Special Weather Statement, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
242 PM MDT Wed May 26 2021

.SHORT TERM...(This evening through Thursday night)
Issued at 150 PM MDT Wed May 26 2021

Active weather pattern today across western and central Wyoming
as a strong shortwave trough moves from west to east. Line of snow
and rain showers from west-central WY to the Bighorns overnight
continues early this afternoon from South Pass to Johnson County,
with thunderstorms developing by mid morning. The storms so far
have produced brief heavy rain, small hail up to half an inch in
size, and wind gusts from 30-40 mph. A secondary line of storms is
behind this primary line by about 50-75 miles and seems to be
associated with the cold front moving eastward. The showers and
thunderstorms will continue for the next few hours, with
marginally strong storms possible for the rest of the afternoon
over Johnson and Natrona Counties. The secondary line of storms so
far is not as strong, likely because of the modified boundary
layer from the first line. Models continue to show the northern
part of the forecast area with moderate precipitation into the
evening hours. Also, the southern two-thirds of the area should
see a cold front move west to east and windy WNW wind to follow
through the early evening. This system has a decent comma head on
the back side, which should keep precipitation going across
northern WY until after midnight.

Shortwave ridging then moves over the area Thursday morning, with
lingering cloud cover and a slight chance of light showers over
the Bighorns and northern Johnson County early in the morning.
Skies will be mostly clear and temperatures will return to near
normal. The southern part of the state will see breezy west wind
continue. Another strong trough moves into Washington late
Thursday pushing high-level moisture and clouds over NW WY
overnight.

.LONG TERM...(Friday through Wednesday)
Issued at 106 PM MDT Wed May 26 2021

After Thursday's brief ridge, a trough will move east from
Washington, clipping the northern half of our area. This means
another round of isolated showers and thunderstorms Friday
afternoon, mainly limited to far northern Wyoming. A cold front will
follow Friday night, keeping temperatures a bit cooler on Saturday
for most locations. Additionally, rather diffuse zonal flow is
expected Saturday as height falls are realized across CA/NV. The
overall upper level flow looks messy, but isolated showers and
thunderstorms look possible again on Saturday afternoon, although
most areas should remain dry. Sunday and Monday will feature a
better chance for increased coverage of showers and thunderstorms,
especially across central and eastern portions during the afternoon.
Ridging will begin to increase Monday night, with a warming trend
beginning Tuesday. Isolated thunderstorms cannot be ruled out for
both Tuesday and Wednesday, especially east of the Divide.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday)
Issued at 1136 AM MDT Wed May 26 2021

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

Rain and snow showers will continue in the NW WY mountains through
03Z with some obscurations and MVFR conditions. Then conditions will
improve in NW WY after 03Z. KRKS will likely stay dry through the
period. Gusty wind will occur after the cold front moves through the
west with gusts to around 30 knots, with higher gusts possible at
KRKS. Wind will decrease around 02Z in most locations, with
conditions gradually clearing through Thursday morning.

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

Scattered showers and thunderstorm activity will move east this
afternoon through 00Z as a cold front also moves through the area.
Local MVFR conditions are expected in storms. Gusty wind will occur
after the cold front passes. Gusts around 30 knots will be common.
Wind speeds will decrease around 02Z in most locations. Isolated
showers will persist in northern WY after 00Z through about 06Z.
Some mountain obscuration will occur today.

&&

.FIRE WEATHER...
Issued AT 200 PM MDT Wed May 26 2021

Storm system is moving through the state today, and has brought
showers and thunderstorms to the northern two-thirds of the state.
Thunderstorms have brought brief heavy rain, small hail, and gusty
outflow - and the storms are likely to continue through sunset.
Overnight rain and snow moistened the environment up quite a bit,
though southern WY remained fairly dry and windy. A cool front
will move through the area this afternoon, with windy WNW wind
following through sunset. Lingering rain/snow showers will
continue overnight across northern WY as the storm system moves
eastward. High pressure moves over western and central WY on
Thursday, with a return to normal temperatures and breezy west
wind across southern WY. A weak system on Friday will generate
gusty southwest wind and isolated showers and thunderstorms.

&&

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

&&

SHORT TERM...McDonald
LONG TERM...Myers
AVIATION...Myers
FIRE WEATHER...McDonald

Hazardous Weather Outlook
National Weather Service Riverton WY
240 AM MDT Wed May 26 2021

WYZ001>020-022>030-270845-
Yellowstone National Park-Absaroka Mountains-Cody Foothills-
North Big Horn Basin-Southwest Big Horn Basin-
Southeast Big Horn Basin-Owl Creek and Bridger Mountains-
Bighorn Mountains West-Bighorn Mountains Southeast-
Northeast Johnson County-Southeast Johnson County-
Teton and Gros Ventre Mountains-Jackson Hole-
Wind River Mountains West-Wind River Mountains East-
Upper Wind River Basin-Wind River Basin-Lander Foothills-
Green Mountains and Rattlesnake Range-
Natrona County Lower Elevations-Casper Mountain-Star Valley-
Salt River and Wyoming Ranges-Upper Green River Basin Foothills-
Upper Green River Basin-South Lincoln County-
Rock Springs and Green River-Flaming Gorge-East Sweetwater County-
240 AM MDT Wed May 26 2021

This Hazardous Weather Outlook is for Western and Central
Wyoming.

.DAY ONE...This Afternoon and Tonight.

Scattered thunderstorms possible across much of the
area. Some storms could be strong with hail and strong winds,
especially in northern and eastern areas.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Friday...Showers and isolated thunderstorms are possible through the
afternoon and evening across far northern Wyoming.

Sunday and Monday...Widespread showers and thunderstorms are
possible across central and western Wyoming.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions.

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