Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 221949
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
149 PM MDT Tue Aug 22 2017

.SHORT TERM...Tuesday night through Friday

Right now all is quiet across western and central Wyoming. There
could be a couple of showers or thunderstorms that may creep into
southern Wyoming late this afternoon or evening with a bit of
moisture surging in from the south, but that would be about it. In
addition, some smoke has returned to the area, especially in the
north so we added areas of smoke to most areas. Mainly dry
conditions should continue through tonight.

The weather looks to become more active on Wednesday as the ridge
axis shifts to over to a bit east of Wyoming and allows some
monsoonal moisture to move up the backside of the ridge mainly
into western and southern Wyoming. This means a better chance of
showers and thunderstorms for this area. A few may spread East of
the Divide during the evening, but most areas in this vicinity
should remain rain free. There will be more clouds though, and
this should decrease high temperatures by a few degrees. With the
increase of moisture West of the divide, fire conditions should
also improve somewhat.

It looks like more of the same for Thursday and Friday. Thursday
will likely be the most active day with a chance of showers and
thunderstorms everywhere. The models diverge a bit more for Friday
however. At this point, we kept continuity with the best chances
across northern and central portions of the state. Temperatures
should average close to normal both Thursday and Friday.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY) ISSUED AT 225 AM MDT TUE
AUG 22 2017

THE MODELS SEEM TO BE IN BETTER AGREEMENT IN BRINGING THE SHORTWAVE
/CUT OFF LOW ACROSS CANADA AND THE NORTHERN ROCKIES FRIDAY NIGHT,
THUS FLATTENING THE RIDGE OVERHEAD AND RESULTING IN A CHANCE OF
EVENING THUNDERSTORMS FRIDAY, MAINLY IN NORTHERN WYOMING, WITH WEAK
INSTABILITY. THEN THE AREA OF HIGH PRESSURE WILL REESTABLISH ITSELF
OVER THE WESTERN UNITED STATES FOR THE WEEKEND WITH WARMER AND DRIER
CONDITIONS WHEN HIGH TEMPERATURES WILL BE IN THE MID 80S TO LOW 90S
AND UP AROUND 80 OUT WEST. THESE WARM TEMPERATURES WILL CONTINUE
THROUGH TUESDAY. A PACIFIC SHORTWAVE WILL RIDE UP AND OVER THE RIDGE
TUESDAY RESULTING IN AN INCREASING CHANCE OF LATE DAY THUNDERSTORMS
TUESDAY AS THE RIDGE BEGINS TO NARROW. THE GFS AMPLIFIES THE RIDGE
THE MOST WITH 588 HEIGHTS WELL UP INTO SOUTHERN BC AND ALBERTA WITH
MORE FLATTENING OF THE RIDGE AS INDICATED BY THE EURO AND CANADIAN,
SO WILL GO WITH THIS IDEA.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday) Issued at 225
AM MDT Tue Aug 22 2017

Conditions will remain VFR through 12Z/Wed. Moisture to the
southwest of Wyoming will make a gradual return to the southwest
quadrant of the state during the remainder of this afternoon
and tonight. Weak convection, limited by shear and instability,
is beginning to creep back into extreme Southwest Wyoming off the
Uinta Mountains as they drift into extreme Southwest Sweetwater
County. Little chance of impacting KRKS. Drift smoke from any
upstream fires in the Western United States should have little
impact on vsby for the rest of today as the steering flow backs to
a more westerly direction. Mid- cloud deck will push north early
Wednesday, but not expecting precipitation with these clouds.
Diurnally-driven west- northwest wind 10-12kts anticipated at KBPI
and KPNA through and 02Z/Wed. Other terminals to be 10kts or less
through much of the forecast period, with westerly surface flow
west of the Continental Divide and northerly surface flow to the
east for the rest of today with more of a westerly flow by
Wednesday afternoon on both sides of the divide.

&&

.FIRE WEATHER...

Mainly dry weather will continue through tonight. Relative
humidity will also continue to be rather low, below 15 percent in
many of the lower elevations. However, winds should remain light
to moderate for most areas. However, areas of near critical fire
conditions are possible on through this afternoon. Monsoonal
moisture will increase across western and southern Wyoming on
Wednesday. This should raise relative humidity somewhat and
improve fire conditions somewhat. It will also lead to isolated to
widely scattered showers and thunderstorms in areas to the West of
the Divide. Mixing and smoke dispersal will be generally good to
very good for most locations in the afternoon.

&&

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

$$

SHORT TERM...Hattings
LONG TERM...Lipson
AVIATION...Lipson
FIRE WEATHER...Hattings


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