Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 231942

Area Forecast Discussion
National Weather Service Riverton WY
142 PM MDT Wed May 23 2018

.SHORT TERM...(This evening through Saturday)
Issued at 123 PM MDT Wed May 23 2018

Main circulation center is finally lifting nwd into srn MT with
significant wraparound rain/snow continuing in the northwest. Snow
level was as low as 7500 feet in YNP with Lake Yellowstone snowing
all morning long. Pcpn amounts from this system were substantial in
the north half with 1 to 2 inches in the nrn Bighorns (2.99 at Rock
Creek) with two-thirds to around an inch in the srn Bighorns. The
Cody Foothills received widespread 1"+ amounts with local 1.50". The
Dubois to Crowheart area received .60 to .70. Anderson Ridge on the
west side of South Pass received almost 2 inches. Rain and some
higher elevation snow will continue in the northwest into this
evening before gradually decreasing. There will be a few tstms out
and about into early this evening, especially in the sern zones
where an area of 500+ 100mb ML CAPE is brewing along with storms
already. Even the far north has some building CAPE so we`re not
quite done yet. The far nrn part of Johnson County has some
potential for a few stronger storms with convergence around nearby
sfc low. Slight risk covers the a tiny part of nern Johnson. On
Thursday, we start to see shortwave ridging but low level moisture
and daytime heating will start to fire storms over the mountains. A
weak disturbance may get the far west going by late morning
(possibly). More substantial ridging moves in Friday for continued
warming and dry for all but a few mountain locations. On Saturday,
the future Memorial Day storm begins to dig into NV. It is currently
out near 36N/135W. In the short term period, the main effect from
this system (besides the pre-storm warmup) will be the threat of
thunderstorms in the west Saturday. We see the cyclonic nose of the
jet moving nwd into swrn WY Saturday along with the first shortwave
lifting nwd across wrn WY. A few of these storms could be quite
strong. One other area could be nrn Johnson if the frontal boundary
hangs in across the area. This is showing up more on the NAM than
the GFS. The weather just deteriorates after this period the
remainder of the Memorial Day weekend but more on that below.

.LONG TERM...(Saturday night through Wednesday)
Issued at 123 PM MDT Wed May 23 2018

Saturday night into Sunday morning a Pacific Low will move across
Northern Nevada/Utah headed towards Southern Wyoming. Widespread
shower and thunderstorm activity should be expected through Sunday
and into Monday. Temperatures will cool slightly with the increased
cloud cover. GFS indicates the highest rain amounts could be in
Southern Big Horn Basin where a significant amount of rain has
already fallen and flooding issues are already a concern. As the low
progresses over Wyoming Monday expect more showers and thunderstorms
through the day, but coverage should be more isolated. The low will
be to the east by Tuesday but showers and afternoon thunderstorms
will linger in and around the mountainous areas. Wednesday will see
weak ridging and dryer weather.


.AVIATION...(For the 00Z TAFS through 00Z Thursday afternoon)
Issued at 123 PM MDT Wed May 23 2018

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

MVFR/low end VFR ceilings/visibility values at and around KJAC until
Thursday morning. VCTS will be possible at KBPI until around 02Z and
KJAC, KPNA, and KRKS until around 01Z Thursday. Mountains will be
obscured at times. Wind gusts to 30 knots and small hail will occur
with any stronger storms. Most terminals will have fog in the area
tomorrow morning but not confident enough yet to put it as

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

Widespread showers and isolated TSRA with MVFR conditions are
expected at KCOD until around 02z Thursday with lingering showers in
the area until 12Z Thursday. VFR ceilings are expected rest of the
area. VCTS is expected at KWRL until around 02Z Thursday. Very
isolated showers are expected at KRIW and KLND through 10Z Thursday.

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


Issued AT 123 PM MDT Wed May 23 2018

After the showers gradually wind down in the northwest, the overall
Thursday into Friday will show a considerable drying and warming
trend. There will still be a good chance of showers and
thunderstorms Thursday in the northwest though but otherwise, most
areas will be dry Thursday through Friday. Temperatures will become
quite warm with 60s and 70s across the lower elevations Thursday and
70s to 80s Friday. Min rh`s will dry out by Friday but most areas
will still be in the 20 to 30 percent range except for 279 where min
rh`s could drop to around 15 percent or less Friday afternoon. There
will be some breezy areas Thursday from Rock Springs to Casper and
in the lee of the mountain ranges. Less wind is expected Friday.
Mixing and smoke dispersal will range from very good to excellent on
Thursday and generally good to very good Friday except excellent in
the southeast part of the district.





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