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000
FXUS65 KRIW 152320
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
520 PM MDT Mon Apr 15 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms will continue through the afternoon,
  most widespread across northern and central Wyoming. Gusty
  wind and brief heavy rain is the main concern.

- Rain showers will increase across Natrona and Johnson counties
  this evening, lingering through early Tuesday morning.

- Strong wind expected in Johnson County late tonight through
  Tuesday morning.

- Cold temperatures and snow returns Tuesday night through
  Wednesday night. The northern mountains will see the most
  snow, with lower elevations seeing light accumulations at
  times.

&&

.DISCUSSION...
Issued at 438 PM MDT Mon Apr 15 2024

Temperatures will peak a little cooler today as a weak cold front
moves east across the area. This is related to a low pressure system
passing directly to our south, currently centered over the
Utah/Colorado border. Showers are ongoing early this afternoon, and
will increase in coverage as instability rises with peak heating. A
few thunderstorms are expected, with the greatest chances across
northern Wyoming where gulf moisture advection will help maximize
instability. Western Wyoming should also see decent convective
coverage, aided in part by Pacific moisture converging with easterly
low level flow over the higher terrain. Given temperature/dewpoint
depressions of 30 to 40 degrees, gusty outflow winds will be the
primary concern through the afternoon. Additionally, storms will not
be moving particularly fast, and brief heavy rain is also a threat.

Lee cyclogenesis will ramp up this evening ahead of the low, further
enhancing gulf moisture advection to eastern Wyoming. Moisture will
converge over Johnson and Natrona counties, leading to a period of
decent rain there this evening through the overnight hours. In
particular, eastern Natrona County is most favored to see rainfall
amounts over half an inch (50-70 percent according to the latest
HREF). The other variable  worth noting is the strong northerly wind
that will ramp up tonight with the building surface pressure
gradient. Johnson County should bear the brunt of this, and we have
issued a High Wind Warning to account for winds gusting to 60 mph.

Precipitation will end Tuesday morning as brief transitory ridging
moves in behind the low. This will lead to a mild and breezy day
ahead of the next system following quickly on its heels. This will
be in the form of a broader Canadian trough that will sweep
southeast across the area beginning Tuesday evening. This will bring
colder temperatures and widespread precipitation through Wednesday
night. Heavy accumulating snow is expected in the mountains -
especially the Bighorns and Absarokas which will see a foot or two.
Lower elevations east of the Divide should see at least a rain/snow
mix during the overnight/morning hours. Minor accumulations are
possible, though any light snow will melt quickly as highs both
Wednesday and Thursday will be in the upper 40s. Two areas that
could see a bit more snowfall will be the Cody Foothills and the
foothills of the Bighorns in western Johnson County. These locations
may end up needing an advisory, as totals over 3 inches are possible
(around a 50 percent chance for now). However, there is still
uncertainty in snow levels and/or moisture (unsurprisingly), so will
hold off on upgrading the watches or adding advisories.

Further ahead, broadly cyclonic flow is favored to remain over the
area into the weekend. This will keep temperatures on the cooler
side, with continued chances for precipitation across the northern
half of the area.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 518 PM MDT Mon Apr 15 2024

Gusty winds, rain and isolated snow showers will continue as the
front moves across the CWA. VFR prevails through the TAF period with
the exception of KJAC which will see MVFR ceilings after 02Z and
KCPR after 07Z. In addition to rain showers, isolated thunderstorms
continue this afternoon for any site, (10%-20% chance) but most
favored near KCPR, KJAC and KBPI.

KCPR has the potential for heavier rain, with MVFR conditions
possible (40%) from 07Z to 15Z. Strong wind gusts around 30kt
and possible 40kt+ will develop through the Bighorn Basin after
02Z and into the Wind River Basin after 04Z. Similar winds will
also occur through Johnson and Natrona counties, as well as
Sublette and Sweetwater counties. Stronger winds will continue
until at least 22Z Tuesday, with shower activity clearing 13Z
to 15Z.

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...
Winter Storm Watch from Tuesday evening through Wednesday
evening for WYZ002-008-009.

High Wind Warning from 3 AM to noon MDT Tuesday for WYZ010-011.

&&

$$

DISCUSSION...Myers
AVIATION...Rowe/Swanson