Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 230749
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
149 AM MDT Tue May 23 2017

.SHORT TERM...Tuesday through Thursday night
Issued at 150 AM MDT Tue May 23 2017

Almost all of the showers out there have ended or will come to an
end early this morning. Following the ending of the showers ridging
will build across the area and bring a pleasant and mild day with a
good deal of sunshine for all areas by afternoon. Temperatures will
be warmer than previous days but likely still below normal for most
areas. We did go above MOS guidance for most areas however with the
sunshine expected. We also can`t rule out some fog in some areas
that got rain this morning, but whether or not to include it will be
a game time decision. Winds should remain light to moderate to most
areas today. However, there could be some increase in wind tonight
across some of the higher elevations and also in vicinity of Clark
as mid level winds increase as a cold front approaches from the
west.

Wednesday will start off dry for all areas and continue into early
afternoon. However, as the front approaches, there will be a chance
of a few thunderstorms developing across northern and western
Wyoming. The models continue to have differences on coverage with
the NAM the wetter model and the GFS drier. For the most part, we
made few changes to continuity. The models do show some decent winds
at 700 millibars of 40 to 45 knots across much of the area. As a
result, windy conditions are likely across much of western Wyoming
as well as the southwestern Wind Corridor. It will also warm things
significantly with the west to southwest flow. Highs in the 80s will
be likely in many areas East of the Divide. As a result, this could
increase snow melt and lead to some rises in the rivers. There are
some differences in the models at night however. The NAM shows some
showers and thunderstorms breaking out across central Wyoming
although this was the first run to show that. The GFS, meanwhile,
has been more consistent in keeping precipitation mainly across
the south with some jet energy riding across the front as it drops
southward. For now, we like the GFS idea.

AS for Thursday, it will be much cooler behind the front, about 15
to 20 degrees cooler in many spots. With low heights over the area,
there will also likely be some showers and thunderstorms around. The
models do disagree on placement however. So for now, we left
continuity alone for the most part with the best chance across the
northwest and southern portions of the state.


.LONG TERM...(Wednesday through Monday)
Issued at 150 AM MDT Tue May 23 2017

Medium range period starts out quite unsettled as fairly strong
shortwave dives swd down larger scale trough/upper low over srn
Saskatchewan/Manitoba. Models have been reasonable consistent in
tracking this low through ern ID or far wrn WY late Friday into
Friday night. This track is very favorable for a period of lower
elevation rain and higher mtn snow over the sw half of the area over
into the upslope areas along the Wind River Mountains. Right
entrance region of a jet streak may also help the far south during
the day Friday. Bumped up pops well above the model blend as they
were once again woefully underdone. Snow levels will probably be
above 9K during the day Friday and 7.5-8K Friday night. Some
significant higher elevation snow is possible especially around
the Wind Rivers where we could see .50 to .75 inches of liquid
with at a tenth to a third across the nearby lower elevations with
locally higher amounts. Cyclonic nw flow looks like it may
actually last into Saturday for scattered mountain rain/snow
showers and a few showers/storms around the lower elevations.
Higher concentration of showers/storms may exist along convergence
of old frontal boundary in the swrn zones where nw and ne winds
converge. We should start to see building heights Sunday although
now the GFS keeps the cyclonic nw flow through Sunday and even the
GEM and Euro have some moisture in the nw flow which generates
afternoon convection. Will confine any showers to just the
mountains for now with temps starting to moderate. Even Monday we
may see a weak ripple in the nw flow combining with good daytime
heating to get some showers and thunderstorms forming off the mtns
and then moving s-se late in the day, especially along and east
of the divide. Heights build in Tuesday but ridge is still not
strong enough to keep weak disturbances in the flow away and these
combined with strong daytime heating leads to at least building
mtn showers/isold storms with a few trying to come off the
mountains late in the day. Temps do gradually warm through the
period after a fairly cool, unsettled start Friday where many
lower elevations will only be in the 50s. By the end of this
period, we`ll be well up into the upper 60s to upper 70s for the
lower elevations.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday night)
Issued at 150 AM MDT Tue May 23 2017

Patchy fog may occur until 15Z around the KCPR and KRKS airports.
Will keep VCFG in the forecast for those two sites. Otherwise, VFR
conditions will occur today and tonight at the terminal sites.

&&

.FIRE WEATHER...
Issued at 150 AM MDT Tue May 23 2017

High pressure will bring dry and mild weather for all areas today.
Wind should remain light to moderate for the most part. Relative
humidity will fall to around 20 percent in some areas but should
remain above critical levels. Mixing and smoke dispersal will range
from poor in the northwest to good in south and east. Windy
conditions will develop in many areas late tonight and into
Wednesday with isolated thunderstorms possible in northern and
western Wyoming later in the day Wednesday.&&

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

&&

$$

SHORT TERM...Hattings
LONG TERM...Skrbac
AVIATION...Ross
FIRE WEATHER...Hattings


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