Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 190945
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
345 AM MDT TUE AUG 19 2014

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 345 AM MDT TUE AUG 19 2014

PER PREVIOUS DISCUSSION...MONSOONAL SURGE ONGOING EARLY THIS
MORNING WITH DEEP SUBTROPICAL MOISTURE CARRIED NORTHWARD INTO
THE REGION AHEAD OF A LOW PRESSURE SYSTEM OFF THE CENTRAL
CALIFORNIA COAST. A SHORTWAVE EJECTED FROM THE LOW WAS RESPONSIBLE
FOR SHOWERS AND A FEW EMBEDDED THUNDERSTORMS OVER THE SOUTHERN
PORTION OF THE FORECAST AREA EARLY THIS MORNING. CONTINUED MOIST
ADVECTION...DAYTIME WARMING AND THE NORTHWARD TRANSIT OF THE
SHORTWAVE WILL BRING INCREASED SHOWERS AND THUNDERSTORMS FROM LATE
MORNING THROUGH THE AFTERNOON. LATEST BUFR SOUNDINGS INDICATED
PRECIPITABLE WATER VALUES IN EXCESS OF 1 INCH ACROSS SOUTHEAST
UTAH AND EXTREME WEST-CENTRAL AND SOUTHWEST COLORADO THIS
AFTERNOON RAISING THE POTENTIAL FOR HEAVY RAIN. HOWEVER...CONCUR
WITH PREVIOUS FORECAST ASSESSMENT THAT FLASH FLOOD POTENTIAL
MITIGATED BY CLOUD COVER AND FAVORABLE STORM MOTION IN EXCESS OF
15 TO 25 MPH. THAT SAID...LOCALIZED HEAVY RAIN MAY STILL RESULT IN
LOCALIZED FLOODING. AS ALLUDED TO EARLIER...CLOUD COVER WILL KEEP
AFTERNOON HIGHS COOLER AS COMPARED TO YESTERDAY AVERAGING AROUND
10 DEGREES LOWER ON AVERAGE.

AN UNUSUAL SEASONAL CHANGE TO THE SYNOPTIC PATTERN AS THE
SUBTROPICAL RIDGE GETS SHUNTED TO THE GULF COAST AND A PACIFIC
TROUGH DOMINATES. TONIGHT DISORGANIZED ENERGY EJECTS OFF THE
SOUTHERN CALIFORNIA LOW WITH AN ASSOCIATED JET STREAK ORIENTED
SW-NE OVER NE UTAH. SOUTH OF THIS FEATURE MOISTURE IS IMPRESSIVE
ERODING FROM 1.2 INCHES TO AROUND AN INCH TOWARDS WEDNESDAY
MORNING. NOCTURNAL STORMS WILL BE PRODUCING HEAVY RAIN AT TIMES
BUT STORM MOTION WILL BE TO THE ENE AT 20KTS. THIS SPEED WILL
REQUIRE TRAINING OF WET CELLS TO PRODUCE FLOODING ISSUES. STILL
WHERE HEAVY RAIN FALLS TODAY WILL BE THE THREATENED AREAS FOR
POTENTIAL FLOODING TONIGHT. MOISTURE DECREASES TOWARDS THE NE SO
THE PARK/GORE/STEAMBOAT AREA LOOKS LESS LIKELY TO GET HEAVIER
SHOWERS. EVEN THERE THE POTENTIAL IS NOT ZERO. GUSTY STORM WINDS
WILL LIKELY BE WIDESPREAD WITH SMALL HAIL IN THE HOTTEST CELLS.

WEDNESDAY THE CALIFORNIA LOW WORKS OVER SAN DIEGO WITH A
DEFORMATION AXIS STRETCHED INTO NE UTAH AND BEYOND. MOISTURE
ERODES TO AROUND 0.75 INCH WHICH WILL PRODUCE SCATTERED LATE-DAY
CONVECTION. TEMPERATURES REMAIN WELL BELOW NORMAL.

.LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 345 AM MDT TUE AUG 19 2014

AT THE SYNOPTIC SCALE THE MODELS ARE STILL NOT IN GOOD AGREEMENT
ON HOW TO HANDLE THE UNUSUAL FOR AUGUST WEST COAST TROUGH. TIMING
OF ITS SLOW PROGRESSION IS IN DOUBT. BUT THROUGH THURSDAY NIGHT WE
REMAIN IN A PERTURBED SW FLOW WITH A WEAK JET STREAK OVER UTAH.
PRECIP WATER VALUES REMAIN NEAR AN INCH IN THE FOUR CORNERS TO
AROUND 0.75 INCH FURTHER NORTH. THIS IS SUFFICIENT FOR SCATTERED
DIURNAL THUNDERSTORMS AND ISOLATED NOCTURNAL STORMS FAVORING THE
SOUTHERN ZONES. THE TROUGH AXIS APPROACHES THE REGION THURSDAY
NIGHT FOR ENHANCED DYNAMICAL SUPPORT AND PERHAPS INCREASED
NIGHTTIME THUNDERSTORMS. GUSTY WINDS AND SMALL HAIL REMAIN A
THREAT WITH STRONGER CELLS.

MODELS CONTINUED TO HANG ONTO LONGWAVE TROUGH OVER THE WEST
THROUGH THE REMAINDER OF THE WEEK. ECMWF DEVELOPS MORE OF A SPLIT
BY FRIDAY ALLOWING SUBTROPICAL MOISTURE TO CONTINUE TO MOVE INTO
THE AREA. THE TROUGH IN THE GFS WAS MORE COHERENT AND THUS FLOW
INDICATED TO BE MORE WESTERLY AND DRIER. REGARDLESS...BOTH
SOLUTIONS CONTAIN ENOUGH MOISTURE FOR DIURNAL SHOWERS AND
THUNDERSTORMS DURING THE LATTER PART OF THE WEEK. UNSETTLED
CONDITIONS LIKELY TO CONTINUE INTO THE WEEKEND. ECMWF NEAR
STAGNANT WITH VERY LITTLE CHANGE RELATIVE TO THAT DESCRIBED
EARLIER. MEANWHILE...GFS REMAINED MORE ZONAL. GIVEN POSITIONING
OF THE TROUGH...COMBINED WITH DAILY SHOWERS AND THUNDERSTORMS
...EXPECT TEMPERATURES WILL REMAIN BELOW NORMAL THURSDAY THROUGH
THE WEEKEND.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 345 AM MDT TUE AUG 19 2014

A SURGE OF MONSOONAL MOISTURE WILL BRING AN INCREASE IN SHOWER AND
THUNDERSTORM ACTIVITY TODAY. THE DEEPEST MOISTURE WILL IMPACT
EASTERN UTAH AND EXTREME WESTERN COLORADO FIRST WITH STORMS FIRING
AFTER 15Z. THIS ACTIVITY WILL SPREAD EASTWARD AND BECOME MORE
WIDESPREAD AS THE AIRMASS BECOMES WARMER...WETTER...AND MORE
UNSTABLE DURING THE AFTERNOON. MOUNTAINS WILL BE FREQUENTLY
OBSCURED AND TAF SITES WILL HAVE THUNDERSTORMS IN THE VICINITY AND
FACE A GOOD CHANCE OF HAVING STORMS MOVE OVERHEAD. THESE STORMS
WILL BE CAPABLE OF PRODUCING MVFR/IFR VSBY IN HEAVY RAIN. A
DISTURBANCE IMPACTING THE REGION OVERNIGHT WILL KEEP SHOWER AND
THUNDERSTORM ACTIVITY CONTINUING THROUGH 12Z/WED.

&&

.HYDROLOGY...
ISSUED AT 345 AM MDT TUE AUG 19 2014

MONSOONAL MOISTURE WILL RETURN TODAY AS AN UPPER LEVEL LOW OVER
CALIFORNIA PULLS DEEP SUBTROPICAL MOISTURE INTO THE REGION.
SHOWERS AND THUNDERSTORMS WILL INCREASE IN COVERAGE FROM WEST TO
EAST THROUGHOUT THE DAY...PEAKING DURING THE LATE AFTERNOON AND
EVENING THEN CONTINUING OVERNIGHT INTO WEDNESDAY MORNING. EXPECT
SOME SMALL STREAM AND ARROYO FLOOD ISSUES BY WEDNESDAY MORNING IN
THE USUAL PROBLEM AREAS. HOWEVER...DO NOT EXPECT SUFFICIENTLY
WIDESPREAD COVERAGE OF TORRENTIAL DOWNPOURS TO WARRANT FLASH FLOOD
WATCH.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...NL/JOE
LONG TERM...JOE/NL
AVIATION...NL
HYDROLOGY...NL/JAM


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