Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 202029
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
229 PM MDT Mon Mar 20 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 108 PM MDT Mon Mar 20 2017

Shortwave moving into the sw attm with showers expected to increase
and spread ne from the swrn sections to the nern sections this
evening (along with a few possible tstms). Shortwave/vort energy
expected to intersect the front around Casper with widespread rain
showers/slgt chc thunder this evening. As this system and frontal
system come into play further north, the temps trend cold enough to
change the rain over to snow later this evening into the early
morning hours before ending. Some indication of freezing drizzle
potential for the Cody Foothills and nrn Johnson County and will
continue to see if I want to add that back in. Front becomes more
entrenched tonight and hangs around for most areas east of the
divide on Tuesday for another cool day across the north especially.
Further south in Natrona and especially Fremont County it`s a
tougher call as front erodes some allowing some late day warming.
Lowered temps overall but didn`t go too low in the south half. Weak
ripples in the sw flow will aid in showers in and near the higher
terrain on Tuesday, especially in the afternoon. The next system and
associated frontal boundary hits the far west later Tuesday evening
into Wednesday morning with another round of more organized mtn snow
and valley rain or rain and snow mixed. Still sub-advisory but a 3-6
hour shot of steady snow. Digging trough then starts moving onto the
srn CA coast late Wednesday and then heads towards the 4-corners on
Thursday. Jet couplet may form over the sw Wed evening leading to a
significant band of showers and possibly a few tstms. This area of
jet support lifts nwd into the far nrn zones by 12z Thursday. A
widespread band of showers will likely lift nwd from swrn Wyo into
ncntrl Wyo Wednesday night. What happens during the day Thursday is
a tougher call. The GFS has been the most bullish developing a mid
level (H7) low over sern Fremont County Thursday morning with
widespread cold rain potentially changing to snow, especially near
the foothills of Central Wyo. The NAM has some cold rain or rain and
snow mix in the far north with just some convective looking showers
developing over ern Sweetwater Thursday morning and lifting ne
across the ern zones in the afternoon. The Euro does not have the
mid level circulation as far north but still has some QG forcing and
left nose of cyclonic jet support. Will continue the trend of
increasing pops and will also lower temps considerably east of the
divide on Thursday. Will continue to watch this closely the next
couple days. Longwave pattern still favors weakening of this system
or the srn track but this time of the year, just one little mid
level circulation with jet/qg support on the nrn part of the upper
low could be enough to get us a shot of steady cold rain or snow in
the lower elevations.


.LONG TERM...(Thursday night through Monday) Issued at 108 PM MDT
Mon Mar 20 2017

By 00Z Friday, the energy from the splitting southern stream
system becomes more focused across southern Colorado and New
Mexico with the remnants of the weak closed 700mb low over South
Central Colorado opening up. Only an additional inch or less of
snowfall can be expected across the Southern Wind River Mtns, the
Southern Big Horn Mtns as well as the lower elevations of
Sweetwater, Southeast Fremont, and Natrona Counties after the rain
turns to snow there later Thursday evening. Snow totals by Friday
morning should total up to 3 to 6 inches across most of the
mountains with lighter amounts in the northwest. The snow
accumulations will be spottier across areas west of the divide
where the precip will be more showery. The higher elevations in
the vcnty of Beaver Rim and Jeffrey City could see 1 to 2 inches
of snow by Friday morning.

Friday and Friday night will be precip free with a positively tilted
transitory ridge in place. Temperatures will be a bit milder Friday
except little change in Sweetwater County.

Then on Saturday, the next upstream Pacific trough will approach the
Rockies with high elevation snow developing along with low elevation
rain. Just like the weather system that we anticipate for this
coming Thursday, this system will likely split with the mean ridge
just to our east, with the southern stream energy shifting to the
Southern Rockies by Monday. However, the northern stream energy
should be enough to keep precip going in the far west Sunday and
spreading to Northern Wyoming, east of the Divide Sunday,. Then on
Monday, most of the precip should be focused across northern
Wyoming. Many of these areas have the potential to see between one
half to three quarters of an inch of precip so significant snowfall
is possible in the mountains. This event is still a long way off and
plenty of time to interrogate precip amounts.

Low-elevations snowmelt over western valleys will continue localized
flooding through the extended.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday afternoon)
Issued at 108 PM MDT Mon Mar 20 2017


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

Rain and high mountain snow will continue through 06Z Tue. Local
MVFR conditions will occur in NW WY along with mountain obscuration
at times. Scattered showers and isolated thunderstorms will develop
in Southern Wyoming and continue into this evening. Then showers
will become isolated after 06Z Tue. Then mountain snow showers and
low elevation rain showers will develop again after 18z Tuesday.

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

A cold front has become nearly stationary in central WY today. North
of the front areas of low clouds and areas of rain will continue
over portions of Northern Wyoming, including KCOD, producing MVFR
conditions. In central WY, VFR conditions will continue for the rest
of this afternoon with scattered showers continuing to develop from
north to south along with isolated thunderstorms from the Red Desert
to KCPR through the remainder of this afternoon. This activity will
continue into this evening. Areas of MVFR ceilings will occur east
of the divide after 01Z along with some mountain obscuration.
Showers will become isolated after 06Z Tue. Isolated showers will
redevelop from the Red Desert to Casper as well as over the Big Horn
Mountains after 20Z Tuesday afternoon.

&&

.FIRE WEATHER...
Issued AT 108 PM MDT Mon Mar 20 2017

A weather disturbance moving northeast across the area today from
southwest Wyoming to north central Wyoming will bring a band of
widespread showers and possibly a thunderstorm through tonight. Rain
may change to snow in the far northern part of the district. Fire
danger will be low for most areas this week as a series of weather
systems move through the area, especially Thursday and over the
weekend. There will be some gusty wind though Wednesday in the
southern parts ahead of our Thursday system and there is a small
chance of isolated thunderstorms in the afternoon hours in the south
and west.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 6 PM MDT Tuesday evening for
WYZ013-023-025>027.

&&

$$

SHORT TERM...Skrbac
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...Skrbac


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