Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 191919
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
119 PM MDT Thu Jul 19 2018

.SHORT TERM...This evening through Friday

The only radar activity today was a straggling nw to se oriented
series of weak, southeast bound showers that actually was
significant enough to wet the ground in the Northern Big Basin
earlier this morning. They were significant enough to potentially
affect a chip and seal operation in that area. This was likely the
last of the out of season wrap around activity to affect our CWA,
likely associated with the cyclonic flow of the H7 circulation
now centered over southwest Minnesota. Red flag conditions are
beginning right on schedule at high noon in our southwest zones
today. Will let the red flag warning for zones 277 and 279 ride
through 8 pm this evening. Hot and dry weather will be the main
theme through Friday, with high temps hotter Friday than today.
We could easily see highs in the upper 90s Friday afternoon in the
Big Horn Basin. Any late day convection that occurs today will
likely be just out of reach to the northeast of our CWA. After the
flat ridge axis tracks east across central Wyoming Friday around
18Z, the steering flow will become difluent from the west-
southwest along with the right rear quad of the upper jet
overhead. Add some moisture and instability into the mix from the
subtropical high bulging in from the southwest and we see an
increasing chance of late day thunderstorms spreading northeast
into southwest Wyoming late Friday. Some of this activity could
possibly reach as far northeast as the west slope of the Wind
River Mtns.

.LONG TERM...Friday night through Thursday night

Thunderstorms over SW WY will be waning Friday evening, with
additional showers lingering through the overnight hours. Isolated
showers will also be possible Friday night over NW portions. An
upper level ridge will continue to build over the region Saturday,
in advance of an upper low over British Columbia/Alberta. Minor
shortwaves moving across the forecast area from the southwest
Saturday will develop isolated to widely scattered afternoon
thunderstorms. The associated cold front, from the upper low, will
begin to enter northern portions Sunday morning and proceed
southward through the day. Most of this progress will be east of
the Divide. Isolated to scattered afternoon storms will develop
once again, with the best chances occurring over western portions.
Showers and storms will gradually subside Sunday night, as the
front becomes stationary over the I80 corridor. Fire weather
conditions will be near-critical once again on Saturday in the
central basins, as afternoon RH values remain in the middle teens.
Monday through Thursday, a couple of weak cold front will move
through the area. The first will be Tuesday night, which will
mainly impact the Bighorn Basin and eastern portions. The second
front will be on Thursday, which will mainly impact areas east of
the Divide.

Temperatures are expected to be above average and hot ahead of the
cold front. Temperatures are then expected to be seasonal through
the rest of the forecast period.

&&

.AVIATION...For the 00Z TAFS through 00Z Saturday

The region should see mainly dry conditions from 00Z Friday until
00Z Saturday with unlimited ceilings. Surface W-NW wind
10-20G25-30kt will prevail across southwest Wyoming (KRKS, KPNA,
KBPI) this afternoon until around sunset this evening. There is a
chance of late day thunderstorms spreading northeast into
southwest Wyoming sometime after 22Z Friday, possibly affecting
KRKS.

&&

.FIRE WEATHER...
Issued AT 112 PM MDT Thu Jul 19 2018

...RED FLAG WARNING IN EFFECT FOR ZONES 277 AND 279 THROUGH 8 PM
THIS EVENING...

A combination of low humidity, dry fuels and a gusty wind will
continue to bring critical fire weather to Zones 277 and 279 for the
rest of this afternoon and early evening. In Zone 280, near critical
conditions are possible but the wind is not expected to be strong
enough. Non critical fire weather is expected elsewhere for the rest
of today with wind not expected to be strong enough or relative
humidity not low enough. Mixing and smoke dispersal will range from
good in the north to excellent in the south. Fire conditions should
improve on Friday, with less wind and somewhat higher relative
humidity. With the higher humidity will come an increasing chance of
late day thunderstorms for southwest Wyoming Friday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for WYZ277-279.

&&

$$

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


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