Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 202056

Area Forecast Discussion
National Weather Service Riverton WY
256 PM MDT Thu Jul 20 2017

.SHORT TERM...(This evening through Friday)
Issued at 234 PM MDT Thu Jul 20 2017

This evening is shaping up to be one of the more active windows
of opportunity for active weather this week. A well defined
shortwave will be making landfall onto the Pacific Coast today
along with a lead vorticity lobe tracking east across the area.
With PBS of around n inch stream in from the southwest with the
monsoon moisture and instability in place, it appears we have a
good shot of thunderstorm activity during the next 24 hours. the
timing of this feature will result in the majority of this
activity to fire up after 00z this evening. However, there is
already convective activity with sold lightning just to the west
close to the Idaho/Montana border. This activity will move east
and become rejuvenated from afternoon heating resulting in a
fairly active period for the remainder of this afternoon in our
western zones. then this convection will spread to areas east of
the divide after 00z this evening. As it does, this band of
convection will encounter increasing speed and directional shear
as the storm cells approach Natrona and Johnson Counties where we
have a slight risk of severe for strong winds and large hail. it
appears that johnson county stands the best chance of any severe
activity this evening along with a Urn shear factor of 93 by 03Z
this evening.

Then as high pressure builds in from the west, we can look forward
to a dry weekend, Temperatures will start out relatively cooler,
with the biggest cool down expected in Johnson county Friday. There
should be some lingering shower activity in the Casper area Friday
morning and dissipating just after 12z. Otherwise, the only other
activity expected Friday will be some lingering monsoon moisture and
instability for the southern tier zones to experience some sold
to widely sct convective activity Friday afternoon.

Saturday and Sunday will be dry with a warming trend with highs back
up in the low to mid 90s in the central basins and 80s in the
western valleys.

.LONG TERM...(Friday night through Thursday)
Issued at 234 PM MDT Thu Jul 20 2017

Monday will be the hottest day of the week with high temperatures
flirting with the century mark in the Big Horn basin. Then the
temperatures will slowly cool off during the rest of the week
through Thursday as the "ring of fire" consisting of monsoon
moisture laden wet thunderstorms rides up and over the large
bubble of high pressure over the Western United States Tuesday and
Wednesday, along with increasing clouds and wet thunderstorm
activity, thus cooling the daytime high temps. The models are in
better agreement with the overall trend then they were yesterday
keeping the high over us with weak disturbances rounding the


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 234 PM MDT Thu Jul 20 2017

Expect mainly VFR conditions to continue through the forecast
period. Kept in the mention of VCTS/SHRA for most locations
through the majority of the forecast period until close to 06Z
Friday. KCPR and KBYG stand the best chance of lowered vsbys and
cigs as well as any small hail from thunderstorms this afternoon.
Another round of isolated to widely scattered thunderstorms is
expected across southern Sweetwater County Friday afternoon. KRKS
may get grazed by these storms.


Issued AT 234 PM MDT Thu Jul 20 2017

Monsoonal moisture and a passing cold front will move through the
area and bring an increased chance of showers and thunderstorms.
These storms have a better chance of bring wet with a chance of
hail and erratic winds as well. Relative humidity should remain
somewhat higher than recent days as well. For the most part, wind
should remain light to moderate outside of any shower or
thunderstorm. Mixing and smoke dispersal will generally range from
good to very good but fair in some of the Basins. Another round of
isolated to widely scattered thunderstorms is expected across
southern Sweetwater County Friday afternoon. KRKS may get grazed
by these storms.




LONG TERM...Lipson
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