Flood Watch 3, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
300 PM MDT WED MAY 18 2011

.SHORT TERM...TONIGHT THROUGH SATURDAY
SHOWERS CONTINUE TO STREAM INTO THE SOUTHERN HALF OF THE STATE
THIS AFTERNOON. AREAS ACROSS THE EXTREME SOUTHWESTERN CORNER OF
THE CWA ARE REPORTING SHOWERS OF MIXED RAIN AND SNOW...WHILE OTHER
AREAS ARE REMAINING RAIN. THE BIG CHALLENGE OF THE CURRENT
FORECAST DEALS WITH THE PROGRESSION AND STRENGTH OF THE
APPROACHING AREA OF LOW PRESSURE.

THE GFS AND NAM MODELS HAVE CONTINUED TO COME FURTHER IN-LINE WITH
EACH OTHER WITH THE 12Z RUN. THE AREA OF LOW PRESSURE...WHICH IS
CURRENTLY LOCATED AROUND CENTRAL UTAH WILL CONTINUE TO DIVE
SOUTHEAST THIS EVENING...APPROACHING THE FOUR CORNERS AREA BEFORE
HEADING EASTWARD. THE CORE OF THE LOW PRESSURE WILL THEN MOVE EAST
THROUGH COLORADO. DURING THIS TIME SNOWFALL...WHICH WILL BE HEAVY
AT TIMES WILL IMPACT THE CENTRAL MOUNTAINS INCLUDING THE ABSAROKA
AND EASTERN SLOPES OF THE WIND RIVER MOUNTAINS.

BY MIDNIGHT...THE AREA OF LOW PRESSURE WILL BEGIN TO LIFT NORTH.
AS WRAP AROUND BEGINS TO DEVELOP...ADDITIONAL AREAS WILL BEGIN TO
EXPERIENCE HEAVIER SNOWFALLS...INCLUDING THE GREEN MOUNTAINS AND
RATTLESNAKE RANGE. THE UPPER WIND RIVER BASIN INCLUDING THE AREA
AROUND DUBOIS WILL ALSO BEGIN TO EXPERIENCE SOME HEAVIER
SNOWFALL...ESPECIALLY NORTHWEST OF DUBOIS. WIDESPREAD SHOWERS WILL
IMPACT THE CWA THURSDAY. MODELS DEMONSTRATE H7 TEMPERATURES OF -5
TO -3 DEGREES CELSIUS TOMORROW. THESE TEMPERATURES REMAIN ON THE
BORDERLINE FOR THE CONVERSION OF RAIN AND SNOW ACROSS THE LOWER
ELEVATIONS OF THE WIND RIVER BASIN AND NATRONA COUNTY. SOME
QUESTION STILL EXISTS OVER THE LANDER FOOTHILLS...WHO REMAIN IN
THEIR WINTER STORM WATCH. CURRENT BELIEF IS THAT ADDITIONAL AREAS
WILL NEED TO BE INCLUDED IN WINTER WEATHER HIGHLIGHTS BY THE
MORNING HOURS...BUT WILL LEAVE TO NEXT CREW TO MAKE THE FINAL
CALL. IN ADDITION TO SNOW CONSIDERATIONS...MODELS CONTINUE TO
INTRODUCE BREEZY TO WINDY CONDITIONS FOR MANY AREAS EAST OF THE
CONTINENTAL DIVIDE FOR THURSDAY AFTERNOON. THIS MAY COMBINE WITH
THE POTENTIAL FOR LIGHT SNOW AND RAIN TO CREATE HAZARDOUS
CONDITIONS.

SHOWER ACTIVITY WILL LINGER WITH THIS SYSTEM THROUGH THE MAJORITY
OF THE FORECAST PERIOD...DUE TO WRAPAROUND AS THE SYSTEM MOVES
NORTH INTO THE NORTHERN PLAINS.

.LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY
MAJOR LATE SEASON STORM WILL LIKELY STILL BE LINGERING AROUND
EASTERN WYOMING ON SATURDAY BEFORE FINALLY MOVING EAST. SNOW WILL
CONTINUE OVER THE NORTHERN MOUNTAINS WITH SCATTERED TO NUMEROUS
RAIN SHOWERS. GRADUAL IMPROVEMENT SATURDAY NIGHT WITH BRIEF
SHORTWAVE RIDGING. ANOTHER STORM IS POSSIBLE EARLY NEXT WEEK. THE
ECMWF IS MOST AGGRESSIVE WITH THIS SYSTEM DEVELOPING ANOTHER CLOSED
CIRCULATION TO OUR SOUTH MONDAY INTO TUESDAY. THE GFS IS MORE OPEN
AND FURTHER NORTH. THIS SYSTEM IS CURRENTLY PASSING JUST SOUTH OF
KAMCHATKA AND THE CURRENT PATTERN WOULD CERTAINLY SUPPORT ANOTHER
CLOSED LOW OVER THE GREAT BASIN AND CENTRAL ROCKIES. WILL KEEP AT
LEAST CHANCE POPS IN DURING THIS PERIOD AND SEE HOW THE TRENDS LOOK
TONIGHT. HIGH TEMPERATURES WILL END UP BEING WAY TOO WARM MONDAY AND
TUESDAY IF THE ECMWF IS CORRECT. I WILL START NUDGING THESE DOWN
FURTHER IF THE EVIDENCE CONTINUES TO SUPPORT THE ECMWF TOMORROW
NIGHT. DRIER AND WARMER ON WEDNESDAY WITH THE NEXT SHORTWAVE RIDGE
MOVING OVERHEAD.

&&

.AVIATION...
RAIN AND MOUNTAIN SNOW WILL IMPACT AREAS EAST OF THE DIVIDE AND OVER
THE SOUTHWEST THROUGH THURSDAY EVENING AS A VERY MOIST STORM SYSTEM
SETS UP OVER THE CENTRAL ROCKIES.  AREAS SUCH AS KRKS...KLND AND
KRIW COULD TURN TO SNOW BY 12Z THU...BUT UNCERTAINTY REMAINS AT THIS
TIME.  SCATTERED SHOWERS ARE POSSIBLE OVER THE FAR WEST.  EXPECT
MVFR AND EVEN IFR CIGS AND VSBYS WITH WIDESPREAD TERRAIN
OBSCURATIONS.  GUSTY NORTHEAST WINDS WILL IMPACT THE AREA AS
WELL...WITH GUSTS 30-40KT OVER SOUTHEAST FREMONT AND SWEETWATER
COUNTIES.

&&

.HYDROLOGY...
COOLER TEMPERATURES WILL PREVAIL FOR THE NEXT COUPLE DAYS AS A
STRONG AREA OF LOW PRESSURE IMPACTS THE FORECAST AREA. THESE
CONDITIONS WILL SLOW SNOWMELT ACROSS WESTERN WYOMING...AND WILL
ALLOW FLOODING CONCERNS TO WEAKEN OVER THIS AREA. THE STORM
FORECAST TO IMPACT MUCH OF THE STATE THURSDAY AND INTO FRIDAY
MAY HAVE A SIGNIFICANT AMOUNT OF LIQUID PRECIPITATION WITH IT TO
IMPACT AREAS EAST OF THE CONTINENTAL DIVIDE. THESE CONDITIONS WILL
CONTINUE TO BE MONITORED FOR THEIR POTENTIAL TO INCREASE WATER LEVELS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM 6 PM THIS EVENING TO NOON MDT FRIDAY
WYZ002-007>009-015.

WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO NOON MDT FRIDAY
WYZ019.

WINTER STORM WATCH FROM THURSDAY MORNING THROUGH FRIDAY MORNING
WYZ018.

WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON MDT FRIDAY
WYZ016.

&&

SHORT TERM...BRANHAM
LONG TERM...SKRBAC
AVIATION...TWB
HYDROLOGY...BRANHAM

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