Severe Thunderstorm Warning 27, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
1059 AM MDT Sun Jun 28 2020

.SHORT TERM...This afternoon through Monday night

Clouds have spread over the Cowboy State this morning. Showers
continue over the Jackson/Star Valleys, spreading northeast into
southern portions of the Bighorn Basin. This trend will continue
through the rest of the morning, even lifting more northward toward
Yellowstone, as these bands of showers stretch back into ID. Based
on surface obs, the cold front is draped along portions of central
WY to southwestern portions. The forecast remains that the eastern
flank of the front will push northward this afternoon. This will be
the focal point of the strongest storms, where shear and instability
will be greatest. A surface low will develop along the front over
portions of Johnson/Campbell counties this afternoon and evening,
adding to the severe threat. Elsewhere, strong surface winds will
develop this afternoon over southern and central portions. South to
southwest winds 25 to 30 mph, with gusts of 45 to 50 mph, will occur
in these areas. Showers and storms over these areas this afternoon
could easily increase these winds, causing strong, damaging wind
gusts. Locally heavy rain will also be a concern this afternoon,
with precipitable water values of 0.60" to 0.80" are once again in
place across the forecast area.

The thunderstorm threat will decrease this evening, while showers
continue through the overnight hours. These showers look likely from
southern Lincoln County to western Big Horn County. Rainfall amounts
through tonight remain largely unchanged, ranging between 0.30" to
0.50" over southwestern portions, 0.60" to 0.75" from the
Jackson/Star Valleys to the Cody Foothills, and around 1 inch in the
western mountains. Snow levels will fall tonight, dropping to
around 9000 feet by the predawn hours Monday morning.

The cold front will progress eastward over central and southern
portions tonight, becoming stationary from eastern Johnson County
southward to eastern Sweetwater County. Cooler temperatures will be
in place across the forecast area Monday, with rain showers being
confined mainly west of the Divide. Some of the showers will spill
east of the Divide near Dubois, Crowheart, Cody and Lovell. Rainfall
amounts will be much lower in these areas, compared to Sunday, with
up to 0.20" through the day Monday. Gusty southwest winds will
return Monday afternoon as well, with gusts of 35 to 45 mph
occurring in the vicinity of the front.

Showers will continue across much of the area Monday night, with
isolated areas of wetting rain. Overnight temperatures will remain
mild east of the Divide, with readings dropping into the 30s over
the far west.

.LONG TERM...Monday night through Saturday
Issued at 139 AM MDT Sun Jun 28 2020

A closed low along ID/MT area, with the associated trough
extending southward into UT, will keep the south-southwesterly
flow across the region. Shower activity will be widespread across
the forecast area, with the heaviest amounts across the
northwest, north and northeast. Thunderstorm activity will also
develop across much of the region. Tuesday and Wednesday show
continued south-southwest flow across WY on Tuesday and
Wednesday, and are now in a little better agreement on the
movement of the closed 500mb low into MT. The pattern is still
keeping a moist flow across the region for showers and storms
through Wednesday.

Temperatures will show a slow decline through Wednesday, before
starting to warm up into next weekend. Models are still trying to
kick the trough out to the northeast Thursday, with a nice drying
trend moving in. Flow will be more westerly, allowing for a
series of shortwaves to move through MT and clip northern WY. The
north and northwest will still see some afternoon and evening
convection Thursday, Friday and Saturday.

&&

.AVIATION...For the 18Z TAFS through 18Z Monday

Showers continue to move across the region this afternoon. Most
areas will remain in VFR conditions with MVFR cigs/vsby possible
in heavier showers. Gusty winds will also continue across KRKS,
KRIW, KLND, and KCPR as well as at KBPI and KPNA through the
afternoon. A round of scattered thunderstorms is expected to erupt
by mid afternoon at KWRL, KRIW, KLND, and KCPR, and will continue
through early evening. These storms may produce strong gusty
winds, heavy rainfall, and possible small hail. Expect possible
IFR conditions in thunderstorms. Thunderstorms will transition to
showers with MVFR cigs and vsby possible after around 03Z Monday.
Widespread rainfall with local MVFR cigs/vsby will continue across
KJAC, KBPI, KPNA, and KCOD overnight and through Tuesday morning.
Some embedded thunderstorms are also possible in theses showers.

&&

.FIRE WEATHER...

Wetting rains will continue over far western zones, with
accumulations of up to an inch through tonight. Areas from RKS to
CPR will see gusty southwest winds up to 50 mph at times, while
humidity values fall to around 25 percent. Thunderstorms in this
corridor could have even higher gusts at times. Strong to possibly
severe storms will be possible over portions of zone 281 this
afternoon.

&&

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

SHORT TERM...LaVoie
LONG TERM...Swanson
AVIATION...Fisher
FIRE WEATHER...Straub/LaVoie

Hazardous Weather Outlook
National Weather Service Riverton WY
409 AM MDT Sun Jun 28 2020

WYZ001>020-022>030-291015-
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-
409 AM MDT Sun Jun 28 2020

This Hazardous Weather Outlook is for Western and Central
Wyoming.

.DAY ONE...Today and Tonight.

Widespread showers and thunderstorms expected for western and
central WY today and tonight. Some thunderstorms could be severe,
with very gusty winds. Areas around Johnson County may also see a
threat for hail this afternoon. Persistent rainfall across
northwestern WY may lead to some localized flooding.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Showers and thunderstorms will continue into the day Monday, with
some localized gusty winds with stronger thunderstorms.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report any significant weather
conditions.

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