Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Riverton Wyoming
406 am MDT Tuesday Jul 29 2014

Short through Thursday night
today is likely going to turn out to be a cool wet day...not because
of cool air advection...but from an abundance of
cloudiness...rainfall and evaporative cooling. High temperatures today will
be 20 degrees cooler than they were on Monday in many areas. A deep
layer of monsoon moisture with multiple cloud layers will prevent
solar insulation for strong convection but will supply widespread
rainfall. Since convection will be relatively weak...decided against
a Flash Flood Watch for any location in the County Warning Area but we opted to
mention possible locally heavy rainfall through an Special Weather Statement. The most
abundant rainfall will be in the southwest half of the County Warning Area with much
drier air looming to the north over Montana. A shortwave riding up
and over the ridge over The Rockies will spin off an 500 mb closed low
over Utah/Idaho with moisture encased within this feature. An asct
700 mb low will become established over southwest Wyoming which will help
draw in cool moist Gulf air from the east undercutting the middle and
upper level monsoon moisture. So with cool air in place and
resultant weak not think widespread heavy rainfall
will occur. The most dramatic shortwave as seen on the WV loop is
way down in southern Arizona. Since that shortwave would not arrive
here today or tonight based on its speed...will not bother trying to
time that feature for now.

On Wednesday...shower activity will retreat to the south over
southern Wyoming as the 700 mb low drifts to the Wyoming/Colorado border. Fresh
convection is then expected on Wednesday afternoon mainly over far
western Wyoming as weak impulses ride up and over the stationary ridge.
Temperatures will warm on Wednesday about 5 to 10 degrees.

Then on Thursday the next prominent shortwave riding up and over the
ridge will spin off a closed low over Nevada and will track to
Idaho. This feature will likely produce a good chance of
thunderstorms in western Wyoming and the Big Horn Mountains temperatures will warm
another 5 degrees or so Friday.

Long term...Friday through Tuesday

The extended period looks unsettled with weather systems rotating
around the upper high which stays over the Arizona and New Mexico
area per the GFS model. On the European model (ecmwf) model the upper high is
forecast to move east toward Texas/eastern New Mexico next Monday
and Tuesday. Thus the GFS and European model (ecmwf) models have different timing of
these systems. This makes forecasting the days of a higher chance of
showers and storms more difficult. At this point Friday and next
Monday and Tuesday look more active than Saturday and Sunday...which
may see activity more isolated. Have adjusted the forecast in this
direction but model timing is likely to change in the coming days
so expect revisions to the weekend and early next week forecast.
High temperatures will be on the warm side but only a few places reaching
90 degrees on certain days. Depending on cloud cover some days may
see highs in the upper 70s to middle 80s in the valleys east of The
Divide. Expect mild overnight lows through the period. Would also
expect higher relative humidity at night and during the afternoon
due to the expected shower and thunderstorm activity. This pattern
will hopefully help some of the areas that have been quite dry
the past month.


Aviation.../12z issuance/
isolated shower activity should be ongoing this morning with an
extensive middle level cloud deck between 080-140 kft above ground level. Deep
monsoonal moisture in place...a weak disturbance and daytime heating
will result in scattered to numerous showers and thunderstorms
developing between middle morning and noon. 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 and could
keep the main precipitation type as rain showers...limiting ts coverage. Thus will
not prevail ts at any terminal...and only have thunderstorms in the vicinity at area
terminals during the afternoon/early evening. Periods of MVFR/IFR
conditions are expected especially central/southern terminals...but
uncertainty and timing preclude prevailing MVFR/IFR at any terminal
at this time. 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. Mountains will be obscured much of the time
through at least early this evening.


Fire weather...
a more significant push of moisture expected for today 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
humidity is expected for today. Wednesday will see a continuation
of shower activity.


Riw watches/warnings/advisories...none.



Short term...lipson
long term...Arkansas
fire weather...lipson

National Weather Service Glossary of Abbreviations