Area Forecast Discussion
Issued by NWS Riverton, WY

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907
FXUS65 KRIW 240650
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1150 PM MST Mon Jan 23 2017

.UPDATE...

Upgraded the winter weather advisory to a winter storm warning for
the Wind River Basin. Satellite and Radar imagery shows a distinct
circulation across SE Fremont with only a very slow push
north/northeast which allow for heavy snow to continue on the
north/northeast side for at least a few more hours. 4 to 6 inches
are already observed in Riverton/Lander. Updated WSW is already
out. Have also included 06Z aviation discussion.

&&

.PREV DISCUSSION... /issued 753 PM MST Mon Jan 23 2017/

UPDATE...

Quick update to include the Upper Wind River Basin (Dubois and
Crowheart areas) into a winter weather advisory through Noon
Tuesday. Reports have about 2 inches already, and with the mid-
level circulation still to come could see another 1 to 3 inches.
No other changes to ongoing forecast at this time.

PREV DISCUSSION... /issued 232 PM MST Mon Jan 23 2017/

SHORT TERM...Tonight through Thursday

Snow has been falling in the west...southwest and south today and
some snow is now developing in the central zones as of 21Z.
Cooling cloud tops are occurring in the region ahead of this
weather system that is forecast to move through the Rocky
Mountain region tonight and exit Tuesday afternoon. Snowfall out
west and southwest has been decent so far. The snow will continue
in the west and southwest through Tuesday morning. In the central
zones, snow will continue to increase in coverage the rest of the
daylight hours with decent snow amounts expected through Tuesday
morning. Expecting the best snowfall rates later this evening
through sunrise Tuesday. In the north, the snow will develop this
evening and continue through Tuesday morning. Current warnings and
advisories will not be altered for now. Will have to monitor the
central zones later tonight to see if an upgrade might be needed.
Worded the statement with locally higher amounts. The snow will be
decreasing over the region Tuesday afternoon from north to south.
Lingering light snow in the mountains Tuesday night into Wednesday
morning. Then scattered light snow for the Western mountains
Wednesday afternoon and night and even into Thursday as this upper
level trough hangs around through Thursday. Mainly dry for the
rest of the region Wednesday through Thursday. Temperatures will
be on the cold side Tuesday through Thursday as 700 MB temps do
not vary much during this timeframe. Lows will be tricky due to
cloud cover Tues night, but with a clearing sky Wednesday night,
it will get very cold in the valleys and basins.

LONG TERM...Thursday night through Monday

Beginning of FCST, boundary layer warming with residual moisture
under exiting cold air aloft will allow from a short period of snow
showers to continue but wind down west of the Divide Thursday night
perhaps into a few hrs of Friday morning before mid/upr ridging
slowly begins to make inroads across the FA with the ridge axis
orientation from cntrl California to the nrn high plains by Saturday
night. This will mostly keep a clipper front out of the ern FA over
the same time frame. Above and to the northwest of this ridge out
over the EPAC Saturday night, a modest shortwave trof is fcst to
exist. This SW trof will top the rather strong ridge and arrive
near/over nrn/nwrn WY Sunday evening...moving into the Plains by
Monday morning. This will also generate a front that will push
through the region east of the Divide Monday morning. With the storm
track taking a northerly route around the ridge, the FA will be cut
off from significant moisture with little in the way of
precipitation falling through the end of the forecast period. ATTM,
it appears that the wrn CONUS will have to wait until mid to end of
next week before the Pacific opens back up.

AVIATION.../06Z ISSUANCE/

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

Widespread MVFR/IFR conditions in snow and/or low ceilings are
expected through Tuesday morning. Gradual improvement is expected
from north to south Tuesday afternoon, but MVFR ceilings and light
snow or flurries could be stubborn across southwest and southern
Wyoming through the evening hours. The JAC terminal has the best
shot at VFR conditions albeit on the low end Tuesday with potential
for brief MVFR/IFR in snow showers. Tonight, once the stratus and
flurries dissipate fog will be the main issue. Will have some VCFG
to account for this.

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

IFR conditions, with airfield minimums at times, are expected
through 15Z across central Wyoming including Wind River Basin and
Natrona County. Across northern Wyoming, IFR/MVFR conditions are
expected through 18Z but airfield minimums are not expected.
Improving conditions are expected from north to south Tuesday
afternoon and evening. KLND and KCPR will be the most stubborn
terminals where MVFR conditions could linger into the evening hours.
A moist boundary layer and light winds could result in fog forming
tonight across much of the area once the stratus deck lifts/scatters
out. Will have VCFG to account for this.

FIRE WEATHER...

Periods of snow through Tuesday afternoon in most places. The
heaviest snow will fall through Tuesday morning with lighter snow
occurring through Tuesday afternoon. Scattered mountain snow
showers Wednesday and dry Thursday. Mixing heights will remain
fairly low through Thursday with poor to fair smoke dispersal.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST Tuesday for WYZ014-015-
019-020-022-026-028>030.

Winter Storm Warning until 5 PM MST Tuesday for WYZ018-023>025-
027.

Winter Storm Warning until noon MST Tuesday for WYZ012-013-017.

Winter Weather Advisory until noon MST Tuesday for WYZ002-005-
007-016.

&&

$$

SHORT TERM...AR
LONG TERM...Braun
AVIATION...WM
FIRE WEATHER...AR



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