Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 131732
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1130 AM MDT Thu Jul 13 2017

.SHORT TERM...(Today through Saturday night)
Issued at 128 AM MDT Thu Jul 13 2017

Imagery shows flat trof/ridge/trof across the CONUS with the ridge
axis cutting north to south through cntrl MT/wrn WY. Bermuda high
reaching wwd through the sern CONUS to the srn Rockies. SFC has
widespread low pressure across the wrn CONUS...high pressure over
srn Canada and sern CONUS. The active SFC front is well south of WY
with only a weak stationary front backed up again the Divide in WY.
No precipitation currently falling anywhere in WY (all to the east).

Through the fcst period, the storm track will remain north of the FA
with a moderately dry and very warm atmosphere across the wrn 2/3s
of WY through Friday encompassing most of the CWA. Saturday will see
a shift in the ridge axis position to the east and this will allow
better, but still marginal, continuing monsoonal flow to affect more
of WY along with a slightly better chance for upper level forcing
and an induced SFC front/trof to affect wrn/nwrn portions of the FA.

Today/tonight the upper ridge orients over WY with the ridge axis
cutting from N to S through wcntrl WY. Again, another day of
monsoonal flow will take place over the srn and cntrl Rockies (with
possible flooding conditions once again over CO/NM) with possibly an
isolated shower/storm mainly over portions of scntrl/sern WY this
afternoon/evening. Friday and Friday night, mostly same story
different day with the center of the upper high now over the Desert
SW/srn Great Basin and the ridge axis cutting more through cntrl WY.
SFC high pressure will also set up a bit further south and east of
Thursday`s location...more over the cntrl Central Plains.
Significant monsoonal moisture will remain well south of the FA for
another day, however the (re)orientation of the flow pattern will
allow a little more weak available mid/upper moisture to make it
into the FA around the upper and lower high pressure systems. This
will allow for a few showers/storms to form mainly over/near the
cntrl/nrn mountains and perhaps some low/mid lvl convergence
boundary/weak front (perhaps the stationary front getting pushed off
the Divide for instance) that could help beat the cap and provide
focus for shower/storm initiation. Any convective precip that does
form will find it hard to move off and away from (too far) the
initiation point under a very weak flow and forcing pattern.
Saturday and Saturday night, the upper ridge axis leans over even
further to the east...oriented from nern WY to swrn WY with the SFC
high just slightly further south over the Central Plains. Very
similar situation to that on Friday with perhaps a little better
chance for a shower/storm over the far nw corner of WY (Yellowstone).
Otherwise, it will be very warm to hot with relatively light wind
except for gusty conditions near any showers/storms.

.LONG TERM...(Sunday through Thursday)
Issued at 128 AM MDT Thu Jul 13 2017

Strong upper ridge of high pressure across the Rockies will begin
to flatten out Sunday and Monday as an Upper low/trough push east
across the Canadian Prairie Provinces. The associated cold front
with this system look to push south across the area Sunday
night/Monday. Models are then showing a Pacific shortwave trough
pushing into northern California/Oregon Monday, and then east
northeast across the Intermountain West/Northern Rockies Monday
night and Tuesday. Models also suggest some upper jet Dynamics
will come into play at times. Overall looks like isolated to
scattered convection will come into play each day across much if
not the entire forecast area. After the system Tuesday, models are
showing some drying with convection becoming more isolated and
mainly over and near mountains Wednesday and Thursday.

Temperatures are expected to be seasonal to slightly above
average through the extended with Sunday being the hottest day in
the long-term with temps 5 to 10 degrees above average.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1130 AM MDT Thu Jul 13 2017

VFR conditions continue to be forecast through the period, with a
slight chance of MVFR under and around any thunderstorms. Isolated
showers and thunderstorms will develop in the vicinity and south of
a KRKS-KCPR line 19z/Thu-03z/Fri, as well as in Johnson County
around KBYG and the Bighorn mountains.  The primary hazard with
these high-based showers and thunderstorms will be erratic wind
gusts 30-40 knots. Otherwise, prevailing surface winds will be
generally light, less than 12 knots across the area.  The NAM is
suggesting some evening showers over the Wind River mountains and
Wyoming Range as well, so have included VCSH for KLND.  A
disturbance from the Great Basin will wrap around the high into
western WY Friday, bringing a chance of showers to the KJAC area,
then spreading eastward through the day.  Look for Friday to be more
active than Thursday with storminess, particularly over the
mountains and from KBYG-KCPR.

&&

.FIRE WEATHER...
Issued AT 128 AM MDT Thu Jul 13 2017

Fuels are now at critical levels for most forecast zones east of the
Divide in addition to portions of southern Lincoln County (Please
see the Fire Weather Forecast product for more information). Today
through Saturday, fire danger low to moderate for most mountain
locations...elevated for all other lower elevations due to very warm
to hot daytime temperatures and low humidity levels. Winds, however,
will continue relatively light across the entire forecast area today
through Saturday. The only exception will occur near any
shower/storm where winds could briefly gust 35 mph or more. Today,
mainly isolated precipitation chances will be found along/near and
south of a Casper Mountain to Evanston, WY line while Friday and
Saturday the emphasis for isolated/widely scattered showers/storms
will mainly occur over/near the area`s mountains or a weak surface
boundary/front stretching through central Wyoming.

&&

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

&&

$$

SHORT TERM...Braun
LONG TERM...Murrell
AVIATION...McDonald
FIRE WEATHER...Braun



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