Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 161720
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1120 AM MDT SAT AUG 16 2014

.UPDATE...
ISSUED AT 1108 AM MDT SAT AUG 16 2014

FIRST STORMS OF THE DAY FIRING ALONG THE ABAJO MOUNTAINS IN
SOUTHEAST UTAH AND ACROSS THE SOUTHERN EXTENT OF THE UNCOMPAHGRE
PLATEAU NEAR DALLAS DIVIDE. THIS ACTIVITY IS EXPECTED TO CONTINUE
THROUGH THIS AFTERNOON AND INTO THE EARLY EVENING HOURS. NO
SIGNIFICANT WAVES AND SHEAR PROFILES REMAIN WEAK...SO STORMS
EXPECTED TO BE SHORT-LIVED AND CONFINED TO THE HIGHER TERRAIN.
EXCEPTION WILL BE ACROSS THE SOUTHERN VALLEYS SOUTH OF THE SAN
JUANS WITH LATEST HRRR RUN SUGGESTIONS A FEW STRONGER STORMS
DRIFTING SOUTH OFF THE SAN JUANS BETWEEN 2 AND 5 PM THIS
AFTERNOON. THIS MAY IMPACT THE DURANGO AND PAGOSA SPRINGS AREAS
WITH GUSTY WINDS...SMALL HAIL AND BRIEF HEAVY RAIN.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 340 AM MDT SAT AUG 16 2014

WATER VAPOR SHOWS DRIER AIR ALOFT ADVECTING ACROSS UTAH AND WRN
COLORADO...BUT ALSO EVIDENT IS AN EMBEDDED DISTURBANCE THAT
MANAGED TO KEEP PERSISTENT NOCTURNAL THUNDERSTORMS IN THE
VICINITY OF KCNY...ARCHES NP...AND MOAB FOR A FEW HOURS. HIGH
PRESSURE OVER UTAH AND WRN COLORADO AND ITS DRIER AIR MASS WILL
BE THE DOMINANT FEATURE TODAY. HOWEVER LOWER LEVEL MOISTURE
(SURFACE DEW POINTS REMAIN AROUND 50F) AND STEEP AFTERNOON LAPSE
RATES WILL TRIGGER SOME AFTERNOON CONVECTION. THE AIR MASS IS
DRIER TODAY AS PRECIPITABLE WATER VALUES HAVE DROPPED TO THREE
QUARTERS OF AN INCH (PER KGJT SOUNDING). AREAL COVERAGE OF STORMS
WILL BE LESS NUMEROUS THAN FRIDAY AFTERNOON. NO DISTURBANCE IS
EVIDENT IN THE MODEL DATA...SO STRONG SURFACE HEATING WILL BE THE
PRIMARY TRIGGER MECHANISM.

A DISTURBANCE PASSES THROUGH THE CANADIAN ROCKIES TONIGHT
FLATTENING THE RIDGE. A VERY WEAK ASSOCIATED WAVE PASSES ALONG THE
CO-WY BORDER...BUT MOISTURE LOOKS VERY LIMITED. SO NOCTURNAL
STORMS ARE NOT EXPECTED.

SUNDAY...PRECIPITABLE WATER VALUES ARE AROUND 0.6 INCH WHICH IS
LOW FOR MID AUGUST. ISOLATED AFTERNOON STORMS ARE POSSIBLE OVER
ALL MOUNTAINS WITH LITTLE RAINFALL CHANCE IN THE VALLEYS. STORM
MOTION WILL BE TO THE EAST AT AROUND 15 KTS. AFTERNOON
TEMPERATURES WILL BE A FEW DEGREES ABOVE NORMAL.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 340 AM MDT SAT AUG 16 2014

LITTLE CHANGE IS EXPECTED SUNDAY NIGHT THROUGH MONDAY. THE BROAD
RIDGE IS CENTERED NEAR THE FOUR CORNERS WITH ONLY MARGINAL
RESIDUAL MOISTURE AVAILABLE FOR LATE-DAY STORMS. A TROUGH IS
DEVELOPING ALONG THE WEST COAST. MOISTURE BEGINS TO SURGE INTO SE
UTAH AS EARLY AS MONDAY AFTERNOON OR EVENING. THERE IS STILL SOME
UNCERTAINTY ON THE TIMING AND DEPTH OF THIS MOISTURE SURGE. BUT
THE GFS AND SREF PRODUCE PRECIPITABLE WATER VALUES OVER AN INCH IN
SE UTAH TOWARDS TUESDAY MORNING. HAVE ADDED ISOLATED LATE NIGHT
THUNDERSTORMS SPREADING NORTHWARD ALONG THE UT-CO STATELINE.

INCREASING CONFIDENCE THAT THE MONSOONAL MOISTURE TAP DEEPENS BY
TUESDAY AND WILL LAST INTO NEXT FRIDAY. THE GFS REMAINS THE MOST
AGGRESSIVE MODEL WITH A SIGNIFICANT LONG WAVE TROUGH ALONG THE
WEST COAST THAT STRENGTHENS THE SOUTHERLY COMPONENT. WITH
TIME...ENERGY EMBEDDED IN THE WESTERLIES ABSORBS THE CLOSED LOW
WITH SHORT WAVE ENERGY MOVING ACROSS THE GREAT BASIN TOWARD THE
CENTRAL ROCKIES. THE ECMWF MODEL SHOWS THE MID LEVEL CLOSED LOW
CIRCULATION ALONG THE CENTRAL CALIFORNIA COAST...ALLOWING FOR A
MONSOONAL MOISTURE INTO UTAH AND COLORADO. BUT THE ECMWF ALLOWS
THE CLOSED LOW TO RETROGRADE WESTWARD. SOME UNCERTAINTY ON HOW
THIS EVOLVES NEXT WEEK AND THIS WILL DICTATE THE STRENGTH OF THIS
MONSOONAL SURGE AND AREAL COVERAGE OF THUNDERSTORMS AND NOCTURNAL
STORM ACTIVITY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1108 AM MDT SAT AUG 16 2014

ISOLATED THUNDERSTORMS WILL CONTINUE ACROSS THE HIGHER TERRAIN
THROUGH 03Z THIS EVENING. A FEW STORMS WILL DRIFT SOUTH OFF THE
SAN JUAN MOUNTAINS...POSSIBLY IMPACTING KDRO AND KPSO. GUSTY WINDS
TO 45 MPH...SMALL HAIL AND BRIEF HEAVY RAINFALL WILL BE POSSIBLE
WITH ANY STORMS. KTEX...KDRO AND KPSO WILL SEE A 30 PERCENT CHANCE
OF THUNDERSTORMS THROUGH 03Z THIS EVENING...OTHERWISE...VFR
CONDITIONS CONTINUE.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...NONE.
UT...NONE.
&&

$$

UPDATE...JDC
SHORT TERM...PF/JOE
LONG TERM...JOE/PF
AVIATION...JDC



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