Special Weather Statement, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
155 PM MDT Tue Apr 27 2021

.SHORT TERM...(This evening through Wednesday night)
Issued at 1204 PM MDT Tue Apr 27 2021

The cold front continues to slowly slide to the east with clearing
skies and precipitation ending late this evening. Natrona and
Sweetwater counties will be the last areas to see the rain showers
departing. There is just enough instability in the southeast,
that an isolated thunderstorm can't be ruled out for this evening.
Tonight a ridge will start to build into the forecast area,
bringing drier weather and northwest flow. Early morning there may
be some areas of patchy fog, but it should be fairly isolated,
and short lived. Overnight lows will be a bit cooler than today,
but highs will start to rebound nicely on Wednesday. Northwest
winds will increase during the morning and be quite gusty in the
southwest and also across Johnson County.

.LONG TERM...(Thursday through Tuesday)
Issued at 155 PM MDT Tue Apr 27 2021

Thursday will see mostly clear to partly cloudy skies over the
area with weak northwest flow as the ridge over the west coast
starts moving east. Temperatures will warm to near to above
normal. A weak shortwave trough is expected to move across
northern Montana keeping conditions moderated. Friday will see the
ridge axis tilt over WY from the Vegas area as the surface
pressure gradient and mid-level flow increase. Skies will again be
mostly clear, becoming partly cloudy in the afternoon especially
across northwest WY. With mid-level temps rising by 6-8C, surface
temps will also warm, with low 80s in some lower elevations east
of the divide. With RH values also getting below 20%, expecting
elevated fire weather conditions over parts of southern and
central WY. Shortwave energy will increase across the northern
Rockies on Saturday, dampening the ridge to bring more zonal flow
over the area. Clouds will increase and temperatures will drop
slightly, but still remain above normal. Enough moisture will
slide across the northern parts to bring isolated showers to
northern WY during the afternoon. Wind gusts up to 40 mph are
likely across the higher terrain and parts of southern and central
WY. At this point, medium-range model guidance differs quite a
bit. The GFS keeps an open wave moving from WNW to ESE through
northern WY on Sunday. Meanwhile, the ECMWF and Canadian Global
dig the 500mb trough into the Intermountain West. Both solutions
bring precipitation to northern WY and Johnson/Natrona Counties,
but the digging trough solution brings more precipitation to a
more widespread area Sunday night into Monday morning as the upper
low moves through the central Rockies. Have modified the forecast
to represent the slower/digging solution with more moisture and
precipitation in the area. Zonal flow should follow on Tuesday
with more moisture and a shortwave trough approaching from the
west.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday)
Issued at 1130 AM MDT Tue Apr 27 2021

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

Rain/Snow showers continue today from southern into central WY, with
clearing starting across northwest WY. VFR expected at KCOD through
the forecast period, with MVFR becoming VFR at KWRL after 28/00Z.
MVFR/IFR conditions to continue from KLND/KRIW to KCPR this
afternoon before becoming VFR with chance MVFR through 28/06Z.
Precipitation to become more showery this afternoon along northwest
edge of storm system, then diminish this evening.  Cannot rule out
chance of patchy fog in some areas early Wednesday morning, though
locations uncertain.  VFR conditions widespread after 18/12Z with
high clouds moving over northwest WY Wed afternoon.  Mountains
obscured today with improvement overnight.

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

Storm system continues to linger with some clearing from the
northwest.  KRKS will remain MVFR with occasional IFR through about
28/01Z with rain/snow mix and east wind.  KBPI/KPNA generally VFR
with possible MVFR due to showers this afternoon.  KJAC likely to
remain VFR for the forecast period, with slight chance of MVFR this
afternoon is showers move over the valley.  Winds generally light
with some gusts up to 20 kts.  Mountain obscurations should decrease
overnight.

&&

.FIRE WEATHER...
Issued AT 1204 PM MDT Tue Apr 27 2021

The cold front will exit the forecast area by tonight and a ridge
will build in behind it. Northwest flow, with increasing gustiness
on Wednesday, especially for the west and across Johnson County.
High temperatures will start to rebound tomorrow, with dry
conditions and clearing skies lasting through at least Friday.
Relative humidity will fall to around 20 percent. Mixing and smoke
dispersal will be range from generally poor tonight, improving to
good to excellent Wednesday afternoon.

&&

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

&&

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

Hazardous Weather Outlook
National Weather Service Riverton WY
1143 AM MDT Tue Apr 27 2021

WYZ001>020-022>030-281200-
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-
1143 AM MDT Tue Apr 27 2021

This Hazardous Weather Outlook is for Western and Central
Wyoming.

.DAY ONE...This Afternoon and Tonight.

Rain and snow showers continuing mainly east of the divide and
across southern Wyoming. The precipitation will slowly diminish
late this afternoon and evening. Some showers are also possible
across western and northern Wyoming. Patchy fog is possible late
tonight into Wednesday morning.

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

Friday and Saturday...Elevated fire weather conditions in the
lower elevations east of the divide, as well as across southwest
Wyoming, due to dry and windy conditions.

Sunday and Monday...A chance of valley rain and mountain snow.
Significant precipitation is possible east of the divide late
Sunday into Monday.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions.

McDonald

Special Weather Statement
National Weather Service Riverton WY
313 PM MDT Tue Apr 27 2021

WYZ030-272200-
East Sweetwater County-
313 PM MDT Tue Apr 27 2021

...SPECIAL WEATHER STATEMENT...

At 312 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 10 miles northwest of Creston Junction to 15
miles southwest of Wamsutter. Movement was northwest at 15 mph.

Pea size hail will be possible with these storms.

These storms will remain over mainly rural areas of northeastern
Sweetwater County, including the following locations... Red Desert
and Tipton.

This includes Interstate 80 between mile markers 155 and 186.

LAT...LON 4154 10842 4210 10798 4211 10788 4180 10767
      4166 10780 4166 10793 4150 10793 4132 10809
TIME...MOT...LOC 2112Z 143DEG 11KT 4186 10784 4148 10814

TL