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

615
FXUS65 KRIW 212245
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
445 PM MDT Fri Apr 21 2017

.UPDATE...
Issued at 440 PM MDT Fri Apr 21 2017

Observations show the snow has changed to mainly rain across the
Cody Foothills with current temps in the mid to upper 30s. Could
see a change over back to snow tonight, but any accumulations will
be minor. Thus elected to cancel the winter weather advisory for
the Cody Foothills.

There is a PNS with rainfall and snowfall amounts. However most of
the data only goes through 9 AM this morning.

&&

.SHORT TERM...(This evening through Monday)
Issued at 220 PM MDT Fri Apr 21 2017

An upper level low pressure center over south central Wyoming
bringing widespread rain in the lower elevations with mountain
snow will gradually move east with showers tapering off from late
evening in the west to early morning in the east. Heaviest
snowfall expected in the Bighorn mountains where a winter storm
warning is in effect until early morning. Other mountain area
have winter weather advisories in effect until late evening. Cool
northwest flow aloft with limited moisture and instability will
bring scattered showers to the west tonight dissipating towards
morning. Snow line should be around 7800 feet. Local accumulations
of 1 to 3 inches are possible. High pressure will bring clearing
and lighter winds on Saturday and Saturday night. Sunday will see
increased moisture as the flow aloft over the west shifts to the
southwest with showers increasing Sunday afternoon through Monday
as winds increase.

.LONG TERM...(Monday night through Friday)
Issued at 220 PM MDT Fri Apr 21 2017

An unsettled weather pattern is still in store for the region
through the extended forecast period. A series of short waves are
expected to rotate east-northeast through the upper trough across
the region. This will result in timing issues related to the weather
systems expected to move across the western U.S. in the westerly
upper flow aloft. Areas generally west of the Divide will likely see
a combination of rain and snow in various periods through the
Wednesday and Friday time frame, with mainly snow expected above
7500 feet in the mountains. Due to the amount of moisture inflow in
the western Mountains and cooler temps especially above 8500 feet,
significant snow accumulations are possible through the Wednesday-
Friday period.

For areas east of the Divide, scattered showers will still spill
eastward into the region, with some locations not seeing much
precip, while others seeing some precip each day. Due to timing
issues, will need to update forecast and better time the
onset/ending of precip into the latter part of the extended forecast
later when timing issues are better determined. Expect temps to be
cooler next week generally at most locations due to the expected
increased clouds/precip.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 220 PM MDT Fri Apr 21 2017

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

Lower layer VFR ceilings are expected to continue at most of the TAF
sites until around 02z, when skies should begin to clear across the
region. Light and variable winds with VFR conditions are then
expected through the rest of the forecast period.

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

Precipitation is expected to gradually lessen in intensity and
coverage this evening across the area from the west to the east.
MVFR ceilings are expected at KCOD and KWRL until between the 06z-
09z time frame, and at KCPR by around 15z Saturday. Elsewhere, VFR
conditions will be the rule. After 15z Saturday, VFR conditions and
improving cloud conditions are expected across the area through the
end of the forecast period.


&&

.FIRE WEATHER...
Issued AT 220 PM MDT Fri Apr 21 2017

An upper level low pressure center over south central Wyoming
bringing widespread rain in the lower elevations with mountain
snow will gradually move east with showers tapering off from late
evening in the west to early morning in the east. Heaviest
snowfall expected in the Bighorn mountains where a winter storm
warning is in effect until early morning. Other mountain area have
winter weather advisories in effect until late evening. Cool
northwest flow aloft with limited moisture and instability will
bring scattered showers to the west tonight dissipating towards
morning. Snow line should be around 7800 feet. Local accumulations
of 1 to 3 inches are possible. High pressure will bring clearing
and lighter winds on Saturday and Saturday night. Sunday will see
increased moisture as the flow aloft over the west shifts to the
southwest with showers increasing Sunday afternoon through Monday
as winds increase. The areas with precipitation and low clouds
continuing in the east on Saturday will have poor smoke dispersal
with low mixing heights, while the rest of the area with clearing
will have much improved mixing with sufficient transport winds
for good or better smoke dispersal. Transport winds will decrease
with high pressure building in on Sunday but overall mixing
heights will be favorable for good smoke dispersal.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight MDT tonight for WYZ002-
007-015.

Winter Storm Warning until 6 AM MDT Saturday for WYZ008-009.

&&

$$

UPDATE...Murrell
SHORT TERM...Baker
LONG TERM...Troutman
AVIATION...Troutman
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.