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Area forecast discussion 
National Weather Service Riverton Wyoming
1120 PM MDT Wednesday Jul 30 2014

Short term...tonight through Thursday (issued at 300 PM mdt)

Certainly much quieter today than yesterday was at this time.
Precipitable water values are much lower than yesterday with the
best moisture pushed to the south of the area. However...there is
still enough moisture around and combined with a weak shortwave
moving through for some showers to linger...mainly south of the Wind
River Range and also across the western mountains. And like
yesterday...where most of the moisture is it is still mostly cloudy
so temperatures and instability are relatively limited. As a
result...few thunderstorms are expected in the south. The best
chance for thunderstorms would be across northwestern areas where
more sunshine will bring more instability. However...there is not a
lot of upper level support even to vast majority of storms would be
of the run of the mill variety.

Any shower activity should really wane after the evening hours as
drier air continues press toward the south across the state. With
the rain there could be some fog in the south so we will add some to
those areas that have received rain today.

As for tomorrow...models indicate that there will not be a lot of
moisture to work with. However...with yet another in the string of
never ending shortwaves moving over the top of the ridge we will
likely have a few thunderstorms around Thursday afternoon...mainly
over the mountains with the high elevation heat source. With more
sunshine temperatures will continue the upward trend more sunshine
and increasing thicknesses but remain near to somewhat below normal
for most locations.

Long term...Thursday night through Wednesday

Overall Thursday night through the weaken...no major changes to forecast
as upper level ridge does not vary much in position through Sat...except to
slightly migrate eastward a few miles...removing the forecast area from northwest flow by
Sat....then broadening and flattening sun. At lower levels...heat low
over the desert SW remain and will keep pumping monsoonal moisture
into the intermountain periodically. While it will not be a constant
stream of moisture or keep precipitation across the County Warning Area the entire
period...the western mountains along with the southern most forecast area will be
affected most through the weekend. Additionally...as the ridge wander
westward...heights will recover and temperatures will will begin a slow rise
back to seasonably warm. Convective forcing through the weekend will
best come from the mountains first and minor upper level disturbances
second.

Monday through Wednesday...best chances in the extended for precipitation will occur in
the Monday/Tuesday timeframe...possibly extending into Wednesday of next week.
This will occur for several reasons...including the movement of
strong positive vorticity advection that will generate high over the Sonora desert this
weekend in response to a small disturbance that shows weakly in the
WV imagery over the southern Baja California this afternoon. This will likely result
in increased positive vorticity as it moves over the heat low and under
the upper high...northward movement...and possibly the formation of a weak
upper low by sun. This will then be drawn up into the Great Basin
through sun with the of the easier to forecast upstream trough kicking out of
and ahead of the large Gulf of Alaska low. These conditions will then
begin to affect the County Warning Area by Monday with a large increase in deep
moisture phasing with a little better upper dynamics in addition to
the development of more low level boundaries like a Lee low and
possible middle level frontogenesis. Only significant change to forecast was
to raise low temperatures Monday night and to lower high temperatures for Tuesday with
significant increases in cloudiness affecting both.

&&

Aviation.../06z issuance/

VFR conditions will prevail through Thursday night. Patchy fog
will occur in southwest Wyoming until 15z with local MVFR conditions.
Isolated showers and storms will form over and near the mountains
after 19z and continue through 02z. Isolated showers will linger
until 06z Friday. Most terminal sites will not see storms or showers
today and this evening. Please see individual terminal forecasts for
details.

&&

Fire weather...

Any thunderstorms this evening should end with the loss of daytime
heating. An upper level disturbance moving over the area will bring
isolated to scattered thunderstorms mainly to the western mountains
and adjacent valleys. An upper level disturbance will ride up and
over the ridge of high pressure parked over The Rockies Friday which
will increase the coverage of thunderstorms Friday with the most
numerous shower activity expected over western Wyoming as far east as the
western edges of the central basins. Temperatures will slowly
recover during the remainder of the work week but will remain at or
below normal for high temperatures.

&&

Riw watches/warnings/advisories...none.

&&

$$

Short term...hattings
long term...Braun
aviation...Arkansas
fire weather...hattings

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