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000
FXUS65 KRIW 221136
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
536 AM MDT Mon Apr 22 2024

.KEY MESSAGES...

- Elevated fire weather today across southern Wyoming.

- Above normal temperatures through the workweek, warmest days being
  Wednesday and Thursday.

- High confidence in a wet pattern Thursday through Sunday.

&&

.DISCUSSION...
Issued at 131 AM MDT Mon Apr 22 2024

An upper-level low in Canada has brought a weak trough/cold front
through the area. The result for today is slightly cooler
temperatures and gusty winds for many. Starting with the
temperatures, highs today dip only a few degrees compared to
yesterday. Most locations peak in the 60s, which is up to 10 degrees
above normal, depending on location.

Wind, and elevated fire weather conditions, is the other aspect to
today. As that upper low moves in the North Dakota area today, the
pressure gradient tightens. This increases winds for most today.
700mb winds are not indicative of high winds, however. The first to
get windy, and where the wind will be strongest, is across the
southern portion of the area, notably Sweetwater County up towards
Muddy Gap, and into the Green River Basin (though somewhat less
there). Gusts in these locations begin to increase shortly after
sunrise, becoming strongest in the afternoon. Gusts 35 to 45 mph are
likely (80%) for the afternoon, with about a 30% chance for stronger
gusts from around Rock Springs towards Casper (Wind Corridor). Winds
decrease after sunset. Elsewhere, winds increase in the afternoon.
Gusts more in the 20 to 30 mph range is likely (80%) for most
locations.

Relative humidities (RH) are also a concern today. Main area of
focus is across southern areas, such as Sweetwater and southern
Sublette Counties, and to a lesser extent eastern Lincoln and a few
spots in Fremont and Natrona Counties. Focusing on Sweetwater and
southern Sublette, minimum RHs between 11% and 20% (80% confidence)
occur this afternoon. There is about a 60% chance for places to get
lower than 15% RH, occurring between 19Z and 01Z. Combined with the
wind gusts, (previous paragraph) elevated fire weather conditions
will be in place over the southern CWA. These conditions are also
isolated for southern portions of Fremont and Natrona Counties.

Precipitation today is very limited. Showers end over the Bighorn
Mountains this morning. Very isolated (30% or less) chances over the
mountains today. Drier air is moving in, with precipitable water
(PWAT) values 25% to 75% of normal.

The pressure gradient weakens for Tuesday, meaning much less wind
across the area. Temperatures are also comparable to today, as a
similar, near zonal, flow remains in place aloft. A combination of a
low west of California and slight ridging over the southern United
States brings some moisture streaming into southwest Wyoming.
Precipitation chances look to begin increasing around noon Tuesday
for Lincoln and Sweetwater Counties. There is a chance (20%) of
thunderstorms with this.

As the low moves eastward and into the continental states, moisture
continues to flow over the area, with shower and thunderstorm
chances Wednesday. At this range, it is difficult to place exactly
where these chances are, given the sensitivity to where moisture is
best and boundaries set up. Thursday/Friday looks to bring the low
into the Utah/Wyoming/Colorado area. This brings more widespread
perception to the area. Currently, temperatures would favor rain for
the lower elevations and snow for the mountains. Being of Pacific
origin, this looks like quite a wet system, bringing in high PWAT
values. Will have to watch trends the next few days to see how this
system evolves. There is still a fair amount of uncertainty, with
cluster analysis showing a variety of wetter and drier solutions.
Confidence is high, however, in a wet pattern Thursday through
Sunday.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 523 AM MDT Mon Apr 22 2024

VFR conditions will continue through the next 24 hours with only
high cirrus continuing through the day. Wind gusts will jump
today, with frequent gusts above 25kts through the day for all
except KJAC, which will be shadowed by nearby mountains. Gusts
at KRKS will jump above 40kts in the afternoon.

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 131 AM MDT Mon Apr 22 2024

Elevated fire weather conditions across southern portions of the
area this afternoon. West winds gusting up to 40 mph, with RHs
dropping as low as 11%. These conditions occur through the
afternoon, with winds decreasing after sunset. See above discussion
for full details.

&&

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

&&

$$

DISCUSSION...Wittmann
AVIATION...Straub
FIRE WEATHER...Wittmann