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Area forecast discussion 
National Weather Service Riverton Wyoming
234 am MDT Friday Aug 1 2014

Short through Sunday night

High pressure remains over the forecast area today...though the axis
of the ridge is not clearly defined in the current pattern. A surge
of moisture returns to the forecast area during the afternoon hours.
Expect showers to generally impact western and northern
Wyoming...though a few areas of southern Wyoming may also see some
activity during the late afternoon and early evening periods.
Storms may contain periods of heavy rainfall... with some
potential existing for flooding. Even with the anticipated storm
coverage...expect temperatures to be warmer today across much of
the forecast area.

Similar conditions expected over the next few days...especially
concerning afternoon surges of moisture. Afternoon showers and
thunderstorms will be present through the majority of the short term
forecast period. The ridge of high pressure will work to become more
organized as it moves eastward. The axis of the ridge is generally
expected to move over western Wyoming by Saturday afternoon.

With the continued influence of the ridge of high pressure...expect
temperatures to generally warm through the period.
Additionally...wind is expected to remain light.

Long term...Monday through Friday

Models struggling with the potential significant shortwave that is
expected to rotate around the bottom of the monsoonal high and then
lift northward over or near US early next week. The GFS has been most
consistent with the brunt of the upper low/trough lifting northward into
the northern Great Basin Monday and then moving east across our area
Tuesday. The Gem is similar just slower in its evolution. The European model (ecmwf)
tonight is lifting the shortwave all the way into Montana before
moving it east and then southeastward back over US on Wednesday. Last night the
European model (ecmwf) kept the brunt of the energy over Colorado. A few GFS
ensembles do this also. The 12z European model (ecmwf) ensembles were generally
further south over Wyoming. Generally siding with the more
consistent op GFS track tonight. Even though the shortwave energy
tracks are all over the place...they all are showing a significant
low and middle level moisture surge with surface dew points climbing
well into the 50s Monday into Monday night. Will go with increasing
probability of precipitation in the SW half to start the period...gradually shifting eastward by
Monday evening. Monday night and Tuesday should see many areas with
a good chance of rain/showers and only a few thunderstorms. Airmass
is more tropical in nature with warmer temperatures above 500 mb leading
to limited instability and thus more showery like our last event.
Heavy rain is definitely possible again with this pattern. Northwest flow
develops behind this disturbance with scattered mountain storms still expected
Wednesday and isolated lower elevation showers...especially downwind
of the mountain ranges. Thursday will see a few showers and
thunderstorms but mainly over the high country. On Friday...a new
upper level low which is expected to move in from off the California coast
may get caught in the circulation around the monsoonal high. The
approach of this system Friday will likely result in another shot of
increasing showers and thunderstorms. This system looks to have
colder air aloft and more instability for thunderstorms. So decent
potential for a wet start and end to the medium range period.
Turning cooler to start the period with a middle week warm up and then
cooler in the west again on Friday.


Aviation.../12z issuance/

East of the Continental Divide...kcpr/kriw/klnd/kwrl/kcod

VFR conditions will prevail through the period. Showers and storms
will form over and near the mountains after 19z and continue through
02z. A few of the storms and showers will drift southeast across the
lower elevations during the afternoon and early evening hours. Most
terminal sites will not be impacted directly by this activity. See
individual terminal forecasts for more details.

West of the Continental Divide...kjac/kbpi/kpna/krks

VFR conditions will prevail through the period. Showers and storms
will form over and near the mountains after 18z and continue through
03z. A few of the storms and showers will drift east or southeast
across the lower elevations during the afternoon and early evening
hours. Terminal sites may be impacted by this activity...see
individual terminal forecasts for more details.


Fire weather...

High pressure over the forecast area will keep warming temperatures
present for the next couple well as generally light wind.
Embedded moisture will continue the trend of afternoon showers and
thunderstorms. Most activity is expected to impact northern and
western Wyoming...though some shower activity may impact additional
areas east of The Divide during the forecast period.


Riw watches/warnings/advisories...none.



Short term...branham
long term...skrbac
fire weather...branham

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