High Wind Watch 18, NWS Riverton, WY

060 
WWUS75 KRIW 200255
NPWRIW

URGENT - WEATHER MESSAGE
National Weather Service Riverton WY
755 PM MST Sun Dec 19 2021

WYZ003-201300-
/O.UPG.KRIW.HW.A.0018.211220T1800Z-211221T1500Z/
/O.NEW.KRIW.HW.W.0023.211220T1900Z-211221T1500Z/
Cody Foothills-
Including the cities of Clark, Cody, and Meeteetse
755 PM MST Sun Dec 19 2021

...HIGH WIND WARNING IN EFFECT FROM NOON MONDAY TO 8 AM MST
TUESDAY...

* WHAT...West winds 30 to 40 mph with gusts 60 to 75 mph 
  expected.
 
* WHERE...Cody Foothills. This high wind event could produce
  similar peak wind gusts at both Cody and Clark. 

* WHEN...From noon Monday to 8 AM Tuesday. The strongest winds are
  expected from 4 PM Monday to 4 AM Tuesday.

* IMPACTS...Damaging winds could blow down power lines and ignite
  fires. Extreme blowover risk mainly for high profile vehicles on
  north to south oriented roads including Highway 120.

* ADDITIONAL DETAILS...Please keep two hands on your steering
  wheel in case of a sudden, strong wind gust. Also make sure your
  Christmas decorations are secure.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

In a parking lot, park into the wind to minimize the possibility 
of your car door hitting another parked vehicle.

&&

$$

21

Area Forecast Discussion
National Weather Service Riverton WY
1101 AM MST Sun Dec 19 2021

.SHORT TERM...Today through Monday

A flat ridge will be in place over the Cowboy State today and
Monday, resulting in a mainly zonal flow pattern. There will be
enough Pacific moisture within this flow to produce upslope snow
showers over northwestern portions today and tonight. Accumulations
will remain light, with 1 to 2 inches possible in the western
mountains tonight. Strong to high winds will continue across
portions of the Wind Corridor and the Cody Foothills today. Wind
prone locations like Clark and Wyoming Blvd on the south side of
Casper could have wind gusts of 60 mph, with gusts of 45 to 50 mph
expected across the rest of these areas. Will not issue any warnings
at this time, due to the isolated nature of this event. These winds
will decrease a bit for Monday, but will remain gusty, as a cold
front makes its way over areas east of the Divide. Temperatures will
warm today, rising to seasonal levels for much of the area. The
exception will be Johnson County, where highs in the middle 40s will
occur. Temperatures will remain seasonal across much of the forecast
area Monday, as a result of the cold front.

.LONG TERM...Monday night through Christmas

In recent model runs, there have been some changes as models
continue to keep zonal flow over the region for the first part of
the period. In the recent runs, models are hinting a stronger upper-
level ridge for Wednesday ahead of Thursday's trough. With this
ridge and the transition to southwesterly flow ahead of the trough,
temperatures will be slightly warmer than previous forecasts. As
Thursday approaches, models have slowed the highlighted feature
down. The ridge breaks down into zonal flow and the western
mountains will begin to see snow a few hours later than compared to
previous model runs. Then as the trough digs over the the Great
Basin, the associated precipitation shield will spread over the
Divide into Friday which has also been slowed down in recent
runs. With this much variability in the forecast, not going to
really discuss details or snow amounts with the exception of
mentioning that models are in agreement with something happening
and a white Christmas is very much possible.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1043 AM MST Sun Dec 19 2021

The main aviation concerns over the next 24 hours consist of
light snow showers and MVFR conditions at KJAC this evening, and
secondarily, gusty winds at KCOD and KCPR. Elsewhere, VFR
conditions prevail, with standing waves (can cause turbulence)
downstream of mountain ranges being the most widespread issue.

Snow-wise, a weather system focused over Montana will bring
modest lift and chance of snow to the Jackson Valley this evening.
Mountains will likely be obscured by snow showers and clouds. High-
resolution models show most snow showers staying over the
terrain, but a few may drift off the Tetons eastward, causing
periods of lowered visibility and snow at KJAC.

Wind-wise, the pressure gradient remains tight between the
Intermountain West and the High Plains, leading to strong winds in
the terrain of Wyoming and breezy winds in the wind corridor from
KRKS to KCPR. Notably, a jet streak moving into western Montana
may provide enough subsidence to push high winds into Cody and
Clark WY Monday afternoon. The HRRR model in particular suggests
the high winds (which usually stay fairly locked to the mid-
slopes of the terrain) may reach the airport and the WY Hwy 120
in the western Bighorn basin.

&&

.FIRE WEATHER...

West to southwest winds, with gusts of 50 to 60 mph, will occur
over portions of zones 276/280/286/289 today, before decreasing
later tonight. A cold front will move through areas east of the
Divide late tonight into Monday. Snow showers will develop this
afternoon and continue tonight over zones 140/415/286. Only 1 to 2
inches are expected tonight. Otherwise, no widespread precipitation
is expected until Wednesday at the earliest.

&&

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

SHORT TERM...LaVoie
LONG TERM...Vorst
AVIATION...VandenBoogart
FIRE WEATHER...LaVoie

Hazardous Weather Outlook
National Weather Service Riverton WY
240 AM MST Sun Dec 19 2021

WYZ001>020-022>030-200945-
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 MST Sun Dec 19 2021

This Hazardous Weather Outlook is for Western and Central
Wyoming.

.DAY ONE...Today and Tonight.

West to southwest winds, with gusts of 45 to 50 mph, will continue
over the eastern foothills of the Absaroka and Wind River
Mountains, as well as in the Wind Corridor from eastern Sweetwater
to Natrona County. Isolated locations may have gusts of 60 mph.

Snow showers will develop this afternoon and continue tonight over
northwestern portions. Accumulations will remain light, with 1 to
2 inches possible in the higher elevations tonight.

.DAYS TWO THROUGH SEVEN...Monday through Christmas.

Wednesday...A chance for snow over far western portions.

Thursday into Friday...Snow likely over far western portions,
with chances spreading across the south Thursday afternoon. There
will be a chance for snow over areas east of the Divide Thursday
night. This activity will continue into Friday.

.SPOTTER INFORMATION STATEMENT...

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