Severe Thunderstorm Warning 15, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
155 PM MDT Sun Jun 11 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 155 PM MDT Sun Jun 11 2017

A large unseasonably strong low pressure trough over the pacific
northwest will slowly approach the area with increasing showers
across the western and northern mountains with embedded isolated
thunderstorms possible in the afternoon and evening hours.  Snow
levels will lower to 8500 feet tonight, and 7500 feet on Monday
night. As colder air moves in stronger winds will move in as well.
A high wind watch has been issued for Sweetwater, fremont and
Natrona counties from noon Monday through 9 pm mdt Monday evening.
Mountain winds of 30 to 40 mph can be expected increasing to 40
to 45 mph by Monday afternoon with 35 to 45 mph winds across
Sweetwater, Fremont and Natrona counties. Snow accumulations above
8800 feet of 10 to 15 inches can be expected in the Tetons and
Gros Ventre mountains with 5 to 10 inches in the northern and
central mountains by late Tuesday. Wednesday will see drying
with some warming and brisk northwest winds.

.LONG TERM...(wednesday night through Sunday)
Issued at 155 PM MDT Sun Jun 11 2017

The effects of the exiting low pressure center will continue to
diminish Wednesday night as the low pressure center moves
northeast across Saskatchewan with continued diminishing winds
and making way for summer to begin several days before the summer
solstice. Northwest winds will continue to diminish and back to a
more westerly direction. Only lingering isold t storms are
expected in the north and east zones Wednesday evening. For
Thursday, a flat ridge of high pressure will be building in from
the west with the jet shifting to the north and a 1019mb sfc high
building into the region. For Friday through Sunday, the Canadian
model wants to move the ridge east all the way to the Midwest with
the GFS and the Euro keeping the flat ridge axis to our west.
With the long wave ridge currently just off the Pacific Coast,
will side with the latter two models. This soln would suggest weak
ripples in the flow closer to the jet to the north skirting our
northern tier zones where we will indicate just isold late day
convective activity in those areas Friday through sunday of next
week. Temperatures will continue to recover with highs in the 70s
at the lower elevations east of the divide and 60s west Thursday
warming to the 80s and 70s Friday through Sunday respectively.

With the added moisture we receive early in the week and warming
temps to follow, another increase in snow melt from the snow that
is left will likely take place, but not nearly as dramatic as
what has taken place these past few days. Some main stem rivers
will be high but not at record levels.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 155 PM MDT Sun Jun 11 2017

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A warm front is expected continue to push northward across
southwest Wyoming during the remainder of this afternoon with
winds switching from southeast to a breezy to windy southerly
wind by late afternoon. The exception to this could be across
Jackson Hole where winds could remain mainly northerly. Isolated
to scattered convection is expected to move into the area from
Idaho along and north of a 20N EMM to 40SE PNA this afternoon,
and last well into the night. VFR conditions are expected except
for brief MVFR/IFR conditions in convection. Also, some LLWS could
develop tonight as southerly flow intensifies. After 18z Monday,
precipitation is expected to become more widespread along with
areas of MVFR and LCL IFr along with mtn obscn. The snow level
will lower to 7000 feet by 00z Tuesday in far Western Wyoming
including KJAC. However, Sweetwater County including KRKS will
remain dry and windy with south winds shifting to westerly at 20
to 30 knots Monday.

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A cold front is expected to remain along the Divide most of
the rest of the day with a northerly to easterly surface flow.
Isolated to scattered convection are expected to redevelop late in
the afternoon/early evening. This convection is expected to lift
northward, but continue well into the night. VFR conditions are
expected except brief MVFR/IFR conditions in any convection.
Southerly LLWS could also develop especially at terminals in the
foothills. After 18z monday, a stronger round of convection is
expected to develop with severe thunderstorms possible over
Johnson County including KBYG, and Northeast Natrona County.
Expect isold MVFR/IFR conditions with these storms.

&&

.FIRE WEATHER...
Issued AT 155 PM MDT Sun Jun 11 2017

A large unseasonably strong low pressure trough over the pacific
northwest will slowly approach the area with increasing showers
across the western and northern mountains with embedded isolated
thunderstorms possible in the afternoon and evening hours.  Snow
levels will lower to 8500 feet tonight, and 7500 feet on Monday
night. As colder air moves in stronger winds will move in as well.
A high wind watch has been issued for Sweetwater, fremont and
Natrona counties from noon Monday through 9 pm mdt Monday evening.
Mountain winds of 30 to 40 mph can be expected increasing to 40
to 45 mph by Monday afternoon with 35 to 45 mph winds across
Sweetwater, Fremont and Natrona counties. Snow accumulations above
8800 feet of 10 to 15 inches can be expected in the Tetons and
Gros Ventre mountains with 5 to 10 inches in the northern and
central mountains by late Tuesday. Wednesday will see drying
with some warming and brisk northwest winds. With breezy to windy
areas and an unstable air mass, mixing heights should be
favorable for very good to excellent smoke dispersal in the
afternoons. The mountains of the west will have poor to fair
smoke dispersal on Monday and Tuesday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Monday afternoon through Monday evening for
WYZ017>020-028>030.

&&

SHORT TERM...Baker
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...Baker

Hazardous Weather Outlook
National Weather Service Riverton WY
114 PM MDT Sun Jun 11 2017

WYZ001>020-022>030-121915-
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-
114 PM MDT Sun Jun 11 2017

...Flood Warnings Remain in Effect in the Wind River and Upper
Green River Basins...

...High wind watch Sweetwater, Fremont and Natrona counties
Monday...

This Hazardous Weather Outlook is for Western and Central
Wyoming.

.DAY ONE...This Afternoon and Tonight

Isolated to scattered thunderstorms across northern and
central areas late in the day and this evening. Isolated strong
thunderstorms possible with hail and strong wind gusts.
Flooding along tributaries and main stem rivers will continue
across the Wind River and Green River Basins, and along the South
Fork of the Shoshone River.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Monday...High winds possible across Sweetwater, Fremont and
Natorna counties in the afternoon and evening. Isolated to
scattered thunderstorms. Some storms could be severe in portions
of Johnson and Natrona Counties. Windy to very windy in much of
central and southern Wyoming. Snow will move into western
mountains later Monday night.

Tuesday....Heavy wet snowfall likely in the the northern and western
mountains, including Grand Teton and Yellowstone National Parks.
Snowfall, slick roads and limited visibility likely over mountain
passes. A few inches of snow possible in far west valleys Tuesday
morning. Very windy across southern and central areas.

.SPOTTER INFORMATION STATEMENT...

Please report any flooding, or thunderstorm wind gusts over 50
mph, or hail.

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