Area Forecast Discussion
Issued by NWS Riverton, WY

Home | 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 150522
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1021 PM MST Wed Feb 14 2018

.SHORT TERM...(This evening through Saturday)
Issued at 229 PM MST Wed Feb 14 2018

The leading edge of deeper Pacific moisture ahead of a Pacific low
pressure trough and cold front moving east across eastern Idaho and
southern Montana will move into the western mountains and northern
Wyoming late this afternoon and early this evening with snow
expected to become widespread especially above 8000 feet through the
evening. Snowfall is expected through Thursday afternoon.  Winds
should pick up at ridge top and across the north through the night
tapering off some later Thursday afternoon. The heaviest snowfall
should be over the Tetons and the southern mountains of Yellowstone
National Park with lighter amounts to the south over the Wyoming and
Salt River ranges and the Wind River mountains. Snowfall amounts of
4 to 8 inches can be expected in the Tetons with 3 to 5 inches
elsewhere in the mountains tonight. the lower elevations will likely
see an inch or two with locally higher amounts up to 4 inches in the
foothills. Snowfall on Thursday is expected to range from 3 to 6
inches in the mountains with another inch possible in the lower
elevations. A break in the snowfall is expected Late Thursday
afternoon and Thursday night with another round of  generally light
snowfall moving into the west on Friday and Friday night.
Temperatures east of the continental Divide will cool from north to
south tonight and remain below normal through Friday before
rebounding on Friday night and Saturday as west flow aloft increases
and brings downslope warming to areas along and east of the
Continental Divide.

.LONG TERM...(Saturday night through Wednesday)
Issued at 229 PM MST Wed Feb 14 2018

The next upstream Pacific shortwave will be making landfall onto the
Pacific coast Saturday night. A strengthening westerly flow directly
off the Pacific out ahead of this approaching trough will enable
snowfall to intensify in the far west as the GFS tracks a lead
shortwave through the area 12Z Sunday. The GFS gives many areas of
Western Wyoming up to one half of an inch of precip for Saturday
night. Then on Sunday the main trough digs across the Pacific NW.
Asct weak sfc troughiness develops over Wyoming before a more
organized area of low pressure becomes established over Utah/Co by
00Z Monday. By 00Z Monday, any strong west southwest winds resulting
in the warm before the storm east of the divide will shut off as the
pressure gradient loosens when the main troughiness moves ovhd. On
Sunday night, snowfall will continue in the far west but at lesser
intensity while snowfall becomes more established east of the divide
as another asct arctic front plows south across Wyoming, mainly east
of the divide, and isentropic lift develops along and north of the
front. the GFS suggests a mid level circulation on Monday tracking
east across South Central wyoming, including Southern fremont County
which could mean some local areas could see exaggerated snowfall
amtns in that general vcnty, along with another such circulation
following behind it to track east across Sweetwater County where
lifted indices are progged to be below zero where more exaggerated
snowfall amtns would occur. This is based on the assumption that the
GFS is correct in placing the main H5 low over Southwest Wyoming by
00Z Tue. The Euro on the, other hand, lags behind with the H5 low
still over Northern Idaho by 00Z Tuesday. The Canadian is the odd
model out which shears out the trough and loses it in the fast
westerly flow. The snowfall will dissipate on both sides of the
divide on Monday night as the trough exits the area. By Tuesday, H7
temps will lower to -23C, so we are looking at highs in the teens
east of the divide with temp inversions likely becoming
reestablished with temps not quite as cold west. Tuesday will be dry
and cold with perhaps lingering flurries out west. Then by mid week
we have introduced a chance of snow to the far west with the next
Pacific trough with the GFS placing us under NW flow and the
Canadian under SW flow where it places a positively tilted trough
upstream over Western Canada.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday)
Issued at 1015 PM MST Wed Feb 14 2018

West of the Continental Divide...KJAC, KBPI, KPNA, and KRKS

Snow will occur in the west through 00Z Friday. Lingering snow
showers will occur through 03Z Friday in the mountains. KJAC will
see MVFR conditions through 20Z with snow, then conditions will
improve to VFR at KJAC airport. KPNA airport will see light snow at
times through 21Z with MVFR conditions from 12Z to 21Z, then
improving to VFR conditions after 21Z. KBPI will see light snow at
times through 21Z with MVFR conditions at times. KRKS will have VFR
conditions through the period with gusty wind from 15Z until 02Z.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

A cold front will move into northern WY around 09Z and into central
WY around 15Z. Areas of snow will develop in northern WY overnight
with areas of snow developing in central WY after 15Z. MVFR to IFR
conditions will occur at the terminal sites. Snow will be ending in
the north by 23Z with VFR conditions prevailing by 00Z. Snow in the
central ends by 05Z Friday with VFR conditions prevailing at 05Z
Fri.

&&

.FIRE WEATHER...
Issued AT 229 PM MST Wed Feb 14 2018

The leading edge of deeper Pacific moisture ahead of a Pacific low
pressure trough and cold front moving east across eastern Idaho and
southern Montana will move into the western mountains and northern
Wyoming late this afternoon and early this evening with snow
expected to become widespread especially above 8000 feet through the
evening. Snowfall is expected through Thursday afternoon.  Winds
should pick up at ridge top and across the north through the night
tapering off some later Thursday afternoon. The heaviest snowfall
should be over the Tetons and the southern mountains of Yellowstone
National Park with lighter amounts to the south over the Wyoming and
Salt River ranges and the Wind River mountains. Snowfall amounts of
4 to 8 inches can be expected in the Tetons with 3 to 5 inches
elsewhere in the mountains tonight. the lower elevations will likely
see an inch or two with locally higher amounts up to 4 inches in the
foothills. Snowfall on Thursday is expected to range from 3 to 6
inches in the mountains with another inch possible in the lower
elevations. A break in the snowfall is expected Late Thursday
afternoon and Thursday night with another round of  generally light
snowfall moving into the west on Friday and Friday night.
Temperatures east of the continental Divide will cool from north to
south tonight and remain below normal through Friday before
rebounding on Friday night and Saturday as west flow aloft increases
and brings downslope warming to areas along and east of the
Continental Divide.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 2 PM MST Thursday for WYZ001-002-
012.

&&

$$

SHORT TERM...Baker
LONG TERM...Lipson
AVIATION...AR
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.