Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 081130
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
0530 AM MDT Sat May 8 2021

.SHORT TERM...(Today through Sunday)
Issued at 300 AM MDT Sat May 8 2021

Water vapor imagery shows an upper low across extreme west-
central Montana early this morning. The associated cold front has
pushed across the forecast area. Cold air advection will continue
today as the trough and upper low continues to pull eastward. By
00Z the upper-level low is expected to be across central Montana.
There will be enough forcing for continued chances for showers
mainly over the northwest and north today. Precipitation type
today will be mainly snow over the far west/northwest, and mainly
valley rain/mountain snow east of the Divide. Although cannot rule
out a few lightning strikes, the atmosphere is pretty stable so
will keep the mention of thunder out the forecast. Models are
showing convergence at 700 millibars across Natrona County from
21Z to 03Z which could serve for an enhanced area of rain during
that time frame. Over the south, elevated fire weather conditions
are expected, but relative humidity will be more marginal, and
temperatures will be below average. Thus will not issue a
Rangeland Fire Danger statement.

After 03Z, models are showing a mainly dry night across the entire
area as some subsidence on the south side of the upper low pulls
across the forecast area. This is expected to change during the day
Sunday as the upper low pulls possibly across northeast Wyoming
into the northern High Plains. Some energy rotating across the
area will give portions of the area chances for showers. The best
chance of precipitation will occur in the afternoon, and once
again mainly over the north. Precipitaion type should be mainly
valley rain/mountain snow. Overall amounts of precipitation on
Saturday and Sunday will be light.

Temperatures both days will be below average with highs some 10 to
as much as 20 degrees below average.

.LONG TERM...(Sunday night through Friday)
Issued at 300 AM MDT Sat May 8 2021

A closed low situated over far western Montana has an associated
trough extending southward across Idaho and clipping northwestern
Wyoming. There will be showers across the northern half of the
forecast area with this system. It will be mainly rain, however
there may be some snow mixed in. Monday will see increasing
precipitation move in from the southwest and spreading through
the morning. This will bring widespread rain showers, mountain
snow, and isolated chance of thunderstorms for Monday and again on
Tuesday, though lesser in coverage. Temperatures will also cool
down for the beginning of the work week with this system.

Wednesday and Thursday will see a nice ridge moving into the
forecast area. This will bring dry weather and warmer temperatures
once again. East of the Divide could see some isolated shower
activity on Wednesday as the previous trough continues to exit the
region. There will be some warming again on Thursday and Friday with
the ridge in place. Models are indicating some minor energy sliding
through the flow across northern Wyoming on Friday, bringing showers
to mainly the northwest. Timing, position and strength continue to
be varied across the models, so we will stick with lower PoPs for
now.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday)
Issued at 0530 AM MDT Sat May 8 2021

Scattered shower activity continues to move across the region and
will exit by the afternoon. Conditions will remain VFR across the
board, with VCSH for KCOD, KWRL, KJAC and KCPR. Wind speeds have
decreased at most sites this morning, but will pick again after
around 15Z. Winds will remain gusty for most locations through the
afternoon. Speeds will then show a gradual decrease after 00Z
Sunday.

&&

.FIRE WEATHER...
Issued AT 300 AM MDT Sat May 8 2021

Much colder with higher afternoon humidity across the fire zones
today. However, zones 277, 278 and 279 look to have critical fire
weather winds from the west and northwest, and near critical
humidity this afternoon as well as no chances for precipitation.
Precipitation will generally be confined to the north today but a
wetting precipitation event is not likely. Precipitation type will
be mainly snow over the far west/northwest while areas east of
the Divide will be valley rain and mountain snow.

Due to breezy winds today, smoke dispersal will range from good to
excellent across the entire area.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Murrell
LONG TERM...Swanson
AVIATION...Swanson/Murrell
FIRE WEATHER...Murrell


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