Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 141929

Area Forecast Discussion
National Weather Service Riverton WY
129 PM MDT Wed Mar 14 2018

.SHORT TERM...(This evening through Saturday)
Issued at 1239 PM MDT Wed Mar 14 2018

Approaching shortwave and associated cold front will aid in lines of
convection forming over nrn UT and sern ID which will move nwd/nnewd
across far west and sw into this evening, then gradually lifting nwd
into nw and ncntrl WY overnight with increasing shower potential. A
few of the storms in especially the swrn corner could produce some
pea hail (<.5"), gusty wind and brief heavy rain (higher elevation
snow). Some heavier rain showers could fall on the snow in the Star
Valley but temperatures will fall quickly during heavier convection.
Could be 50 at the start and then suddenly fall into the upper 30s
with a rain snow mixture. It`ll definitely be a crazy 6-9 hours with
a little bit of everything possible, thunder, small hail,
accumulating snow with spurts of heavy mtn snow showers, and valley
rain showers mixing with or changing to snow during heavier showers.
Will update the SPS as this seems to cover everything just fine.
Local advisory amounts still possible but not confident on
widespread advisory amounts in the west. Snow levels will start
mainly above 8K but that will lower overnight and during heavier
convective showers. Some concern about a quicker changeover to snow
in the far west valleys, especially the Jackson Valley. Will mention
this in the SPS and have the evening crew watch developments
closely. This swath of showers will lift nwd with the shortwave with
an increasing chance of showers spreading into the Cody Foothills
and Bighorn Basin overnight. We also expect some gusty to strong
south wind as this system lifts nwd overnight, including parts of
Central WY. Some snow showers will persist at times in the west
during the day Thursday. Models have backed off on the amount of
moisture wrapping nwwd around our developing surface (and mid level)
low that moves from nern CO into nwrn KS Thursday night. The end
result in most of the convective pcpn that forms stays east of our
area Thursday night. We still have a weaker shortwave lifting nwd
during the day Thursday with some showers developing east of the
divide. A potential stronger shortwave lifts nwd on Friday with
colder mid level temps and some snow showers. Moisture looks quite
limited with this system so most of the snow showers will likely be
in the higher terrain/mtns on Friday. The main upper low then
approaches the far west by Saturday morning with an increasing
chance of snow once again out west through the day Saturday.

.LONG TERM...(Saturday night through Wednesday)
Issued at 1239 PM MDT Wed Mar 14 2018

The aforementioned upper low will be moving across Wyoming
through Sunday. We still expect some snow and rain across the
area. However, the models continue to have the same issues as
yesterday with placement of the steadiest and heaviest
precipitation. As a result, we are still having difficulty
pinpointing where the heaviest will fall. Sunday night into Monday
will see a decrease in the amount of showers as the low moves into
the Plains with the best chance during these periods across
northern Wyoming. With unstable northwesterly flow though, some
showers will remain possible as the system departs. We should
these gradually come to an end as we head into Monday night.

At this point, Tuesday looks mainly dry with high pressure
building into the area. The GFS at this point looks like it is
overdoing showers across the northwest. The models then diverge a
bit for the middle of next week with the approach of the next
system. The GFS is faster in bring the next Pacific trough and
front in on Wednesday while the European is about 12 to 24 hours
slower. Right now, I am inclined to believe the European more
since the GFS has a nasty habit of bringing Pacific systems in a
day or two too quickly this far out.

.AVIATION...(For the 00Z TAFS through 00Z Thursday afternoon)
Issued at 1239 PM MDT Wed Mar 14 2018

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

Scattered to numerous valley rain/mountain snow showers are expected
to gradually expand into the evening. A few thunderstorms are
also possible. Periods with MVFR conditions are likely at KJAC and
KPNA. Thunderstorms could produce small hail and gusty, erratic
winds. The bulk of the shower activity should exit the area after
06Z, with the some fog development possible. Also the rain showers
left could change over to snow in the far western valleys after
09Z Thursday, especially in vicinity of KJAC. Isolated showers on
Thursday may bring brief MVFR conditions and occasional mountain
obscurations, but this should be the exception rather than the

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

VFR conditions are expected through the period for the most part.
The exception will be around KCOD where brief MVFR conditions
will be possible. After about 02Z Thursday, some valley
rain/mountain snow showers are expected to push north, northeast
into the Wind River Basin and then the Big Horn Basin. Brief MVFR
conditions could occur with the shower activity. By 09Z this
activity should be lifting away from the area with decreasing
cloudiness. Some fog could form depending upon how much rain falls
but with the showery nature of the rain, this is hard to pinpoint
exactly. Mainly VFR conditions are expected after 12Z Thursday.

Issued AT 1239 PM MDT Wed Mar 14 2018

The effects of the next spring/winter weather system begin to be
felt west of the Continental Divide this afternoon and evening with
a little everything from rain and snow to thunderstorms with small
hail possible across southwestern Wyoming. 6 to 10 inches of new wet
snowfall will be possible above 8500 feet through the day
Thursday...with rain/snow mixes and much less accumulation below
7500 feet. Cool and showery most locations east of the Divide from
later tonight through Friday. Gustiest winds most probable across
the Wind Corridor from eastern Sweetwater through Natrona Counties
both into this evening and Thursday afternoon again.





LONG TERM...Hattings
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