Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 191659
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1059 AM MDT TUE AUG 19 2014

.UPDATE...
ISSUED AT 1055 AM MDT TUE AUG 19 2014

THE SHIELD OF RAIN SHOWERS IN NORTHWESTERN COLORADO WILL CONTINUE
TO MOVE TO THE NORTHEAST LATE THIS MORNING AND INTO THE EARLY
AFTERNOON. THERE ARE ALREADY SIGNS OF SHOWERS TRAINING IN EAST-
CENTRAL UTAH...AND THOSE RAINFALL RATES ARE LIGHT AT THIS
TIME...ANY RAIN THIS MORNING WILL HELP TO SATURATE THE GROUND FOR
THE HEAVIER RAIN EXPECTED LATER TODAY AND TONIGHT. PRECIPITATION
VALUES RECORDED HAVE GENERALLY BEEN LESS THAN A TENTH OF AN INCH
OVERNIGHT AND THIS MORNING.

FORECAST ON TRACK WITH CLOUD COVER OVER THE CWA KEEPING
STRONG SHOWERS/STORMS SUPPRESSED SO FAR. THERE IS SOME CLEARING
DOWN AT THE FOUR CORNERS WHICH WILL BE SUSCEPTIBLE TO STORMS
DEVELOPING DUE TO DAYTIME HEATING AS WE NEAR THE AFTERNOON.

&&

.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 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1055 AM MDT TUE AUG 19 2014

LIGHT TO MODERATE RAIN SHOWERS OVER NORTHWESTERN COLORADO WILL
CONTINUE TO MOVE NORTHEAST. VCSH IS MOST LIKELY AT
KRIL...KGJT...KASE...AND KEGE THROUGH 20Z. KCNY WILL HAVE ON AND
OFF SHOWERS THROUGH 19Z BUT THEN SHOULD GET A SHORT BREAK EARLY
THIS AFTERNOON. THE FOUR CORNERS WILL HAVE -SHRA AND -TSRA
POPPING UP BEGINNING AT ABOUT 18Z AND CONTINUING ON AND OFF
THROUGHOUT THE NEXT 18 HOURS OR SO. MONSOONAL WILL INCREASE
THROUGHOUT THE AFTERNOON SO THE ACTIVE WEATHER WILL BECOME MORE
WIDESPREAD AFTER 22Z FROM WEST TO EAST. RA AND TS WILL OBSCURE
MANY MOUNTAIN LOCATIONS UNTIL 12Z. STORMS WILL BE CAPABLE OF
PRODUCING MVFR/IFR VSBY IN HEAVY RAIN AT MANY TAF LOCATIONS OVER
THE NEXT 24 HOURS.

&&

.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.
&&

$$

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


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