Area Forecast Discussion
Issued by NWS Riverton, WY

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075
FXUS65 KRIW 300857
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
257 AM MDT MON MAY 30 2016

.SHORT TERM...Today through Wednesday night

Imagery shows SW trof moving into/across wrn/cntrl WY supporting a
few showers and isolated thunderstorms this morning ovr the same
area. SW trof axis is currently cutting down thru cntrl ID with
closed portion of the trof just to the north of ID in swrn Canada.
Sfc has weak low p trof across nrn/ern WY with a developing front
to the northwest of the state.

Today, the upper level trof continues to move across the region,
being reinforced by the much deeper closed portion of the trof
moving into MT. Lee side troffing will deepen across ern WY,
eventually becoming a sfc low p circulation and move into the
cntrl/nrn plains. Frontogenesis will also take place quickly to the
w/nw side of the sfc low. A secondary sfc low will also form ovr
ern/sern CO through the day. Two main areas of convective precip can
then be expected across WY, mainly east of the divide: one, across
southern/southeastern WY in/near/north of the area of maximum
convergence between the two low pressure systems; and two, across
northern/northeastern WY associated with a couple of fronts that
will push through the region beginning by late late morning and
continuing through the evening. This will also be the area that will
the stronger storms of the day with gusty winds and small hail the
main threat. However, there will be a small(er) chance for a few
severe storms between the two fronts in the early/mid afternoon
across mainly Johnson county and points eastward across
northeastern/eastern WY. Deep shear >= 40 kts and CAPE from 500 -
1000 J/Kg may produce isolated rotating storms with large hail and
strong wind the primary threat. However, there will also be a low
chance for a tornado or two early on as LCLs drop quickly behind the
first front and these storms have their best chance at becoming
surface based for a short period...or produce a spin-up on the
outflow gust front.

Tuesday morning through Tuesday night, will be post frontal and cool
with a few lingering showers east of the divide. Then by afternoon,
another front associated with the same moving upper level
trof disturbance will move through the northeastern FA with showers
- both rain and snow - across the Bighorn Mountains, adjacent
foothills, as well as the front as it shears off to the east.
Clearing and cool then relatively cold overnight. Wednesday will be
warmer and drier with little rain chance anywhere except for a
possible stray afternoon shower over the northern mountains.

.LONG TERM...Thursday Through Monday

Models show a weak shortwave pushing east across Montana Thursday into
the northern Plains Thursday night. The associated weak, shallow
cold front is expected to push south, east of the Divide Thursday
night/early Friday morning. At the same time a strong upper ridge
will be across the Great Basin. Moisture will be limited with this
system with isolated convection mainly over the northern
mountains, and adjacent foothills. The strong ridge over the
Great Basin gradually expands and pushes into the Intermountain
West Friday through Sunday. There could be isolated diurnal
convection each of those days...mainly over the mountains...but
overall it will be dry. On Friday the best chance will be over the
north/northeast sections, shifting to the west Sunday. A compact
upper low moving into the Great Basin Monday could give the west a
better shot of isolated to possibly scattered convection.

Temperatures will be 5 to 10 degrees above average through the
period. These warm to very warm temperatures will cause high
elevation snowmelt and associated rises on area creeks and
streams.

&&

.AVIATION.../12Z ISSUANCE/

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

Isolated showers and thunderstorms over the southwest and the
south until 16Z. Wind gusts to 30 knots will be possible
with this activity. Some showers and isolated storms will develop
over northwest WY by 18Z and continue until 00Z. Local
MVFR cigs may occur in NW WY during that time with partial
mountain obscuration. Terminal forecasts will have VFR conditions
prevailing today and tonight with gusty wind from late morning
through early evening.

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

A cold front will push into northern WY this morning and move south
during the rest of the day. Scattered showers and thunderstorms will
occur along and ahead of the front with lingering showers behind the
front. Local MVFR conditions may occur with this activity along with
partial mountain obscuration. A gusty wind will also occur over many
places today. Showers will be ending by 03Z. VFR conditions will
prevail at the terminal sites through the period with a gusty wind
decreasing by 02Z.

&&

.FIRE WEATHER...

Fire danger low as green-up and seasonally cool temperatures with
elevated humidity levels continue across most of Wyoming today. It
will be a little cooler across the forecast area today ...especially
across northern Wyoming. Chances for showers and thunderstorms will
increase mainly east of the divide as an upper level disturbance and
a couple of cold fronts move across the region. Better chances for
measurable rain will occur across northern Wyoming. A few storms may
become strong to severe over Johnson county this afternoon.
Wednesday through Friday will herald in the beginning of a
warming/drying trend with high temperatures reaching into the mid to
upper 80s by the end of the week. Winds through the end of the week
will largely remain at or below 15 mph for all locations.

&&

.RIW Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...Braun
LONG TERM...WM
AVIATION...AR
FIRE WEATHER...Braun



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