Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 231819 AAA

Area Forecast Discussion...UPDATED
National Weather Service Riverton WY
1219 PM MDT Sat Sep 23 2017

.SHORT TERM...(Today through Monday night)
Issued at 300 AM MDT Sat Sep 23 2017

Imagery shows amplified trof over the wrn CONUS with embedded closed
low still centered ovr ID into nrn NV. An amplifying/broadening high
pressure ridge is currently across the ern CONUS (with the exception
of the embedded TS JOSE still east of Long Island, NY). Strong upper
jet also still remains up the ern side of the upper trof through the
srn/cntrl Rockies...over the High Plains and through the Northern
Plains. SFC has modest cyclone over Minnesota with associated cold
front draped to the southwest through a weaker SFC low over ern CO
then on to the west and southwest (across nrn CO/srn WY), eventually
pushing through srn California. Isolated to numerous rain and snow
showers currently moving from south to north across WY with a couple
of embedded thunderstorms.

This morning/today/tonight - the upper high pressure ridge across
the ern CONUS continues to stand its ground while the upper trof
over the western CONUS slows/stalls and digs even more. Lee
cyclogenesis, spawned earlier over nern CO, has since pulled a cold
front through most of the FA...down to around the srn border region
with CO. All the while, the base/axis of the upper trof/closed low
will only translate as far east as wrn/swrn WY (from its ID starting
point a few days ago) today. Moisture will return back into the FA,
after a brief let-up this morning, from the south and east around
the varying near SFC boundaries and fronts as they re-gather in
strength as a cyclone tries to gather itself west of the Continental
Divide near the Four Corners area. The trof axis should eventually
pass through through most of the FA on Monday. This pattern will
keep a nearly stationary front draped backdoor style from the Front
Range of Colorado up/along the Divide through WY while another
front/boundary lays/stays across srn WY/nrn CO through Monday before
finally disappearing.

Periodic bouts of precipitation will continue through Monday morning
with somewhat of a respite this morning. Rain/rain-snow mixes and
all snow will be possible east of the Divide depending on elevation.
Snow across the lower elevations of the Basins may even be possible
late tonight/early Sunday morning...particularly over the higher
higher hills and buttes of wrn and srn Fremont County in addition to
portions of Natrona County. From tonight through Sunday night, from
4 to 16 inches of snow will be possible over the Wind River
Mountains...3 to 9 across the Salt and Wyoming Ranges...2 to 6 over
the southern Absarokas...and 3 to 15 inches across the Bighorn
Mountains. Highest snow totals will be found above 9500 feet. A
Winter Storm Watch is in effect for the Wind River Mountains
beginning tonight and lasting through the day Sunday. Advisory
amounts likely over the Bighorn Mountains. Otherwise, 1 to 6
inches of snow will also be possible across the lower mountain
ranges (Green and Rattlesnake) of the region. The lower elevations
east of the Divide and across southern Wyoming will see anywhere
from a trace to two inches for most areas...with the highest
amounts across srn Lincoln and wrn Sweetwater counties where 2 to
4 inches will be possible.

.LONG TERM...(Tuesday through Saturday)
Issued at 300 AM MDT Sat Sep 23 2017

Tuesday looks dry for most areas. Isolated showers will be
possible over the mountains, but precip would be light. A little
milder on Tue. Wednesday will be dry for most places again.
Isolated showers or storms are possible in the northern mountains
Wednesday afternoon and early evening. Temps on Wed a little
milder. Thursday and Friday look dry and warmer with high pressure
in control. Next Saturday will be dry for most areas. Isolated
showers may occur over the northern Bighorn mountains late
Saturday afternoon. Temps will remain mild next Saturday.


.AVIATION...(For the 18Z TAFS through 18Z Sunday) Issued at 300
AM MDT Sat Sep 23 2017

Thick multilayer cloud decks will be encompassing much of the CWA
along and east of a line extending from western Sweetwater
County, north along the west slope of the Wind River mountains, to
the eastern boundary of Yellowstone Park. This area will have
extensive areas of IFR/MVFR conditions through 18z Sunday along
with mtn obscn. The terminals west of this area including KRKS,
KBPI, and KPNA with have more variability in the height of the
cigs and vsby during this time frame. However, Northwest WY
including KJAC will have VFR conditions along with occasional MVFR
conditions this afternoon with more frequent MVFR conditions
along with LCL IFR conditions after 00Z Sunday as the trough axis
over Eastern Idaho approaches the area. This vast area of lowered
vsby and cigs will include an extensive area of precip with snow
falling above 5500 feet where vsby will be lowest, along with
rain below 5500 feet.


Issued AT 300 AM MDT Sat Sep 23 2017

Fuels at critical levels for most of the low elevation forecast
zones east of the Divide and across southern Wyoming. (Please see
the Fire Weather Forecast product for more information).

Today through Monday will be cool/seasonally cold across the
forecast area. Additionally, copious moisture/rainfall/mountain
snowfall will continue to to spread east of the Divide today...
continuing through Monday. Significant precipitation values can be
expected in one form or another...with everyone east of the Divide
having a chance to get from a quarter inch to as much as an inch of
liquid. Winds will periodically gust 15 to 25 mph across southern
Wyoming today and Sunday before becoming light on Monday. |


Winter Storm Watch from this evening through Sunday afternoon
for WYZ014-015.



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