Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 012249
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
449 PM MDT WED JUL 1 2015

.SHORT TERM...(TONIGHT THROUGH THURSDAY NIGHT)
ISSUED AT 257 PM MDT WED JUL 1 2015

WEAK DISTURBANCE MOVING ACROSS THE WESTERN SLOPE THIS AFTERNOON
AND EVENING WILL BE ENHANCING CONVECTION. SHEAR PROFILE IS VERY
WEAK AND THEREFORE STORM CELLS WILL BE PULSING UP AND DOWN. THE
AIR MASS IS RELATIVELY MOIST (PWAT OF 0.90 ON THE MORNING
SOUNDING)...BUT STORM CHARACTER IS A MIXED BAG. POPULATED DESERT
VALLEY SPOTS WILL BE MORE PRONE TO GUSTY OUTFLOW WINDS. ISOLATED
SPOTS IN THE HIGHER ELEVATIONS...ABOVE 6000 FEET OR EVEN
HIGHER...MAY GET HEAVY SHOWERS THAT LAST FOR 10-20 MINUTES OR SO.
BUT WETTING RAINS WILL NOT BE WIDESPREAD GIVEN THE SMALL SIZE OF
THE DISTURBANCE.

DRIER STABLE AIR FOLLOWS THE DISTURBANCE AND EXPECT STORMS/SHOWERS
TO DISSIPATE FAIRLY QUICKLY ACROSS THE NRN HALF. NOT SO FAST OVER
SW COLORADO WHERE SHOWERS AND ISOLATED STORMS MAY LINGER TO
MIDNIGHT OR PERHAPS LAST A BIT LONGER...EVEN SPILLING INTO SERN
UTAH. THIS IS TYPICAL OF THE SUMMER MONSOON SEASON WHERE LATE
EVENING SHOWERS/STORMS TEND TO BE LOCATED FROM SAN JUAN COUNTY
UTAH...MONTEZUMA AND LA PLATA COUNTIES. BY DAYBREAK...MOSTLY CLEAR
CONDITIONS IS EXPECTED ACROSS THE NORTH WITH CONVECTIVE DEBRIS
CLOUD LINGERING OVER THE FOUR CORNERS REGION.

HORIZONTALLY ELONGATED HIGH PRESSURE WILL HAVE DRIFTED SLIGHTLY
WEST BY THURSDAY ALLOWING SLIGHTLY DRIER AIR TO MOVE BACK INTO
EASTERN UTAH AND WESTERN COLORADO BY THURSDAY EVENING. SHOWER AND
THUNDERSTORM COVERAGE WILL BE GREATLY REDUCED DUE TO MOISTURE
DECREASING AND BECOMING MORE SHALLOW.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 257 PM MDT WED JUL 1 2015

MOISTURE BEGINS TO DRIFT BACK INTO THE REGION FROM THE SOUTH ON
FRIDAY WITH PRECIPITABLE WATER VALUES INCREASING TO 0.75 INCH BY
FRIDAY AND POTENTIALLY HIGHER ON SATURDAY. THE 12Z GFS AND 12Z NAM
ARE QUITE DIFFERENT ON AVAILABLE MOISTURE FORECAST SATURDAY
AFTERNOON BY NEARLY A HALF INCH PWAT DIFFERENCE...SO NOT FEELING
CONFIDENT ON THE PROBABILITY OF HEAVY RAINS AS PREVIOUS MODELS
TRIED TO INDICATE.

MOISTURE FLUCTUATIONS WILL CONTINUE OVER THE NEXT WEEK AS THE
CENTER OF HIGH PRESSURE OVER THE WEST DRIFTS BACK EAST OVER THE
WEEKEND THEN TO THE SOUTH OF UTAH AND COLORADO EARLY NEXT WEEK. NO
CLASSIC LONGER TERM EASTERN UT/WESTERN CO MONSOON SIGNAL PROGGED
YET FOR AT LEAST THE NEXT WEEK WITH HIGH PRESSURE BEING TOO FAR
WEST TO REALLY STREAM SIGNIFICANT MOISTURE INTO THE FORECAST AREA
FOR AN EXTENDED PERIOD OF TIME. MONDAY IS THE ONE EXCEPTION
TO MONSOONAL STYLE MOISTURE - WITH PRECIPITABLE WATER VALUES
INCREASING TO GREATER THAN AN INCH AND EVEN AN INCH AND A QUARTER
IN EASTERN UTAH FOR THE DAY. A DISTURBANCE ON MONDAY WILL BREAK
DOWN THE H7 RIDGE TEMPORARILY AND BRING EXTENSIVE CLOUD COVER AND
MORE NUMEROUS SHOWERS TO NORTHEAST UTAH AND WESTERN COLORADO
ESPECIALLY LATER IN THE DAY. LONG RANGE MODELS BEGIN DECREASING
AVAILABLE MOISTURE ON TUESDAY AGAIN AS THE WIND REGIME KEEPS MOST
OF THE DEEP MOISTURE SOUTH OF THE UTAH AND COLORADO BORDERS
THROUGH THE MIDDLE OF THE WEEK. THAT BEING SAID...THE MODELS DO
FREQUENTLY TRY TO DECREASE AVAILABLE MOISTURE TOO RAPIDLY AFTER A
SURGE OF MOISTURE. THE WEAK MONSOONAL SIGNAL COULD CONTINUE
THROUGH THE MIDDLE OF NEXT WEEK...SO WILL HAVE TO BE REASSESSED IN
FUTURE FORECAST SHIFTS.

MOS GUIDANCE LOOKS TO GENERALLY REMAIN ABOUT 5 DEGREES ABOVE
NORMAL THROUGH SUNDAY BEFORE MAX TEMPERATURES FALL TO NEAR NORMAL
ON MONDAY THROUGH MIDWEEK THANKS TO ENHANCED CLOUD CLOUD AND LIGHT
NORTHWESTERLY FLOW.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 449 PM MDT WED JUL 1 2015

SHOWERS AND THUNDERSTORM ACTIVITY IS A BIT SUBDUED COMPARED TO
EXPECTATIONS 24 HOURS AGO. AS A RESULT VFR CONDITIONS ARE SECURE
AT THE AREA FORECAST TERMINALS...A TREND EXPECTED TO CONTINUE OVER
THE NEXT 24 HOURS. KDRO COULD BE THE TERMINAL MOST IMPACTED
THROUGH 02/03Z AS STORMS DRIFT SOUTHWARD OFF THE SAN JUAN
FOOTHILLS. ISOLATED THUNDERSTORMS CONTINUE TO BE FORECAST FOR
SOUTHERN COLORADO OVERNIGHT...BUT CONFIDENCE NOT HIGH ON LOCATION
OR TIMING SO TAF FORECASTS WILL LEAN TOWARD NO WEATHER IMPACTS.

&&

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

$$

SHORT TERM...PF/JAM
LONG TERM...JAM
AVIATION...15


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