Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 191238
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
538 AM MST Sun Nov 19 2017

.SHORT TERM...(Today through Tuesday night)
Issued at 145 AM MST Sun Nov 19 2017

Imagery now shows ridge/trof pattern, west to east, across the
CONUS. At the moment a split jet is present over the wrn
CONUS...with one branch well to the north in Canada and the other
coming into/through nrn California/NV. Strongest portion of the jet
still resides well off-shore PAC NW with an associated developing
shortwave trof.

Today: Northwest flow aloft and high pressure continuing across the
west with interact with lee troffing east, maintaining gusty west to
southwest winds over the usual spots...nrn/cntrl mountains and Cody
Foothills (G35-55kts) in addition to the Wind Corridor (25-40kts). A
High Wind Warning continues for zone 3 (Cody Foothills) through
Monday.

Tonight: A stronger wind pattern with a better chance for High Wind
conditions across the Absaroka Mountains and Cody Foothills will
occur tonight with strong SFC P, T, and Omega Grads under
increasingly favorable mountain wave production aloft ahead of the
next approaching very strong jet(120-150kt)/SW trof. Gusts to 75 mph
or high may be found both in the mountains and foothills. Areas of
High Wind may also arise over the Wind Corridor and adjacent
foothills from later tonight through the day Monday. A High Wind
Watch has been posted for the Wind Corridor and Lander Foothills
tonight through Monday.

Precip chances will remain out of the FA through tonight before
returning across western WY by mid-day Monday. With the region
already under nw flow aloft, an approaching strong jet (120-150kts)
and associated embedded shortwave will allow all precip to start out
as snow when it first arrives later Monday morning. By afternoon
snow may mix with rain in the valleys. A low enough dew point
depression may keep wet bulb temps low enough to keep it as all
snow. Otherwise, only modest moisture is expected with this system
as it moves through/over a ridge into the western FA. Possible
Advisory (low end Warning?) conditions for the period from Monday
morning through the day Tuesday across a few of the western mountain
groups.

.LONG TERM...(Wednesday through Sunday)
Issued at 145 AM MST Sun Nov 19 2017

A NW flow aloft over the region Wednesday with additional snow
for the higher NW WY mountain elevations with mainly rain below
8000 feet MSL and possible light rain in the Jackson Valley. Dry
elsewhere Wednesday with very mild high temps for mid November.
The weather will not be a turkey on Thanksgiving Day Thursday as
dry weather and very mild high temps will be the rule over the
area. Some moisture moves back into NW WY Thursday night with rain
and snow showers. On Friday, the moisture axis continues for the
west. Rain and higher elevation snow will occur in the west. Dry
weather most places Friday east of the divide. Did add isolated
showers to the northern zones Fri afternoon and evening as the
ECMWF continues to show a front sagging south into northern WY Fri
afternoon. GFS has changed to a drier solution for Fri and Fri
night with only isolated showers at best up north. High temps
still mild on Friday. GFS and ECMWF models differ on Saturday as
the GFS is showing precip in the northwest and north while the
ECMWF is showing mainly dry weather. Have gone with low precip
chance in the NW and N and dry elsewhere for Saturday. A little
cooler for highs on Saturday. Next Sunday the GFS is dry while the
ECMWF has precip for NW WY once again. Will put in low precip
chance for now see how things look tonight. High temps next Sunday
will be on the mild side once again. Overall, the weather pattern
for the Thanksgiving holiday weekend looks rather favorable for
travel with no big storm or cold outbreak. The gusty wind in the
usual wind prone areas would be the main travel concern.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday)
Issued at 535 AM MST Sun Nov 19 2017

Low clouds, producing MVFR/IFR ceilings, will persist in NW WY
through about 18Z. KJAC airport will be impacted by these low clouds
as well.

Otherwise, VFR conditions to occur through the forecast period.
Winds will continue to remain gusty at KCOD and KCPR through the
forecast period. Some LLWS will occur along the east slopes of the
mountains.

&&

.FIRE WEATHER...
Issued AT 145 AM MST Sun Nov 19 2017

Fuels remain at critical levels across over portions of Fremont,
Johnson and Natrona Counties.

Fire weather conditions will be enhanced today as temperatures warm
slightly and the surface/boundary layer dries out with respect to
that on Saturday. RH values will drop into the upper teens to
mid/upper 20s (percent) east of the Divide and across southern
Wyoming while winds gust out of the southwest 25 to 45 mph at times
across the critical fuel zones (see above). Monday will se similar
conditions to those of today (east of the Divide) with even gustier,
possibly High, winds.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from 5 PM Sunday through Monday afternoon for
WYZ002-018>020.

High Wind Warning until 5 PM MST Monday for WYZ003.

&&

$$

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


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