Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 210812
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
212 AM MDT Sat Apr 21 2018

.SHORT TERM...Saturday through Monday night
Issued at 200 AM MDT Sat Apr 21 2018

All in all, things look fairly nice the weekend for just about
everyone. There continues to be some mainly light rain and snow
rotating around an upper level low in the eastern portions of the
county warning area. These should continue to decrease tonight with
all precipitation over by around or shortly after sunrise. Following
that, high pressure will build across the area and bring a dry and
mild day with light to moderate winds for most area. The one place
that could see some breezy conditions is across southern Wyoming but
what most places call breezy in the Cowboy State we call it
Saturday.  The models do bring a weak shortwave that will brush by
to the north and show some light QPF but the models are also
notorious for overdoing the orographic effects with this so we kept
the forecast dry.

The dry weather should hold through Sunday as well. The GFS tries to
bring some showers in late Sunday but this model is notorious for
bring too fast with west to east moving systems so we kept the
forecast dry. Our feeling is that most of the evening should be dry
as well with any heavier precipitation holding off until after
midnight. Otherwise, it will be dry and mild, although with some
increase of high clouds from time to time.

The most active weather still looks to be late Sunday night and
especially into Monday. At this point, there looks to be a decent
chance of snow and rain turning to snow across much of the northern
portions of the area. The models have been fairly consistent in
showing this. This wave has more moisture to work with and has some
right rear quadrant jet support. However, the models have been all
over the place with were the heaviest QPF will be since much of this
is likely to be banded. And as a result, very difficult to pinpoint,
especially this far out. 700 millibar temperatures do crash across
the area as well so many areas will see a chance over the snow.
However, since it is late April, the usual factors come into the
place, such as the warm ground and high sun angle during the daytime
hours that will prevent a lot of accumulation. So, to sum it up. 1)
There is a decent chance of rain turning to snow across the
northern half of the area. 2) The hardest hit area looks to be the
northern third of the state. 3) Details about QPF and snowfall
amounts are still VERY uncertain.

.LONG TERM...Tuesday through Saturday
Issued at 200 AM MDT Sat Apr 21 2018

Lingering light snow Tuesday morning east of the continental
divide should end by early afternoon as the storm system moves out
of the region. Clouds to decrease Tuesday with decent sunshine in
the afternoon through sunset. Cooler day overall with highs in the
40s and 50s. Wednesday looks dry and warmer with highs in the 50s
and 60s. Next weather system dives south southeast into Northern
WY Wed night, mainly along and east of the continental divide. The
central zones will see the impact after midnight Wed night into
Thurs morning. For now it looks like scattered rain showers,
turning to snow showers once the colder air occurs. Impact looks
low at this time. West of the divide looks to miss precipitation
Wed night through Thursday morning. Decreasing clouds Thurs east
of the divide with plenty of sunshine west of the divide. Cooler
day Thurs with highs in the 50s around 60. Friday looks dry and
warmer with highs in the 60s to lower 70s. Models bring in some
high and mid level moisture to the west next Saturday. This would
lead to afternoon and evening showers and isolated thunderstorms.
Dry weather next Saturday east of the divide with very isolated
showers or storms in the Bighorn mountains late Saturday
afternoon. Highs once again in the 60s to lower 70s east of the
divide, 50s to lower 60s in the west.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday)
Issued at 200 AM MDT Sat Apr 21 2018

Areas of MVFR ceilings will persist vicinity and east of a KRKS-KCPR
line through 12z with IFR ceilings prevailing vicinity KCPR. Gradual
improvement will occur from the west and north with prevailing VFR
conditions expected after 15z Saturday.  SKC conditions should then
prevail across the area after 18z Saturday through the rest of the
period.  Winds will generally be light except sfc NW winds 10-20
knots at KPNA-KBPI Saturday afternoon.

&&

.FIRE WEATHER...
Issued at 200 AM MDT Sat Apr 21 2018

High pressure will bring mainly dry conditions through the weekend.
Relative humidity will fall into the teens at times today. However,
winds will remain light to moderate for the most part, keeping fire
conditions below critical. Breezy conditions are possible across
southern Wyoming, but fuels are not critical there. Winds should
remain light to moderate through Sunday. A cold front will move
through Sunday night and Monday and bring much cooler temperatures
along with a chance of rain and snow across mainly the northern half
of the state.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Hattings
LONG TERM...Meunier
AVIATION...AR
FIRE WEATHER...Hattings



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