965
FXUS65 KRIW 180712
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
112 AM MDT Tue Jun 18 2024

.KEY MESSAGES...

- Much cooler today, with highs in the upper 50s to middle 60s.

- Light snow chances continue for the northwest mountains and
  the northern Bighorn Mountains. Afternoon showers and
  thunderstorms develop for the northern half of the area.

- Warming trend through the rest of the week. Hot temperatures return
  to end the weekend and start next week.

- Gulf moisture brings widespread rain chances Friday.

&&

.DISCUSSION...
Issued at 111 AM MDT Tue Jun 18 2024

Notably cooler air has made its way into the state from a cold front
yesterday and last night. Lows this morning are generally in the low
40s east of the Continental Divide. West of the Divide, temperatures
in the upper 20s are common. Would not be surprised if some of the
more cold prone locations see lower 20s. Clearing clouds have
allowed for the best cooling over the Green River Basin and southern
Lincoln County. A similar story occurs for high temperatures today.
Most locations peak in the upper 50s to middle 60s, which are 10 to
20 degrees below average, depending on location.

As the upper low moves northeast out of Montana, some wrap around
moisture keeps precipitation chances across the northern portion of
the state today. This means continued snow for the northern
mountains, including Yellowstone. Additional accumulations are
largely less than an inch, though a few inches are possible in the
Absarokas and northern high elevations of the Bighorns. Overall,
little to no impacts are expected with this additional snowfall.

For liquid (rain) precipitation, chances (20% to 60%) generally
remain over far northern Wyoming, including the Bighorn Basin and
Johnson County. More isolated chances (20% or less) occur for
central areas, including Fremont and Natorna Counties. These chances
peak during the afternoon as daily heating is maximized. Conditions
are not favorable for anything strong, with CAPE less than 100 J/kg.
Some thunder does look to occur though with the stronger showers, so
the occasional outflow gust of 30 to 40 mph is possible.

Gusty winds remain today for the Wind Corridor and some central
locations. Gusts will largely be 20 to 30 mph. As mentioned above,
some stronger gusts are possible with convection. These winds
decrease Tuesday night.

The synoptic pattern Wednesday is a dry, slightly southwest flow.
This keeps precipitation chances to near zero. Temperatures also
rebound to the uppers 60s to middle 70s, only slightly below
average. Thursday starts very similar. A trough approaching from the
west increases moisture across the region, so some afternoon and
evening convection is possible, mainly along and east of the Divide.
Highs Thursday reach near, to a bit above, average.

The pattern becomes more interesting by Friday. A high over the
eastern U.S., combined with the inbound trough, allows some Gulf
moisture to makes its way into the area. How far north the best
moisture occurs is still uncertain, with models currently keep the
best moisture to our south, in Colorado. However, precipitable water
(PWAT) values approaching 200% of normal are possible Friday. As a
result, widespread rain chances remain in the forecast for Friday.
This pattern looks short-lived, though, with that aforementioned
trough moving eastward and cutting off the moisture supply through
Saturday. Ridging looks to build in for Sunday, with hot
temperatures to end the weekend and start next week. Though still
too far out for a very accurate temperature forecast, there are
indications for low to middle 90s.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1004 PM MDT Mon Jun 17 2024

Rain and even some snow showers are ongoing across much of the area
late this evening behind a cold front that has pushed east. This
activity will decrease over the next few hours, leaving VFR
conditions prevailing through most of Tuesday morning. This has also
brought gusty winds, which will linger at KCPR and KRKS all night.
By Tuesday afternoon showers will return to the northern half of the
area as moisture wraps back in to Wyoming. The best chance for
terminal impacts will be at KCOD, but certainly can`t rule out brief
impacts at KJAC and KWRL. This activity will end around sunset
Tuesday.

&&

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

&&

$$

DISCUSSION...Wittmann
AVIATION...Myers