286
FXUS65 KRIW 170859
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
259 AM MDT Thu Jul 17 2025

.KEY MESSAGES...

- Hot, dry, and windy weather will create elevated to critical
  fire weather conditions across much of the area today. A Red
  Flag Warning is in effect from Noon to 8PM today across much
  of southern and central Wyoming.

- Isolated to scattered virga shower and dry thunderstorm
  chances (up to 40%) exist across southern Wyoming this
  afternoon and will be capable of 40 to 50 mph gusty outflows.

- Afternoon and evening shower and thunderstorm potential Friday
  and Saturday. Hot, with limited shower and thunderstorm
  chances Sunday into early next week.

&&

.DISCUSSION...
Issued at 258 AM MDT Thu Jul 17 2025

A weak surface boundary extending roughly in a line from the Teton
Mountains to Rock Springs is evident on 08Z surface observations.
Dewpoints west of the boundary are in the low 30s whereas east of
the boundary, dewpoints in the 50s are common. This boundary is
forecast to wash out by mid-morning as the daytime heating
begins and abundant dry air filters in from the west and
encompassing the entire forecast area by midday today. This dry
air, mostly sunny skies, and deep mixing will allow a return of
seasonal to slightly above normal high temperatures today.

A somewhat tight pressure gradient and deep mixing allowing 20-25kt
700mb winds to mix to the surface will create breezy conditions (25-
30 mph gusts) across much of southern and central Wyoming today.
These conditions, combined with relative humidity values
dropping below 15%, will create critical fire weather conditions
across much of the aforementioned locations this afternoon and early
evening. Thus, a Red Flag Warning has been issued for fire zones
across Natrona, Fremont, Sweetwater, Sublette, and portions of
Lincoln Counties today from Noon to 8PM.

There is also mostly virga shower and dry thunderstorm potential (up
to 40% chance) across far southern Wyoming this afternoon. A weak
disturbance embedded within zonal flow aloft will trek across
southern Wyoming and provide support aloft for convection to fire
off the Unita Mountains and trek east-notheast. Given dewpoint
depressions of 40-50 degrees, any convection will largely be in the
form of virga or dry thunderstorms that will be capable of 40-50 mph
gusty outflows.

By Friday, there is consensus among model guidance in west-southwest
flow aloft as an upper-level trough begins to develop over the
Pacific Northwest and an upper low circulates over southern
California. Increased moisture aloft, thanks to the southern
California low, along with an embedded shortwave across Wyoming will
provide support for shower and thunderstorms along a weak front
Friday afternoon and evening. Convection at this time looks to
initiate off higher elevations of western Wyoming and push east and
becoming more isolated with the low-levels remaining relatively dry.
A similar set up is forecast Saturday afternoon with convection
initiating off higher elevations and trekking east with a weak front.

There is consensus that the Pacific Northwest trough remains and
leaves the Intermountain West in dry west-southwestly flow Sunday
through the first half of next week. Dry and hot weather looks
favorable during this timeframe. Although weak disturbances aloft
pass across the region each afternoon, low shower and thunderstorm
chances remain confined to higher elevations of northern
Wyoming.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 916 PM MDT Wed Jul 16 2025

VFR conditions will persist through the TAF period. The only
site that may have conditions drop below VFR is KCPR where fog
may develop early Thursday morning. For now confidence remains
too low for anything more than VCFG and FEW002. Scattered rain
showers and thunderstorms will develop in the same general area
Thursday afternoon, with possible (30%) impacts at KRKS from
20-01Z.

Wind will become or remain light through Thursday morning, with
increases in wind Thursday afternoon. Most terminals will have wind
of 10-15 knots, with gusts of 20-25 knots Thursday afternoon. Wind
will subside around 02Z Friday.

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...
Red Flag Warning from noon today to 8 PM MDT this evening for
WYZ277>280-283-288-289.

&&

$$

DISCUSSION...Gerhardt
AVIATION...LaVoie/Rowe