660
FXUS65 KRIW 011919
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
119 PM MDT Tue Jul 1 2025

.KEY MESSAGES...

- Warm temperatures prevail with isolated to scattered mostly virga
showers and dry thunderstorms through sunset. Gusty 40-60 mph
outflows will be possible.

- Afternoon showers and thunderstorms chances increase beginning
Wednesday and continuing through Friday. More widespread chances
Thursday and Friday.

- Slow moving showers and thunderstorms producing heavy rainfall
  Thursday and Friday could result in localized flash flooding.

&&

.UPDATE...
Issued at 114 PM MDT Tue Jul 1 2025

The forecast remains on track with hot temperatures and mostly
virga/dry thunderstorm potential this afternoon and evening. Mean
peak 700-mb temperatures ranging from 14C-18C will continue to
support widespread highs in the upper 80s and 90s. Locations where
there is more afternoon cloud cover could see high temperatures a
few degrees below what is currently forecast and vise versa. This
cloud cover is originating from mid-level moisture being advected
into the region by the upper-level high over the Central Rockies and
upper-level low off the coast of California, evident on water vapor
imagery. A weak disturbance aloft rounds the high this afternoon and
provides support aloft, combined with sufficient daytime heating,
for isolated to scattered convection through sunset. Convection
initiation is focused across high elevations of western and
central Wyoming. However, given the dry low-levels with dewpoint
depressions 40-60F degrees, most of this convection will likely
be virga showers/dry thunderstorms. Any virga showers/dry
thunderstorms has potential to produce dry downbursts with 40-60
mph outflows. If a thunderstorm gets strong enough, a brief
downpour could occur. Convection remains on track to dissipate
shortly after sunset, however, lingering high based, light rain
showers over higher elevations cannot be ruled out through
midnight.

The forecast remains on track for increasing shower and thunderstorm
potential for the second half of the work week.

&&

.DISCUSSION...
Issued at 242 AM MDT Tue Jul 1 2025

June has concluded and today marks the start of July. The upcoming
weather pattern for the beginning of July is looking warm and
unsettled across much of the Cowboy State. Warm, above normal
temperatures are forecast over the next few days. Daily chances for
showers and thunderstorms are expected through the remainder of the
week. Southwesterly flow will usher in well above normal PWAT values
for Wednesday through Friday. Convection chances will increase
around the same time with daily coverage becoming more widespread
starting Wednesday.

Today, the first day of July, as mentioned earlier will be warm with
above normal temperatures. Highs today will range from the mid to
upper 80s west of the Divide and low to mid 90s east of the Divide.
An upper level low moving into the Western CONUS today will be the
key weather maker through the week. Multiple small disturbances will
move across the area over the week bringing daily chances for
showers and thunderstorms. Tuesday will see fairly limited
convection being mainly isolated to scattered in nature during the
afternoon and evening. One thing to keep in mind is that the
atmosphere will still be rather dry, which will limit storm
development and likely produce mainly virga showers. These showers
and thunderstorms will be capable of producing some strong outflow
winds due to large dewpoint depressions of 40 to 60 degrees in some
locations, especially southern WY. Showers and thunderstorms will
dissipate shortly after sunset.

Wednesday will see much of the same with warm above normal
temperatures and afternoon showers and thunderstorms. The one
difference will be the influx of well above normal moisture. The
aforementioned upper level low over the western CONUS will aid in
funneling moisture into the region. Models show PWAT values of 0.60
to 0.90 inches which would be nearly 100 to 150% above normal. This
moisture will aid in creating more widespread development of showers
and thunderstorms. The strength of any storms that develop will
still be fairly minimal as CAPE values only look to be around 500-
800 J/kg. Other favorable dynamics are not expected to be in place
which should limit any strong storm development.

Thursday will see the warm and unsettled pattern continue. However,
moisture is expected to increase further with PWATs nearing 1 inch
translating to almost 200% above normal values. This will increase
the chances for periods of heavy downpours as showers and
thunderstorms develop and move across the state during the afternoon
and evening. While storm motion is not expected to be stationary
there will still be the potential for some isolated flash flooding
as a result of this increased influx of moisture. The other concern
that develops on Thursday will be increased chances for strong
thunderstorms. These increased chances are due to higher CAPE values
along with more favorable dynamics as a result of a leeside low
developing over the Northern Plains. While still a few days out the
best chances for strong thunderstorms would be across eastern WY
including portions of Natrona and Johnson Counties.

Looking ahead towards the 4th of July, the unsettled weather
persists with widespread chances for showers and thunderstorms.
Temperatures will cool slightly compared to earlier in the week,
returning to near seasonable values. Above normal PWATs linger which
would create another day with chances for heavy downpours and
isolated flash flooding. The best chances are currently looking to
be across central and northern WY. These may create some
difficulties when it comes to Independence Day celebrations. While
the forecast is not set in stone, it is starting to look more likely
that Friday may be quite unsettled for much of the Cowboy State.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1126 AM MDT Tue Jul 1 2025

Widespread convection is expected this afternoon, generally from 20Z
through 01Z. Most of the convection is expected to be weak virga
showers and isolated thunderstorms with little to no precipitation
reaching the ground. Have thus removed mentions of any -RA with the
TS mentions in the PROB30 groups. Gusty outflow winds will be a
concern with the convection through the afternoon, but confidence
regarding outflow winds is low, and thus have just left the VRB
winds with gusts 20 to 35kt in the TAFs with the the PROB30 TS
mentions. BKN high clouds are expected to persist through the
evening, but should scatter overnight, generally before 06Z. Light
winds (less than 8kts) will persist overnight through Wednesday
morning.

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

&&

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

&&

$$

UPDATE...Gerhardt
DISCUSSION...Dziewaltowski
AVIATION...Hensley