Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 182053
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
253 PM MDT Mon Sep 18 2017

.SHORT TERM...(This evening through Thursday)
Issued at 300 PM MDT Mon Sep 18 2017

A cold wet pacific low pressure trough will bring snowfall
to the western and northern mountains of wyoming this evening.
The heavier snowfall is expected above 8500 feet where 5 to
10 inches of snow can be expected through 9 pm mdt Tuesday
evening. Strong gusty west winds are also expected on the
passes and higher ridges.  Snowfall from 8500 to 7500 feet
is expected to be from 3 to 5 inches.  The lower elevations will
see rain with local heavy rainfall possible.  West to southwest
winds of 30 mph with gusts to 45 mph will be possible Tuesday
in the foothills of the Absaroka and Wind River mountains in the
afternoon.  Precipitation will decrease with partial clearing
Tuesday night and Wednesday with another cold Pacific trough
bringing more snow to the west with cold rain in the lower
elevations Wednesday night and Thursday.

.LONG TERM...Thursday night through Monday night
Issued at 300 PM MDT Mon Sep 18 2017

Synopsis...The forecast remains on track today, as the longwave
trough remains positively-tilted until Sunday. By then, the upper
low begins to fill and shift eastward. The supporting upper-level
dynamics will remain in place through at least Saturday, as a
reinforcing shortwave enters the area. There also could be enough
lift around the upper low on Sunday to keep light precip going
through Sunday night.

Discussion...Not much change from last night`s discussion. The
timing of Thursday`s cold front continues to slow down from
Sunday`s 12Z run. 00Z Friday placement of the front looks to be
through northern Natrona Co. into central Fremont/Sweetwater
counties. By 12Z Friday, there looks to be little movement, being
draped over KCPR, SE Fremont and E Sweetwater counties.
Precipitation will stay confined over northern and western
portions to start the period, gradually shifting eastward Thursday
night into Friday. The strong baroclinic zone associated with the
cold front, placement of the jet and timing of the shortwave will
aid in the precipitation becoming widespread during this time. By
Saturday and Sunday, the areas of precipitation will depend on
the additional shortwaves that round the base of the trough, as
well as the main low itself.

Significant widespread precipitation will be in store through the
period, along with significant mountain snow continuing. Snow
levels should stay above 6500 feet, especially over NW portions.

&&

.AVIATION...For the 18Z TAFS through 18Z Tuesday
Issued at 300 PM MDT Mon Sep 18 2017

VFR conditions will occur at most terminal sites through 12Z
Tuesday. Breezy to windy conditions will occur today at most
terminal sites from late morning through sunset this evening.
A cold front will move into NW WY around 06Z tonight and push
eastward to a KBYG-KRIW-KEVW line at 12Z Tuesday. Rain showers with
high mountain snow will begin in NW WY between 00Z and 03Z this
evening. This precipitation will spread across much of Western WY by
10Z Tue. MVFR conditions will develop over the northwest by 06Z
Tue and increase in areal coverage from 09Z to 12Z Tue in the
west. Mountains will become more obscured with time tonight in the
west. Please see terminal forecasts for more details.

&&

.FIRE WEATHER...
Issued AT 300 PM MDT Mon Sep 18 2017

A cold wet pacific low pressure trough will bring snowfall
to the western and northern mountains of wyoming this evening.
The heavier snowfall is expected above 8500 feet where 5 to
10 inches of snow can be expected through 9 pm mdt Tuesday
evening. Strong gusty west winds are also expected on the
passes and higher ridges.  Snowfall from 8500 to 7500 feet
is expected to be from 3 to 5 inches.  The lower elevations will
see rain with local heavy rainfall possible.  West to southwest
winds of 30 mph with gusts to 45 mph will be possible Tuesday
in the foothills of the Absaroka and Wind River mountains
and across southern Fremont and Natrona counties in the
afternoon.

&&

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

$$

SHORT TERM...Baker
LONG TERM...LaVoie
AVIATION...Hulme
FIRE WEATHER...Baker



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