000
FXUS65 KRIW 212025
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
225 PM MDT Sun Apr 21 2024

.KEY MESSAGES...

- Temperatures climb to above normal today. A passing weather
  system brings scattered precipitation (20% to 60% chances) for
  northern Wyoming, mainly the mountains, this afternoon and
  evening.

- Elevated fire weather concerns this afternoon for portions of central
  and southern Wyoming. Elevated fire weather returns for
  southern Wyoming Monday.

- A wet weather pattern looks in store starting Thursday into at
  least Saturday, but specific details remain in flux.

&&

.DISCUSSION...
Issued at 216 PM MDT Sun Apr 21 2024

A shortwave ridge will continue to move over the Cowboy State today,
leading to high temperatures to be 10 to 20 degrees warmer than
yesterday. The sfc pressure gradient will tighten this afternoon,
irt a trough that will pass over northern portions of the state this
afternoon and evening, as the ridge transitions over the Plains.
Wind gusts of 25 to 35 mph will be widespread this afternoon, as a
result. Elevated fire weather conditions will also develop today
from the dry, warmer and windier conditions. Relative humidity (RH)
values will range from the upper teens into the lower 20s for most
locations. Any critical RHs will be isolated and are not expected to
be widespread this afternoon. A Rangeland Fire Danger (RFD)
statement will remain in effect Natrona, Johnson and Sweetwater
counties from 12 pm to 7 pm today. There is also a chance (20-30%)
for showers across northern portions and the central mountains later
this afternoon into the evening. Any snow will be confined to the
higher elevations and thus, minimizing any potential impacts. The
associated cold front from the trough will enter northern portions
of the CWA after sunset this evening and push southward through the
night, reaching the Divide by sunrise Monday morning. This will keep
winds the winds gusty behind the front and over the mountains
tonight. Wind gusts up to 30 mph will be possible, with locally
higher gusts up to 40 mph possible for areas prone to northwesterly
winds.

The gradient will remain tight Monday, as the Cowboy State gets
squeezed between the trough over Saskatchewan and a ridge over the
Four Corners region. Wind gusts will be much stronger Monday
afternoon as a result, but will be confined to southern portions of
the forecast area due to the cold front becoming stationary along
the Continental Divide. Thus, west-northwest winds with gusts of 35
to 50 mph will occur Monday afternoon. Gusts up to 25 mph will occur
over areas east of the Divide. This will also lead to elevated to
near-critical fire weather conditions across southern portions,
where critical RH values will occur. A RFD statement will be likely
issued again. Temperatures will be 5 to 10 degrees cooler Monday, as
a result of the cold front but will still be slightly above normal.
Any precipitation chance will be confined to far northern portions.

A flat ridge extending from the Four Corners ridge will develop over
the region Tuesday, as the trough moves over the Great Lakes region.
Winds will be much lighter across the CWA and temperatures slightly
warmer. Pacific moisture will reach the Great Basin and begin to
push along the WY/CO/UT border, leading to chances for showers over
far southern portions. Similar conditions return for Wednesday, as
the ridge intensifies irt to an upper low moving onshore over
southern CA. Highs will be 5 to 15 degrees warmer and well above
normal again, with readings in the 70s east of the Divide and for
much of the south. Showers and possible thunderstorms will remain
possible across the south, as well as across western portions
Wednesday afternoon. This will be due to a trough that will
quickly move over the PACNW, bringing moisture and lift to
western portions by the afternoon into the evening.

These two features will be precursors to a more unsettled weather
pattern to end the week. Precipitation chances will become more
widespread Thursday, as the aforementioned upper low moves over the
Four Corners and exits over the Central Plains Thursday night into
Friday. By this time, a second system over the EPAC will move
onshore over the PACNW. The Cowboy State will be between the
deformation zone of the exiting upper low and the diffluent flow
ahead of the approaching Pacific system. This system will keep
moisture advection and precipitation chances continuing Friday
and Saturday, as it moves over the Intermountain West.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1115 AM MDT Sun Apr 21 2024

VFR conditions expected at all locations. The main concern today is
gusty winds, increasing across the CWA after 19-21Z. Gusts 18 to 25
knots will be pretty standard. Most gusts will decrease after 02Z.
Today there will be an increase in mid and high level clouds during
the afternoon and evening hours with a passing weak shortwave.
There is still a chance that KJAC may see an isolated rain shower,
but confidence remains low. Most activity should stay north or
over the mountains. Clouds will scatter out in the early morning
hours tonight, however wind speeds will increase again in the
late morning. Monday will see gusts again 18 to 25 knots, with
KRKS, KPNA and KBPI seeing higher speeds of 30 to 35 knots late
in the TAF period, or just after.


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 216 PM MDT Sun Apr 21 2024

Elevated fire weather conditions will continue this afternoon,
with RH values in the upper teens to lower 20s. Any critical RH
values will be isolated. Wind gusts of 25 to 35 mph will occur
this afternoon, with the higher gusts occurring over
northwestern portions of the forecast area. A cold front will
progress across areas east of the Divide tonight, leading to
cooler temperatures Monday. Gusty north-northwest winds will
occur behind the front tonight. Elevated to near-critical fire
weather conditions will be widespread across southern portions
Monday afternoon. Critical RH values and west-northwest wind
gusts of 35 to 50 mph will widespread across these areas.

&&

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

&&

$$

DISCUSSION...LaVoie
AVIATION...Swanson
FIRE WEATHER...LaVoie