Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 151650
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1050 AM MDT MON SEP 15 2014

.UPDATE...
ISSUED AT 743 AM MDT MON SEP 15 2014

12Z KGJT SOUNDING SHOWING MOISTURE SITTING ON TOP OF STRONG EML.
ACCAS CONFIRMS THERE IS ALSO INSTABILITY IN THIS MOISTURE LAYER AS
WELL. ISOLATED CONVECTION HAS DEVELOPED AND THOUGH MUCH OF THE
RAINFALL MAY NOT REACH THE GROUND HAVE INCREASED POPS THIS MORNING
TO ACCOUNT FOR INCREASED ECHOS ON RADAR. QUICK LOOK AT MODELS AND
SATELLITE IMAGERY SUGGESTS PASSING JET ENERGY MAY BE HELPING POP
THE CONVECTION AS WELL.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 400 AM MDT MON SEP 15 2014

A SLOW INFLUX OF MID-LEVEL MOISTURE CONTINUED ACROSS THE FORECAST
AREA OVER THE PAST 24 HOURS RAISING PRECIPITABLE WATER LEVELS BY
ABOUT 0.10 INCHES. MODELS SUGGEST A SIMILAR INCREASE TODAY AS
MOISTURE FLOWS EAST-NORTHEASTWARD BETWEEN AN EASTERN PACIFIC
TROUGH AND THE SUBTROPICAL HIGH TO THE SOUTHEAST. AS A RESULT...
EXPECT ANOTHER ROUND OF DIURNALLY DRIVEN AFTERNOON SHOWERS AND
THUNDERSTORMS OVER THE MOUNTAINS. SUBCLOUD MOISTURE LACKING SO
EXPECT STORMS WILL BE MORE EFFICIENT PRODUCING WIND THAN RAIN. SAN
JUANS APPEAR FAVORED GIVEN WEAK JET DIVERGENCE LATER IN THE DAY.
TEMPERATURES WILL REMAIN ABOVE NORMAL AS TROUGH BEGINS TO BUILD A
RIDGE OVER THE WEST.

MOST DIURNAL STORMS ARE EXPECTED TO END BEFORE SUNSET THIS EVENING.
BUT MARGINAL MOISTURE LINGERS UP TO THE FOUR CORNERS REGION AND
BOUNDARY INTERACTION THERE COULD KEEP ISOLATED STORMS GOING
BEYOND MIDNIGHT. THESE STORMS WILL PRODUCE MORE WIND THAN RAIN.
CLOUDS AND WIND COULD KEEP OVERNIGHT LOW TEMPERATURES A BIT MILDER
THAN WE SAW LATE LAST WEEK.

THE RIDGE AMPLIFIES OVER THE GREAT BASIN ON TUESDAY PUTTING THIS
FORECAST AREA IN A LIGHT AND SUBSIDENT NW FLOW ALOFT. WARMER THAN
NORMAL AFTERNOON TEMPERATURES WILL BATTLE WITH MID-LEVEL
SUBSIDENCE. THIS WILL LIMIT AFTERNOON STORMS MAINLY TO THE HIGHER
TERRAIN THAT SHOULD END QUICKLY WITH SUNSET.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 400 AM MDT MON SEP 15 2014

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...THE RIDGE AXIS SLOWLY
PROGRESSES TO LIGHT NW FLOW ALOFT TUESDAY NIGHT BACKS TO SOUTH
WEDNESDAY NIGHT AS THE RIDGE AXIS SHIFTS EAST. LOW GRADE
THUNDERSTORM ACTIVITY EXPECTED AGAIN ON WEDNESDAY WITH THE BATTLE
BETWEEN GOOD SURFACE HEATING AND SUBSIDENCE ALOFT. MOISTURE FROM
THE REMNANTS OF ODILE WILL WORK INTO THE WESTERN GREAT BASIN
WEDNESDAY NIGHT BUT SHOWERS ARE EXPECTED TO STAY WELL TO OUR SW.

THURSDAY THROUGH SUNDAY...LATEST GFS AND ECMWF KEEP THE BULK OF
THE MOISTURE FROM ODILE SOUTH OF THE FORECAST AREA THURSDAY WITH
A NOW WEAKER SURGE OF MOISTURE MOVING INTO SOUTHEAST UTAH AND
SOUTHWEST COLORADO LATER IN THE DAY. CONSEQUENTLY...STORMS LIKELY
TO BE MORE SCATTERED THURSDAY AFTERNOON/EVENING. BEST MOISTURE
BECOMES AVAILABLE ON FRIDAY AS PACIFIC TROUGH CLOSES OFF NEAR
KSFO. LOW CENTER NEARLY STATIONARY OVER THE WEEKEND ACCORDING TO
THE ECMWF WHILE THE GFS40 BRINGS IT INTO THE SOUTHWEST AND THUS IS
THE WETTER SOLUTION. REGARDLESS...BOTH MODELS INDICATED AN
UNSETTLED AND COOLER WEEKEND AHEAD IN GENERAL WITH DETAILS A BIT
SKETCHY AT THIS POINT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1050 AM MDT MON SEP 15 2014

VISUAL FLIGHT RULES WILL STAY IN CONTROL AT THE FORECAST TERMINALS
ACROSS EASTERN UTAH AND WESTERN COLORADO OVER THE NEXT 24 HOURS.
HOWEVER INSTABILITY AND BIT MORE MOISTURE WILL LEAD TO A BETTER
COVERAGE OF AFTERNOON THUNDERSHOWERS TODAY...THAN DAYS PAST. THE
MAIN THREAT WILL BE GUSTY OUTFLOW WINDS DUE TO DRY AIR TOWARD THE
SURFACE. BECAUSE COVERAGE WILL STILL BE ON THE ISOLATED TO
SCATTERED SIDE...CONFIDENCE IS NOT HIGH ENOUGH FOR MANY TAF SITES
TO FORECAST THESE WINDS GUSTS BUT WILL USE AMENDMENTS AS
NECESSARY. PATCHY OBSCURATION OF THE TERRAIN MAY OCCUR DURING THE
PEAK CONVECTION PERIOD LATE THIS AFTERNOON BUT ONLY THE HIGHEST
PEAKS APPEAR TO BE AFFECTED.

&&

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

$$

UPDATE...15
SHORT TERM...NL/JOE
LONG TERM...JOE/NL
AVIATION...TGJT


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