Area Forecast Discussion
Issued by NWS Riverton, WY

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896
FXUS65 KRIW 291734
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1134 AM MDT Mon May 29 2017

.SHORT TERM...(Today through Wednesday night)

Imagery shows amplified ridge over the wrn CONUS with a broadening
trof stretching from ecntrl Canada through the nrn Plains then
across the midwest as far south as Arkansas. An embedded shortwave
has moved over/through ecntrl MT and ern WY which continues under NW
flow. The SFC has high pressure currently in place over WY with a
weak trof/boundary near the CO/WY border and a cold front draped
across sern MT and nrn SD. A few isolated light showers are over
cntrl and ern WY.

Monday and Tuesday - the FA will remain under NW flow aloft with
just enough instability in the afternoons and evenings to get a few
isolated showers/thunder mainly over the higher terrain, or closely
adjacent areas, of the FA. Relatively high based showers/storms
providing little rain and gusty winds. Otherwise, general conditions
call for seasonal to below seasonal temps and relatively light winds
(outside of a stronger shower or storm).

Wednesday and Wednesday night, the wrn CONUS ridge axis will begin
to move over wrn WY, with plenty of sun and much warmer temperatures
beginning to induce lower SFC pressure. Additionally, a minor ridge
riding wave shows up in mdls that will move through the the upper
lvl flow during the day and perhaps aid in breaking the
cap...especially over the higher terrain of wcntrl/swrn
WY...providing a few chances for some elevated convection...again
with relatively little precip but gusty winds with ML CAPE ranging
from 500 to 1000 J/KG where the cap is weak enough. CAPE values east
of the Divide will be higher overall...but much better capped and
without a strong enough trigger to work with to initiate...so not
expecting much of anything ATTM.

This will also mark the beginning of a prolonged warm(ing) period
where strengthening potential for some flooding will develop along
creeks, streams and rivers due to increasingly rapid mountain
snowmelt.

.LONG TERM...(Thursday through Monday)

Flooding concerns from snowmelt runoff increase into early next
weekend as forecasted consecutive warm to very warm days would
cause rapid mountain snowmelt.

Models show the northern stream of a splitting western
CONUS trough lifting northeast across the Northern Rockies
Thursday/Thursday night and then into the High Plains Friday. The
associated cold front should push across the area Thursday night.
Isolated to locally scattered convection will be possible as this
system pulls across the forecast area with the best chances
looking to be across the west/northwest Thursday
afternoon/evening. Cooler conditions are expected Friday with a
continued chance of convection especially over the north/northeast
sections of the area.

Global models show an upper low/trough pushing into Pacific
Northwest/SW Canada in the Saturday night/Sunday time frame, and
then progressing east across the northern Rockies Monday. Ahead of
this features enough moisture and instability remain for mainly
diurnal convection across the mountains and downstream adjacent
foothills. The trough could be close enough by late Sunday for
their to be more convection Sunday compared to Saturday.

Temperatures are expected to range between 5 and 10 degrees above
average in the extended. These warm temps will cause rapid
mountain snowmelt, and will elevate flooding concerns late this
week into early next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday morning)

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

VFR conditions will prevail through Tuesday. Scattered showers and
isolated thunderstorms will develop after 20Z and continue through
03Z Tue. Gusty wind to 35 knots and small hail are likely with some
of the storms. Showers will become isolated after 03z and end around
06Z Tuesday. Another round of scattered showers and isolated
thunderstorms will develop again Tuesday after 20z.

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

VFR conditions will prevail through Tuesday. Isolated showers and
thunderstorms will develop after 20Z over and near the mountains.
This activity will end by 04Z Tuesday. Gusty outflow wind to 35
knots will occur near the storms. Scattered showers and isolated
thunderstorms will develop again over the continental divide
Tuesday afternoon with a few moving off the mountains near KCOD
and KLND after 21z Tue.

&&

.FIRE WEATHER...

Fire danger low across the forecast area through Tuesday as all
fuels are currently in green-up and high temperatures and minimum RH
values remain at or below seasonal and above 20 percent
respectively. Isolated showers or storms today and Tuesday most
likely to occur over the higher terrain and closely adjacent
foothills. Gusty winds with this activity possible into the
evenings. Wednesday, fire danger will elevate some across southern
WY as RH values drop into the lower to mid teens (percent) and west
winds gust 20 to 25 mph at times. Smoke dispersion will be good to
excellent in the afternoons. Flooding potential will also begin to
go up from Wednesday going forward as warming temperatures
greatly increase snowmelt.

&&

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

&&

$$

SHORT TERM...Braun
LONG TERM...Murrell
AVIATION...Ross/PS
FIRE WEATHER...Braun



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