Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 121714
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1114 AM MDT Sat Aug 12 2017

.SHORT TERM...Saturday through Monday night

Much like last night, there are only a few light showers leftover
from the convection and most of the night should be mainly dry. The
NAM, which has handled the convection fairly well the past couple of
days, shows a few showers with a shortwave moving through portions
of central Wyoming this morning so we added some isolated POPS to
account for that.

Otherwise, the next three days look to be a broken record; wash,
rinse repeat or whatever repetitive statement you want to use. In
other words, most areas starting off mainly clear in the morning and
then having some afternoon cloud buildup and isolated to widely
scattered thunderstorms each afternoon and evening as a series of
shortwaves swing across the area. And much like recent days, most
areas will have a chance each afternoon and evening thunderstorm.
However, most areas will remain rain free on any given day. As for
temperatures, high temperatures should remain near to slightly below
normal for through the weekend. As for the chance of stronger
thunderstorms, the best chance will be in the expected areas, mainly
Johnson and Natrona County where the best moisture will be found.
With rising thicknesses on Monday and flow turning more
southwesterly, Monday at this point looks to be the warmest day. And
with the southwest flow, breezier conditions will likely return to
areas favored by this pattern, mainly from Rock Springs through
Natrona County.

.LONG TERM...Tuesday through Saturday

Overview...A cold front will bring a chance of showers and
thunderstorms along with cooler temperatures across the area on
Tuesday. Mainly dry weather with a warming trend will follow
Wednesday through Saturday.

Discussion...Upper air pattern at the start of this period features
Omega-block with upper ridge over central Canada flanked by upper
lows near Hudson Bay and northern British Columbia/Alberta, with
trough extending from western Canada southward into the Great Basin.
In comparison to the ECMWF, GFS is more amplified and slower to lift
southern extension of this trough out of the Great Basin across the
Rockies Tuesday and Wednesday.  With blocking pattern downstream,
the slower solution is preferred.  The slower GFS still times the
main shortwave and associated cold front to move across the area
Tuesday morning, with most precipitation out of the area by Tuesday
evening.  Broad trough will remain across the Rockies on Wednesday,
but a drier post-frontal westerly flow will prevail across the area.

Broad trough over the area is replaced by broad ridge across the
Intermountain West/Rockies by Friday.  Flow is expected to gradually
back over the weekend as upstream trough amplifies across the Gulf
of Alaska/NE Pacific.  The latest scenario for the Eclipse, Aug.
21st, is for this trough to continue to amplify and possibly slowly
progress onto the NW coast with warm and dry SW flow across Wyoming.
There is still low confidence in these details with some agreement
among medium-range guidance this morning but still a lack of run-to-
run consistency.  The overall trend is toward a drier SW flow over
Wyoming.

&&

.AVIATION...18Z Issuance

A line of showers and isolated thunderstorms will continue to move
east across swrn/srn Wyoming early this afternoon. Wind gusts from
20 to 30 kts and some low VFR cigs will be possible at times.

Otherwise, VFR conditions to prevail through the forecast period.
VCTS at all sites after 18Z with the main threat brief heavy rain,
small hail, and gusts over 30 kts with local MVFR conditions
possible. Additionally, outflow boundaries from this convective
activity east of the divide will cause erratic gusty winds for brief
periods through 02z this evening. Isolated showers with a
thunderstorm or two will re-occur 08z-18z Sunday vcnty KRKS, KBPI
and KPNA...after 12z Sunday for KCOD.

Note: The LND TAF has been NILed as of 00Z/Sat. ASOS observations
have not been available for a week, and there is no estimated
time of return of service. With the runway being under
construction through the end of October and no observations, the
TAF will be NILed until further notice.


&&

.FIRE WEATHER...

Fire conditions should remain through critical levels through the
weekend. A couple of upper level disturbance will move through the
area and bring isolated to widely scattered thunderstorms each
afternoon and evening. However, most areas should stay largely dry
each day. Relative humidity should remain above critical levels with
winds light to moderate. However, erratic and gusty winds will be
likely around any shower or thunderstorm. Mixing and smoke dispersal
will range from fair to good in the basins and deeper valleys to
very good in the normally breezier locations. Lower humidity and
breezier conditions may return from the Red Desert through Natrona
County early next week.

&&

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

$$

SHORT TERM...Hattings
LONG TERM...Meunier
AVIATION...Braun
FIRE WEATHER...Hattings



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