Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 221745
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1145 AM MDT Tue May 22 2018

.SHORT TERM...Tuesday through Thursday night
Issued at 200 AM MDT Tue May 22 2018

Things have mainly quieted down overnight across the county
warning area but this is not expected to last long. This looks to
be the most active day of the week as a surge of moisture moves in
from the south in association with a shortwave spinning around an
upper level low in the Great Basin. This means showers and
thunderstorms developing this afternoon and evening, and more than
likely a good coverage of them across much of the area. The next
question is, how strong will they get? At this point, the Storm
Prediction Center has Johnson and Natrona County in a marginal
risk with the rest of the area in a general risk. Looking at
forecast soundings, there is not a ton of CAPE to work with. The
highest values, as expected are across eastern areas where there
will be more sunshine this morning and hence, more instability.
Don`t think there is a big chance of damaging wind gusts given
smaller temperature / dew points spreads, but there could be a wet
microburst. There could be some hail as well, although shear does
not look tremendously strong. As a result, most hail would be of
the small variety although there could be a lot of it. And this
leads to the greatest threat, heavy rain. Precipitable waters
approach and eclipse 1 inch in some places, which is rather high
for this part of the country. As a result, plenty of moisture to
work with. There is still a question of where since the models
still have poor agreement of the heaviest QPF and because this is
convective it is not possible to pinpoint. There could be some
localized flooding, but not enough confidence any kind of a flood
watch though. These thunderstorms could continue into the night as
well although drier air will move in from the south through the
night.

The last two days of the forecast period will decreasing coverage of
storms. By Wednesday, the best chance will be across northern and
western Wyoming with gradually decreasing chances further south and
east. However, everyone will still have a chance of one. Winds may
become gusty as well across the southwestern Wind Corridor with a
tightening pressure gradient. By Thursday, with ridging building
across the state resulting in less moisture and higher heights, only
isolated storms are expected and mainly confined to the western
mountains.

.LONG TERM...Friday through Tuesday
Issued at 200 AM MDT Tue May 22 2018

A warm and dry day on Friday with very isolated showers or storms
over the mountains. High temps in the mid 70s to mid 80s across
the area. It now appears that a weather system will settle over
the Great Basin of Nevada and western Utah Saturday and remains
there Sunday and even Monday (Memorial Day). For Saturday, most of
the area will be dry with some showers and thunderstorms over the
western mountains and valleys in the afternoon and evening.
Another warm day expected with 70s and 80s, a few lower 90s in the
Big Horn basin. The potential for showers and thunderstorms
increases for Sunday and Monday as disturbances rotate from south
to north through our area. Timing these features this far out is
tough and will no doubt change each day. For now, be prepared for
periods of unsettled weather with many dry hours in between on Sunday
and Monday. Sunday high temps will be in the 70s to lower 80s
east of the divide with 60s to lower 70s west of the divide.
Monday looks to cool down with 60s in the west and 70s in the
east. Next Tuesday could be cooler with a chance of showers and
storms as the weather system is forecast to get closer to our area.

&&

.AVIATION...For the 18Z TAFS through 18Z Wednesday
Issued at 1145 AM MDT Tue May 22 2018

West of the Continental Divide...KJAC/KBPI/KPNA/KRKS

VFR conditions to prevail into this afternoon. Scattered SHRA/TSRA
are expected to develop at the TAF sites after 20Z with more
predominant TSRA expected toward 01Z, continuing through around the
06Z-07Z time frame. MVFR ceilings and rain showers are expected
toward the end of the forecast period with thunderstorms expected to
slowly dissipate after 07Z. Mountains will be obscured at times.
Wind gusts to 30 knots and small hail will occur with stronger
storms.

East of the Continental Divide...KCPR/KCOD/KRIW/KLND/KWRL

Expect showers and thunderstorms to be on the increase by this
afternoon with widespread showers and thunderstorms expected tonight.
Some storms will be quite strong to possibly severe, especially in
the eastern zones. MVFR ceilings will be predominant at most
locations after 02Z.

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 200 AM MDT Tue May 22 2018

A surge of moisture lifting northward across Wyoming with bring
clouds and at least scattered showers and thunderstorms for all
areas today, especially in the afternoon and evening. Some heavy
rain is possible with these storms with a good chance of a wetting
rain where storms set up. Winds should remain light to moderate
except in and near any shower or thunderstorm. Relative humidity
will remain above critical levels. Mixing and smoke dispersal will
range from poor in the basins and good in the breezier areas.

&&

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

&&

$$

SHORT TERM...Hattings
LONG TERM...AR
AVIATION...Hulme
FIRE WEATHER...Hattings



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