Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 260844
Area Forecast Discussion
National Weather Service Riverton WY
244 AM MDT TUE JUL 26 2016
.SHORT TERM...Today Through Thursday Night
High pressure over the area will see some modifications today. A
disturbance moving through Canada/Montana will flatten the ridge,
introducing a more zonal flow to the area. Moisture will move over
the area, with the threat of showers and thunderstorms this
afternoon. Gusty outflow wind to 50 mph will be possible in
thunderstorm locations, especially across northern Johnson county
where models are putting the best instability. Thunderstorms will be
most plentiful over the central mountains, though the southern third
of the state will also see some potential for storm activity today.
Most activity will weaken with the loss of daylight this evening,
though isolated storms will remain possible over the northern
mountains and into Natrona and Johnson counties.
The area of high pressure over the desert southwest will be able to
amplify Wednesday morning. However, a weak cold front will move
through northeastern Wyoming, with another round of afternoon
showers and thunderstorms anticipated. Storm coverage looks more
impressive on Wednesday than it does today, though models decrease
convective indices. Regardless, gusty wind will be possible again
with storm activity. Slightly cooler temperatures are anticipated
Wednesday afternoon, but should only decrease local temperatures by
a few degrees.
Models demonstrate an increasing northwest flow across the area on
Thursday. This will increase afternoon wind, especially those areas
favoring a northwest flow. This would include portions of the Wind
River Basin, and the Upper Green River Basin. This flow will also
bring in moisture to the northeastern half of the state, with
isolated to scattered showers and thunderstorms possible.
.LONG TERM...Friday Through Tuesday
A weak frontal boundary over the east and some energy in the WNW
flow aloft will result in isolated convection east of the Divide
while areas over the far west/southwest should remain dry and
hot. Some monsoonal moisture begins to spread northeast into the
area Saturday, with isolated...mainly mountain convection possible
both east and west of the Divide. Any storms Saturday should be
mainly dry which could cause new fire starts.
On Sunday models are showing a weak, but distinct wave pushing
northeast into the forecast area in between a trough pushing into
the Pacific NW and the Subtropical Ridge over the Southern
Rockies/Plains. This disturbance combined with some monsoonal
moisture should give the entire area a chance of isolated to
locally scattered convection. Thunderstorms appear to be a mix of
wet and dry thunderstorms, but after an extended hot and dry
period there could be several new fire starts.
Models indicate the main energy from the Pacific NW trough will
lift northeast across the extreme Northern Rockies into south-
central Canada Monday. The associated weak cold front is expected
to push south, east of the Divide Monday. This front combined with
lingering modified monsoonal moisture will be enough for isolated
to locally scattered convection across the entire area with a
better shot east of the Divide. Not much change on Tuesday with a
weak boundary over the east and enough moisture over the west to
keep isolated convection across the entire area with peak heating.
Temperatures will be 5-10 degrees above average through the extended.
VFR conditions will prevail today and tonight. Isolated showers or
storms will develop over the region after 19z and continue until
04z. Outflow wind gusts of 35 to 45 knots will be the main hazard
near showers or storms.
Smoke will continue to be an issue near active wildfires. This will
impact visibility at times in the valleys through 18z. Smoke plumes
are expected to reform this afternoon into the evening hours,
sending columns of smoke across portions central WY.
Fire weather conditions will see improvement today, with lighter
wind anticipated across western and central Wyoming. Daytime
humidity will still decrease into the upper single digits for some
locations this afternoon, but afternoon shower activity will help to
increase area humidity. Afternoon showers and thunderstorms will
remain a part of the forecast for the next couple of days. Generally
light wind also expected through Wednesday. Winds will shift more to
the northwest on Thursday, which could mean some areas of stronger
wind. This situation will continue to be monitored.