Area Forecast Discussion
Issued by NWS Riverton, WY

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902
FXUS65 KRIW 252147
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
247 PM MST Sat Feb 25 2017

.Short Term...Tonight Through Tuesday

Sufficient low and mid level moisture in west northwest flow
aloft to support continued light snowfall over western mountains
Tonight. Variable mid and upper level clouds will drift over areas
east of the Continental divide. Temperatures will remain cold
with slight warming. Areas of brisk west winds will blow over and
near the east slopes of the mountains and through the wind
corridor from Rock Springs to Casper area. Flow aloft slowly
shifts to the west southwest on Sunday with increasing moisture
through Sunday night and Monday. Snowfall of 3 to 6 inches every
24 hours with local 9 inch amounts in the Tetons and Southwest
Yellowstone National Park continues through Tuesday.  East of the
divide wind will gradually increase with warming in the windy
areas with cold air remaining rather trapped in the Big Horn and
Wind River basins. Temperatures slowly rise through Mid Week.
Brisk winds at ridgetop and pass levels will continue with a
gradual increase Monday night and Tuesday. Little if any of the
precipitation over the western mountains will make it east of the
mountains.

.Long Term...Tuesday Night Through Saturday

Beginning of FCST, frontogenesis will occur to the north of WY
Tuesday afternoon as the back-end of an upper trof approaches and
cross the region...offering an increased chance for precip/snow east
of the Divide Tuesday night with the help of FROPA. However, this
looks to be a quick hitter east of the Divide with perhaps an inch
or so through Wednesday morning...with the better chances over the
Bighorn mountains and the adjacent plains to the east across Johnson
and northern Natrona counties.

Wednesday through Thursday, with be post frontal with high pressure
at the SFC, NW flow aloft, and some lee troffing trying to get
planted east of the Continental Divide. This set-up will keep the
northwest portion of the FA slightly unstable, and with a little
extra mountain lift, will keep the mountains across all of northern
WY under modest POPs. Temperatures through this Thursday will also
remain largely below seasonal so snow melt/flooding should remain in
check.

Friday, an embedded upper level SW trof /jet streak will cruise
through a slowly building ridge, flattening it and allowing for
increased lee troffing potential. Unfortunately, this pattern will
also likely produce strong gusty winds...bordering on `High` for the
usual suspect areas from Friday afternoon through much of the day
Saturday. Temperatures will also respond to this wind/lee side
troffing set-up, rising to near seasonal norms...and starting
another period of melt-off...hopefully not to an extreme. Precip
will be hard to come by until later Saturday or Saturday night with
the passage of a more vigorous storm system out of the PAC NW.

&&

.Aviation.../00Z Issuance/

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

VFR to occasional MVFR conditions to prevail through the forecast
period. A relatively weak and dry upper level disturbance will
continue across the forecast area tonight resulting in a few snow
showers west of the Divide, particularly vcnty KJAC. Most of these
snow showers will decrease in coverage across the western mountains
later this evening, perhaps lingering across far northwest WY
through Sunday morning. The mountains will also continue obscured at
times with prevailing MVFR conditions expected near and north of
KJAC through the early morning hours. A small increase in shower
potential is expected once again across the western/northwestern
mountains by late in the afternoon. Additionally, LLWS will be
possible vcnty KBPI-KRKS beginning this evening and lasting into
Sunday morning if winds decouple and become relatively light at the
surface.

LLWS will be possible
at some locations beginning this evening and continuing into the
morning hours after winds decouple.

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

Primarily VFR conditions to prevail through the forecast period. A
lee side surface trough will continue into the early morning hours
with southwest wind 10-15 knots and gusts near 20-30 knots
prevailing from vicinity 50SM NE KRKS to near KCPR into the mid-
morning hours before increasing late Sunday morning with gusts 25 to
35 kts once again. Areas of blowing snow and partial terrain
obscurations will be possible with these winds. Additionally, LLWS
will be possible vcnty KCOD-KWRL-KCPR beginning this evening and
lasting into Sunday morning for locations where winds decouple and
become relatively light at the surface. Isolated to scattered snow
showers north of a KCOD-KBYG line will clear off in the 2z-6z time
frame.

&&

.FIRE WEATHER...

Sufficient low and mid level moisture in west northwest flow
aloft to support continued light snowfall over western mountains
Tonight. Variable mid and upper level clouds will drift over areas
east of the Continental divide. Temperatures will remain cold
with slight warming. Areas of brisk west winds will blow over and
near the east slopes of the mountains and through the wind
corridor from Rock Springs to Casper area. Flow aloft slowly
shifts to the west southwest on Sunday with increasing moisture
through Sunday night and Monday. Snowfall of 3 to 6 inches every
24 hours with local 9 inch amounts in the Tetons and Southwest
Yellowstone National Park continues through Tuesday.  East of the
divide wind will gradually increase with warming in the windy
areas with cold air remaining rather trapped in the Big Horn and
Wind River basins. Temperatures slowly rise through Mid Week.
Brisk winds at ridgetop and pass levels will continue with a
gradual increase Monday night and Tuesday. Little if any of the
precipitation over the western mountains will make it east of the
mountains. Poor smoke dispersal is expected through Tuesday in the
valleys. The windy areas over and near the mountains and through
the wind corridor may experience fair to good smoke dispersal in
the afternoons through Tuesday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

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



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