoming.  ECMWF has been consistent with development of lee side low
near or just north of Sheridan on Sunday with CAPES ~1000J/Kg
wrapping from central High Plains into NE Wyoming, so a few
strong/severe storms could develop with this setup.  Upper low over
the Intermountain West will become increasingly fragmented as it
shears out NE Sunday into Monday, and more organized, heavier
precipitation should be out over the Plains by Monday ahead of
surface cold front.  Upper trough is expected to `reload` over the
west as shortwave digs down the west coast Monday and Tuesday. This
system is expected to close off near the Four Corners region on
Wednesday, the heavier precipitation with this system is expected to
remain south and east of the area, or from Colorado to SE Wyoming
with lighter, scattered activity across most of southern and central
Wyoming.


&&

.AVIATION...For the 12Z TAFS through 12Z Thursday night

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes

Some mountain snow/valley rain showers with a period of MVFR
ceilings will quickly exit the area from north to south between 08Z
and 14Z Thursday. Strong northerly wind early this morning will
quickly weaken by or shortly after 12Z. Skies are expected to be SKC
across the entire area by 18Z with lights winds, which should remain
that with the remainder of the TAF period.

West of the Divide...KBPI/KJAC/KPNA/KRKS Routes

VFR conditions are expected through the TAF period with mainly SKC
conditions and light winds. The main exception will occur across
Sweetwater County, where breezy east/northeasterly is expected
through mid-morning.

&&

.FIRE WEATHER...

A strong ridge will build over the region today and Friday,
keeping conditions warm and dry. Min RH values will reach critical
values again today across southern portions and the Wind River
basin. These values will spread to include all but the far west
Friday and Saturday, however, winds will be light today and
Friday. Gusty south to southwest winds will occur across much of
the area over the weekend, with Red Flag conditions possible.


&&

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

$$

SHORT TERM...LaVoie
LONG TERM...Meunier
AVIATION...Murrell
FIRE WEATHER...LaVoie



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