Severe Thunderstorm Warning 13, NWS Grand Junction, CO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
300 PM MDT SAT JUN 12 2010

.SHORT TERM...TONIGHT THROUGH MONDAY...

STRONG CLOSED LOW CIRCULATION CENTERED OVER THE LOWER COLORADO RIVER
BASIN TRIGGERING WIDESPREAD CONVECTION ACROSS THE COUNTY WARNING
AREA TODAY.  THE COMBINATION OF THE BAROCLINIC ZONE CROSSING THE
WESTERN SLOPE TODAY AND THE JET CORE ROUNDING THE BASE OF THE TROUGH
CAUSING STRONG UPWARDS MOTION.  WIDESPREAD SHOWERS HAVE STABILIZED
THE AIR MASS ACROSS NWRN COLORADO...BUT SE UTAH AND EXTREME SW
COLORADO AND UPSTREAM AREAS LIKE NRN ARIZONA HAS HAD MORE SURFACE
HEATING AND EXPECT SOME STRONG CELLS TO FORM.  MARGINAL SEVERE
STORMS WILL BE POSSIBLE GIVEN THE CURRENT SHEAR.  EARLIER SEVERE
STORM THAT DEVELOPED OVER OURAY COUNTY AND TRACKED ACROSS MONTROSE
AND ERN DELTA COUNTY SHOWED PRONOUNCED OVERHANGING TOP...BUT THE
STORM HEIGHT WAS RELATIVELY LOW INDICATING THAT STORMS ARE LOW
TOPPED.  SNOW LEVELS TO DROP AROUND 8000 FEET OVERNIGHT BUT
ACCUMULATIONS WILL BE SPOTTY AS SHOWERS TAPER OFF.  SOME MOUNTAIN
PASSES WILL BECOME SLIPPERY AS SOME SLUSH FORMS ON THE HIGHWAYS.
WILL ADDRESS THIS WITH A SPECIAL WEATHER STATEMENT...BUT THIS WILL
NEED TO MONITOR FOR POSSIBLE LATE SEASON WINTER WEATHER ADVISORY.

CLOSED UPPER LOW WEAKENS AS IT EJECTS ACROSS NE UTAH ON SUNDAY AND
THE STRONGER GRADIENT FLOW WILL HAVE SHIFTED EAST OF THE DIVIDE.
EXPECT LOW TOP CONVECTION TO FOLLOW THE CLOSED LOW AND EXPECT
NUMEROUS SHOWERS NORTH OF I70.  SEVERE STORMS NOT EXPECTED GIVEN THE
LACK OF SHEAR...BUT CANNOT BE COMPLETELY RULED OUT.

MONDAY...THE MAIN CLOSED LOW WILL HAVE REFORMED OVER THE DAKOTA
STATES.  THE GFS SHOWS A SECONDARY VORT CENTER SWINGING THROUGH THE
WESTERN SLOPE MONDAY MORNING...ASSOCIATED WITH THE POSITIVELY TILTED
TROUGH AXIS.  THIS FEATURE COULD TRIGGER ADDITIONAL SHOWERS...BUT
EXPECT DRYING TREND ONCE THE TROUGH AXIS MOVES EAST.  THE MODELS
HINT THAT THE TROUGH MAY BE SLOW TO DRAG ACROSS WRN COLORADO...SO
HAVE BOOSTED POPS TO CHANCE ACROSS THE WESTERN SLOPE MOUNTAINS.

.LONG-TERM...MONDAY NIGHT THROUGH SATURDAY...

MEAN LONG WAVE TROUGH EXPECTED TO HOLD ALONG THE WEST COAST THROUGH
THIS PERIOD. THIS WILL KEEP ERN UT AND WRN CO UNDER SOUTHWEST AND
GENERALLY DRY FLOW ALOFT. GFS AND ECWMF APPEAR TO BE COMING INTO
BETTER TIMING AGREEMENT ON LIFTING A SHORTWAVE TROUGH OUT OF THE
GREAT BASIN AND ACROSS THE NORTHERN ROCKIES...WITH THE SRN EXTENT OF
THE TROUGH SWEEPING ACROSS NE UT/NW CO ABOUT THURSDAY. MODELS KEEP
MOISTURE CONCENTRATED NEAR THE LOW CENTER AND SPARSE OVER OUR AREA
...SO WILL KEEP THE CURRENT SLIGHT CHANCE OF THUNDERSTORMS FOR THE
MTNS WED-THU. MAY SEE SOME SMALL EMBEDDED DISTURBANCES IN THE SW FLOW
FOR NEXT WEEKEND AS ANOTHER TROUGH DROPS DOWN OVER THE PAC NW.
TEMPERATURES SHOULD AVERAGE NEAR NORMAL.

&&

.AVIATION...

WIDESPREAD SHOWERS WITH SCATTERED THUNDERSTORMS WILL BLANKET MUCH
OF WESTERN COLORADO AND EASTERN UTAH THROUGH EARLY SUNDAY.  EXPECT
WIDESPREAD MVFR CIGS TODAY AND TONIGHT...ESPECIALLY OVER THE
MOUNTAINS WITH LOCAL IFR CONDITIONS POSSIBLE NEAR THE STRONGER
SHOWERS AND THUNDERSTORMS.  SNOW LEVELS WILL TEMPORARILY FALL TO
8000 FEET BETWEEN 06Z-15Z LATE TONIGHT AND EARLY SUNDAY MORNING.

&&

.HYDROLOGY...

FLOWS CONTINUED TO GRADUALLY DECREASE ALONG MANY OF THE HEADWATER
STREAMS AND CREEKS IN NORTH-CENTRAL COLORADO AND NORTHEASTERN UTAH.
THE RETURN OF COOLER TEMPERATURES COMBINED WITH THE DEPLETION OF
SNOWPACK IN THE MOUNTAINS OF NORTHEASTERN UTAH AND NORTH-CENTRAL
COLORADO WILL RESULT IN DECREASED FLOWS AND LOWERING RIVER LEVELS.
HOWEVER...THE ONGOING POTENTIAL FOR SHOWERS IN THE COLORADO RIVER
HEADWATERS REGION AND THE YAMPA RIVER HEADWATERS REGION IS BEING
CLOSELY MONITORED.

RECREATIONALISTS SHOULD USE CAUTION WHEN BOATING AND RAFTING IN THE
COLD...FAST FLOWING RIVER WATERS. LARGE QUANTITIES OF DEBRIS HAVE
BEEN OBSERVED IN MANY RIVERS. ALSO...THE HIGH WATERS CAN QUICKLY
ERODE RIVER BANKS MAKING THEM UNSTABLE TO WALK ON OR NEAR.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

.CO....NONE.
.UT....NONE.

SHORT TERM.....PF
LONG TERM......JAD
AVIATION.......TGJT
HYDROLOGY......TGJT

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
550 AM MDT SAT JUN 12 2010

COZ001>014-017>023-UTZ022>025-027>029-131145-
ANIMAS RIVER BASIN-ARCHES/GRAND FLAT-CANYONLANDS/NATURAL BRIDGES-
CENTRAL COLORADO RIVER BASIN-
CENTRAL GUNNISON AND UNCOMPAHGRE RIVER BASIN-
CENTRAL YAMPA RIVER BASIN-DEBEQUE TO SILT CORRIDOR-
EASTERN UINTA BASIN-EASTERN UINTA MOUNTAINS-
ELKHEAD AND PARK MOUNTAINS-FLAT TOPS-
FOUR CORNERS/UPPER DOLORES RIVER-
GORE AND ELK MOUNTAINS/CENTRAL MOUNTAINS-GRAND AND BATTLEMENT MESAS-
GRAND VALLEY-LA SAL AND ABAJO MOUNTAINS-LOWER YAMPA RIVER BASIN-
NORTHWEST SAN JUAN MOUNTAINS-PARADOX VALLEY/LOWER DOLORES RIVER-
ROAN AND TAVAPUTS PLATEAUS-SAN JUAN RIVER BASIN-SOUTHEAST UTAH-
SOUTHWEST SAN JUAN MOUNTAINS-TAVAPUTS PLATEAU-
UNCOMPAHGRE PLATEAU AND DALLAS DIVIDE-UPPER GUNNISON RIVER VALLEY-
UPPER YAMPA RIVER BASIN-WEST ELK AND SAWATCH MOUNTAINS-
550 AM MDT SAT JUN 12 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN UTAH AND WESTERN
COLORADO.

.DAY ONE...TODAY AND TONIGHT

NUMEROUS SHOWERS AND THUNDERSTORMS WILL OCCUR ACROSS WESTERN COLORADO
AND EASTERN UTAH THROUGH TONIGHT. GUSTY WINDS TO NEAR 50 MPH...HAIL
UP TO ONE INCH IN DIAMETER AND HEAVY RAIN WILL ACCOMPANY THE
STRONGEST STORMS.

MANY CREEKS...STREAMS AND RIVERS ACROSS WESTERN COLORADO AND
NORTHEAST UTAH WILL CONTINUE TO RUN FAST AND HIGH...WITH SEVERAL
RUNNING NEAR BANKFULL THROUGH TONIGHT.

PLEASE VISIT THE NATIONAL WEATHER SERVICE GRAND JUNCTION WEBSITE AT
WEATHER.GOV/GJT FOR THE LATEST WEATHER INFORMATION.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE CHANCE FOR THUNDERSTORMS WILL CONTINUE THROUGH SUNDAY AND OVER
THE NORTH ON MONDAY. DRIER CONDITIONS ARE THEN EXPECTED FOR REMAINDER
OF THE WEEK.

RIVERS ARE EXPECTED TO SLOWLY DECREASE INTO EARLY NEXT WEEK AS
TEMPERATURES REMAIN BELOW NORMAL THROUGH TUESDAY.

.SPOTTER INFORMATION STATEMENT

SPOTTER ACTIVATION MAY BE NEEDED TODAY DUE TO STRONG THUNDERSTORMS.

TGJT

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