Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 220920 CCA
AFDRIW

Area Forecast Discussion...CORRECTED
National Weather Service Riverton WY
320 AM MDT Tue Oct 22 2019

.SHORT TERM...(Today through Thursday)
Issued at 254 AM MDT Tue Oct 22 2019

A moist northwest flow in combination with isentropic upglide/warm
air advection this morning over the northwest will result in snow
developing in that region toward sunrise. This snow is then
expected to expand southward into far western Wyoming by late
morning. High temperatures on Tuesday should be 5 degrees warmer
than what occurred on Monday. Snow levels over the west today
should increase to between 6500 and 7500 ft msl. A few inches of
snow are expected across the northwestern mountains today.

A low-amplitude trough along the central British Columbia Coast
early this morning will deamplify today as it pulls southeast into
the northern Rockies of Montana/Idaho. This shortwave trough is
then expected to pull across the forecast area tonight. On the
heels of this trough, a shortwave trough in the Gulf of Alaska now
will push southeast across the northern Rockies on Wednesday. The
associated cold front is expected to push into northern Wyoming
late tonight, and sweep southward to the Divide by mid to late
morning. The precipitation is expected to occur generally along
and just behind the cold front with the second wave keeping
chances of snow into Wednesday evening. The precipitation in the
lower elevations looks to begin as rain and snow depending on
elevation, but change to snow in couple hours after frontal
passage. Overall precipitation amounts still look to be light. The
light snow ends Wednesday night with dry and unseasonably cool
temperatures on Thursday.

.LONG TERM...(Thursday night through Tuesday)
Issued at 254 AM MDT Tue Oct 22 2019

Weak ridging and north-northwest flow will continue the dry weather
with cold overnight temperatures in the teens to upper 20s. Friday
morning. The highs on Friday will be the warmest of the period
across most of the state. Saturday will also see warmer highs, with
morning lows rebounding as well across the region.

The next front will move into northwestern Wyoming early Saturday
morning before moving further south across the state through the
evening. GFS and ECMWF are in disagreement with the timing of the
front, with the GFS being more aggressive in the eastward
progression. The position of the jet across central Wyoming combined
with the upslope flow would seem to favor Sunday afternoon and
evening as the best period for widespread light snow. The pattern
does not look very favorable for heavy western mountain or valley
snow. Temperatures will again drop will below seasonal normals for
Sunday and Monday with most areas only reaching the upper 20s and
30s for highs, and Monday morning lows dropping into the single
digits to mid teens.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1118 PM MDT Mon Oct 21 2019

Mainly dry conditions for all but the northwest corner of the
state overnight. Expect all terminals to be VFR through
12Z/Tuesday with KJAC the only terminal with the potential for
light snow showers between 09Z- 12Z/Tuesday. Light snow will
increase across northwest Wyoming through the day Tuesday with
IFR/MVFR likely at KJAC after 14Z/Tuesday. All other terminals to
remain VFR with the main aviation hazard being gusty westerly
surface wind. KRKS will see a slight decrease in wind speed
overnight, but overall 20-30kt wind speeds will prevail. Tuesday
afternoon will see 15-25kt surface winds blow at KCPR, KRIW, KBPI,
and KPNA. Mountain top obscurations will continue west of the
Divide through the forecast period, becoming more widespread and
lowering during the day Tuesday.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued AT 254 AM MDT Tue Oct 22 2019

Scattered to numerous snow showers over the northwest with a few
inches of snow expected in the mountains. Mainly dry elsewhere
with warmer temperatures today. Breezy west to northwest winds are
expected mainly over southwest Wyoming, the wind corridor from
Rock Springs to Casper, and in the mountains. Smoke dispersal will
generally be poor to fair over the north, good over central
zones, and good to very good over the south. A cold front will
push south across the area late tonight and Wednesday. Cooler,
wind northerly flow, and a chance of snow with a storm system late
tonight through Wednesday night. Snow accumulations are expected
to be light at this time with the best chance over northern
Wyoming.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Murrell
LONG TERM...Swanson
AVIATION...STRAUB
FIRE WEATHER...Murrell


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