Special Weather Statement, NWS Riverton, WY

Area Forecast Discussion
National Weather Service Riverton WY
1123 AM MDT MON AUG 8 2016

.SHORT TERM...Today Through Wednesday Night

Updated to add Natrona and the rest of Sweetwater County into the
Red Flag Warnings. RH looks quite low after 1-2 pm and winds
should be enough to verify plus haines are running 5-6. Possibly
even a late day thunderstorm to add to the mix in Natrona.

Imagery shows a similar set-up to that of the last couple of days
with a broad ridge over the central CONUS, a broad trof to the east
and a sharp/strong/deep trof to the west and centered over WA. The
central portion of the high is located over TX and northern MX. The
surface shows continued high pressure over the central CONUS and low
pressure across the west/southwest...some heat induced/reinforced
over the desert SW. this weakening monsoonal set-up has allowed
better moisture to stream up over the southern/central Rockies and
through eastern WY and MT.

Today, vigorous drying begins across the CWA while surface winds
turn out of the southwest within these drying lower levels as a weak
front pushes into eastern WY...then with building low pressure
across eastern WY on Tuesday. RH values look to drop significantly
both days, ranging from the single digits to around 20 percent for
most of the FA. This together with southwesterly surface flow
gusting between 20 and 30 mph at times in the afternoon across
portions of southwestern and central WY today and over nearly
the entire CWA Tuesday may produce Red Flag conditions in the
afternoons...buoyed by some possible isolated, mostly dry,
thunderstorms east of the Divide on Monday. There will be slight
chances for a morning shower across the northwest Tuesday...north
during the afternoon. A Red Flag warning is in place for far
southwest WY and a portion of central WY today. A Fire Weather Watch
has been issued for all of the FA on Tuesday.

Wednesday, dry, but not quite as dry as Tuesday, with a weaker
pressure grad and slightly less instability decreasing surface wind
flow. Best chances for another day of Red Flag conditions will occur
across portions of south central to central WY. However, even then
it would be for very marginal critical conditions. Only a couple of
isolated showers/storms possible over the northern mountains.

.LONG TERM...Thursday Through Monday

At the surface, a quasi-stationary cold front should be along and
east of the Divide Thursday through Saturday. In the upper levels,
models show a shortwave trough pushing east across ID into western
WY Thursday, and then across the entire area Thursday night. This
shortwave trough interacting with a surface front and additional
overall moisture should result isolated to scattered convection
across much of the forecast area. Due to the wind shear especially
east of the Divide, some thunderstorms could be on the strong side.
In wake of this shortwave trough, northwest flow is expected
Friday and Saturday. Enough moisture and instability for some
convection along and east of the Divide Friday becoming more
isolated on Saturday with less moisture to work with, and
increasing heights aloft. Except for thunderstorms especially on
Thursday, fire weather concerns Thur-Sat should be minimal day as
winds outside of thunderstorms are projected to be light.

On Sunday, medium range models show ridging over the area with a
trough pushing into the Pacific Northwest. This should result in
drier, warmer and potentially breezy southwest winds developing.
Models then have significant differences with the ECMWF pushing a
part of the trough across the area, while the GFS lifts the
trough northward with little impact, except for perhaps fire
weather concerns.
&&

.AVIATION.../18Z ISSUANCE/

West of the Continental Divide...KJAC/KBPI/KPNA/KRKS

Generally dry conditions anticipated at area terminals through the
forecast period. However, isolated showers and thunderstorms will
be possible over the mountains, with showers causing periodic
mountain obscurations. Otherwise, generally VFR conditions are
anticipated across the area, with some gusty wind possible this
afternoon.

East of the Continental Divide...KCOD/KCPR/KLND/KRIW/KWRL

Isolated showers and thunderstorms will be possible this
afternoon, impacting the area through around 01z-03z this evening.
Gusty wind may accompany any storm activity today, with some
erratic winds possible at terminals. VFR conditions then
widespread after 03z, with some lingering showers over the
northern and central mountains. Periods of mountain obscurations
will be possible with storm activity today. Even outside of storm
activity, gusty wind will develop this afternoon and continue
through the same time period of 01z-03z this evening.

&&

.FIRE WEATHER...

...Red Flag Warning for portions of southwestern and central Wyoming
Today...

...Fire Weather Watch for most of the western two thirds of Wyoming
Tuesday...

Fire danger elevated across the forecast area today with Red Flag
conditions across small portions of southwest and central Wyoming.
RH values begin to drop back into the lower teens (percent) for much
for much of the lower elevations today, with only mid 20s in the
mountain zones. At the same time, winds will begin to increase out
of the southwest across most of the area west of the Divide and into
portions of central WY.

Tuesday will be slightly drier overall across the entire forecast
area while the surface environment becomes more favorable for
producing more widespread and gustier winds. As all of the forecast
area has critically dry fuels to work with, a Fire Weather Watch has
been issued for most of the western two thirds of WY.

While Wednesday will be nearly as dry as Tuesday, the surface
pressure gradient will generally weaken across WY keeping winds
below Red Flag criteria for the most part. One area to watch may be
over portions of south and south central WY.

&&

.RIW Watches/Warnings/Advisories...
Red Flag Warning until 8 PM MDT this evening for WYZ277-279-289.

Fire Weather Watch from Tuesday afternoon through Tuesday
evening for WYZ140-275>283-285>289-300-414>416.

Red Flag Warning until 8 PM MDT this evening for WYZ280-300.

&&

SHORT TERM...Braun/PS
LONG TERM...WM
AVIATION...Branham
FIRE WEATHER...Braun

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
320 AM MDT MON AUG 8 2016

WYZ001>020-022>030-091200-
YELLOWSTONE NATIONAL PARK-ABSAROKA MOUNTAINS-CODY FOOTHILLS-
NORTH BIG HORN BASIN-SOUTHWEST BIG HORN BASIN-
SOUTHEAST BIG HORN BASIN-OWL CREEK AND BRIDGER MOUNTAINS-
BIGHORN MOUNTAINS WEST-BIGHORN MOUNTAINS SOUTHEAST-
NORTHEAST JOHNSON COUNTY-SOUTHEAST JOHNSON COUNTY-
TETON AND GROS VENTRE MOUNTAINS-JACKSON HOLE-
WIND RIVER MOUNTAINS WEST-WIND RIVER MOUNTAINS EAST-
UPPER WIND RIVER BASIN-WIND RIVER BASIN-LANDER FOOTHILLS-
GREEN MOUNTAINS AND RATTLESNAKE RANGE-
NATRONA COUNTY LOWER ELEVATIONS-CASPER MOUNTAIN-STAR VALLEY-
SALT RIVER AND WYOMING RANGES-UPPER GREEN RIVER BASIN FOOTHILLS-
UPPER GREEN RIVER BASIN-SOUTH LINCOLN COUNTY-
ROCK SPRINGS AND GREEN RIVER-FLAMING GORGE-EAST SWEETWATER COUNTY-
320 AM MDT MON AUG 8 2016

...RED FLAG WARNING FOR PORTIONS OF SOUTHWEST AND CENTRAL WYOMING
THIS AFTERNOON AND EARLY EVENING...

...FIRE WEATHER WATCH FOR MOST OF THE WESTERN TWO THIRDS OF
WYOMING TUESDAY AFTERNOON AND EARLY EVENING...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

VERY DRY...WARM AND BREEZY CONDITIONS ACROSS SOUTHWEST AND
CENTRAL WYOMING...RESULTING IN ELEVATED TO CRITICAL FIRE WEATHER
CONDITIONS. ISOLATED LATE DAY THUNDERSTORMS OVER PORTIONS OF
CENTRAL WYOMING...SOME STRONG WIND GUSTS POSSIBLE.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

TUESDAY AND WEDNESDAY...VERY DRY...WARM AND BREEZY CONDITIONS
CONTINUE ACROSS MOST OF WYOMING...RESULTING IN ELEVATED TO
POSSIBLE CRITICAL FIRE WEATHER CONDITIONS. ISOLATED THUNDERSTORMS
NORTH ON WEDNESDAY.

THURSDAY...ISOLATED TO SCATTERED THUNDERSTORMS. SOME STRONG
THUNDERSTORMS POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ARE URGED TO REPORT WIND GUSTS OVER 45 MPH. THANK YOU.

21

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RIVERTON WY
1250 PM MDT MON AUG 08 2016

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1116 AM     HAIL             COLTER BAY VILLAGE      43.90N 110.64W
08/07/2016  E1.00 INCH       TETON              WY   PUBLIC

&&

PS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
153 PM MDT MON AUG 8 2016

WYZ004>006-082030-
SOUTHEAST BIG HORN BASIN-SOUTHWEST BIG HORN BASIN-NORTH BIG HORN
BASIN-
153 PM MDT MON AUG 8 2016

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN WASHAKIE...NORTH
CENTRAL HOT SPRINGS AND SOUTHWESTERN BIG HORN COUNTIES UNTIL 230 PM
MDT...

AT 152 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 9
MILES SOUTHEAST OF GOOSEBERRY CREEK...OR 23 MILES SOUTHEAST OF
MEETEETSE...MOVING NORTHEAST AT 30 MPH.

HALF INCH HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.

THIS STORM WILL REMAIN OVER MAINLY RURAL AREAS OF NORTHWESTERN
WASHAKIE...NORTH CENTRAL HOT SPRINGS AND SOUTHWESTERN BIG HORN
COUNTIES...INCLUDING THE FOLLOWING LOCATIONS: BADLANDS OVERLOOK.

THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO
STATIONS AND AVAILABLE TELEVISION STATIONS FOR ADDITIONAL INFORMATION
AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.

LAT...LON 4380 10851 4403 10862 4426 10819 4383 10795
TIME...MOT...LOC 1952Z 247DEG 28KT 4395 10848

13

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
159 PM MDT MON AUG 8 2016

WYZ020-082030-
NATRONA COUNTY LOWER ELEVATIONS-
159 PM MDT MON AUG 8 2016

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

AT 159 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM
OVER TEAPOT ROCK...OR 28 MILES NORTH OF CASPER...MOVING NORTHEAST AT
30 MPH.

HALF INCH HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.

THIS STORM WILL REMAIN OVER MAINLY RURAL AREAS OF NORTHEASTERN
NATRONA COUNTY.

THIS INCLUDES INTERSTATE 25 BETWEEN MILE MARKERS 210 AND 219.

THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO
STATIONS AND AVAILABLE TELEVISION STATIONS FOR ADDITIONAL INFORMATION
AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.

LAT...LON 4313 10632 4329 10642 4347 10608 4315 10607
TIME...MOT...LOC 1959Z 247DEG 28KT 4324 10628

13

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
204 PM MDT MON AUG 8 2016

WYZ030-082045-
EAST SWEETWATER COUNTY-
204 PM MDT MON AUG 8 2016

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN SWEETWATER COUNTY UNTIL
245 PM MDT...

AT 203 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR
WAMSUTTER...MOVING EAST AT 30 MPH.

PEA SIZE HAIL AND WIND GUSTS UP TO 50 MPH WILL BE POSSIBLE WITH THIS
STORM.

THIS STRONG THUNDERSTORM WILL BE NEAR...
  CRESTON JUNCTION AROUND 215 PM MDT.

THIS INCLUDES INTERSTATE 80 BETWEEN MILE MARKERS 175 AND 198.

LAT...LON 4177 10800 4200 10756 4189 10750 4166 10751
      4166 10793 4164 10793
TIME...MOT...LOC 2003Z 250DEG 27KT 4168 10784

13