Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Riverton Wyoming
222 am MDT sun Mar 16 2014
Short term...Sunday through Tuesday night
After a brief respite...it looks like active weather will return to
the County Warning Area known as western and central Wyoming. The
only concerns early this morning is a bit of wind around The
Crossroads of universe...Clark...but nothing unusual for them.
Also...a bit of fog has formed in Natrona County where last nights
snow melted and left flow level moisture. Otherwise...an area of
high pressure will bring a mixture of sunshine and high clouds along
with near to above normal temperatures. There will be a bit of a
breeze in the southwestern wind corridor...but nothing unusual.
However...this is Wyoming in March so you know it will not last.
Wind will begin to increase once again tonight as the pressure
gradient begins to tighten up as the next storm approaches from the
west. The first place to see the effects will be...once again...the
usual areas around the Cody foothills...mainly Clark. With 700
millibar winds increasing over 50 knots and a possible mountain wave
development we have hoisted a high wind watch beginning at 5 PM
tonight and running into Monday morning. Meanwhile...the gradient
will continue to tighten through the night and the aforementioned
strong 700 millibar winds developing further south we have also
issued high wind watches for the wind prone areas from Rock Springs
through Natrona County starting later Sunday night and running
The system will then arrive in western Wyoming Monday
morning...probably between around 8 am and noon. There is a decent
amount of moisture with it. However...it is fast moving and this
should help to limit accumulations a bit. Right now we have advisory
level numbers in the grids and they looked reasonable.
However...here like many other areas it will become quite windy with
the strong 700 millibar winds being mixed to the surface by the
approaching front and trough axis. The heaviest snow is expected in
the afternoon with the trough axis kicking through. Meanwhile...east
of The Divide the main story will be for strong wind. Quite a
pressure gradient will develop ahead of the front with the NAM
indicating a 27 millibar pressure gradient across the state Monday
afternoon. This combined with the strong wind aloft and front could
produce strong winds across much of the state Monday afternoon. More
high wind watches may be needed but still some time to pinpoint
where. Both the GFS and NAM MOS indicate sustained winds over 40
knots in Rock Springs with GFS especially impressive...though maybe
a bit overdone at 48 knots. As for precipitation...there will be
good forcing. However...with the strong west to southwest wind there
will also be strong downsloping during the day so shadow areas like
the western Big Horn basin and Wind River basin may be mainly dry so
we kept probability of precipitation to slight. The best chance during the day would be
across Big Horn range. There could even be a few
thunderstorms...especially if temperatures can warm significantly
ahead of the approaching front.
The wind should decrease somewhat Monday night as we lose daytime
heating and the core of the low level winds shifts east. The threat
then shifts to the threat of snow. At this time...it looks like a
similar setup to the previous system. The downsloping flow and fast
movement of the system should kick most of the moisture east of the
area. However...once again there is a second piece of energy that
will rotate down from Montana into eastern portions of the County
Warning Area. This should be Post frontal so much of the
precipitation should fall as snow. As for amounts...with the fast
movement we kept amounts below advisory level but a couple of inches
are still possible. Advisories may be needed with blowing snow and
possible freezing roads with the rapid drop in temperatures but will
hold off with the wind threat looking more important at this time.
Tuesday looks like a much cooler day with northwest flow. A few rain
ands now showers may fall...but most areas should be dry most of the
time. Any shower activity should cease after dark as high pressure
shuts off any lift.
Long term...Wednesday through Sunday
A breezy...mild and mainly dry day is expected Wednesday...ahead of
a shortwave trough in the west northwest flow expected to impact the
forecast area Wednesday night and Thursday. The associated Pacific
cold front is expected to push east across the area late Wednesday
night into Thursday morning...with the bulk of the precipitation
across the northwest and northern portions of the area. 700mb
temperatures suggest much of the precipitation would be snow even in
the lower elevations in the Big Horn Basin. A weaker system in the
west northwest flow could impact the area Friday with an emphasis
for precipitation...mainly snow across the north. Global models
continue to show more of the same next weekend with typical timing
and location issues this far out. Thus have broad brushed slight
probability of precipitation over the mountains and kept mainly dry conditions in the lower
elevations for next weekend.
Temperatures in the extended are expected to be seasonal to below
average at times. High temperatures Thursday and Friday will probably be 10
to 15 degrees below average...especially over the north.
West of The Divide...kjac/kpna/kbpi/krks routes
VFR conditions with mainly scattered-broken cs will prevail through 12z
Monday. Mountain top winds will increase Sunday evening with areas
of low level wind shear developing along with increasing SW winds at the surface.
East of The Divide...kcpr/kcod/klnd/kriw/kwrl routes
VFR conditions will prevail through 12z Monday with mainly scattered-broken
cs. A Lee side surface trough will intensify Sunday and Sunday
night with winds increasing across the wind corridor vicinity krks-kcpr
and along the eastern foothills through the day Sunday. Mountain
top winds will rapidly increase Sunday evening with areas of low level wind shear
increasing. Vicinity kcod will be especially prone to strong erratic
wind gusts Sunday night.
Expect warm and dry conditions today with breezy conditions east of
the absarokas and from the Red Desert through Casper. Wind will
increase tonight and especially tomorrow ahead of an approaching
system from the west. Monday looks to be a windy day for many areas.
Snow will return to the west during Monday morning and spread east
of The Divide late Monday into Monday. A few thunderstorms are even
possible Monday afternoon.
high wind watch from late tonight through Monday evening
High wind watch from this afternoon through Monday morning