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259
FXUS65 KRIW 271950
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
150 PM MDT Tue Jun 27 2017

.SHORT TERM...(This afternoon through Wednesday)
Issued at 150 PM MDT Tue Jun 27 2017

Mid level circulation has moved ne into swrn MT with lead band of
weak convection moving across central WY. Stronger convection
forming on the sern edge of the circulation center and moving into
the far nw attm. That looks to be the active area as it spread east
and northeast over the next several hours. Farther south, it looks
more gusty/strong higher based storms with 50-60 mph wind potential.
Next shortwave for Wednesday arrives later in the day so a better
chance for more of the area to get in on some stronger storms,
mainly north half. Swd moving frontal boundary will likely be a
focus as it drops south during the afternoon and early evening.
Cooler Thursday with less instability but still favorable nw flow
and enough to get some developing over the mtns and then moving se
across some of the downwind areas. Northwest flow continues Friday
with decent potential for storms forming over the nrn and central
mtns and then moving se across the lower elevations. Some upslope e-
se flow could start to develop around a surface high to the north
but models are not showing any real moisture increase so instability
is limited in the models attm. If some low level moisture does get
drawn wwd by Friday afternoon, it would make it much more
interesting east of the divide with good sheer profile. For now,
just indicating scattered showers/storms over the mtns and isold
moving se off the ranges later in the day/evening.

.LONG TERM...(Wednesday night through Monday)
Issued at 150 PM MDT Tue Jun 27 2017

The weekend looks to be characterized by high pressure over the
desert southwest, low pressure over the Northern Plains to Great
Lake area, with Wyoming in between with moderate moisture and weak
instability along and east of the divide.  Friday night into
Saturday morning should see some mountain and maybe foothills
showers across northern WY.  Both the GFS and ECMWF indicate a weak
shortwave trough moving over the area in northwest flow Saturday
afternoon into the evening hours.  This disturbance should increase
convective and shower activity primarily along and east of the
divide and keep temperatures slightly below normal for this time of
the year. The eastern part of the state should see continued
activity on Sunday as weak high pressure builds over the
Intermountain West. Monday will see the high pressure move eastward
over WY, and with 700mb temps climbing to the 15-18C range,
afternoon temperatures should reach the mid 80s and low 90s.
Northern WY should see some showers and isolated thunderstorms
overnight from Monday into Tuesday as a weak disturbance moves
through MT.  Similar conditions are currently expected for Tuesday
as well as the northern stream across MT and southern Canada remains
active and keeps high pressure suppressed to the southern Rockies.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday afternoon)
Issued at 150 PM MDT Tue Jun 27 2017

A low pressure system is currently moving through southern MT and
northern WY this afternoon.  An initial line of weak showers and
isolated thunderstorms with some very gusty W to NW wind, currently
from about KBYG SW to KRKS, is moving eastward through the area.
Stronger thunderstorms have now entered NW WY associated with the
colder core of the system, and they are moving eastward as well.
These storms are producing heavy rain, some small hail, frequent
lightning, and outflow wind over 40 kts.  Expect the higher terrain
to be obscured at times with the lowered ceilings and precipitation.
 As the afternoon continues, the storms are expected to strengthen
across the northern half of the area, with the primary threat being
moderate size hail around 1 inch and wind gusts potentially over 50
kts.  Breezy to windy conditions can be expected this afternoon and
evening, mainly from the west, then switching to the north around
00Z at some locations due to outflow from storms and the progression
of the overall system.  Expect brief MVFR/IFR conditions at many
terminals due to the storminess.  VFR conditions then expected after
03Z except for MVFR with lingering showers.  Another disturbance
will impact the area Wednesday afternoon and evening.

&&

.FIRE WEATHER...
Issued AT 150 PM MDT Tue Jun 27 2017

All fuels are currently in green-up and below critical levels for
all locations. Fire danger remains low across all mountain
areas...but will continue somewhat elevated in the afternoons across
the lower elevations east of the Divide and over portions of
southern WY. These areas with elevated fire concerns will generally
coincide with low afternoon RH values and/or gusty winds...through
Thursday. Winds will become west to northwest 20 to 35 mph through
this evening...west to northwest 15 to 30 on Wednesday...and north
to northwest 5 to 20 on Thursday...all days with higher gusts in the
afternoons and especially near stronger showers/storms...especially
through this evening. Showers and isolated to scattered
thunderstorms will move across the area into this evening with some
remaining overnight. Some storms could produce wind gusts from 45
to 60 mph. Smoke dispersal will generally be very good to
excellent on Wednesday and good across the north Thursday to
excellent in the far south.

&&

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

&&

$$

SHORT TERM...Skrbac
LONG TERM...McDonald
AVIATION...McDonald
FIRE WEATHER...Skrbac