Flood in Wyoming, May 15 to 19, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
305 AM MDT SUN MAY 15 2011

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

WEAK EASTERLY UPSLOPE FLOW CONTINUES EAST OF THE CONTINENTAL DIVIDE
THIS MORNING BRINGING A LOW TO MID LEVEL STRATUS DECK TO MANY
AREAS.  CLOUD TOPS HAVE SHOWN A WARMING TREND AND CONVECTIVE CLOUDS
IN WESTERN WYOMING AND ACROSS IDAHO AND UTAH HAVE DIMINISHED IN
COVERAGE.  SOME CLOUD EROSION HAS BEEN SEEN OVER EASTERN SOUTH
DAKOTA SO HAVE LEFT PATCHY FOG IN THE FORECAST FOR THE BIG HORN
BASIN AND JOHNSON AND NATRONA COUNTIES SHOULD THE STRATUS ERODE OVER
THOSE AREAS LATER THIS MORNING.  WYOMING REMAINS SANDWICHED BETWEEN
A LARGE BUBBLE OF HIGH PRESSURE OVER SOUTH CENTRAL CANADA AND A
LARGE UPPER LOW JUST OFF SHORE OF NORTHERN CALIFORNIA.  WARM
ADVECTION FROM THE SOUTHWEST WILL BRING WARMER TEMPS TO THE SOUTH
AND WEST TODAY.  WHILE MOST OF THE INSTABILITY ASSOCIATES WITH THIS
SYSTEM WILL REMAIN TO THE WEST AND NORTHWEST...SOME SHOWERS AND
THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON ACROSS THE WESTERN
MOUNTAINS AS UPPER DIFLUENCE ACROSS THE REGION INCREASES THE
OPPORTUNITY FOR CONVECTION TO DEVELOP.  WARMER TEMPERATURES ARE
EXPECTED EAST OF THE CONTINENTAL DIVIDE BUT IF CLOUD COVER
PERSISTS...TEMPERATURES WILL REMAIN WELL BELOW NORMAL.  A FLOOD
WATCH REMAINS IN EFFECT FOR THE SALT RIVER IN STAR VALLEY WITH THE
POSSIBILITY OF WARM TEMPERATURES AND RAIN TO FALL ON THE SNOWPACK.
CONFIDENCE IN CONVECTION DIRECTLY AFFECTING THIS AREA IS LOW BUT IF
STORMS DEVELOP OVER THIS AREA...THE RIVER WILL NEED TO BE WATCHED
FOR RISES.  A SHORTWAVE ROTATING ABOUT THE WESTERN LOW WILL BRUSH BY
WESTERN WYOMING EARLY MONDAY INCREASING COVERAGE OF PRECIPITATION IN
THE WESTERN MOUNTAINS.  UPPER FLOW BACKS TO THE SOUTH MONDAY NIGHT
AS THE LOW MOVES ASHORE AND BRINGS COLD ADVECTION ALOFT...BRINGING
SNOW SHOWERS TO THE WESTERN MOUNTAINS AND DESTABILIZING AREAS EAST
OF THE DIVIDE OF TUESDAY.  SCATTERED SHOWERS WITH A FEW EMBEDDED
THUNDERSTORMS ARE POSSIBLE DURING THE DAY TUESDAY.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

THE LONG RANGE MODELS ARE IN FAIRLY GOOD AGREEMENT ON WEDNESDAY.
AN UPPER TROUGH IS STILL FORECAST TO MOVE INTO THE ROCKIES WEDNESDAY
WITH THE UPPER LOW NEAR THE FOUR CORNERS AT 00Z THURSDAY. THEN
DIFFERENCES OCCUR ON WHERE THIS SYSTEM WILL GO WEDNESDAY NIGHT
THROUGH FRIDAY. THE GFS MODEL TAKES THE STORM TO NORTHEAST COLORADO
AT 00Z FRIDAY AND THEN NORTH TO SE WY/WRN NEBRASKA PANHANDLE AT 00Z
SATURDAY. THE GEM MODEL HAS A FARTHER SOUTH TRACK AND PLACES THE
UPPER LOW IN WESTERN KANSAS AT 00Z SATURDAY. THE ECMWF CONTINUES TO
BE ODD WITH A NORTH TRACK FROM THE FOUR CORNERS TO SOUTHWEST WY AT
00Z FRIDAY AND NORTH TO NW WY AT 00Z SATURDAY. THE UKMET AT 00Z
SATURDAY PLACES THE UPPER LOW ALONG THE WY/CO BORDER. IT SEEMS A BIT
EARLY TO KNOW WHERE THIS STORM WILL EVENTUALLY GO AND SOME OF THE
GFSENSEMBLE MEMBERS LEAN TOWARD THE OPERATIONAL 00Z GFS POSITION AT
12Z FRIDAY NEAR SE WY/NE CO. I HAVE RAISED THE PRECIP CHANCE WED
THROUGH FRI WITH THE POTENTIAL FOR A DECENT RAIN AND HIGH ELEVATION
SNOW EVENT FOR AREAS EAST OF THE DIVIDE. THE WEST WOULD SEE MORE
SCATTERED PRECIP AFTER WEDNESDAY ONCE THE STORM CROSSES THE DIVIDE.
THE STORM THEN MOVES EAST INTO THE PLAINS SATURDAY PER THE GFS MODEL
WHILE THE ECMWF IS STILL AN OUTLIER SPINNING THE STORM INTO MONTANA.
WENT WITH LOW PRECIP CHANCE SATURDAY. NEXT SUNDAY LOOKS MOSTLY DRY
WITH HIGH PRESSURE MOVING INTO THE REGION. TEMPS WILL BE COOLING
DOWN WED THROUGH FRIDAY AND WOULD NEED TO GO COLDER IF THE STORM
INDEED DOES IMPACT OUR AREA DURING THAT TIMEFRAME. THEN TEMPS TO
WARM NEXT WEEKEND AS THE SUNSHINE RETURNS.

&&

.AVIATION...

WEST OF THE DIVIDE...INSTABILITY WILL INCREASE ALONG THE DIVIDE THIS
AFTERNOON WITH SCATTERED SHOWERS AND THUNDERSTORMS DEVELOPING MAINLY
ALONG THE SPINE OF THE WIND RIVER MOUNTAINS INTO NORTHWEST WYOMING
OR VNCTY KPNA-KJAC LINE ALONG WITH BRIEF MVFR CONDITIONS AND HIGHER
MOUNTAIN OBSCURATIONS.  SHOWER AND THUNDERSTORM ACTIVITY WILL BE
MORE ISOLATED VCNTY KRKS-KBPI AND WESTWARD.  SHOWERS AND
THUNDERSTORMS WILL DECREASE FROM THE SOUTH IN THE EVENING.

EAST OF THE DIVIDE...SOME LINGERING LOW VFR CLOUD DECKS WITH HIGHER
MOUNTAIN OBSCURATIONS WILL DECREASE ALONG THE EAST SLOPES THIS
MORNING LEAVING PREVAILING VFR FEW-SCT110-130 MSL AFTER 16Z.  MOST
OF THE AREA WILL BE STABLE WITH SFC SE WIND AT 10-20KT.  SOME
INSTABILITY ALONG THE DIVIDE WILL RESULT IN SCATTERED SHOWERS
ISOLATED THUNDERSTORMS VCNTY AND WEST OF A KLND-KU25-KCOD LINE.
IMPROVING CONDITIONS ARE EXPECTED AFTER 03Z MONDAY.

&&

.FIRE WEATHER...

SHOWERS AND A FEW THUNDERSTORMS CAN BE EXPECTED TODAY IN THE WESTERN
MOUNTAINS AND POSSIBLY SWEETWATER COUNTY.  WARMER TEMPERATURES WILL
LOWER RH VALUES...PARTICULARLY IN THE SOUTH.  CLOUD COVERAGE WILL
DETERMINE HOW DRY IT GETS EAST OF THE DIVIDE.  IF CLOUD COVER
PERSISTS AS IT HAS THIS MORNING...HUMIDITY WILL STAY UP WITH LOWER
DAYTIME TEMPERATURES.  MONDAY WILL SEE WARMER TEMPERATURE EAST OF
THE DIVIDE WITH GREATER COVERAGE OF SHOWERS AND THUNDERSTORMS
BECOMING SNOW AT HIGH ELEVATIONS MONDAY NIGHT.

FIRE WEATHER STATEMENT...

PLEASE NOTE...THE FIRE WEATHER DISCUSSION WILL BE TEMPORARILY
REPLACED WITH A HYDROLOGY DISCUSSION IN THE AREA FORECAST DISCUSSION
(AFD) FROM MAY 15TH THROUGH JUNE 30TH TO ADDRESS FLOODING CONCERNS.
FIRE WEATHER DISCUSSIONS WILL CONTINUE TO BE AVAILABLE WITH THE FIRE
WEATHER FORECAST (FWF).

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

FLOOD WATCH THROUGH MONDAY MORNING WYZ023.

&&

SHORT TERM...BERC
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BERC

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
400 AM MDT SUN MAY 15 2011

WYZ001>020-022>030-161200-
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-
400 AM MDT SUN MAY 15 2011

...FLOOD WATCH FOR THE SALT RIVER AND TRIBUTARIES IN STAR VALLEY
THROUGH MONDAY MORNING...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

ISOLATED THUNDERSTORMS ARE POSSIBLE OVER THE MOUNTAINS OF WESTERN
WYOMING THIS AFTERNOON AND EVENING.

THE SALT RIVER IS EXPECTED TO RISE TO NEAR BANKFULL STAGE AT 5.5 FEET
SUNDAY...AND CRESTING TO NEAR 5.8 FEET BY LATE MONDAY MORNING. FLOOD
STAGE IS 6.0 FEET.

SNOWMELT RUNOFF IS EXPECTED TO INCREASE AGAIN THIS AFTERNOON FOR
FURTHER RISES IN CREEKS AND STREAMS IN STAR VALLEY THROUGH SUNDAY
MORNING. SCATTERED RAIN SHOWERS ARE ALSO EXPECTED THIS AFTERNOON AND
TONIGHT OVER STAR VALLEY.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

ISOLATED THUNDERSTORMS ARE FORECAST IN FAR WEST WYOMING MONDAY. THEN
COVERAGE OF STORMS WILL INCREASE TUESDAY AND WEDNESDAY OVER THE
REGION AS A STORM SYSTEM BEGINS TO MOVE CLOSER TO WYOMING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT.

TEAM RIVERTON