Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 220902
Area Forecast Discussion
National Weather Service Riverton WY
302 AM MDT Sat Apr 22 2017
.SHORT TERM...Saturday through Monday night
The story for today should be for improving weather as the low
pressure that brought the rain and mountain snow exits stage east
through the day. Any lingering showers in the east should end by
noon with increasing amounts of sunshine through the day as
transitory high pressure moves across the area. Snow could linger in
the Bighorns through the early morning. All areas should be dry
from this afternoon through Saturday night although temperatures
will average a bit below average.
However, the respite will be brief as another Pacific trough and
front approach the west. However, this system does not have a lot of
moisture to work with and most of the initial energy going north of
the area so much of the precipitation on Sunday should remain fairly
light. However, there is some instability so it could end up being
more convective. And of course, we all know that the models can
perfectly pinpoint where the showers will pop up (note sarcasm).
Meanwhile, areas East of the Divide should remain largely dry and
warmer with many areas approaching 70 degrees. A few showers and
thunderstorms may spread East of the Divide Sunday evening however
as the front passes and gets a bit of an assist from some left front
quadrant jet energy. Most of the these showers should end after
midnight Sunday night.
Another front, this one a bit cooler and with more moisture to work
with will approach Monday. Both the NAM and GFS have come in a bit
slower so we reduced POPS in the morning. However, the models then
diverge on the details of the forecast, especially the placement of
the best QPF both West and East of the Divide. So for now, we did
not make many changes from Monday afternoon through Monday night.
.LONG TERM...(Tuesday through Saturday)
Issued at 300 AM MDT Sat Apr 22 2017
Tuesday through Friday will see a series of weather systems move
through the Rocky Mountain region as a mean trough takes hold. The
long range models are all in agreement with the weather pattern,
but they have timing differences of the individual weather systems
that will move through WY. It appears the west will see periods of
rain and snow in the valleys while the mountains will see periods
of moderate to heavy snow. The precipitation in the west should
be on the decline Friday night. East of the continental divide, a
daily chance of rain showers Tuesday and Wednesday. Late Wednesday
night temperatures may get cold enough for snow at the lower
elevations. This snow would last through midday Thursday if the
GFS and Canadian models verify. Plenty of time to watch this
potential for spring snow. Scattered rain showers next Friday for
areas east of the divide. Next Saturday may still see lingering
showers over the area in a cool northwest flow pattern. Overall,
high temps will be near to below normal Tue through Saturday. With
this active weather pattern, expect some brisk wind at times
during the week.
WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES
Very patchy morning fog will be possible over western valleys.
Otherwise mainly SKC to some fair weather cumulus will be observed
today with mainly light winds. Tonight will see increasing
EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES
Improving conditions are expected between 09Z and 15Z in the lower
elevations as the rain showers end, and ceilings lift to low VFR
levels, or scatter out. Northern Johnson County and Bighorn
Mountains including KBYG could see MVFR ceilings linger through
early afternoon. Some areas that clear out during the predawn hours,
mainly over the Wind River Basin, and western Big Horn Basin could
see some fog development. This should also lift/scatter out by
around 15Z. Otherwise fair weather cumulus, and mainly light winds.
Tonight, increasing wind or LLWS in the wind corridor and on the lee
side of mountain ranges, as well as increasing cirrus.
High pressure building across the area will end any showers by noon
with a balance of the day mainly dry with increasing amounts of
sunshine. Wind should remain light to moderate for the most part.
Mixing and smoke dispersal should be in the poor to fair category
for most areas. Relative humidity should remain below critical
levels. A cold front will approach the west on Sunday and bring a
chance of showers although heavy amounts of rain and snow are not
expected. A few thunderstorms are also possible. Areas East of the
Divide should be dry and warmer on Sunday with a gusty breeze
developing from Rock Springs through Casper.