Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 200527
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1127 PM MDT FRI AUG 19 2016

.SHORT TERM...Tonight through Monday

Imagery shows broad troffing across much of the CONUS with modest
ridges over both coasts. An embedded shortwave trof is currently
plowing down the west-side of the main trof and into/through
northwest WY...pushing a vigorous cold front through the FA. SFC now
has this front draped from east central Wyoming into south central
Wyoming then back up to the northwest and into eastern ID. Most
showers and embedded thunder are located post frontal early this
afternoon across central Wyoming...headed east southeast at 35 mph.
Brief heavy rain and wind gusts to 35 mph have been the main
threats.

The front will continue to push south through WY through the rest of
today with high pressure rapidly building into the FA behind said
front...stabilizing and clearing skies as it does. This afternoon,
near record low high temperature along with showers and a few
embedded thunderstorms will continue behind the front, mainly from
eastern Fremont county and eastward across Natrona county...pushing
south and east...clearing the area this evening. Small hail, brief
heavy rain and gusty winds 30 to 40 mph will be the main threat.
Tonight, clearing and drying will begin overnight with some lower
elevations west of the Divide...particularly the Jackson and Star
Valleys and the western portion of the upper Green River Basin and
Foothills...getting down to (near) the freezing mark for a brief
period near sunrise. Yellowstone will also see (near) freezing
temperatures overnight. SPSs have been hoisted for these areas.
Portions of the Wind River Basin will likely see lower elevation
temperatures near sunrise ranging from the mid 30s to the lower
40s...with an isolated bottom area somewhere getting near 32.

Saturday through Monday, warming a drying begins with RH values
dropping back into the lower and mid teens by Sunday...enhancing
fire danger once again...with near critical conditions on Monday
over much of the FA...especially from southern Natrona, Natrona,
eastern/western Fremont, Sweetwater and across much of western
Wyoming including Yellowstone NP where gusty winds will be maximized
ahead of an approaching upper level trof. There will also be a
modest increase for precip chances across the northwest zones with
the approaching front as well as across southwest Wyoming with some
slight increases in moisture from the south rotating into the
region around high pressure to the southeast.

.LONG TERM...Monday Night Through Friday

Pattern starts to transition back to a much cooler/colder nw flow
during this period. Strong upper trough moves across Montana Monday
night with a cold front pushing swd Monday night into Tuesday for
the beginnings of our cooldown across all but the sw where it will
take another day or so to get the next front to back in there. It
looks like another shortwave will dive sewd down the back side of
this trough pushing another even colder airmass southward Wednesday
into Wednesday night. The next shortwave may dive se in this flow
Wednesday night into Thursday with one last s to sewd moving cool
shortwave coming down next Friday. The GFS dives that system west of
us while the 12z Euro has it diving south out of Montana. Friday may
end up being our best bet of showers and a few thunderstorms. The
roller coaster will be in full force the next week with our current
sharp cooldown, then back to the heat late in the weekend through
Monday then cooling back down significantly Tuesday through Friday
once again. Doesn`t look quite as cool as the current setup but
current guidance does show h7 temps cooling down to the +2 to +4c
range Wed and Thu with even lower readings near the nrn border. We
may not have the significant pcpn/low cloud impact as much but we`ll
still have upslope on top of those cool mid level temps to at least
have the potential to keep temps in the 60s east of the divide.
Plenty more time to see how this pattern evolves but hemisphere
longwave analysis is showing the mean ridge retrograding off the
coast once again by the middle of next week after a brief shift
inland early next week.

&&

.AVIATION.../06Z ISSUANCE/

A few remaining patches of gusty wind will continue to weaken
overnight, with widespread VFR conditions anticipated. The
potential exists for the development of patchy fog over KCPR and
KJAC this morning, and any development should dissipate by 16z
this morning. Otherwise, the current pattern will leave VFR
conditions across the terminals with generally light wind
anticipated through the TAF period.

&&

.FIRE WEATHER...

Fire weather conditions low to moderate most locations. RH values
will range from the lower 20s (southwest) to as much as 80 percent
for most of the area. Through the day today the forecast area will
see a drastic change in the weather as an early fall type weather
system continues to impact Wyoming. A large upper level trough has
pushed across WY with an embedded strong shortwave trough moving
across WY today...pushing through a couple of cold fronts, shifting
the winds out of the north to northeast, greatly decreasing
temperatures and increasing moisture and precipitation
chances...especially east of the Divide. Many northern and central
mountain locations picked up between a quarter of an inch and a half
an inch of precipitation with these systems along with accumulating
snow overnight last night through early this morning above 9000
feet. Upper level ridging with warming and drying is expected once
again over the weekend with elevated to critical fire weather
conditions across much of WY on Monday.


&&

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

$$

SHORT TERM...Braun
LONG TERM...Skrbac
AVIATION...Branham
FIRE WEATHER...Braun



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