Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 140445
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1045 PM MDT Sun May 13 2018

.SHORT TERM...This evening through Wednesday
Issued at 205 PM MDT Sun May 13 2018

Overview...The upper level low remains over NE NV today and remain
nearly stationary through much of the forecast period. The low is
expected to finally fill and slowly lift NE toward E ID by
Wednesday afternoon. A frontal boundary will surge back and forth
between southern Natrona/Fremont counties and the I-80 corridor
through southern WY today and Monday. By Tuesday, this boundary
looks to either wash out or push further south out of the CWA.

Discussion...A band of light showers over Johnson and Natrona
counties has finally dissipated this afternoon. Clearing skies from
this morning (that aided in this morning`s fog) continues across
central and eastern portions. This will help develop convection this
afternoon, as sfc dewpoints remain in the middle 30s west of the
Divide and the middle 40s east of the Divide. Areas west of the
Divide will be aided by weak shortwaves moving northward over E UT
and W WY. Similarly, the tail end of the light showers from this
morning, could become more convectively active and impact eastern
portions.  All other locations (especially the northern and central
mountains) could see convective activity due to daytime heating.
Temperatures will be warmer today, but still slightly below normal.

Widely scattered showers will return Monday. The best chance for
thunderstorms will across Natrona and Sweetwater counties, along the
frontal boundary. CAPE values will range between 500 to 1000 J/kg
and LI values of -2 to -4. However, sfc winds and mid level winds
will only be 5 to 10kt. So, any severe potential will be very
limited.

Convective activity will continue Tuesday and Wednesday, with the
best chances for storms occurring west of the Divide. Temperatures
will be seasonal Monday and Tuesday, rising slightly above normal by
Wednesday.

.LONG TERM...Wednesday night through Sunday night
Issued at 205 PM MDT Sun May 13 2018

Medium range period begins with our pesky upper low remnant still
over cntral ID/ern OR area with a new upper low moving into ecntrl
CA/wcntrl NV. Our old low is absorbed into this new system at it
slowly tracks towards nrn UT on Friday. The system will likely
weaken into a disorganized center on Saturday as it meanders
around swrn/scntrl WY or nrn CO area. Ridge starts to take back
over on Sunday but instability may remain in the far west for
afternoon convection.

The period begins with decent instability across the far west into
early evening with a chance of showers/tstms. Possible embedded
disturbance also ahead of our new upper low over the CA/NV border.
On Thursday, we see approaching front in the west with increasing QG
forcing from the south along with developing instability. An
increasing chance of tstms is expected in the west and perhaps
across the far nrn (especially nrn Johnson) where nrn plains
shortwave pushes a front into the north late in the day/early
evening. Upslope starts to develop east of the divide as this front
from the north drops down and at the same time, we seeing increasing
qg forcing spreading ewd on top of it along with multiple
disturbances. Some good instability will likely occur near the front
as it pushes south across ern Fremont/Natrona and then into
Sweetwater County Friday. It looks like there will be a good chance
of showers and some thunderstorms spreading east Thursday night
through Friday, continuing east of the divide Friday night and
possibly into Saturday morning. Certainly unsettled with the
possibility of a period of steadier showers with the ocnl thunder
threat. It looks better east of the divide by Saturday afternoon
with some instability keeping aftn showers/isold tstms out west.
With the upper low all but gone later Saturday night, it should dry
out. The aforementioned instability out west Sunday afternoon though
may result in sct aftn showers/isold storms. Some return flow
moisture along our ern border will have to be watched for late day
tstms in Johnson and Natrona County. Much cooler Friday east of the
divide with upslope, low clouds and potential off and on rain
showers with some tstm potential.

&&

.AVIATION...For the 06Z TAFS through 06Z Tuesday
Issued at 1045 PM MDT Sun May 13 2018

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

Isolated showers will occur overnight into the morning. Patchy fog
with local IFR conditions are possible in the western valleys,
including KJAC airport. This will occur until about 16Z. Scattered
showers and isolated thunderstorms will develop after 19Z in the
west and occur through about 03Z Tuesday. Local MVFR conditions will
occur with thunderstorms. Mountains will be obscured at times.

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

Isolated showers will occur overnight into the morning. Low clouds
will continue to develop overnight producing MVFR to IFR ceilings in
most locations by 12Z. The low clouds will dissipate by 18Z with VFR
conditions prevailing again. Scattered showers and isolated
thunderstorms will develop after 20Z and continue through 05Z Tue.
MVFR conditions will occur with thunderstorms. Mountains will be
obscured at times.

&&

.FIRE WEATHER...
Issued AT 205 PM MDT Sun May 13 2018

Widely scattered showers with isolated embedded thunderstorms will
occur across much of the forecast area this afternoon, moving from
south to north. The best chances for these will occur over western
and eastern portions. Overall, today will be a much drier day
than Friday or Saturday, with most areas rain free. Temperatures
will be a bit warmer, but still slightly below normal. Relative
humidity will remain above critical levels with winds generally
light to moderate. Mixing and smoke dispersal will range from poor
to fair for most areas east of the Divide, as well as northwestern
portions of the state. Mixing and smoke dispersal will be good
over western portions and very good across the south. Although
convective activity will remain widely scattered Monday, mixing
and smoke dispersal will range from fair to good.

&&

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

&&

$$

SHORT TERM...LaVoie
LONG TERM...Skrbac
AVIATION...AR
FIRE WEATHER...LaVoie



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