Flooding in Wyoming, February 10 to 23, 2017

Area Forecast Discussion
National Weather Service Riverton WY
502 AM MST Fri Feb 10 2017

.UPDATE...High Wind Warnings expired at 500 AM for central WY.

.SHORT TERM...Today through Sunday night

Imagery shows dirty wet ridge across much of the western and central
CONUS with a warm and relatively deep plume of moisture continues
flowing into and across the Western USA from the EPAC. Upstream, a
rather fast moving and small SW trof exists, still to the west of
the coast. Fast and nearly zonal flow is located across the FA this
morning with many areas of strong wind continuing to gust over the
foothills...supported by near SFC conditions of extreme positive
omega and a very strong thermal gradient. Otherwise, SFC has general
high pressure across the desert southwest and southern Rockies with
lower pressure to the north/northeast and a rather strong pressure
gradient dividing the two areas...including across WY where west to
southwest winds continue gusting to 40+ mph. Moderate to heavy
precipitation, both liquid and frozen, is flowing into western
WY...with snow levels around 8000 ft. Additionally, the unseasonably
warm conditions and wind are causing areas of rapid snowmelt
ATTM...with many of the foothill areas of central and northern WY
currently under flood advisories or warnings...in addition to those
in place out west over the Jackson and Star valleys. This currently
includes the Lander area with local flooding is already occurring
with water running across some roads such as Hwy 287 which is going
to be closed near the old radio station. Finally, most of the
western FA is also under a mix of Winter Storm Warnings and
Advisories...including southern Lincoln county.

Through tonight: As very moist flow continues into/across western
Wyoming, heights and temperatures begin to drop this morning as the
western SW trof rushes towards the region. This should allow colder
air aloft to flow across the FA from the northwest with rain/drizzle
or rain mixed with snow turning to all heavy wet snow sometime
around sunrise across the west. Another 3 to 8 inches of snow should
fall across the mountains above 7000 feet by the end of day...with 2
to 6 inches in the valleys and other lower elevations west of the
Divide. Tonight as a front moves through the area...the area of
precipitation will get pushed south, with most significant QPF
across the southern zones with mainly very light snow possible over
the northwest. Sweetwater county, through Saturday morning, should
generally see anywhere from 1 to 3 inches of new snowfall... with
the heavier snow across the southern and eastern most portions of
the county.

Saturday through the end of the fcst: Upper trof/SW moves through
the area and pushes a stronger front through the region east of the
Divide...offering a chance for precipitation...a rain/snow mix or
light snow, with little, if any, accumulation - certainly staying at
an inch or less for most locations...including the mountains.
Saturday evening, the trof axis passes out of the eastern FA and
except for a few possible light lingering showers across the
mountains, precip will have ended and modest flat ridging will
begin...but this time without the moisture. After a relatively cold
start Sunday morning, temperature and winds will also be more
moderate, with high temps centered near or just below seasonal
averages.

.LONG TERM...Monday through Friday

An upper level ridge will occur over the western U.S. Monday
through Tuesday. Then the ridge moves into the Rockies Mountain
region Wednesday and Thursday. Dry weather for all areas Monday
through Thursday night. A weather system enters the Great Basin
on Friday and will spread rain and snow into western WY Friday
afternoon through Friday night. It will be dry east of the
continental divide next Friday. Temperatures will be at or above
normal through the period. This means 30s and 40s east of the
divide and 20s and 30s in the west. The snow covered basins will
see inversions develop and this will hold down high temps
somewhat. Lows will be seasonably cold for this time of year.

&&

.AVIATION.../12Z ISSUANCE/

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

Periods of MVFR/IFR conditions will occur across west and southwest
Wyoming today in low ceilings with rain changing to snow at various
times. VFR conditions are expected at RKS through the morning, but
lower ceilings are expected to develop in the afternoon with periods
of rain changing to snow in the evening. During the evening, the
bulk of the snow across the west will end with VFR conditions, but
continue across Sweetwater County. Mountains will be obscured with
IFR/LiFR conditions through much of the period.

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

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

Turbulence will be the main issue through the forecast period. Low
level wind shear and/or windy west to southwest wind will be common
this morning with winds gradually decreasing this afternoon and
evening. Otherwise, VFR conditions with considerable mid/high level
cloudiness. Precipitation is expected to remain along and west of
the Divide.

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

&&

.FIRE WEATHER...

Fire Danger low for all of WY through the next week as a good
existing and increasing mountain snow pack will combine with
seasonal temperatures and less wind by Saturday to keep fire danger
low for the next week. Heaviest snowfall of the period will
generally be located west of the Divide and above 7500 feet. Smoke
dispersion fair to good this afternoon, good to very good Saturday
afternoon, and then poor on Sunday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

Winter Weather Advisory until 5 PM MST this afternoon for WYZ013-
023-027.

Winter Storm Warning until 5 PM MST this afternoon for WYZ001-
002-012-014-015-024.

High Wind Warning until 8 AM MST this morning for WYZ003.

Winter Weather Advisory until 5 PM MST this afternoon for WYZ025-
026.

&&

SHORT TERM...Braun
LONG TERM...AR
AVIATION...WM
FIRE WEATHER...Braun

Hazardous Weather Outlook
National Weather Service Riverton WY
504 AM MST Fri Feb 10 2017

WYZ001>020-022>030-111200-
Yellowstone National Park-Absaroka Mountains-Cody Foothills-
North Big Horn Basin-Southwest Big Horn Basin-
Southeast Big Horn Basin-Owl Creek and Bridger Mountains-
Bighorn Mountains West-Bighorn Mountains Southeast-
Northeast Johnson County-Southeast Johnson County-
Teton and Gros Ventre Mountains-Jackson Hole-
Wind River Mountains West-Wind River Mountains East-
Upper Wind River Basin-Wind River Basin-Lander Foothills-
Green Mountains and Rattlesnake Range-
Natrona County Lower Elevations-Casper Mountain-Star Valley-
Salt River and Wyoming Ranges-Upper Green River Basin Foothills-
Upper Green River Basin-South Lincoln County-
Rock Springs and Green River-Flaming Gorge-East Sweetwater County-
504 AM MST Fri Feb 10 2017

...Winter Storm Warnings and Advisories for the Western Mountains
and some lower elevations west of the Divide through today...

...High Wind Warning for portions of northern Wyoming until 800 AM...

...Assorted flood advisories and warnings across portions of
central...northern and western Wyoming today...

.DAY ONE...Today and Tonight

Today...Periods of snow...heavy at times...continuing across
western Wyoming. Increasing snow chances across southern Wyoming
tonight. Warm temperatures, wind and snow melt in addition to some
rain across some lower elevations could cause some local flooding
through in the western valley today. Additionally...the warm
temperatures, wind, and snow melt across some lower elevation
foothills east of the Divide could cause some local flooding
through this evening.

High winds around the Cody Foothills will be decreasing after 8 AM
this morning.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Saturday...Snow ending across the western forecast area...light
snow east of the Divide...and very gusty north winds across
Johnson county Saturday afternoon and evening.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report snowfall amounts, rainfall
amounts and any flooding.