215
FXUS65 KRIW 200749
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
149 AM MDT Thu Jun 20 2024

.KEY MESSAGES...

- Showers and thunderstorms are possible (15% to 40%) this
  afternoon and into the night, mainly east of the Continental
  Divide. More widespread showers and thunderstorms develop
  Friday.

- Hot Sunday and Monday. Hot and dry weather continues through
  next week.

&&

.DISCUSSION...
Issued at 146 AM MDT Thu Jun 20 2024

Temperatures continue to climb today, with highs sitting right
around, to just above, average for mid-June. A high over the eastern
U.S. combines with a trough sitting over the west coast to funnel
some moisture into Wyoming this afternoon. The NAM projects
precipitable water (PWAT) values in the 150% to 175% of normal range
mid-afternoon. The best moisture looks to remain to the east, with
some isolated to scattered (15% to 40%) showers and storms
developing from Sweetwater County into central Wyoming, including
Fremont, Natrona, and Johnson Counties. Some development over the
Absarokas are also possible (20% to 30%). Isolated chances (about
20%) continue overnight for those mentioned locations, and also the
eastern Bighorn Basin, but an overall downward trend in rain
coverage occurs into the night.

Better moisture begins to make its way into the state late Thursday
night into Friday morning. Aided by some shortwave energy entering
from the west, widespread shower and thunderstorm chances occur
across the area Friday. Some showers may still be going on from
overnight, with some more showers developing in the morning. Showers
really ramp up in coverage during peak heating Friday afternoon. The
least likely (15% to 30% chances) places to get any rain will be far
western Wyoming, including northern Lincoln County, north through
Yellowstone. High-resolution models are projecting a fairly large
swath of scattered to numerous (40% to 70% coverage) showers and
thunderstorms moving across the area between 1pm and 7pm, from
western Wyoming to Johnson/Natrona Counties in that timeframe. This
will be the best shot for rain through the day. Rain quickly comes
to an end Friday evening, leaving a dry night.

Saturday starts what will be a mostly dry and hot next week. High
pressure begins to build in over the Four Corners Region. This
leaves the area hot and dry for the weekend. Highs Saturday begin to
climb. By Sunday, highs will be firmly in the middle 90s east of the
Continental Divide, with upper 80s and a few low 90s west. 700mb
temperatures are around 18 to 19 degrees Celsius, which could bring
100 degree temperatures to places in the eastern Bighorn Basin. For
reference, average highs this time of year are in the upper 70s to
middle 80s. Temperatures look just as hot Monday. To say Tuesday
looks cooler is a bit of an overstatement, but highs are looking a
few degrees cooler. High pressure looks to remain through at least
next Thursday, maybe Friday. This will keep these above average
temperatures in place. Shift of Tails is also on board, highlighting
much of the area in at least the 60th percentile for high
temperatures, with some 80th percentiles Sunday and Monday. A few
shortwaves look to move through during next week, though these seem
to have little impact; perhaps a shower or two is possible depending
if they are strong enough, but overall conditions remain dry.

The GFS and ECMWF are showing a trough in the timeframe of next
Friday (6/28). This could be what breaks the hot and dry pattern,
but being so far out, there is low confidence in this model
projection.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 941 PM MDT Wed Jun 19 2024

A weather system will approach the area over the next 24 hours and
ahead of it energetic southwesterly flow will bring mid-level clouds
overhead. Scattered convection is likely (60-70%) in portions of
central and eastern Wyoming Thursday afternoon. Most of this
convection will not impact any terminals, but there is a 20-30%
chance of an isolated thunderstorm at KCPR from 21Z/Thurs to
01Z/Fri, so have included a PROB30 group to account for this threat.
Conditions will remain VFR at all terminals through the TAF period.
Wind will be light for most terminals (10 knots or less) and wind
direction will change several times over the next 24 hours. The
strongest wind will be at KCPR and KRKS Thursday afternoon.
Gusts of 20 to 25 knots will occur at these terminals. Toward
the end of the TAF period (Thursday evening) very isolated
convection is possible (10-20%) in the Wind River Basin and
southern Bighorn Basin.

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...Wittmann
AVIATION...Rowe