Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Riverton Wyoming
317 am MDT Thursday Jul 30 2015
Short term...today through Saturday night
Hot and dry through the period with no significant precipitation
expected. As the heat and low humidity persist...fire danger will
grow. The good news is that there will not be much wind to speak
of. There is a chance for some gusty wind along the i25 corridor
tomorrow as thunderstorms east of the area collapse but that is a
bit of a reach.
Long term...Sunday through Thursday
The GFS and European model (ecmwf) models differ somewhat in the extended. Those
differences would have a moderate impact on the region come Monday
through Tuesday night and then again next Thursday. The GFS keeps
Sunday very warm to hot with very isolated coverage of storms in
the mountains and extreme SW Sweetwater County where a storm or
two over the Uinta Mountains may drift northeast over that area.
The European model (ecmwf) model is on the same Page as the GFS Sunday. From Monday
through next Thursday the GFS model has a southwest flow over the
region. In this flow...weak weather disturbances pass through from
time to time. GFS model does show a gradual increase in middle level
moisture which would lead to more coverage of afternoon and
nighttime showers and storms with each passing day. The European model (ecmwf)
model is still rotating a fairly strong weather system/easterly
wave around the west side of the upper high Monday. This system
impacts much of the area Monday afternoon through Tuesday night.
It would bring more clouds...cooler temperatures and a much better chance
of showers and storms. The Canadian model is not as strong with
this system and splits it as it moves toward Wyoming Monday night into
Tuesday. Certainly it is the time of year to be looking for weather
systems rotating around the predominate upper level high pressure
dome. The European model (ecmwf) model has a chance of showers and storms on Wednesday
and then again next Thursday with another fairly decent weather
system crossing the state. It seems prudent at this time to keep
an eye on this potential weather system in the coming days and
then adjust forecast for higher precipitation chance. This means I will
lean with the GFS model and keep isolated to widely scattered
showers and storms in the forecast Monday through next Thursday. Strong
wind gusts would appear to be the biggest threat from storms.
Locally heavy rain could be a threat next Wednesday and Thursday as the
potential for higher dewpoints loom. As for high temperatures...the GFS
keeps the heat turned up with 80s and 90s Monday through next Thursday.
The European model (ecmwf) has 70s and 80s highs Monday through next Thursday. I have
chosen the warmer side of guidance for now. The final concern for
next week would be the fire threat from lightning strikes in the
lower elevations that have plenty of cured Brown grass to ignite.
VFR conditions are expected through 12z Friday. A few cumulus will be
possible across northern Wyoming terminals after 18z Thursday. Winds
will also remain light and generally variable an under 10 knots
through the period with the exception of areas with normal diurnal
variations like kjac and kbpi.
Building high pressure will continue mainly clear...warming...and
dry conditions through the end of the week. Generally light winds
are expected through the weekend...with only a few light breezes
possible Thursday and Friday afternoon/evening across central
Wyoming. Minimum relative humidity values are expected to remain in the single
digits to low teens through the weekend across the south and
areas east of The Divide...with upper teens to 20s across the
west. Relative humidity will have a hard time recovering
overnight...especially at middle slope where rhs may not rise out of
the middle 20s...especially in the central Wyoming ranges. Dry
conditions are expected through at least Saturday. Isolated
thunderstorm chances will return Sunday into early next
week...mainly across northern and western portions.