Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Riverton Wyoming
1100 PM MDT Monday Jul 28 2014
Short term...tonight through Tuesday
After a decent period of dry conditions...expect some changes to
arrive through the forecast period. Radar and satellite indicate the
presence of increasing moisture across western and central
Wyoming...with some shower activity starting over the central and
western mountains. Showers and thunderstorms will be found over the
area today...especially west of The Divide. Shower and thunderstorm
coverage is anticipated to weaken during the overnight hours...with
relatively dry conditions expected east of The Divide.
Activity will increase again on Tuesday...with widely scattered to
scattered shower and thunderstorm activity expected. Temperatures
are anticipated to be significantly cooler as well under the
increased cloud cover and shower activity. Model analysis continues
to indicate increasing precipitable water values...indicating the
potential for heavy rain...especially east of The Divide during the
Long term...Tuesday night through Monday
Precipitation will still be ongoing across the area Tuesday evening
with easterly flow continuing. However...both the NAM and GFS have
trended a bit drier...especially later Tuesday night in showing some
much drier air pressing into the area out of Montana. As a result we
have cut probability of precipitation and quantitative precipitation forecast a bit for late at night...mainly across the
northern half of the County Warning Area. This trend continues on
Wednesday...especially on the GFS with an area of precipitable
waters dropping down to under 0.40 inches across much of the County
Warning Area east of The Divide by Wednesday evening. The NAM is not
as aggressive but also drops much drier air into a similar area.
However...we are not ready to go all the way as a compromise we have
removed the precipitation for around the northeastern half of the
County Warning Area but kept it across western and southern areas.
However...even here we have trimmed probability of precipitation and removed the heavy rain
wording. We also raised temperatures a bit for Wednesday with a bit
more sunshine expected.
Things may become a bit more active again for Thursday as another
shortwave rounds the top of the ridge. Models have been fairly
consistent in bringing more moisture and higher probability of precipitation to western
Wyoming. Continuity showed this fairly well so we made few changes.
Meanwhile...east of The Divide it still looks drier. We allowed for
isolated probability of precipitation in some areas but at this point most areas look to be
precipitation free most of the time.
The remainder of the forecast period is what I call a shampoo bottle
instruction forecast. In other words...wash...rinse...repeat.
Monsoonal moisture will be found over the area into the weekend. At
the same time...shortwaves will be topping the ridge over the area.
This will put the area in...according to johnny Cash or social
distortion depending on your age and musical taste...the ring of
fire. This will result in daily chances of mainly diurnal showers
and thunderstorms...especially in the higher elevations and in
western areas. However...the timing of the individual shortwaves
past day 3 is like tying to herd cats and as a result pinpointing a
more active day is difficult at best. At this point we kept things
generic and toward climatologically favored locations.
Isolated shower activity should continue through the night into
Tuesday morning...with an extensive middle level deck gradually
lowering. Deep monsoonal moisture in place...a weak disturbance and
daytime heating will result in scattered to numerous showers and
thunderstorms developing by midday across the entire area. The most
widespread rain showers/thunderstorms and rain should be over the central and southern areas.
Widespread cloud cover and associated precipitation should limit
instability...keeping the main precipitation type as rain showers perhaps limiting
ts coverage. Having said that will prevail thunderstorms and rain across many of the
terminals over central/southern areas based on what occurred
upstream in Utah on Monday. Periods of MVFR/IFR conditions are
expected in those areas...but uncertainty and timing preclude
prevailing MVFR/IFR at any terminal. Although winds will be variable
due to the convection...prevailing winds will generally be easterly.
Much of the convection is expected to gradually end from the north
to south between 00z and 09z Wednesday. Mountains will be obscured
much of the time through at least early this evening.
Moisture is expected to steadily increase over the next couple days.
Showers and thunderstorms will be present...with a lull anticipated
east of the Continental Divide tonight. Another significant push of
moisture expected for Tuesday with widespread shower and
thunderstorm activity. Showers are anticipated to contain heavy
rain...helping to alleviate some fire weather concerns.
Additionally...cooler temperatures and increased daytime is expected
for Tuesday. Wednesday will see a continuation of widespread shower
activity as a period of wet conditions sets up across the forecast