Severe Thunderstorm Warning 13, NWS Grand Junction, CO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
216 PM MDT SUN JUN 21 2009

.SHORT TERM...TONIGHT THROUGH TUESDAY...
SOMEWHAT ACTIVE DAY ACROSS THE NORTHERN HALF OF THE FORECAST
AREA AS CONVECTION STARTED FIRING BEFORE 7 AM AND HAS YET TO
YIELD TO THE DRIER AIRMASS SPREADING NORTHEAST. SCATTERED CONVECTION
FIRING ON THE EDGE OF THE DEEPER MOISTURE...WHICH IS VERY EVIDENT
IN WV IMAGERY...ESPECIALLY WHEN OVERLAYING THE LIGHTNING DATA.
SEVERAL STORMS HAVE PRODUCED HAIL BETWEEN PEA SIZE AND ONE HALF INCH
OVER OUR CWA...WITH MOST ACTIVITY FOCUSED OVER MOFFAT AND ROUTT
COUNTIES.  SECOND SURGE OF ACTIVITY COMING OFF THE WASATCH AND INTO
NORTHEAST UTAH NEAR A WEAK MID LEVEL IMPULSE LIFTING NORTHEAST
TOWARD SOUTHWEST WYOMING. STEEP MID LEVEL LAPSE RATES AND NICELY
SHEARED ENVIRONMENT WILL CONTINUE TO SUPPORT STRONGER CELLS THROUGH
LATE THIS AFTERNOON...ALTHOUGH SOMEWHAT CONCERNED THAT GROWING CIRRUS
BLOW-OFF FROM EARLIER STORMS WILL START TO DIMINISH UPDRAFT
STRENGTH...KEEPING HAIL SIZES UNDER THE SEVERE ONE INCH CRITERIA.
STILL POTENTIAL EXISTS FOR AN ISOLATED SEVERE STORM OR TWO THROUGH
EARLY THIS EVENING...MAINLY ACROSS DAGGATT...UINTAH...MOFFAT AND
ROUTT COUNTIES. AS DRIER AIR CONTINUES TO WORK NORTH THIS EVENING...
CONVECTION WILL QUICKLY DIMINISH...WITH CLEAR SKIES EXPECTED OVER
MOST OF THE FORECAST AREA BY MIDNIGHT.

DRY CONDITIONS THEN EXPECTED TO DOMINATE THE FORECAST AREA THROUGH
MONDAY NIGHT WITH HEIGHTS RISING IN RESPONSE TO STRENGTHENING HIGH
PRESSURE OVER THE PLAINS. MOISTURE STARTS TO WORK BACK NORTH INTO
THE REGION BY TUESDAY REACHING THE FOUR CORNERS EARLY IN THE DAY...
SPREADING NORTHEAST BY AFTERNOON. HAVE INCREASED POPS FOR TUESDAY
AND DROPPED MAX TEMPS SLIGHTLY IN EXPECTATION OF MORE CLOUD COVER
AND INCREASE SFC MOISTURE. STILL SHOULD BE ABLE TO BREAK THAT 90
DEGREE MARK IN THE GRAND VALLEYS...AND MOST LOCATIONS WILL SEE THEIR
WARMEST DAYS SO FAR THIS SEASON.

.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...

MODELS CONTINUE TO INDICATE A NORTHWARD SURGE OF MOISTURE ACROSS THE
FORECAST AREA AFTER MIDWEEK...AS A LARGE MS VALLEY AND GULF COAST
RIDGE WORKS WESTWARD. MODELS DIFFER...HOWEVER...ON THE HANDLING OF
THE PERSISTENT WEST COAST TROUGH WHICH NOW FORMS A CLOSED LOW OFF
THE SRN CA COAST AT MIDWEEK. 12Z GFS THE FASTEST AT EJECTING THIS
LOW NE THU-FRI...WHILE 21/12Z ECWMF DOES NOT BRING IT ACROSS
THE GREAT BASIN UNTIL THE WEEKEND. ECMWF ESPECIALLY WOULD BE A
FAVORABLE PATTERN FOR MOISTURE TRANSPORT NORTHWARD. WILL LEAN TOWARD
THE SLOWER ECWMF AT THE MOMENT. THEREFORE...ANTICIPATE AN INCREASING
CHANCE OF SHOWERS-THUNDERSTORMS LATER IN THE WEEK. SLIGHT DIP IN
TEMPS LATE IN THE WEEK AS WELL WITH AN INCREASE IN CLOUD COVER.

&&

.AVIATION...
SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS NORTHWEST
COLORADO AND NORTHEASTERN UTAH THROUGH 03Z THIS EVENING. A FEW
STORMS WILL PRODUCE HAIL UP TO THREE QUARTERS OF AN INCH...BRIEF
HEAVY RAIN...AND GUSTY WINDS TO 50 MPH...WITH LOCAL MVFR CIGS AND
VSBYS. CONDITIONS WILL IMPROVE AFTER 03Z. VFR CONDITIONS EXPECTED
OVER THE ENTIRE REGION ON MONDAY WITH HIGH PRESSURE BUILDING IN.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

SHORT TERM.....JDC
LONG TERM......JAD
AVIATION.......JDC

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
425 AM MDT SUN JUN 21 2009

COZ001>014-017>023-UTZ022>025-027>029-220100-
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-
425 AM MDT SUN JUN 21 2009

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

.DAY ONE...TODAY AND TONIGHT...

SCATTERED THUNDERSTORMS WILL MOVE NORTH AND OUT OF THE AREA BY
EARLY THIS AFTERNOON AS AN UPPER LEVEL DISTURBANCE EXITS THE
FORECAST AREA TO THE NORTH. EXPECT BRIEF HEAVY SHOWERS...
OCCASIONAL LIGHTNING AND LOCAL SMALL HAIL FROM THESE STORMS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY...

EXPECT ISOLATED AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS OVER
THE VALLEYS...WITH SCATTERED SHOWERS AND THUNDERSTORMS OVER THE
MOUNTAINS EACH DAY. BRIEF HEAVY RAINFALL...SMALL HAIL AND GUSTY WINDS
WILL OCCUR WITH THE STRONGER STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED TODAY OR TONIGHT.

CJC

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
434 PM MDT SUN JUN 21 2009

COZ001-002-UTZ024-212330-
CENTRAL YAMPA RIVER BASIN-EASTERN UINTA BASIN-LOWER YAMPA RIVER
BASIN-
434 PM MDT SUN JUN 21 2009

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN UINTAH...NORTHWESTERN RIO
BLANCO AND WESTERN MOFFAT COUNTIES UNTIL 530 PM MDT...

AT 434 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM 30 MILES NORTH OF DINOSAUR...OR 39 MILES EAST OF
NAPLES...MOVING NORTHEAST AT 40 MPH.

PENNY SIZE HAIL IS EXPECTED WITH THIS STORM.

PF

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
436 PM MDT SUN JUN 21 2009

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0351 PM     HAIL             MAYBELL                 40.52N 108.08W
06/21/2009  E1.00 INCH       MOFFAT             CO   CO-OP OBSERVER

0420 PM     HAIL             12 NW CRAIG             40.64N 107.71W
06/21/2009  E1.25 INCH       MOFFAT             CO   TRAINED SPOTTER

&&

JDC

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