Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 170908
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
308 AM MDT Fri Mar 17 2017

.SHORT TERM...Friday through Sunday night

Seeing how a lot of peoples minds are on college basketball for the
next few days. We will compare the days of the forecast to what
happens in the tournament from day today.

Today is what a lot of people refer to as a chalk day. In other
words, not a ton of excitement with fairly benign conditions.
Ridging will build across the area with the continuation of mild
temperatures and a mixture of clouds and sunshine. Temperatures will
be a few degrees cooler than recent days, but still pleasant. In
addition, there will be much less wind than recent days.

However, the madness will pick up a bit on Saturday. It will remain
dry so precipitation will not be an issue. However, the wind machine
will begin to crank up again as another system moves into the west
and tightens the pressure gradient across the area. 700 millibar
winds will increase but at this time do not look likely to reach
high wind criteria. However, there will be other parts of the story.
The unusual thing or the upset to use tournament language, will be
the temperatures and one other thing. 700 millibar temperatures will
be very warm, close to 8 Celsius in some areas. That means many
areas should see highs into the 70s and in some areas well into the
70s. I would not rule out a spot or two seeing a high temperatures
making to 80. However, with the warm temperatures and gusty winds,
fire danger is likely to increase. With relative humidity creeping
down toward 15 percent in some areas, fire danger may become high.
As a result, we will continue the fire weather watch. And in
addition, with the warm temperatures snow melt will continue with
the threat of flooding continuing to loom.

Things then turn more active as we head into Saturday night and
Sunday and ramps the excitement up. The aforementioned trough will
approach the area from the west and spread precipiation into the
west. It does appear a bit slower, so most areas should be dry
during the evening. We also removed any POPS east of the divide for
Saturday night. The system is fairly warm however, with 700 millibar
temperatures running anywhere from minus 2 in the north to plus 1 in
the south. This would put snow levels from 7500 to 9000 feet so any
accumulation would be over the mountains. The models are continuing
to struggle with the position of the heaviest precipitation however.
As a result, we will make only minor tweaks. Meanwhile, East of the
Divide some showers will spread east of the Divide. In addition,
with the mild temperatures and some upper level divergence and jet
energy, there could even be a few thunderstorms. The best chance of
this would be across the north. With more cloud cover, expect
temperatures to be a bit cooler but still above normal for the
middle of March.


.LONG TERM...Monday through Friday

A quasi-stationary front is expected to be along or just east of
the Divide Monday. This baroclinic zone combined with disturbances
in the westerly flow, as well as a hint of isentropic lift over
the front will result in precip chances across much of the area.
Models continue to have little continuity with placement of
precipitation, except for an emphasis across the west due to
westerly flow orographic effects. Looks like western valleys above
6500 feet will see snow changing to rain in the afternoon, but
the bigger challenge in snow levels will be across the northern
portions of the forecast area, east of the Divide where snow
levels could easily be at valley floors across northern Wyoming
(Johnson, N. Bighorn Basin). Farther south into central Wyoming,
precip in the valleys look to be all rain. However, precipiation
amounts look be mainly light at this time.

A transitory ridge moves across the area late Monday night into
Tuesday with mainly dry conditions expected. The frontal boundary
across the area Monday is expected to lift northward as a warm
front late Monday night into Tuesday with warmer temperatures
especially east of the Divide.

A quick moving disturbance in the southwest flow ahead of the main
trough is expected to move northeast from Nevada into southwest
Montana Tuesday night/early Wednesday with the associated cold
front moving into Western Wyoming late Tuesday night or Wednesday.
This will give the west another decent shot of precipitation while
keeping area east of the Divide mainly dry, warm and breezy/windy.
Elevated fire weather behavior possible east.

The deep trough across the West is expected to split Wednesday
night/Thursday with the main energy pushing across the Great Basin
into the central/southern Rockies. Deep surface cyclogenesis is
expected to occur across the Colorado Frontrange Thursday. As this
occurs and some forcing with mean trough pushes over the area, the
entire area will have a chance of precipitation. Would me more
excited for significant precipitation east of the Divide if models
were showing a surface high sliding south out of Canada, but they
are not.

Drier and warmer conditions are expected Friday as this potential
storm system moves away from the area.

&&

.AVIATION.../12Z ISSUANCE/

VFR conditions will prevail across the area through 12z Saturday
under a dry westerly flow, scattered mid to high clouds. A
stationary frontal boundary near a vicinity KCPR-KRIW line will lift
north and east Friday morning with prevailing surface west winds 10-
20 knots vicinity of a KCPR-30SM south KLND line.  Surface winds
will be primarily S-SE north of this line.  Mid-level southwest flow
will increase Friday night with areas of LLWS possible east of the
Continental Divide, vicinity KCOD-KDUB-KLND.

&&

.FIRE WEATHER...

...FIRE WEATHER WATCH IN EFFECT FOR ZONES 280 AND 281...

Today looks fairly be quiet with high pressure over the area. expect
dry conditions with winds remaining light to moderate in a vast
majority of areas. Mixing and smoke dispersal will be generally fair
to poor. Fire danger will increase on Saturday as a combination of
gusty southwest winds, warm temperatures and relative humidity
falling into the teens in some areas. Critical fire conditions are
possible across the lower elevations of Natrona and Johnson
Counties. Therefore, the Fire Weather Watch will continue.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Saturday afternoon through Saturday
evening for WYZ280-281.

&&

$$

SHORT TERM...Hattings
LONG TERM...WM
AVIATION...AEM
FIRE WEATHER...Hattings



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