Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 152015
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
115 PM MST Sun Jan 15 2017

.Short Term...Tonight Through Wednesday

High pressure will remain in place tonight through Monday
with a gradual warming trend. Fog will remain a threat in the
valleys and basins.  Expect areas of dense fog to again increase
across Sweetwater county this evening and remain a problem Monday
morning so will let the Dense Fog Advisory run through noon
Monday. Monday night as the upper flow shifts from the north to
the west...clouds will begin to move into the west and wind will
increase along and near the east slopes of the mountains east of
the Continental Divide and through the wind corridor from Rock
Springs to Casper. The windy areas will warm significantly with
the trapped valleys and basins warming slower. The amount of
warming is the most difficult part of the forecast in the short
term with the main question areas being the eastern Big Horn basin
the Northern and central Wind River basin and the western valleys
including Yellowstone National Park. Clouds and light snow are
expected late Tuesday night and Wednesday in the western mountains
with low snow accumulations. Tuesday and Wednesday will be the
warmest days.

.Long Term...Wednesday Night Through Sunday

The extended forecast has continued to increase in difficulty
as the extended models waffle about with the strength and path of
incoming Pacific low pressure troughs.  As they move into the
the Pacific Northwest the trend has been for the main energy and
moisture to dive south southeast into the Great Basin and Desert
Southwest and northern old Mexico. this has path the amount of
moisture that moves into western wyoming in question and the
threat of organized snowfall in the west has significantly
decreased. The extended models do spread patches of precipitation
all over the place across the northern and central Rockies. Have
lower chances of precipitation generally with the western
mountains looking the best for at least light snowfall. Generally
temperatures cool through Sunday.

&&

.Aviation.../00Z Issuance/

The Rock Springs /KRKS/ terminal remains in fog, although the area
of fog in Sweetwater County started to shrink but has leveled off in
size with KRKS temporarily around 2 miles vsby attm for much of the
rest of the afternoon. KRKS is expected to be at or below airfield
minimums once again after 01z this evening tonight through Monday
morning. Most of the mid-high level clouds from the south will
remain to the east of most of Sweetwater County and KRKS. The slight
westerly breeze that is expected to develop this afternoon and
evening over Sweetwater County will only enhance the fog at KRKS
from the localized upslope flow on the west side of the butte that
KRKS is situated upon. Another stubborn patch of fog is entrenched
from the town of Shoshoni to Boysen Reservoir and the south end of
the Wind River Canyon but is finally starting to shrink. This patch
of fog will remain northeast of the KRIW terminal for the most part
this afternoon. With warm air advection aloft expected tonight and
Monday, patchy fog is expected once again at KBPI, KJAC, KLND, KPNA,
and KRIW tonight and Monday morning. Otherwise, winds will be mainly
light through the period except for KCPR where southwest winds today
will blow at around 10 knots and 12 to 22 knots Monday.

&&

.Fire Weather...

High pressure will remain in place tonight through Monday
with a gradual warming trend. Fog will remain a threat in the
valleys and basins.  Expect areas of dense fog to again increase
across Sweetwater county this evening and remain a problem Monday
morning so will let the Dense Fog Advisory run through noon
Monday. Monday night as the upper flow shifts from the north to
the west...clouds will begin to move into the west and wind will
increase along and near the east slopes of the mountains east of
the Continental Divide and through the wind corridor from Rock
Springs to Casper. The windy areas will warm significantly with
the trapped valleys and basins warming slower. The amount of
warming is the most difficult part of the forecast in the short
term with the main question areas being the eastern Big Horn basin
the Northern and central Wind River basin and the western valleys
including Yellowstone National Park. Clouds and light snow are
expected late Tuesday night and Wednesday in the western mountains
with low snow accumulations. Tuesday and Wednesday will be the
warmest days. With cold air trapped in the valleys and basins
with increasing temperature inversions...mixing will be limited
and wind will be light combining for poor smoke dispersal expected
through Tuesday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon MST Monday for WYZ028>030.

&&

$$

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



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