Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 231008
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
408 AM MDT SAT AUG 23 2014

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 408 AM MDT SAT AUG 23 2014

A BROAD AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS WAS ONGOING
OVER NORTHEAST UTAH AND NORTHWEST COLORADO EARLY THIS MORNING. A
VIGOROUS SHORTWAVE DRIVING A COOL FRONT ACROSS THE NORTHWEST
PORTION OF THE FORECAST AREA PROVIDED THE FORCING FOR THIS
ACTIVITY WHILE SUBTROPICAL MOISTURE SUPPLIED BY THE MONSOON
PROVIDED THE FUEL. PW VALUES NEAR 0.9 INCHES HAS ALLOWED FOR
EFFICIENT RAIN PRODUCTION...SO IT COMES AS NO SURPRISE THAT HEAVY
RAIN HAS BEEN REPORTED OVER THE EASTERN UINTA BASIN.

DRIVEN BY A 90 KT JET ROTATING THROUGH THE BASE OF THE MID-LEVEL
LOW CENTERED OVER SOUTHERN IDAHO...THIS SYSTEM WILL TRACK
STEADILY EASTWARD ACROSS THE AREA DURING THE DAY. LIFT CONTINUES
TO FAVOR THE NORTH SO BOOSTED POPS SIGNIFICANTLY NORTH OF THE I-70
CORRIDOR. MEANWHILE...TO THE SOUTH MODELS INDICATED THE SOUTHERN
MOST ZONES UNLIKELY TO SEE MUCH ACTIVITY SO LEFT LOW CHANCE POPS
THERE. CLOUDS AND SIGNIFICANTLY COOLER TEMPERATURES WILL INHIBIT
STRONG CONVECTION SO THE THREAT OF EXCESSIVE RAIN IS RATHER LOW.
HOWEVER...MODERATE TO HEAVY RAIN IN SOME AREAS OF STEEP TERRAIN
COULD LEAD TO LOCALIZED MUD OR DEBRIS FLOWS.

THE WESTERLY FLOW BEHIND TODAY`S SHORTWAVE TROUGH WILL BRING IN
DRIER CONDITIONS BY THE EVENING AND OVERNIGHT. THE NAM SHOWS PWAT
NUMBERS IN NORTHEAST UT DROPPING TO LESS THAN A QUARTER INCH...
WITH PWATS LESS THAN HALF AN INCH ACROSS THE ENTIRE NORTHERN HALF
BY MIDNIGHT. THEREFORE EXPECT SHOWERS AND THUNDERSTORMS WILL
QUICKLY DIMINISH...LINGERING LONGEST OVER THE CENTRAL AND NORTHERN
DIVIDE. AS SKIES CLEAR...NIGHTTIME TEMPERATURES ARE EXPECTED TO BE
QUITE COOL FOR THE SEASON...ESPECIALLY OVER THE NORTH. THE 00Z RUN
HAS TRENDED COOLER THAN PREVIOUS RUNS WITH THE MET GUIDANCE GOING
FOR 35 F AT CAG.

THE NEXT SHORTWAVE WILL DROP INTO EASTERN WA ON SUN WITH THE FLOW
BECOMING SOUTHWEST OVER OUR AREA BY MIDDAY. THEREFORE THE DRYING
TREND WILL REVERSE ITSELF WITH PWAT NUMBERS INCREASING TO .75 INCH
ACROSS EASTERN UT BY LATE AFTERNOON. HOWEVER SUNDAY SHOULD STILL
BE MOSTLY A DOWN DAY AS FAR AS CONVECTION IS CONCERNED. BUT A FEW
STORMS MAY DEVELOP OVER THE HIGHER MOUNTAINS DURING THE AFTERNOON.
MORE SUNSHINE WILL ALLOW A MODERATE INCREASE IN HIGH
TEMPERATURES...BUT THEY WILL STILL REMAIN WELL BELOW NORMAL.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 408 AM MDT SAT AUG 23 2014

GENERAL TROUGHINESS WILL REMAIN OVER THE WESTERN CONUS EARLY IN
THE WORK WEEK...WITH THE NORTHWEST SHORTWAVE MOVING INTO THE
NORTHERN GREAT BASIN ON MONDAY. THE SOUTHWEST FLOW AHEAD OF THIS
TROUGH WILL CONTINUE TO PULL MOISTURE INTO THE AREA...HOWEVER
MODELS KEEP THIS ON THE MODEST SIDE. BOTH THE GFS AND NAM HINT AT
A WEAK EMBEDDED DISTURBANCE PASSING ACROSS THE NORTHERN PORTION
OF OUR FORECAST AREA SUNDAY NIGHT. WITHOUT A BOOST FROM DAYTIME
HEATING EXPECT ONLY A FEW NOCTURNAL SHOWERS...WHICH SHOULD BE
LIMITED TO THE NORTHERN HALF OF THE CWA. MONDAY SHOULD SEE AN
UPTICK IN CONVECTION AS THE UPPER TROUGH APPROACHES...AND
MOISTURE WILL BE A LITTLE MORE PLENTIFUL. HOWEVER MOST SHOWERS
WILL BE OVER THE HIGHER TERRAIN. TEMPERATURES WILL AGAIN INCREASE
A FEW DEGREES...INCHING CLOSER TO NORMAL VALUES.

ECMWF AND GFS CONTINUED TO SHOW SIGNIFICANT DIFFERENCES FROM
MIDWEEK ONWARD. GFS40 PUSHES ANOTHER SHORTWAVE TROUGH ACROSS THE
AREA TUESDAY INTO TUESDAY NIGHT. ECMWF SIMILAR ON TUESDAY...SO
BOTH MODELS PREDICTING A FAIRLY ACTIVE 24 HOUR PERIOD THROUGH
WEDNESDAY MORNING WITH SCATTERED SHOWERS AND THUNDERSTORMS AND
RELATIVELY COOL TEMPERATURES. HOWEVER...PROGRESSIVE GFS40 DRIVES
THE TROUGH THROUGH LATE TUESDAY NIGHT WITH NORTHWEST THEN WESTERLY
FLOW SETTING UP FOR THE REST OF THE WEEK. IN THIS SCENARIO...SUNNY
TO PARTLY SUNNY SKIES WILL ALLOW TEMPERATURES TO REBOUND TO NEAR
NORMAL AS HIGH PRESSURE SETS UP OVER THE SOUTHWEST. IN DIRECT
CONTRAST...ECMWF SLOWLY MOVES THE LOW OVER THE REGION DURING THE
REMAINDER OF THE WEEK FOR CONTINUED UNSETTLED AND COOL CONDITIONS.
BLENDED SOLUTIONS FAVOR THE GFS AND THEREFORE MADE FEW CHANGES.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 408 AM MDT SAT AUG 23 2014

AN UPPER LEVEL TROUGH AND SURFACE COLD FRONT WILL BRING CLOUDS
...SHOWERS...AND THUNDERSTORMS TO THE AREA OVERNIGHT. TAF SITES
ALONG AND NORTH OF I-70 MAY SEE SOME OF THIS PRECIP WHILE AREAS
SOUTH WILL SEE MAINLY CLOUDS AND MORE ISOLATED SHOWER ACTIVITY.
SHOWERS AND STORMS WILL CONTINUE THROUGH ABOUT 03Z/SUN WITH SOME
SHRA AND TSRA EXPECTED FOR MANY TAF SITES. IFR/MVFR POSSIBLE UNDER
THE STRONGER STORMS DUE TO LOW CIGS/VIS. MTN OBSCURATIONS ARE
EXPECTED AGAIN. DRY CONDITIONS RETURN AFTER 06Z/SUN.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...NL/EH
LONG TERM...EH/NL
AVIATION...TGJT


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