High Wind Warning 10, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
314 AM MDT FRI MAY 28 2010

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
COMPLEX CLOSED UPPER LOWS SPINNING OVER THE WESTERN WESTERN STATES
EARLY THIS MORNING. THESE CIRCULATIONS WILL GRADUALLY MORPH INTO
ONE CIRCULATION LATER TODAY. NUMERICAL MODEL SOLUTIONS IN GOOD AGREEMENT
THROUGH TODAY WITH THE MUCH STRONGER SOUTHERN SHORT-WAVE TROUGH/VORT
LOBE OVER CENTRAL CALIFORNIA LIFTING NORTHEASTWARD THROUGH WESTERN
WYOMING THIS EVENING. THE ASSOCIATED STRONG SURFACE COLD FRONT
WILL MOVE THROUGH AREAS WEST OF THE DIVIDE THIS AFTERNOON WITH
WIDESPREAD RAIN AND HIGH MOUNTAIN SNOWFALL EXPECTED THROUGH MID EVENING.
MODEL SOLUTIONS DIVERGE TONIGHT AND SATURDAY MORNING...WITH THE
GFS FASTER AND MUCH DRIER THAN THE 00Z NAM AND ECMWF SOLUTIONS. LOWERED
PRECIP CHANCES SATURDAY AFTERNOON AND EVENING...COMPROMISING
BETWEEN THE SLOWER AND WETTER ECMWF AND THE BONE DRY GFS GIVEN THE
THIS UNCERTAINTY. MOST GLOBAL MODEL SOLUTIONS LEANING TOWARD A
FARTHER NORTH SOLUTION WHICH WOULD LEND SOME CREDENCE TO THE GFS
AND THE FASTER WEST TO EAST JET LEVEL FLOW OVER WYOMING. ECMWF HAS
BEEN QUITE CONSISTENT...HOWEVER...THE PAST SEVERAL DAYS WITH THE
WETTER SOLUTION...BUT TRENDING DRIER AND FARTHER NORTH WITH THE
CLOSED H7 AND H5 CIRCULATIONS. FLOOD WATCH STILL A POSSIBILITY FOR
JOHNSON COUNTY FOR SATURDAY AND SATURDAY EVENING...BUT SEEMS LESS LIKELY
WITH LOCAL QPF AMOUNTS IN THE WETTEST OF SOLUTIONS BELOW THREE
QUARTERS OF AN INCH. THE DAY SHIFT CAN TAKE A LOOK AT THE 12Z SOLUTIONS
WITH PLENTY OF ONSHORE DATA AVAILABLE AS THE CLOSED LOW AND
NORTHWEST JET MOVE INLAND THIS MORNING. LOWERED PRECIPITATION
CHANCES FOR SUNDAY AND SUNDAY NIGHT...ESPECIALLY EAST OF THE
DIVIDE WITH ONLY A WEAK...SLIGHTLY UNSTABLE...CYCLONIC WESTERLY
FLOW REMAINING IN ALL GLOBAL MODEL PROGS OVER CENTRAL WYOMING.

.LONG TERM...MEMMORIAL DAY THROUGH FRIDAY
MEMORIAL DAY LOOKS MOSTLY DRY WITH A SLIGHT CHANCE OF MOUNTAIN
SHOWERS AND STORMS AS WELL ACROSS LOWER ELEVATIONS NORTHERN WY.
THIS IS WHERE THE BEST INSTABILITY WILL BE AS WELL AS LOW LEVEL
MOISTURE. THE ACTIVITY WILL LINGER INTO THE EVENING HOURS WITH
ONLY ISOLATED SHOWERS AFTER MIDNIGHT. A SHORTWAVE MOVES INTO THE
WESTERN STATES ON TUE AND INTO WESTERN WY WY TUE NIGHT. THIS WILL
LEAD TO A HIGHER CHANCE OF SHOWERS AND STORMS IN THE WEST. EAST OF
THE DIVIDE A SLIGHT CHANCE OF SHOWERS AND STORMS IN THE NORTH AND
EAST PORTION OF THE CWA IN THE TUE AFTERNOON...THEN POSSIBLY A
LITTLE BETTER COVERAGE TUE NIGHT AS THE SYSTEM MOVES ACROSS WY.
GFS IS SLOWER THAN THE ECMWF MODEL ON WED IN MOVING THE SHORTWAVE
OUT OF THE REGION. THIS WOULD LEAD TO A SLIGHT CHANCE OF STORMS IN
THE EAST ZONES WED PM WITH LESS ACTIVITY ELSEWHERE. MADE MINOR
CHANGES TO THE FORECAST. THE LONG RANGE MODELS DIFFER THURS AND
FRI WITH RESPECT TO TEMPS AND PRECIP CHANCE. THE ECMWF IS COOLER
AND WETTER OVER REGION WHILE THE GFS IS DRIER AND WARMER. THE
DIFFERENCE LIES IN THE FACT THAT THE GFS HAS MORE RIDGING OVER THE
INTERMOUNTAIN REGION WHILE THE ECMWF HAS LOWER 500MB HEIGHTS AND
KEEPS MOISTURE STREAMING INTO NW WY. FOR NOW HAVE USED A BLEND IN
SOLUTIONS AND WILL KEEP SLIGHT CHANCE OF AFTERNOON AND EVENING
SHOWERS AND STORMS THURS AND FRI OVER THE MOUNTAINS AND NORTH. AS FOR
TEMPS SEASONAL HIGHS THROUGH TUE THEN COOLER WED. GFS HAS WARMER
TEMPS FORECAST THAN THE ECMWF THURS AND FRI. CHOSE TO LEAN TOWARD
WARMER GFS NUMBERS BUT NOT AS WARM THE MEX GUIDANCE FIGURES.

&&

.AVIATION...
STRONG SOUTH TO SOUTHWEST WINDS ARE EXPECTED TO DEVELOP ONCE AGAIN
OVER MUCH OF THE AREA TODAY BETWEEN 15Z AND 20Z TODAY...AND LAST
THROUGH EARLY EVENING.  THE STRONGEST WINDS ARE EXPECTED TO BE
ACROSS SWEETWATER COUNTY...INCLUDING KRKS TERMINAL WHERE SUSTAINED
WINDS OF 25 TO 35KT WITH GUSTS TO 45KT WILL BE LIKELY. A MAJOR STORM
SYSTEM OVER THE WEST WILL FINALLY BEGIN TO PUSH EAST INTO THE AREA
LATE TODAY THROUGH SATURDAY. THE ASSOCIATED COLD FRONT WILL MOVE
THROUGH LATE THIS AFTERNOON...AND SHOULD BE THROUGH MUCH OF THE
FORECAST AREA BY 06Z SATURDAY.  THE BEST CHANCE FOR SHOWERS AND
ISOLATED THUNDERSTORMS WILL BE OVER THE NORTHWEST THIS AFTERNOON
THROUGH THE NIGHT.  AHEAD OF THE FRONT...DRY CONDITIONS ARE
EXPECTED...BUT ALONG AND BEHIND THE FRONT...THERE WILL BE A CHANCE
FOR SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS.  VFR CONDITIONS
ARE EXPECTED AHEAD OF THE FRONT EXCEPT NEAR CONVECTION. IN WAKE OF
THE FRONT LATE THIS AFTERNOON/TONIGHT...SOME AREAS OF MVFR CEILINGS
ARE EXPECTED TO DEVELOP OVER THE FAR WEST VALLEYS...INCLUDING
KJAC...AS WELL AS AREAS EAST OF THE DIVIDE...ESPECIALLY THE CODY
FOOTHILLS AND JOHNSON COUNTY.

&&

.FIRE WEATHER...
A LARGE PACIFIC STORM SYSTEM WILL MOVE TOWARD THE DISTRICT TODAY.
THE ASSOCIATED SURFACE COLD FRONT AND NUMEROUS SHOWERS WILL PUSH
INTO AREAS WEST OF THE DIVIDE DURING THE AFTERNOON. WINDY
CONDITIONS ARE EXPECTED ONCE AGAIN TODAY ALONG AND EAST OF THE
DIVIDE AS THE COLD FRONT APPROACHES AND STRONG MID-LEVEL FLOW NEAR
MOUNTAIN TOP SURFACES IN THE LOWER ELEVATIONS. STRONG SOUTH TO SOUTHWEST
WIND AND VERY WARM TEMPERATURES ALONG WITH A DRY AIRMASS ARE
ANTICIPATED THIS AFTERNOON FROM EASTERN SWEETWATER COUNTY EAST
INTO NATRONA AND JOHNSON COUNTIES. THE COLD FRONT AND SCATTERED
SHOWERS WILL MOVE THROUGH AREAS EAST OF THE DIVIDE THIS EVENING.

&&

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

&&

SHORT TERM...CHURCH
LONG TERM...AR
AVIATION...WM
FIRE WEATHER...CHURCH

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