Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 251032
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
332 AM MST Sat Feb 25 2017

.SHORT TERM...Saturday through Monday night

It looks like winter has made a return and will stick around for a
few days. However, since it is late February and not late December,
we do not expect the extreme temperatures of January. However,
temperatures will continue to be below normal, especially in areas
that received the heavy snow over the past couple of days. As a
result, we kept temperatures well below MOS guidance. In addition, a
trough will be swinging across the area. There is not a ton of
moisture to work with, but it will be enough to keep some snow
showers going. This will especially be the case in the west where
some steep lapse rates may bring some locally heavy snow showers. It
is hard to pinpoint the location however. In addition, there could
be enough lift for a bit of snow in the Cody. Given the history of
under doing precipitation in that area, we added some POPS for this
afternoon. Most of the showers should end at night except for the
northwest. In addition, with gusty wind developing ahead of the
trough, some blowing snow may develop. We will continue to Special
Weather Statement for today.

We should be in between systems on Sunday with only a few mainly
orographic showers across the west. Temperatures will be tricky in
the basins with the inversions. Again, we kept numbers below MOS
guidance. Gusty winds will also continue across the normally wind
prone areas as well. Snow will increase across the west late Sunday
and especially Sunday night as another trough approaches along with
the support of some modest jet dynamics. This system does not appear
really strong though and does not have a ton of moisture to work
with some heavy snow is not expected at this time.

On Monday another piece of energy will move into the west with
another chance of light to moderate snow. There is some disagreement
East of the Divide however. The GFS is showing some moisture moving
into central Wyoming with some upper level divergence providing some
lift and actually breaks out some light snow on Monday afternoon.
The NAM has a drier solution however. For now, we bumped up POPS a
bit, especially near Natrona County but kept them in the slight
category for now but they may need to be bumped up a bit if the
trend continues.

.LONG TERM...Tuesday through Saturday

A weather system passes through the region on Tuesday with snow
for most mountains and scattered light snow for the lower
elevations. A northwest flow aloft is the weather pattern
Wednesday through Friday. Moisture in the northwest flow will keep
some light snow going in the NW WY mountains and in the northern
Bighorn mountains. There will be periods when the snow picks up in
intensity and may require a highlight. The rest of the area will
be dry Wed through Fri. Next Saturday the long range models differ
on the weather pattern. The GFS has a strong weather system
diving through the area in the northwest flow aloft. This would
lead to a chance of precipitation over much of the area. The ECMWF
model has a west flow aloft and keeps precip in NW WY. Have
blended the solutions for now and have a chance of precip in the
west and north zones. Breezy to windy areas Wed through Fri and
possibly next Saturday as well. Temps will be on the cold side
Tuesday, then gradual warming through Friday. Next Saturday was
blended as the GFS was colder and the ECMWF model was mild. End
result was near seasonal highs. Low temps will vary widely each
night. The snow covered basins with little or no wind will be
fairly cold. The places that have a breeze will be much milder.

&&

.AVIATION.../12Z ISSUANCE/

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

A break in snow showers, prevailing VFR conditions will occur this
morning. An upper level disturbance will bring another round of
snow showers across the western mountains and vicinity KJAC this
afternoon, with mountains becoming frequently obscured and
prevailing MVFR conditions expected at KJAC through the early
evening. Drier conditions with surface west wind 20-30 knots will
prevail across the southwest along the I-80 corridor Saturday
afternoon. Snow showers will decrease in coverage across the
mountains late Saturday evening through Sunday morning.

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

Patchy valley fog will partially obscure terrain vicinity KWRL, KRIW
and KLND through 16z. A lee side surface trough will strengthen this
morning with southwest wind 20-30 knots, gusts near 40 knots,
prevailing from vicinity 50SM NE KRKS-KCPR through early Saturday
evening.  Gusty west winds are also expected to develop along the
eastern foothills from vicinity KCOD-KDUB-KLND. Areas of blowing
snow and partial terrain obscurations will be likely with these
winds.  An upper level disturbance will spread isolated to scattered
snow showers vicinity and north of a KCOD-KBYG line Saturday
afternoon with the Bighorn Mountains becoming mostly obscure north
of U.S. Highway 16.  This activity should clear the north 3z-6z
Sunday leaving prevailing VFR conditions across the area.

&&

.FIRE WEATHER...

Fire Danger should remain low for all of Wyoming through the
weekend as a good existing snow pack combines with seasonal to
below seasonal temperatures. Gusty west to southwest can be
expected at times across portions of central and southern WY as
well as the Lee of the Absarokas. Smoke dispersion will be fair to
very good across most of the forecast area each afternoon through
at least Monday. The exception would be some of the deeper basins
and valleys which had heavy snow where inversions may linger
through the day.

&&

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

&&

$$

SHORT TERM...Hattings
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...Hattings


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