998
FXUS65 KRIW 021141
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
541 AM MDT Thu May 2 2024

.KEY MESSAGES...

- Mainly dry today with critical fire weather for Natrona County
  this afternoon.

- A weather system will spread showers across the much of the
  area tonight and tomorrow. Small accumulations of snow are
  possible late tonight and Friday morning, including in the
  lower elevations.

- Unsettled weather returns Sunday night and continues much of
  next week with below normal temperatures, gusty to strong wind
  and rounds of showers. Details of the placement in intensity
  of the rounds of precipitation remains highly uncertain.

&&

.DISCUSSION...
Issued at 338 AM MDT Thu May 2 2024

Lets play a game this morning. Let us see if you can guess the word
that will describe the over the next week or so. It is a nine letter
word. Still don`t know? OK, it starts with a U. Still don`t know? If
means that the weather will be active but some up and downs. If you
guessed unsettled, you are correct. No prizes will be given though.
We are a government agency after all.

Today will be somewhat more settled. Other than a few mountain
showers, most of the day will be dry, with only a 1 in 5 chance of
showers through the daylight hours. The main concern will be fire
weather; ore specifically, in Natrona County. Some areas had Red
Flag Conditions for several hours today. And with a gusty wind
expected to develop and dew points expected to drop into the single
digits, we have issued a Red Flag Warning for this location. In
other zones, fuels are not critical and one that is, Johnson County,
wind will be less and humidity only has a 1 in 5 chance of reaching
criteria.

The first shortwave and cold front will move into the area tonight
and move across through Friday. It could get interesting in a few
locations. Models have come into decent agreement with the main
impacts across the southern two thirds of the state. The system does
not have a ton of moisture to work with though. I do have some
concerns though. There will be some left front quadrant jet energy
for the system to tap into. In addition, temperatures will be cold
enough for snow across most areas, including the lower elevations.
The problem is that, given the dynamic nature of the system, with
snow will be of the showery and banded variety and models all have
different solutions in placement of the bands. Impacts would not be
widespread though. In addition, with the warm ground snow would have
trouble sticking to the roads, especially anything that falls after
around 8 am or so given the high May sun angle. So to sum it up, we
have high confidence that some locations will wake up to a coating
of snow Friday morning (more than 1 in 2). However, pinpointing
locally higher amounts has low confidence (less than 1 in 4). As
for specific amounts, probabilistic guidance gives the western
valleys have less than 2 in 5 chance of an inch or more of snow,
and the chance is less than 1 in 10 in almost all locations
East of the Divide. Friday looks rather chilly as well, with
temperatures averaging 10 to 15 degrees below normal.

If there is some good news, it is that at least part of weekend
looks fairly nice for most locations. This will especially be the
case for Saturday as ridging moves over the area, bring the nicest
day of the period with near to somewhat above temperatures and dry
conditions. This will not last though as the next Pacific cold front
and trough approaches. This will spread snow showers into the west
much of the day. In areas East of the Divide, most areas will be dry
most of the day courtesy of southwest, downsloping flow. This will
bring gusty to strong wind to many areas though. And there are some
50 knot barbs at 700 millibars appearing as well. This brings the
possibility of some high winds into the picture. The chance is less
than 1 in 4 at this point, but we will have to watch it carefully.

Much of next week looks rather unsettled with below normal
temperatures and rounds of precipitation. An upper level low will
move towards Wyoming on Monday and bring an unsettled day with rain
and snow across portions of the area. This first storm looks warmer
for Monday, with 700 millibar temperatures of minus 5 or warmer,
which would keep snow levels about 6000 feet so most populated areas
would have mainly rain, with snow at the higher elevations. With a
tight pressure gradient, strong to high is possible as well.

Uncertainty then increases starting on Tuesday, some models are
showing a blocking ridge developing over the central portions of the
country, which would keep the upper level low and general
troughiness of the area at least through Thursday and possibly into
Friday. With tight pressure gradient remaining, wind will likely
remain strong to high for much of the time as well. This will
especially so in areas favored by west to northwesterly flow, Like
Buffalo, the northern Big Horn Basin and Sweetwater County. However,
slow moving and meandering upper level lows make details of the
forecast like precipitation amounts, timing and intensity very hard
to predict this far out. So, to sum things up starting Monday, we
have fairly high confidence (around a 3 in 4 chance) of a cool,
blustery and unsettled pattern continuing through much of the week.
However, confidence in the details of each day remains very low.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 540 AM MDT Thu May 2 2024

VFR conditions will continue to prevail for most sites through the
period. Westerly and northwesterly winds will increase at most
terminals later this morning into the early part of the afternoon.
Gusts 20 to 30kts will be common at many sites through 00Z-02Z.
Winds then decrease, but a cold front could bring briefly gusty
northerly winds to KCOD, KWRL, KRIW, and KCPR late in the period.

Mostly clear skies exist across the region to start the period, with
only FEW to SCT high clouds streaming across the north and west.
Satellite indicates some scattered low clouds with decks around
FL006 developing across the western WY valleys. There is a 10%
chance that these could briefly make their way into KJAC terminal
through 14Z, but they should quickly scatter out. Due to low
confidence, have left mentions out of the TAF.

The next shortwave will make its way into the region late in the
period. Cigs will decrease from west to east across the region. Cigs
around FL050 to FL070 develop between 18Z and 00Z across west of the
Divide terminals, crossing the Divide between 00Z and 03Z. Snow
showers will also begin to develop and move west to east late in the
period. Greatest confidence in IFR or lower conditions is at KJAC,
but other west of the Divide terminals except KRKS as well as
several east of the Divide terminals, most notably KLND, also could
see Cigs drop to IFR late in the period. There is less confidence in
Vsby decreases to IFR, as this will be dependent on exact locations
of the snow showers.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued at 338 AM MDT Thu May 2 2024

A combination of relative humidity falling toward 10 percent and
wind gusting to 30 to 40 mph will bring critical fire weather to
Natrona County this afternoon. Elsewhere, local elevated fire
weather is possible but wind or humidity is not expected to
reach critical levels. Concerns will ease tomorrow as showers
and higher humidity spreads across the area.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 8 PM MDT this evening for
WYZ280.

&&

$$

DISCUSSION...Hattings
AVIATION...Hensley
FIRE WEATHER...Hattings