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000
FXUS65 KRIW 151734
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1134 AM MDT Mon Apr 15 2024

.KEY MESSAGES...

- Unsettled and cooler weather has arrived with an active week
  of weather ahead.

- Scattered showers and thunderstorms are likely this afternoon/evening
  with parts of Natrona and Johnson County having the best
  chance of seeing gusty winds and small hail.

- Winds increase this evening through Tuesday morning, with
  strong gusts of 45+ mph possible in parts of the Bighorn
  Basin. Johnson County likely sees stronger gusts greater than
  55 mph, leading to a High Wind Watch now in effect.

- The chance for accumulating snow and below normal temperatures
  arrive by Wednesday, with Winter Storm Watches for the Bighorn
  and Absaroka Mountains.

&&

.DISCUSSION...
Issued at 401 AM MDT Mon Apr 15 2024

Unsettled and cooler weather makes a return to the Cowboy State
today. Highs will be 10-15 degrees cooler than the past few days,
but still above normal. A few isolated showers are possible over
western WY this morning with the remainder of the state staying
mostly dry until the afternoon. Winds are expected to become breezy
by the afternoon, before further increasing by the evening.

Today is the start of an unsettled weather pattern, with two
disturbances that look to be the key contributors. The first
disturbance is a Pacific low, now over the Great Basin and has led
to the increased clouds over the region this morning. An associated
cold front will move through the state early this morning, making
its way through the state by the evening. The majority of the state
looks to remain dry for the morning, but precipitation begins to
develop by the early afternoon. Showers look to become widespread
through the afternoon and evening, with most of the state having a
(50-80%) chance of seeing at least a brief shower. Thunderstorms are
a possibility this afternoon and evening, with most of the state
having a chance (15-35%) for a few rumbles of thunder. CAPE values
across much of the CWA look to range from 1000 to 1500 J/kg. Shear
although not incredibly strong is present, with EBWD values around
20-30 knots. CAMs are showing swaths of storm relative helicity for
much of the state, which may allow for the development of a
structured storm or two. There does look to be some potential for a
few strong thunderstorms to develop this afternoon/evening. If any
were to develop, the main hazards would likely be strong gusty
outflow winds and small hail.

The late evening Monday into the early morning Tuesday timeframe
will see light to moderate rainfall across eastern parts of Johnson
and Natrona Counties, specifically areas east of the I-25 corridor,
as the low shifts east and 700mb flow becomes more northerly. The
heaviest rainfall looks to occur over this area with QPF amounts of
0.50 to 1.00 inches by late Tuesday morning. Tuesday will see lee
cyclogenesis occur as a potent low develops over the central High
Plains. The pressure gradient will tighten quickly during the very
early morning hours Tuesday, with 700 mb winds nearing 50+ knots in
parts of the eastern CWA. Surface winds will increase during this
time period with parts of the Bighorn Basin and the eastern CWA
having a (30-60%) chance of seeing periodic gusts of 45+ mph.
Johnson County has the best chance (40-70%) of seeing strong wind
gusts greater than 60+ mph. Due to this, a High Wind Watch remains
in effect starting at 3 am Tuesday through noon. Winds decrease and
showers dissipate by the late morning, as the low moves farther east
and the pressure gradient relaxes.

The second disturbance arrives early Wednesday morning across parts
of northern WY. Models have come into a better agreement regarding
the track of this disturbance. The setup is a trough moving south
from Canada and digging across the Northern Rockies. Impacts
currently look to be limited to the higher elevations of northern
WY, where colder temperatures will be present and should support
accumulating snow. 700 mb temperatures range from -10 to -15 Celsius
by Wednesday night, which will create some chilly lows for Thursday
morning. Precipitation looks to be mainly limited to the northern
half of the CWA with the highest QPF currently across the Absarokas
and Bighorns. Due to these high QPF values along with cold enough
temperatures to support snow in these higher elevations, Winter
Storm Watches have been issued for these ranges. Snow in YNP looks
to be enough for advisory criteria, but highlights have not been
issued at this time. Lower elevation basins look to have a chance of
seeing some snowfall, but the question remains to how much will
accumulate. Currently, Johnson County may have the best chance of
seeing snowfall amounts that near-advisory criteria, but there still
is uncertainty regarding this, so no low elevation highlights have
been issued. The main bulk of energy moves out by Thursday morning,
with periodic rain/snow showers lingering through the end of the
week.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1129 AM MDT Mon Apr 15 2024

A cold front will move across the CWA today through late
tonight, accompanied by gusty winds and rain showers. VFR
prevails through the TAF period with the exception of KJAC which
will see MVFR ceilings after 02Z and KCPR after 07Z. Gusty
winds this morning will become more widespread this evening and
overnight. Rain showers will develop this afternoon, with the
best chances occurring over far western portions by 20Z. The
latest model runs continue to show at least a 15% chance at all
sites between 21Z and 01Z. In addition to rain showers,
thunderstorms are possible this afternoon for any site,
(10%-15%) 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 winds 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. Gusts around 30 kt will
be common, with higher gusts of 40+ kt occurring in the Bighorn
Basin and Johnson County.

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 Watch from late tonight through Tuesday morning for
WYZ010-011.

&&

$$

DISCUSSION...Dziewaltowski
AVIATION...Swanson/LaVoie