Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 281725
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1125 AM MDT Sun May 28 2017

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

Imagery shows amplified ridge over the wrn CONUS with an amplified
positively tilted trof stretching from ecntrl Canada through the nrn
High Plains then across the cntrl Rockies. An embedded shortwave is
moving over/through ncntrl MT and headed toward WY now under NW
flow. The SFC has high pressure currently entrenched over WY. A
couple of light showers are over the nrn Bighorn Mountains early
this morning.

For the rest of the Memorial Day Weekend forecast - today through
Tuesday - the FA will remain under NW flow aloft with enough
instability in the afternoons and evenings to get
showers/thunder...with the best day of the three being today as a
small upper level disturbance moves south across the cntrl and
ern FA this afternoon...perhaps inducing weak frontogenesis as
does. CAPE values will range from 400 to 1000 J/kg by mid to late
afternoon with effective shear values from 15 to 20 kts through
mid evening. Shower/storm movement should generally be from the
northwest at 20 to 30 kts. Coverage will be isolated to widely
scattered for the most part...perhaps scattered over some higher
terrain. The main concern from any stronger storms today would be
small hail of less than a half inch and gusty winds to 35 kts.
Showers/thunder will be much more isolated Monday and Tuesday
mainly along and west of the Divide. Otherwise, general conditions
call for seasonal to below seasonal temps and relatively light
winds (outside of a stronger shower or storm).

.LONG TERM...(Wednesday through Sunday)

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

Models show a splitting trough over the West Coast Wednesday with
some energy sliding northeast across the Northern Rockies late
Wednesday night/Thursday while the weaker southern energy pushes
into Southern California/Desert Southwest. Looks like ahead of
this spitting trough on Wednesday, convection should be diurnal
driven, and mainly across the west. As the northern portion of
spitting trough pushes across the area Thursday would expect
isolated to scattered convection with an emphasis across the
northwest and north. Models continue struggle on the amount of
ridging in wake of this splitting trough, and ahead of eastern
Pacific trough progged to push east across Pacific
Northwest/Northern Rockies next weekend. The 00Z ECMWF and GFS
show the Cowboy State being at the base of any trough next
weekend with the ECMWF about a day faster. For now will go with
mainly slight chances over the mountains into some adjacent
foothills.

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 from middle
of next week and beyond.

&&

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

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

VFR conditions will prevail through Monday. Scattered showers and
isolated thunderstorms will occur after 20Z over and along the
mountains until 03Z Monday. Gusty wind to 30 knots and small hail
are likely with some of the storms. Showers will become isolated
by 06Z Monday. Isolated showers and thunderstorms will develop
again on Memorial Day after 20z.

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

VFR conditions will prevail through Monday. Scattered showers and
isolated thunderstorms will occur after 20Z over and along the
mountains until 03Z Monday. Gusty wind to 30 knots and small hail
are likely with some of the storms. Showers will become isolated
by 06Z Monday and end by 09Z Monday. Isolated showers and
thunderstorms will develop over the mountains on Memorial Day
after 20z.

&&

.FIRE WEATHER...

Fire danger low across the forecast area through the holiday weekend
as all fuels are currently in green-up and much of the forecast area
has received some form of precipitation over the last few days.
Isolated to widely scattered showers or storms today most likely to
occur along and east of the Divide...best over the higher terrain.
Small hail and gusty winds possible into the evening. More isolated
chances for precip Monday and Tuesday. Additionally, high
temperatures and minimum RH values will remain at or below seasonal
and above 20 percent respectively through Tuesday. Winds too will
remain relatively light through the period (except for gusty periods
near stronger showers/storms). Smoke dispersion will be good to very
good in the afternoons.

&&

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

&&

$$

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


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