Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 241757 AAA
Area Forecast Discussion...Update
National Weather Service Riverton WY
1158 AM MDT WED AUG 24 2016
.SHORT TERM...Wednesday through Friday night
We will be moving into a more Fall like pattern for the next few
days. A cold front has passed through much of the state and turned
flow to the north. Temperatures will continue the downward trend
as well. We did raise high temperatures a couple of degrees since
there will be sunshine much of the day and guidance came in
higher. Nevertheless, temperatures will be below normal. In
addition, relative humidity will also rise across the northern
portions of the state and decrease fire danger for much of the
area. Humidity will remain low in the south, but with less wind
and cooler temperatures conditions should improve. In the far
southwest, conditions may be borderline for critical but better
than yesterday so we will stick with a headline for near critical
The forecast will also turn wetter. After a dry morning, an upper
level disturbance dropping from the northwest will bring some
showers and thunderstorms to northern areas this afternoon. QPF may
be a little overdone, but some rain looks to be a decent possibility
this afternoon and evening for many locations east of the Divide and
in the northwest. And across the higher elevations there could even
be some snow.
Thursday looks like a taste of fall for many areas with a trough
over the area and eastern flow increasing. Some areas will likely
not get out of the 50s. Another shortwave will also round the base
of the longwave trough and bring another round of showers and
isolated thunderstorms. With the cool temperatures and low wet bulb
zero levels, small hail would likely be the main threat. The driest
weather and warmest weather would be found across southern Wyoming.
And with the cool temperatures, snow will again be possible across
the higher elevations.
On Friday, the last shortwave will round the trough and bring
another round of showers and thunderstorms. With more sun expected,
temperatures should begin to rebound a bit however. It will still be
below normal however. And again, the most precipitation will fall
across the northern two thirds of the state. Any showers should come
to an end later Friday night as the trough lifts out and ridging
begins to rebuild across the area.
.LONG TERM...Saturday through Wednesday
Synopsis...A dry and warmer westerly flow will prevail over the
area through the period. Breezy and very dry conditions will bring
elevated fire weather conditions across the south on Saturday.
Temperatures will return to above normal Sunday through mid-week.
Discussion...Cold upper trough currently over the northern Rockies
will eject east across the plains Friday night and Saturday.
Upstream, amplified upper ridge over the eastern Pacific is expected
to retrograde along or west of the 150W Meridian leading to
downstream trough along west coast and broad ridging across the
southern tier of the U.S. More weight is given to ensemble means
holding trough along the west coast though mid-week with h5 heights
in the 588-591 DM range across Wyoming Sunday-Wednesday. Very low
relative humidity in the single digits and teens will combine with
gusty west wind 15-20 mph across the south to produce elevated to
critical fire weather conditions across the southern half of the
area Saturday afternoon. Winds should be lighter Sunday through
Tuesday. Temperatures will remain seasonably cool on Saturday and
then warm into the 80s to lower 90s across the basins and valleys
Sunday through Wednesday.
West of the Divide...VFR conditions will occur through 12z Thursday.
Isolated showers and thunderstorms will develop over northwest WY after 18z and
continue through 18z Thursday. KJAC will be impacted by this
activity at times this afternoon and tonight. Smoke from nearby
wildfires may reduce visibility in the Jackson area at times.
Southwest WY will be mostly dry through the period.
east of the Divide...VFR conditions will occur east of the divide through 00z.
Isolated showers and storms will develop after 19z...initially near
the mountains...then spreading over the lower elevations during the
afternoon and evening hours. Low clouds will develop over northern
WY after 00z with MVFR conditions prevailing by 06z Thurs over the
north. In central WY...isolated showers and storms will occur after
21z and continue through 06z Thurs. Low clouds and rain showers
will develop in central WY around 06z Thurs with MVFR conditions
prevailing by 09z and continuing through 15z at the terminal sites.
Fire weather should improve today as cooler temperatures and higher
relative humidity move behind a cold front across the northern two
thirds of the state. Relative humidity will fall into the teens
across southern Wyoming one more day. However, with lighter wind
fire danger should not be critical. The exception will be in Zone
277 where near critical fire conditions may be possible for a time
this afternoon. An upper level disturbance will bring showers to the
northern half of the state this afternoon and tonight. Smoke
dispersal and mixing will generally poor to fair east of the divide
and across the north and good to very good in the south. Showers
will be possible Thursday and Friday as well.