Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 151656
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1056 AM MDT Sun Apr 15 2018

.SHORT TERM...Today through Tuesday night
Issued at 156 AM MDT Sun Apr 15 2018

Moisture in west northwest flow aloft will continue to bring snow
showers to the mountains mainly above 8500 feet with rain snow mix
below today and tapering off in the evening. East of the Continental
Divide dry conditions with a warming trend are expected with
increasing downslope winds. Tonight will be mainly dry with
southerly flow increasing becoming rather strong and gusty on
Monday. The southwest winds across Sweetwater, Fremont and Natrona
counties with low relative humidity may bring elevated fire weather
concerns. A Fire Weather Watch has been issued in Natrona county due
to the combination of the critical fuel status, winds gusting in the
30-40 MPH range , temperatures in the low 70s, and RHs below 15
percent. As the south southwest flow continues and a Pacific trough
to the west approaches, showers will return to the area on Tuesday
with a cold front in the north bringing cooling. Initial looks at
snow totals show most accumulations in the mountains and that only
being advisory levels.

.LONG TERM...Wednesday through Sunday
Issued at 156 AM MDT Sun Apr 15 2018

A storm currently in the northern Pacific near 44 north, 175 East
will be the main weather player for the Cowboy State in the
extended. Medium range models show this storm pushing into N.
California as an upper low on Wednesday. Global models are in good
agreement with this system pulling into the southern Great Basin
Thursday, then eastward to around the Four Corners area Thursday
night before slowly pushing into the southern/central High Plains
Friday into Friday night. Overall both the ECWMF and GFS are in
decent agreement, but have slightly different timing by about 6-12
hours especially as this upper low becomes cut off from the main
steering currents Friday. Convection (valley rain/mountain snow)
could begin on Thursday, but the bulk/heaviest precipitation is
expected in the Thursday night/Friday time frame. Models show an
easterly upslope flow developing on the north side of the upper
low with the potential for a decent amount of precipitation
developing across central/southern parts of the forecast area with
little across the far west/northwest areas. Although precip type
will be on the edge of rain vs snow, models are hinting at enough
cold air damming/upslope effects for the precip to fall as mainly
snow especially across the Wind River Basin and eastern Sweetwater
County. Casper could stay rain longer with this system until
colder air pushes into the area Friday morning. This system will
have to be watched for the potential for a significant wet
snowfall generally southeast of a Rock Springs-Riverton-Kaycee
line with the best shot probably across the Wind River Basin. This
of course will depend on the exact track of the storm, and there
is plenty of time to watch how this all unfolds. For now have
trended with higher PoPs and cooled temperatures Thursday night
thru Friday evening.

In wake of this system, a warming trend with mainly dry conditions
are expected next weekend.

&&

.AVIATION...18Z Issuance

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

VFR conditions will occur through the forecast period. A gusty to
possibly strong wind will develop at many sites after 16Z Monday.

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

Snow showers over the NW WY mountains will occur at times through
00Z Monday. Local MVFR conditions will occur with some mountain top
obscuration. KJAC airport will see rain or snow showers until 12Z
with MVFR conditions at times. Then VCSH will remain in the terminal
forecast through 02Z at KJAC with VFR conditions. The rest of the
area will see VFR conditions through the period. More showers may
move toward the western mountains Monday morning but should hold off
until after 18Z Monday. A gusty wind will develop after 17Z Monday.

Please see the Aviation Weather Center for the latest information on
icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued AT 156 AM MDT Sun Apr 15 2018

Snow and rain showers will continue in the west today and into this
evening. All other areas will see continued high pressure leading to
warm and dry conditions. Winds will get a little gusty this
afternoon in the wind corridor from Rock Springs to the Green
Mountains. The windy and warmer areas will see good or better smoke
dispersal while the west with increasing clouds and areas of
precipitation will have poor to fair smoke dispersal.

Monday will be more of a fire threat in Sweetwater, Fremont, and
Natrona Counties. Clearing skies, temperatures at or near the 70s,
and strong gusting winds are of concern. A Fire Weather Watch has
been issued for Natrona County from noon Monday to 7PM. The
increased wind will produce deep mixing on with Very good to
excellent smoke dispersal.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from noon Monday through Monday evening for
WYZ280.

&&

$$

SHORT TERM...Hulme
LONG TERM...Murrell
AVIATION...Hattings
FIRE WEATHER...Hulme


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