Special Weather Statement, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
429 PM MDT Sat May 1 2021

.SHORT TERM...(This evening through Sunday night)
Issued at 125 PM MDT Sat May 1 2021

The leading edge of the trough is moving across the region now,
sparking scattered showers. Cloud cover has been thick enough in
most places to hold down some of the daytime heating, which has
limited lightning so far today. There's still ample dry air near
the sfc, and this will be helped by the forward speed of the
showers to produce locally gusty winds around any showers through
the afternoon. Initial shower activity will be waning after sunset
with loss of daytime heating.

The cold front will be dropping southward overnight tonight,
entering north WY around midnight, near the Divide by sunrise,
and exiting south into CO by noon. Northerly push should be
increasing lighter rainfall across the state throughout the state
on Sunday, with some snow accumulations for the Absarokas, Big
Horns, and Wind River ranges due to orographic lift of frontal
moisture. Temperatures will be noticeably cooler tomorrow, with
highs struggling into the 50s during the afternoon.

.LONG TERM...(Monday through Saturday)
Issued at 125 PM MDT Sat May 1 2021

Lingering showers will continue across the central and eastern parts
of the CWA as the trough very slowly shifts eastward; however,
models hint at a slight upper-level shortwave within the overall
general flow. This perturbation and strong, northwest flow will
allow precipitation across the western mountains into Tuesday. As a
trough digs, the precipitation will continue in the western
mountains before spilling over the divide late Tuesday into
Wednesday. Temperatures will favor rain showers in the basins while
snow is likely in the highest elevations. A ridge quickly build
behind the departing trough late Wednesday evening. This ridge
remains in place through the remainder of the week. This will allow
temperatures to climb back into the mid-70s by next weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 427 PM MDT Sat May 1 2021

Isolated to locally scattered convection will continue through
this evening, and will have VCTS at all terminals through this
evening. Thunderstorm outflow winds could impact terminals as
well. Along with convection, winds are expected to increase in
coverage. Wind gusts could exceed 25 knots at all terminals before
diminishing after 02Z. Widespread precipitation is expected to
increase across northern terminals after 12Z tomorrow and remain
through the period. VCSH is expected across southern terminals as
the main precipitation shield shifts south especially after 18Z.
Mountaintop obscuration may be possible through the period due to
lower cig heights.

&&

.FIRE WEATHER...
Issued AT 125 PM MDT Sat May 1 2021

Dry air remain in place today, but humidity readings below 20
percent remain limited to far southern WY. Gusty winds continue
for the Wind River basin, natrona County, and across zone 289
currently. Some light showers have been moving across the state
today, and will continue through sunset. A few lightning strikes
are possible across central WY later this afternoon, along with
locally gustier winds by any showers. A cold front moves across
the state tonight and tomorrow morning, bringing cooler
temperatures and widespread light rain and snow Sunday and
Monday.

&&

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

&&

SHORT TERM...Straub
LONG TERM...Vorst
AVIATION...Vorst
FIRE WEATHER...Straub

Hazardous Weather Outlook
National Weather Service Riverton WY
405 AM MDT Sat May 1 2021

WYZ001>020-022>030-021015-
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-
405 AM MDT Sat May 1 2021

This Hazardous Weather Outlook is for Western and Central Wyoming.

.DAY ONE...Today and Tonight.

Scattered afternoon showers and thunderstorms expected this
afternoon. Light mountain snow accumulation across the north
tonight.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Sunday and Monday...Valley rain and mountain snow likely at
times. Significant precipitation is possible especially over
central and south-central areas late Sunday into Monday.
Significant mountain snow possible, especially on the eastern
slopes of the Wind River Mountains.

Tuesday and Tuesday night...Valley rain and mountain snow will
occur again, especially over the northwest corner of the forecast
area.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions, according to standard operating procedures.

Special Weather Statement
National Weather Service Riverton WY
404 PM MDT Sat May 1 2021

WYZ001>020-022>030-020130-
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-
Including the cities of Lake, Mammoth, Old Faithful, Clark, Cody,
Meeteetse, Basin, Greybull, Lovell, Powell, Shell, Thermopolis,
Ten Sleep, Worland, Buffalo, Kaycee, Jackson, Dubois, Riverton,
Shoshoni, Lander, Jeffrey City, Casper, Afton, Alpine,
Star Valley Ranch, Thayne, Pinedale, La Barge, Big Piney, Farson,
Kemmerer, Cokeville, Rock Springs, Green River, and Wamsutter
404 PM MDT Sat May 1 2021

...Strong Winds from Showers and Thunderstorms This Afternoon and
Evening...

This is a special weather statement from the National Weather
Service Office in Riverton.

* WHAT...Strong wind gusts between 45 and 55 mph with localized
  higher gusts from any showers and thunderstorms. These winds can
  be well away from the showers and thunderstorms.

* WHERE...Western and Central Wyoming.

* WHEN...Through 8 PM.

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Special Weather Statement
National Weather Service Riverton WY
709 PM MDT Sat May 1 2021

WYZ020-022-020145-
Casper Mountain-Natrona County Lower Elevations-
709 PM MDT Sat May 1 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN NATRONA COUNTY UNTIL
745 PM MDT...

At 708 PM MDT, Doppler radar was tracking a strong thunderstorm over
Beartrap Meadows County Park, which is about 10 miles south of
Casper, moving northeast at 45 mph.

Wind gusts up to 50 mph will be possible with this storm.

This strong thunderstorm will be near...
  Evansville and Casper around 720 PM MDT.

This includes Interstate 25 between mile markers 176 and 193.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Infrequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4259 10633 4269 10652 4286 10639 4315 10614
      4311 10607 4280 10607
TIME...MOT...LOC 0108Z 218DEG 39KT 4275 10634

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