Area Forecast Discussion
Issued by NWS Riverton, WY

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS65 KRIW 200209
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
809 PM MDT Thu Oct 19 2017

.UPDATE...
Issued at 809 PM MDT Thu Oct 19 2017

Updated to allow the Red Flag Warning to expire.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 307 PM MDT Thu Oct 19 2017

...Strong winds with low relative humidity Friday...
...Snow with strong winds Friday afternoon and night in the mountains...

Ahead of a Pacific low pressure trough, strong winds are expected
developing late Friday Morning continuing through Friday evening.
Southwest winds of 25 to 35 mph with gusts to 45 mph are
expected. Local wind gusts to 55 mph may occur around Clark.
Relative humidity is expected to drop to 17 to 23 percent in the
afternoon.

The Pacific low pressure trough is expected to bring areas of
moderate to heavy snow showers to the mountains developing
Friday morning and becoming more widespread Friday afternoon
and night. Snowfall of 3 to 5 inches is expected above 8500 feet
with areas of 5 to 8 inches above 9500 feet. The snow level will
fall into the valleys during the evening with 1 to 2 inches possible
below 8500 feet. The snow showers will be accompanied by strong west
winds of 30 to 40 mph with gusts to 50 mph on the passes and higher
ridges.

Snowfall will taper off Late Friday night and Saturday.  Wind
will continue to blow across the south into central areas while
decreasing to the north as cold air moves south behind a front.
Temperatures will drop.  West flow will bring another Pacific
low pressure trough into the west with increased snowfall on Sunday
and winds increasing east of the divide becoming quite windy south and
central and along the east slopes of the mountains.

.LONG TERM...(Sunday night through Thursday)
Issued at 307 PM MDT Thu Oct 19 2017

Beginning of fcst, post frontal and under brisk wnw flow aloft with
the main body of a 130-150kt jet lying just to the north over MT. A
strong P GRAD will lay roughly along the Divide with west to
southwest SFC winds gusting 35 to 50 mph across the Wind Corridor.
Additionally, Sunday night through Monday morning another "typical"
near or high wind pattern across the Absaroka (possibly the Wind
River Mountains) develops with strong upper level wind speeds and
good mountain wave production combine with also strong cross barrier
temp/pressure/omega gradients. Have therefore greatly increased wind
speeds/gusts across those areas over that provided by the standard
model output. Otherwise, precip chances move and end from west to
east mainly across nrn WY Monday with ridging, warming and drying
returning to the FA as well as most of the wrn CONUS...lasting into
next week. Wednesday will likely be the warmest day of the week...at
least 3 to 8 deg warmer than what is currently being dealt (H7 temps
ranging from 7.5 to 10.5 east of the Divide - model depending)
...so this area will obviously need to be nudged with (modest)
increases over the next several days. Otherwise, good overall model
agreement through most of the rest of the forecast period shows
that the next WX system does not affect WY until perhaps Wednesday
night or Thursday morning. For a day 7 - 8 rather large un-focused
system, modest POPs look OK ATTM...especially when taking the a
possibly broad spatial scale into account.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday)
Issued at 307 PM MDT Thu Oct 19 2017

VFR conditions will occur through 15Z Friday. A period of gusty
southwest wind will occur today from 50NE KRKS to KCPR through about
02Z Friday. LLWS will become increasingly common to some extent from
this evening through Friday morning at all terminal sites ahead of
an approaching upper level trof and associated cold front. CIGs will
begin lowering along the western border of WY Friday morning with
MVFR conditions and increasing chances for precipitation by late
morning or mid-day at KJAC...in the afternoon at KPNA and KRKS.
Mountain obscuration is also expected to increase through Friday
morning.


&&

.FIRE WEATHER...
Issued AT 307 PM MDT Thu Oct 19 2017

...Strong winds with low relative humidity Friday...
...Snow with strong winds Friday afternoon and night in the mountains...

Ahead of a Pacific low pressure trough, strong winds are expected
developing late Friday Morning continuing through Friday evening.
Southwest winds of 25 to 35 mph with gusts to 45 mph are
expected. Local wind gusts to 55 mph may occur around Clark.
Relative humidity is expected to drop to 17 to 23 percent in the
afternoon.

The Pacific low pressure trough is expected to bring areas of
moderate to heavy snow showers to the mountains developing
Friday morning and becoming more widespread Friday afternoon
and night. Snowfall of 3 to 5 inches is expected above 8500 feet
with areas of 5 to 8 inches above 9500 feet. The snow level will
fall into the valleys during the evening with 1 to 2 inches possible
below 8500 feet. The snow showers will be accompanied by strong west
winds of 30 to 40 mph with gusts to 50 mph on the passes and higher
ridges.

&&

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

&&

$$

UPDATE...Murrell
SHORT TERM...Baker
LONG TERM...Braun
AVIATION...Braun
FIRE WEATHER...Baker


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.