Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 200402 AAA

Area Forecast Discussion...UPDATED
National Weather Service Riverton WY
1002 PM MDT WED OCT 19 2016

.UPDATE...Added 06z aviation discussion.




Patchy fog and LIFR cigs may partially obscure terrain across the
western valleys through 18z.  The snow-covered Upper Green River
Basin will be most prone to fog formation this morning.  Otherwise,
VFR conditions will prevail through the period with generally light
surface winds - 10 knots or less.  Increasing mountain top winds
will result in increasing turbulence Thursday night; however, these
stronger winds are expected to remain around FL 10kft and higher.


VFR conditions prevail through 12Z Friday.  A strengthening lee side
surface trough will bring prevailing southwest surface winds 20-
30kts vicinity 50NE KRKS-KCPR late Thursday morning and afternoon.
Some gusty downslope winds will also develop vicinity KDUB-KCOD
early Thursday morning through Thursday night.  Strengthening
mountain top winds may result in some mountain wave activity
and LLWS vcnty KCOD to the Montana border 00z-12z Friday.


.PREV DISCUSSION... /issued 315 PM MDT WED OCT 19 2016/

SHORT TERM...Tonight through Thursday

The last of the trough and cyclonic curvature is now moving over
northern and central Wyoming and continues to produce some rain and
snow showers. The best coverage is from southeast of Worland into
Natrona County and also off of the Wind River Range. More will
continue this afternoon before decreasing in coverage after sunset
as we lose the heating of the day and the instability as well. All
showers should end by later this evening with a balance of the night
dry. Across some of the western valleys, there could be some patchy
fog so we added that to the forecast.

Quiet weather will be the rule tomorrow as ridging builds back over
the area. A weak shortwave moving by to the north could bring a some
high clouds, especially to northern portions of the County Warning
Area. It does look dry though. 700 millibar winds will increase a
but and will bring a gusty wind to some areas, mainly the
southwestern wind corridor and the lee of the Absarokas. But through
this period, wind should not be strong enough to reach high wind
criteria. With chilly temperatures aloft, temperatures will average
near to below normal.

LONG TERM...Thursday Night Through Wednesday

A large ridge will influence weather over the intermountain west through
Monday morning with generally dry conditions and warming, seasonal
temperatures expected. The axis of the ridge will pass through
much of the state late Sunday evening, bringing a more
southwesterly flow over the area.

This southwest flow will introduce a surge of moisture across the
southern portion of the state by late Monday morning, though
models vary coverage a bit, and may reach over the western
mountains and valleys as well. Periods of showers will then
remain possible through late Tuesday evening, especially impacting
the southwestern half of the state with some coverage reaching
east of the divide as well.

A stronger wave will then move over the Pacific Northwest on Tuesday
afternoon/evening, and its axis will move into the intermountain
west through Wednesday. This will keep shower activity present
over the area, though models demonstrate a slightly increased
coverage across the northern basins and into the western mountains
than may be experienced with the earlier system. This system will
also bring some cooler air over the area, with some additional
mountain snowfall possible.


Any rain and snow showers should end by 03z as the atmosphere
becomes more stable as a trough moves away to the east. Across some
of the western valleys, patchy fog may form after 08Z. Other than
patchy fog in some locations, expect VFR conditions from 12Z
Thursday through 00Z Friday. A gusty wind will develop in the
afternoon in the lee of the Absarokas and across the southwestern
wind corridor from KRKS through KCPR.


Fire concerns should remain below critical through Thursday. Rain
and snow showers around this afternoon will come to an end during
the evening. Dry weather will rule from later tonight through
Thursday and through the weekend. A gusty wind will develop tomorrow
afternoon in the lee of the Absarokas and from Rock Springs through
Casper. However, with cool temperatures relative humidity should
remain above critical thresholds.


.RIW Watches/Warnings/Advisories...


SHORT TERM...Hattings
LONG TERM...Branham
FIRE WEATHER...Hattings is the U.S. government's official web portal to all federal, state and local government web resources and services.