Severe Thunderstorm Warning 77, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
217 PM MDT Thu Aug 15 2019

.SHORT TERM...Tonight through Friday

Evidence of the next approaching shortwave is noted with the
increasing CU field across YNP currently. near-term models
continue to note some convection developing around 6pm or so just
to the west and moving east into NW WY. Also of note is the
convection off to the east of CPR, with multiple weak boundaries
moving sporadically across central WY. These boundaries look to
continue sparking showers and thunderstorms near Natrona County
the next few hours. Since this activity is mostly east of CPR
already, progressing the boundaries into westerly flow aloft will
have a tough time getting forcing boundaries further west. Areas
south of the divide will remain in a dry westerly wind the rest of
the day, with minimal cloud cover expected.

The approaching wave will move across norther WY overnight
tonight. Showers that do form in NW WY will likely have enough
mid level support to continue with showers across the remainder
of northern WY through the rest of the night. Once the sun sets,
activity will be lighter in nature, and should be well into
eastern WY by sunrise.

With the main mid level support departing east on Friday, rain
chances will be limited to the higher elevations across north
Wyoming during the afternoon. Models still look overly optimistic
in overall chances, with little in the way of measurable rain
expected, even in the mountainous areas. Southern Wyoming again
remains dry with minimal cloud cover and a dry west wind
continuing.

.LONG TERM...Friday night through Thursday

We still look to have decreasing chances of precipitation over the
long term period. There will still be a few leftover showers and
storms over portions of the area Friday evening before ending by
midnight. On Saturday, a weak shortwave moving across Montana could
bring isolated storms to portions of northern Wyoming. However, with
a vast majority of the forcing remaining north of the state line,
these still look to be fairly few and far between.

Ridging is still expected to build northward toward the end of the
weekend and the first part of next week. This should bring hot
temperatures and mainly dry conditions. All the models have dry
conditions Sunday and Monday. A couple of models have isolated
activity Tuesday and Wednesday. However, it is largely confined to
the mountains. And since the models tend to vastly overestimate the
activity in the mountains this far out, we made the forecast dry. As
for possible fire concerns, expect gusty winds across many areas
through Sunday with the pressure gradient remaining fairly tight.
Starting the beginning of next week, with the ridge building further
northward, there should be less wind and therefore, fewer fire
concerns. Relative humidity should remain quite low however,
possibly falling into the single digits at times early next week.
&&

.AVIATION...00Z Issuance

West of the Divide (JAC/PNA/BPI/RKS): Southern TAFs will remain
breezy from the west, as the weak front remains along the Divide.
A couple showers may reach JAC late this afternoon or this
evening, but most activity should remain well to the north of
there. Winds reaching near 20 knots with gusts approaching 30 are
possible this afternoon. Light and variable winds will return
overnight, with mostly clear skies still expected. Another day of
breezy west winds expected Friday.

East of the Divide (COD/WRL/JAC/RIW/LND): Northern TAFs will be
affected by lighter north winds behind the weak front along the
Divide. Showers and thunderstorms are expected to develop in the
Big Horn Basin late this afternoon, before moving southeast. A few
of these may briefly reach CPR, but most storms are expected to
remain to the north through the evening. Another round of isolated
showers and thunderstorms is possible on Friday for COD/WRL,
otherwise this region remains in light northerly flow and modest
SCT daytime CU.

&&

.FIRE WEATHER...

Elevated fire weather conditions continue for southwest Wyoming
this afternoon, with RH values below 15 percent and west winds of
15 to 20 mph. Areas north of the divide remain at lower threat as
humidity is higher and north winds are much lighter. Showers and
thunderstorms are expected to move across northern WY overnight,
with occasional lightning strikes and light amounts of
precipitaion.

Friday will be similar to today, with SW WY continuing the dry
westerly winds and low humidity, while northern WY continues with
slightly higher humidity and light north winds.

The front moves out of the area during the day Saturday, with much
drier air pushing across all of WY. All the lower elevations
across western and central Wyoming will fall below 15 percent by
Sunday, while westerly winds pick up across the state. Near-
critical conditions will continue into the day Monday, with
single-digit humidity possible for SW WY and breezy southwest
winds.

&&

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

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

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Special Weather Statement
National Weather Service Riverton WY
521 PM MDT Thu Aug 15 2019

WYZ012-013-160100-
Teton and Gros Ventre Mountains-Jackson Hole-
Including the city of Jackson
521 PM MDT Thu Aug 15 2019

...Thunderstorms will move across Teton County through 7 PM...

An area of showers and thunderstorms will move east across Teton
County through 7 PM. Frequent lightning, gusty winds, small hail,
and locally heavy rain is possible with these storms.

Special Weather Statement
National Weather Service Riverton WY
822 PM MDT Thu Aug 15 2019

WYZ020-160245-
Natrona County Lower Elevations-
822 PM MDT Thu Aug 15 2019

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN NATRONA COUNTY UNTIL
845 PM MDT...

At 821 PM MDT, Doppler radar was tracking a strong thunderstorm over
Teapot Rock, which is 28 miles north of Casper, moving southeast at
45 mph.

Half inch hail and winds in excess of 30 mph will be possible with
this storm.

This storm will remain over mainly rural areas of northeastern
Natrona County.

LAT...LON 4318 10643 4331 10639 4350 10627 4349 10608
      4302 10608
TIME...MOT...LOC 0221Z 299DEG 40KT 4325 10627

Myers

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