Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 280501 AAA
AFDRIW

Area Forecast Discussion...UPDATED
National Weather Service Riverton WY
1101 PM MDT TUE SEP 27 2016

.UPDATE...Added 06z aviation discussion.

&&

.AVIATION.../06Z ISSUANCE/

VFR conditions with unlimited ceilings will continue to prevail
through 12z Thursday.  Surface high pressure sliding southeast
across the High Plains will result in a prevailing east to southeast
wind around 10 knots east of the Continental Divide Wednesday
afternoon.  An upper level disturbance drifting north across the
Great Basin will spread isolated to widely scattered showers north
to a vicinity KJAC-KLND-KRWL line by 12z Thursday.

&&

.PREV DISCUSSION... /issued 233 PM MDT TUE SEP 27 2016/

SHORT TERM...Tonight Through Wednesday

High pressure remains anchored over the state through the overnight
hours.  This will leave continued dry conditions, with mostly clear
skies and warming temperatures. Isolated patchy morning fog may be
possible, but dewpoint depressions on model analysis are not
supportive for formation. Consequently, opted to leave fog wording
out of current forecast.

An area of low pressure is expected to move through the desert
southwest beginning early Wednesday morning, and continuing to move
northeast through Wednesday. Moisture associated with this system
may be enough to increase cloud cover over the southern portion of
Lincoln county and into the western portion of Sweetwater county,
but shower activity is not anticipated to begin through the late
afternoon hours.

LONG TERM...Wednesday night to Tuesday

The stretch of dry weather looks to end on Wednesday night as
moisture from an upper level low now Near California begins to move
into southwestern portions of the state. As for Thursday, it looks
to be a day dominated by south to southwesterly flow with some
moisture. That means the chance of a few showers and thunderstorms
across areas West of the Divide. Meanwhile, downsloping flow should
keep most areas east of the Divide dry with the exception of some
areas near the mountains. Temperatures should be similar to
Wednesday with downsloping flow counteracting the effects of more
cloud cover.

At this point Friday looks to be less active as the moisture moves
out and transitory shortwave ridging moves across the state. As a
result we restricted POPS to the slight variety and kept them
confined mainly to the higher elevations. Temperatures should again
average above normal although a couple of degrees cooler than on
Thursday.

The pattern then becomes more unsettled and cooler as we head into
the weekend and into the first part of next week as a trough digs
into the western portion of the country. That much we know. However,
there are still model differences in regard to timing and intensity
of the individual shortwaves and fronts moving around the parent
trough. The models are in decent agreement through Saturday with a
front moving through, but again it looks like mainly a West of the
Divide event with areas further east mainly dry with one more day of
warm temperatures.

The details then diverge as we head into Sunday. It will be cooler,
but in regards to placement of the best chance of precipitation
confidence is very low at this time. The lack of confidence
continues through Monday and Tuesday as well. As a result, we only
made minor tweaks to the forecast past Sunday. We do agree with the
previous shift that things may get interesting Monday night into
Tuesday with some cooler air moving that could bring some measurable
snow out west. A lot of time to watch it, but something to look at
for sure.

AVIATION.../00Z ISSUANCE/

Widespread VFR conditions expected across western and central
Wyoming through the TAF period. A few mountain-related clouds may
form this afternoon, but skies are generally anticipated to be
clear through Wednesday morning. An approaching area of low
pressure will increase cloud cover from southwest to northeast
Wednesday morning and afternoon. Generally light wind
anticipated, though wind across the area will increase slightly
after 18z Wednesday as the area of low pressure advances.

FIRE WEATHER...

Quiet fire weather conditions expected through Wednesday as high
pressure remains anchored over the area. An area of low pressure
will move through the desert southwest on Wednesday, introducing
shower activity to southwestern Wyoming by the evening hours.
Temperatures will cool slightly under the influence of this
approaching system through the remainder of the week. Fire weather
concerns will generally remain low over the next few days.

&&

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

$$

SHORT TERM...Branham
LONG TERM...Hattings
AVIATION...AEM
FIRE WEATHER...Branham


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