Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 232024
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
124 PM MST Thu Nov 23 2017

.SHORT TERM...(This evening through Sunday)
Issued at 112 PM MST Thu Nov 23 2017

...High Winds will blow in the Absarokas, Cody Foothills and
the Green and Rattlesnake ranges through tonight...

Strong west winds aloft will continue to surface and bring high
winds to portions of the Absarokas and Cody Foothills as well as
along the Green Mountains and Rattlesnake Range through tonight.
Pacific moisture in strong west flow aloft will bring increasing
snow to the higher mountains of western wyoming with mainly rain
below 8700 feet tonight and Friday tapering off Friday night. Most
areas above 8700 feet can expect 3 to 6 inches of snow with areas
around 10 inches above 10000 feet with wind gusts tonight around
60 mph.  A cold front will move south through Friday morning
bringing increased showers to the north and colder air with a wind
shift to the north and northeast bringing an end to the high winds.
Temperatures will drop 15 to 20 degrees in the east with many areas
falling around 10 degrees from todays temperatures.  The flow aloft
will remain westerly but with decreasing mountains with at least
partial clearing with temperatures rebounding through Sunday.

.LONG TERM...(Sunday night through Thursday)
Issued at 112 PM MST Thu Nov 23 2017

The weather looks to take a more active turn as we head into Sunday
night and Monday as another in the series of Pacific cold front and
troughs move toward the area. The models still have some timing
differences though. The GFS continues to be more progressive and
faster with the system, moving into the north and west for Sunday
night and out of the area by later Monday night. In contrast, the
European is around 6 to 12 hours slower with the front with
associated upper level low closing off more and passing a bit closer
to Wyoming than the GFS. For now, we kept continuity for the most
part. There is a decent amount of upper level support with the
system and it appears to have a little more moisture to work with so
some highlights may be needed in the west, advisories at least.
Precipitation does look like it would spread East of the Divide with
this system as well. With warm temperatures initially, it would
likely start as rain before changing over the snow before ending.
Amounts are still uncertain but with the progressive nature of it we
do not expect heavy snow at this time although rain changing to snow
could bring some road problems on Monday. Precipitation should end
later Monday night as the low moves away to the south and east.

Tuesday through Wednesday at this point look dry and cooler.
Temperatures are difficult though, especially East of the Divide
where inversions will likely set up in areas that get snow and
doesn`t mix well. The coolest night still looks to be Tuesday night
with a clear sky, light wind and the long late November nights. How
much snow cover there is will be is still up for debate. The models
then diverge toward mid week with the next system, with, once again,
the GFS more progressive with some some possible snow across
northern Wyoming and the European keeping the ridge in place and
having mainly dry weather.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday)
Issued at 112 PM MST Thu Nov 23 2017

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes

The main issue again through 18Z Friday will be windy to strong
west/southwest wind and/or LLWS in the wind corridor from South Pass
to Casper, lee side of mountain ranges and adjacent foothills
especially the Cody Foothills. Otherwise VFR conditions with lee-
enhanced high cloudiness are expected. After 06Z Friday, a cold
front will begin to drop southward into northern Wyoming switching
winds to the north with the possibility of some mountain snow/valley
rain showers, although it is still difficult to pinpoint them at
this time. Wind should begin to decrease after 18Z Friday after the
front moves through and the pressure gradient decreases.

West of the Divide...KBPI/KJAC/KPNA/KRKS Routes

Mainly VFR conditions are expected early this evening. Tonight, an
approaching storm system will result in a chance of some mountain
snow/valley rain showers especially after midnight. The approach of
this system will result in breezy southerly winds at KJAC terminal
later today into the overnight hours. If the winds would decouple
tonight, then LLWS would be an issue at KJAC. After 06Z Friday, have
prevailed KJAC with some -SHRA, but kept ceilings in the low MVFR
range as the south/southwest flow usually keeps ceilings higher than
what MOS guidance give us. Conditions should improve after 18Z as
the front moves away to the south.

Please see the Aviation Weather Center for the latest information on
icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued AT 112 PM MST Thu Nov 23 2017

Strong west winds aloft will continue to surface and bring high
winds to portions of the Absarokas and Cody Foothills as well as
along the Green Mountains and Rattlesnake Range through tonight.
Pacific moisture in strong west flow aloft will bring increasing
snow to the higher mountains of western wyoming with mainly rain
below 8700 feet tonight and Friday tapering off Friday night. Most
areas above 8700 feet can expect 3 to 6 inches of snow with areas
around 10 inches above 10000 feet with wind gusts tonight around
60 mph.  A cold front will move south through Friday morning
bringing increased showers to the north and colder air with a wind
shift to the north and northeast bringing an end to the high winds.
Temperatures will drop 15 to 20 degrees in the east with many areas
falling around 10 degrees from todays temperatures.  The flow aloft
will remain westerly but with decreasing mountains with at least
partial clearing with temperatures rebounding through Sunday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 5 AM MST Friday for WYZ002-003-019.

&&

$$

SHORT TERM...Baker
LONG TERM...Hattings
AVIATION...Hattings
FIRE WEATHER...Baker



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