Special Weather Statement, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
255 PM MDT MON AUG 29 2011

SHORT TERM...TONIGHT THROUGH THURSDAY
SHORTWAVE MOVING ACROSS WESTERN MONTANA WITH MID TO UPPER LEVEL
SPEED MAX ROTATING ACROSS SOUTHERN MONTANA. SURFACE DEW POINTS
HAVE HELD UP ACROSS MUCH OF THE AREA AS EXPECTED WITH 40S TO LOWER
40S COMMON. ENOUGH CAPE TO FIRE A FEW STRONGER STORMS INTO THE
EVENING HOURS. AIRMASS DRIES OUT IN THE WESTERLY FLOW TOMORROW AND
WARMS UP WITH POTENTIAL CRITICAL FIRE WEATHER CONCERNS IN PORTIONS
OF CENTRAL WYOMING...ESPECIALLY FROM LANDER AND RIVERTON EAST TO
NATRONA COUNTY. WINDS ARE RH'S ARE MARGINAL BUT CALCULATED NUMBERS
GIVE MIN RH'S AROUND 14 PERCENT WITH SW WINDS OF 15-20 MPH WITH
GUSTS OF 25 TO 30 MPH. COMBINE THAT WITH ONGOING FIRES AND ITS
ENOUGH FOR A WATCH AT LEAST. RESIDUAL MOISTURE AND MAX HEATING MAY
BE ENOUGH TO FIRE A FEW MAINLY MOUNTAIN STORMS AND OFF THE UINTAS.
EVEN DRIER AIR MAY FILTER IN WEDNESDAY AHEAD OF OUR APPROACHING
THURSDAY TROUGH. POTENTIAL FOR MORE WIDESPREAD RED FLAG CONDITIONS
MAY DEVELOP ON WEDNESDAY. HOWEVER...WE DO SEE SOME INCREASE IN MID
LEVEL MOISTURE ALREADY SNEAKING UP FROM THE SOUTH TUESDAY NIGHT
AND WEDNESDAY MORNING WITH A FEW SHOWERS DEVELOPING. ENOUGH
MOISTURE AND INSTABILITY WILL LIKELY REMAIN INTO WEDNESDAY
AFTERNOON FOR SOME HIGHER BASED ISOLATED THUNDERSTORMS TO ADD TO
THE FIRE WEATHER CONCERNS. OUR FIRST POTENTIAL COLD TROUGH THEN
MOVES IN THURSDAY WITH AN INCREASING CHANCE OF SHOWERS AND
THUNDERSTORMS ACROSS THE NORTH FIRST AND THEN SPREADING SOUTHEAST
ALONG THE SHARP COLD FRONT. NEW ECMWF IS WEAKER WITH THE LOW
SIMILAR TO OLDER GFS RUNS SO WE'LL HAVE TO WATCH THIS CLOSELY. A
LOT OF THE PROBLEM IS WITH THE SHORTWAVE BEHIND THIS ONE AND
WHETHER IT HELPS TO DEEPEN IT OR JUST KICK IT OUT QUICKER. FIRE
WEATHER CONCERNS WILL CONTINUE IN THE SOUTH AHEAD OF THIS COLD
FRONT THURSDAY. SHARPLY COOLER CONDITIONS ARE EXPECTED BEHIND THIS
COLD FRONT WITH THE FIRST HINT OF SNOW POSSIBLE JUST BEYOND THIS
PERIOD IN THE NORTHWEST AND NORTHERN MOUNTAINS.

LONG TERM...THURSDAY NIGHT THROUGH MONDAY
THURSDAY NIGHT AND FRIDAY WILL CONTINUE TO SEE THE EFFECTS OF A
LARGE PACIFIC TROUGH WITH WINDY CONDITIONS ACROSS THE CWA AND
SHOWERS AND THUNDERSTORMS IN THE NORTH...PARTICULARLY IN THE
NORTHWEST MOUNTAINS AND THE BIGHORNS.  12Z ECMWF IS MORE PROGRESSIVE
WITH THIS FEATURE BUT HAVE LEFT POPS IN THROUGH FRIDAY MORNING FOR
THE BIGHORNS.  A LIGHT DUSTING OF SNOW IS NOT OUT OF THE QUESTION
FOR THE HIGHEST ELEVATIONS OF NORTHERN WYOMING.  DRIER CONDITIONS
FOLLOW WITH NORTHWEST FLOW RESUMING.  A MORE RELAXED PRESSURE
GRADIENT WILL ALLOW FOR LIGHTER WIND BY SATURDAY.  MEDIUM RANGE
MODELS IN GOOD AGREEMENT BUILDING A LARGE RIDGE OVER THE WESTERN
CONUS ON SUNDAY BRINGING ABOUT A WARMING TREND AND CONTINUED DRY
CONDITIONS.  RIDGE BUILDING ALLOWS FOR MONSOON MOISTURE TO INCH ITS
WAY BACK TOWARD THE AREA MONDAY.  CONFIDENCE IS LOW THIS FAR OUT ON
BRINGING THE MOISTURE INTO SOUTHERN WYOMING IN TIME FOR MAXIMUM
HEATING MONDAY WILL WILL TAKE A WAIT AND SEE STANCE ON CONVECTIVE
POTENTIAL FOR MONDAY UNTIL FURTHER MODEL RUNS CAN BE MONITORED.

AVIATION...
VFR CONDITIONS CAN BE EXPECTED THROUGH THE FORECAST PERIOD FOR MOST
OF WESTERN AND CENTRAL WYOMING.  OCCASIONAL PERIODS OF MVFR VSBY IS
POSSIBLE IN AREAS OF ISOLATED SHOWERS AND THUNDERSTORMS THROUGH
06Z.  BREEZY TO WINDY CONDITIONS WILL DEVELOP AFTER 18Z TUESDAY
ALONG THE KRKS TO KCPR CORRIDOR.  20 TO 30 KT WIND WILL BE POSSIBLE
ALONG THE RIDGETOPS OF WESTERN WYOMING AND IN THE AREA OF KJAC AND
KAFO.

FIRE WEATHER...
FIRE WEATHER CONCERNS WILL BE ON THE INCREASE THE NEXT COUPLE DAYS
AS A WARMER...DRIER AND BREEZY TO WINDY PATTERN DEVELOPS. THE
HIGHEST POTENTIAL FOR EXTREME FIRE WEATHER CONDITIONS WILL BE OVER
FIRE ZONES 280 AND 283 TUESDAY AFTERNOON AND EARLY EVENING WHEN
TEMPERATURES AROUND 90 COMBINE WITH MIN RH'S AS LOW AS 12-15
PERCENT AND SOUTHWEST WINDS OF 15 TO 20 MPH WITH GUSTS UP TO 30
MPH. MORE WIDESPREAD CRITICAL FIRE WEATHER CONDITIONS ARE POSSIBLE
ON WEDNESDAY IN MANY AREAS AND ACROSS THE SOUTHERN ZONES ON
THURSDAY AHEAD OF A SHARP COLD FRONT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM TUESDAY AFTERNOON THROUGH TUESDAY
EVENING WYZ280-283.

&&

SHORT TERM...SKRBAC
LONG TERM...BERC
AVIATION...BERC
FIRE WEATHER...SKRBAC

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
216 PM MDT MON AUG 29 2011

WYZ001>020-022>030-301200-
ABSAROKA MOUNTAINS-BIGHORN MOUNTAINS SOUTHEAST-
BIGHORN MOUNTAINS WEST-CASPER MOUNTAIN-CODY FOOTHILLS-
EAST SWEETWATER COUNTY-FLAMING GORGE-
GREEN MOUNTAINS AND RATTLESNAKE RANGE-JACKSON HOLE-LANDER FOOTHILLS-
NATRONA COUNTY LOWER ELEVATIONS-NORTH BIG HORN BASIN-
NORTHEAST JOHNSON COUNTY-OWL CREEK AND BRIDGER MOUNTAINS-
ROCK SPRINGS AND GREEN RIVER-SALT RIVER AND WYOMING RANGES-
SOUTH LINCOLN COUNTY-SOUTHEAST BIG HORN BASIN-
SOUTHEAST JOHNSON COUNTY-SOUTHWEST BIG HORN BASIN-STAR VALLEY-
TETON AND GROS VENTRE MOUNTAINS-UPPER GREEN RIVER BASIN-
UPPER GREEN RIVER BASIN FOOTHILLS-UPPER WIND RIVER BASIN-
WIND RIVER BASIN-WIND RIVER MOUNTAINS EAST-WIND RIVER MOUNTAINS WEST-
YELLOWSTONE NATIONAL PARK-
216 PM MDT MON AUG 29 2011

...FIRE WEATHER WATCHES ARE IN EFFECT FROM 1 PM TO 8 PM TUESDAY
FOR FIRE ZONES 280 AND 283...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

ISOLATED TO WIDELY SCATTERED THUNDERSTORMS ARE EXPECTED ACROSS
WESTERN AND CENTRAL WYOMING...ESPECIALLY DURING THE AFTERNOON
AND EVENING HOURS. THE STRONGEST STORMS ARE EXPECTED TO OCCUR ACROSS
NORTHERN WYOMING. HAIL...STRONG WINDS...AND DANGEROUS CLOUD TO GROUND
LIGHTNING WILL BE THE MAIN HAZARDS.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

ELEVATED FIRE WEATHER BEHAVIOR IS POSSIBLE TUESDAY AND WEDNESDAY...
DUE TO VERY WARM TEMPERATURES...LOW RELATIVE HUMIDITY AND WINDY
CONDITIONS.

EXTREME FIRE WEATHER BEHAVIOR COULD EVEN OCCUR THURSDAY OVER
SOUTHWEST AND SOUTHERN SECTIONS...AS A MAINLY DRY COLD FRONT MOVES
ACROSS THAT AREA.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT ANY SIGNIFICANT WEATHER.

TEAM RIVERTON

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