451
FXUS65 KRIW 210334
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
934 PM MDT Thu Jun 20 2024

.KEY MESSAGES...

- Scattered rain showers and a couple isolated thunderstorms
  this evening along and east of the I-25 corridor.

- More numerous in coverage Friday mid afternoon through the
  evening east of the Divide.

- Warming trend and mainly dry conditions this weekend and into
  next week.

&&

.DISCUSSION...
Issued at 1106 AM MDT Thu Jun 20 2024

Current IR depicts southwest flow across the CWA from the base
of a L/W trough along the west coast. Visible satellite shows
low stratus across the I-25 corridor from Kaycee to Casper but
slowly starting to burn off with daytime heating as of late this
morning. This should erode by mid afternoon allowing for the
atmosphere to reinvigorate itself for some development this
evening and into the overnight hours.

By 23-00Z this evening, expect some storm development across the
southeast half of Natrona County and pushing east by sunset
around 02-03Z. Much of the instability and more ample low level
moisture will be pushed further east in the state and into the
high plains, so, even with marginal severe clipping the county,
these should just be general to weak storms and short lived.
Otherwise, warmer temperatures and relatively light winds with
some breezes for the I-25 corridor. Some redeveloping storm to
general rain shower activity expected with more confidence
towards midnight with a subtle mid level wave over a more
moist lower atmosphere as a better situated advection push from
the southeast. This should occur near the Wind River Basin
towards Natrona and push northeastward through sunrise Friday
morning. Not enough instability to substantiate to anything
during nighttime cooling with lingering low level stratus
lingering in the same areas through much of Friday morning
before burning off with heating once again.

Friday will see a redevelopment of more scattered thunderstorms
and numerous rain showers with a stronger PVA signature
supporting a shortwave up the L/W pattern to a ridge well
eastward. Initiation will all be dependent on the aforementioned
burning off of the lower clouds but ample low level moisture
will be more prevalent into the mid to late afternoon for points
east of the Divide. The main concerns will be gusty outflows
with marginal severe weather possible during this time frame.
DCAPE values over 500J/kg and steeper lapse rates further east
one goes across the CWA will help support this. Any widespread
severe weather, however, is not expected again with the much
better ingredient to the east and northeast in the state and
into the upper Great Plains. The better concern for the CWA will
be for areas across Natrona and Johnson Counties for flooding
concerns. PWAT values are expected to be over 3/4 of an inch up
to and possibly over an inch further north and northeast,
Buffalo included. This overall system is not overly progressive,
and thus, allowing for some slower movement further north and
northeast in the CWA. Early indications with a multitude of
models in agreement on this taking place, boosting confidence in
the process. Storms will drastically weaken towards sunset with
radiational cooling and push east of the CWA before midnight.

The weekend will see a warming trend continue with mainly dry
conditions going forward in the long term forecast. The
subtropical high near west Texas will continue to build with
increasing convergence aloft with ridging extending through the
upper Rockies as well. Temperatures east of the Divide should
soar into the mid 90s for some with upper 90s to near 100
degrees not out of the question for the Bighorn Basin. This will
allow for a blocking pattern that will keep a deep upper level
low out of the Gulf of Alaska to skirt to the north. Even
missing to the north, slightly cooler or not as hot temperatures
expected by next week`s end but will minimal precipitation
chances that look to be mainly for northern parts of the CWA and
for the higher terrain.

All in all, today and especially Friday look to be the best
chances for any widespread accumulation going forward with
drought and fire weather conditions expected to worsen in the
coming weeks.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 933 PM MDT Thu Jun 20 2024

Scattered rain showers and thunderstorms have developed in central
Wyoming this evening. These rain showers and thunderstorms will
impact KCPR/KRIW/KLND for a few hours overnight before shifting
north toward KWRL later tonight into Friday morning. Have prevailing
-SHRA and VCTS at KCPR through 07Z/Fri and TEMPO groups with -SHRA
at these other terminals where convection will be more isolated
tonight. Wind direction varies greatly across the area and this will
continue through Friday afternoon.

The main weather system will push through Friday afternoon, which
will lead to widespread convection. Current thinking is convection
will begin developing around 18Z/Fri and travel east, exiting the
area by 02Z/Sat. Thunderstorms will be strong Friday afternoon, with
strong outflow/downdrafts likely (80%) and isolated severe wind
gusts/large hail possible (10-20%), especially near KCPR. Very
little convective activity is expected near KJAC, so only have a
period of VCSH Friday afternoon. At all other terminals there
is a PROB30 group with -TSRA and variable gusty wind. Conditions
will be mostly VFR, but MVFR conditions appear likely (70%) at
times Friday afternoon as showers and storms move through the
area. The strongest storms will be able to drop VIS down to IFR,
especially if they produce hail.

Please see the Aviation Weather Center and/or CWSU
ZDV and ZLC for the latest information on icing and turbulence
forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Lowe
AVIATION...Rowe