Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Riverton Wyoming
328 am MDT sun Apr 19 2015

Short term...Sunday through Tuesday night

We finally have a change in the weather pattern. A cold front and
associated trough as swept across the state and has kicked the
persistent upper level low out of Colorado and into the plains
states like a soccer Ball kicked by David Beckham. There is still a
bit of unstable northwest flow that is bringing some mainly light
precipitation across the central and southern portions of the state.
The echoes appear to be slowly weakening and should be almost gone
by sunrise.

For today...expect a cooler day today with a mixture of clouds and
sunshine. With the unstable northwest flow continuing across
portions of the area along with a weak jet streak and shortwave
providing a bit of additional left and some daytime heating...a few
showers will be found around the area. This time...the best chance
will be across the western portion of the state with some added
orographic enhancement. However...moisture will be lacking so any
amounts should be fairly light. Most of these showers should end by
Monday morning.

Monday looks to be a warmer day across the area. One more weak
shortwave will rotate through the area with another chance of
showers...once again for the western portion of the County Warning
Area. Like the wave on Sunday...there is not a ton of moisture for
the system to work with so most showers should be light. The models
are in fair agreement with the general area...with the best chance
in the southwestern portion of the state. This energy should exit
stage southeast by late Monday night. As for Tuesday...mainly dry
weather will be the rule. Again...there may be just enough
instability for a few showers across the higher elevations of the
west but most areas should stay rain free.

Long term...Wednesday through Sunday

Through the extended...models are in general agreement with a strong
upper low centered over Ontario/Quebec...and eastern Pacific energy
splitting as it moves into the West Coast/rockies area. The strong
and broad upper low over southeast Canada/NE U.S. Is projected to keep a
quasi-stationary frontal boundary across the Front Range. The main
energy from the first splitting system is expected to impact
Southern California/Desert Southwest Thursday...ejecting into the
south Central Plains Friday. This system will probably be followed
by another splitting trough pushing across The Rockies Saturday
night/Sunday time frame.

Despite a mean hemispheric ridge over the forecast area for the
extended...there will be daily chances of convection due to the
combination of weak forcing from splitting troughs moving across the
region...a quasi-stationary boundary east of The Divide into the
High Plains...along with daytime heating and weak instability. There
will undoubtedly be better days for convection...but decided to
broad brush probability of precipitation instead of pinpointing those days this far out with
much uncertainty in the details.

Temperatures in the long term are expected to be seasonal to
slightly above average.


Aviation.../12z issuance/

East of The Divide...kcod/kcpr/klnd/kriw/kwrl routes

Showers to end by 14z. Areas of MVFR conditions due to low clouds
until 17z. Then isolated showers during the afternoon with scattered
showers in the mountains along the Continental Divide...the absaroka
and Wind River mountains. An isolated thunderstorm is possible from
20z until 03z Monday. The showers will decrease by 06z Monday.

West of The Divide...kbpi/kjac/kpna/krks routes

Isolated showers from kpna to krks overnight with local MVFR
conditions...until 14z. Then in the afternoon showers will redevelop
over and near the mountains with an isolated thunderstorm possible
from 20z until 03z Monday. A few showers could pass by the terminal
sites from 21z until 03z. Then showers to dissipate by 06z Monday.

Fire weather...

Expect cooler but somewhat drier weather today as low pressure moves
away. Some showers will be still be possible...especially in the
west but most areas will be dry most of the time. There will be a
chance for showers off and on this week through Tuesday but nothing
widespread. Temperatures will slowly warm and relative humidity drop
through Tuesday. However...winds and humidity should stay below
critical values.

Riw watches/warnings/advisories...


Short term...hattings
long term...wm
fire weather...hattings

National Weather Service Glossary of Abbreviations