204
FXUS65 KRIW 142059
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
259 PM MDT Tue May 14 2024

.KEY MESSAGES...

- Showers and thunderstorms will continue across the region
  through sunset. Gusty winds 45 to 55 mph will be main threat
  from storms, with a SPC Marginal threat for isolated 60 mph
  gusts.

- Isolated showers and thunderstorms return Wednesday
  afternoon.

- Friday will bring widespread breezy west winds ahead of a weak
  cold front. The combination of dry air and breezy winds will
  lead to elevated fire weather concerns.

&&

.DISCUSSION...
Issued at 255 PM MDT Tue May 14 2024

A shortwave trough moving through the region this afternoon is
providing lift for numerous thunderstorms. With CAPE on the
order of 200 to 400 J/kg, and 20 to 30 kt of deep layer shear,
a handful of reports of small pea-sized to half-inch diameter
hail agree well with this analysis, and the stronger storms are
likely to produce brief heavy rain and similar small hail
through sunset this evening. The more widespread threat with
these storms will be gusty winds on the order of 40 to 50 mph. A
few isolated gusts up to 60 mph are possible (20% chance),
especially across southern Wyoming where shear is highest. The
SPC highlights this in their severe convective outlook, with
southern Wyoming being under a Marginal Risk.

Temperatures Wednesday will be a near repeat of today, which is
very close to seasonal averages. Isolated showers and
thunderstorms are likely (60% chance) again, but these will
mainly be confined to the high terrain.

Temperatures warm by about 10 degrees on Thursday with a drying
atmosphere. Upper atmospheric flow becomes more zonal, with a
lack of any forcing mechanism for shower activity. On Friday,
temperatures warm a few more degrees ahead of the next weather
system. A tightening pressure gradient will lead to breezy
winds, and this combined temperatures 10 to 15 degrees above
average will lead to elevated fire weather concerns, mainly in
the 11 AM to sunset timeframe. Moisture will be limited with
this weather system, but currently northern Wyoming looks to
have the best opportunity for rain Friday night due to better
synoptic forcing to the north.

Temperatures remain slightly above average for the weekend,
with isolated, mainly-mountain-based showers remaining in the
forecast. A large and diffuse trough moves over the
Intermountain West early next week, but weather models are not
currently showing any confidence for distinct shortwaves that
would affect Wyoming at this time. Have stuck with consensus
model guidance showing slight chances (15 to 35% chances) for
daily showers.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1028 AM MDT Tue May 14 2024

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals

In and out MVFR ceilings at JAC damming across the valley, but
VFR at all other TAF sites. Gusty northwest to westerly winds up
to 18-25kts to start the period through peak heating. Increasing
storm chances on station between 20-01Z at all sites carrying
tempo during these times with the hit and miss nature of these
isolated thunderstorms. Outflow boundaries exceeding 40kts are
possible at RKS but confidence low dependent on the vicinity of
these aforementioned storms. After 01Z, storms and winds will
diminish into the overnight hours with improving skies by
Wednesday morning.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

VFR conditions expected for all sites with breezy northwesterly
winds up to 15-25kts. Increasing thunderstorm activity after 21Z
as storms west of the Divide push east and expand in coverage.
Tempo groups carried for these times through 00-01Z before
weakening due to nearing sunset and capping of the environment.
Any severe weather activity looks to stay south with only
possible gustier outflow winds over 30kts possible. Otherwise,
quieter conditions after 01Z with diminished winds into the
overnight hours. Lingering light rain at CPR after 06Z with MVFR
ceilings likely IAW some of the LAMP/BUFKIT sounding data
(70-80%). Improving conditions for other locations with CPR to
follow into the next TAF cycle.

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...VandenBoogart
AVIATION...Lowe