Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 131554 AAA
AFDGJT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
954 AM MDT SAT SEP 13 2014

.UPDATE...
ISSUED AT 954 AM MDT SAT SEP 13 2014

STILL LOOKING LIKE A VERY QUIET DAY. VISIBLE SATELLITE IMAGERY
SHOWS A CLEAR SKY OVER ERN UT AND WRN CO...SAVE A FEW WISPS NEAR
THE WY BORDER. MORNING SOUNDINGS CONFIRM A VERY DRY AIRMASS OVER
THE REGION AND UPSTREAM. MAYBE JUST ENOUGH MOISTURE IN THE MID TO
UPPER LEVELS ACROSS THE SOUTH TO CONTINUE WARRANT OF LOW POPS OVER
THE SAN JUAN MTNS. NOTICED THAT MORNING TEMPS WERE RUNNING BEHIND
THE FORECAST AND THAT LATEST GUIDANCE KEEPS THE AREA TOUCH COOLER
THAN FORECAST. SO UPDATED TO TWEAK THE TEMPS DOWN A LITTLE FOR
TODAY.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 411 AM MDT SAT SEP 13 2014

A SLIGHT SHIFT IN THE PATTERN WILL RESULT IN SOUTHWEST FLOW OVER
THE SOUTHERN ZONES TODAY. THIS WILL INTRODUCE SOME MID-LEVEL
MOISTURE WHICH WILL FUEL ISOLATED THUNDERSTORMS OVER THE SAN JUAN
MOUNTAINS THIS AFTERNOON. PW VALUES ONLY ABOUT 0.50 INCHES SO DO
NOT EXPECT HEAVY RAIN WITH THIS ACTIVITY. MEANWHILE...ADVECTION OF
WARMER AIR WILL CAUSE TEMPERATURES TO RETURN TO NEAR NORMAL LEVELS
THIS AFTERNOON.

ANY CONVECTION THAT DEVELOPED TODAY...WILL QUICKLY WIND DOWN EARLY
THIS EVENING. HOWEVER A FEW MORE CLOUDS MAY HANG AROUND BEYOND
MIDNIGHT. THEREFORE OVERNIGHT LOW TEMPERATURES SHOULD BE A LITTLE
MORE MILD...AND CLOSER TO NORMAL READINGS.

ON SUNDAY...THE AXIS OF THE EASTERN PACIFIC RIDGE WILL MOVE INLAND
ALONG THE WEST COAST...WITH A LOW PRESSURE TROUGH OVER EASTERN
CANADA EXTENDING INTO THE NORTHERN PLAINS STATES TO THE OHIO
VALLEY AND EASTWARD. MODELS SHOW A SHORTWAVE DROPPING INTO THE
BACKSIDE OF THE TROUGH AND BRUSHING THE NORTHERN PORTION OF OUR
FORECAST AREA. THIS WILL RESULT IN INCREASED WINDS OVER NORTHWEST
CO SUN AFTERNOON. THIS IMPULSE ALONG WITH DAYTIME HEATING MAY
PRODUCE A FEW MOUNTAIN SHOWERS IN THE AFTERNOON. TEMPERATURES WILL
CLIMB A FEW DEGREES.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 411 AM MDT SAT SEP 13 2014

THE UPPER RIDGE AXIS SLOWLY CRAWLS EAST...ARRIVING OVER THE GREAT
BASIN BY LATE MONDAY. THEREFORE...LITTLE CHANGE TO THE MOSTLY DRY
FORECAST THROUGH MIDWEEK. A FEW SHOWERS AND THUNDERSTORMS MAY
DEVELOP OVER THE HIGHER TERRAIN EACH AFTERNOON BEFORE QUICKLY
GOING TO BED IN THE EVENING. IN SPITE OF THE RIDGE SLOWLY
APPROACHING...DAYTIME HIGHS ON MONDAY ARE PROGGED TO DROP A TAD
AFTER SUNDAY/S SHORTWAVE BRUSH-BY THEN REMAIN NEAR NORMAL THROUGH
WEDNESDAY.

CONSENSUS BETWEEN THE GFS AND ECMWF NOT AS GOOD AS IT WAS WITH THE
11/00Z RUNS. 12/00Z ECMWF A BIT MORE PROGRESSIVE THAN THE GFS
BRINGING AN EASTERN PACIFIC TROUGH ASHORE EARLY THURSDAY WHICH
FORCES THE RIDGE AXIS EAST OF THE DIVIDE. THIS ALLOWS MOISTURE
FROM HURRICANE ODILE TO MOVE INTO THE NORTHERN BAJA PENINSULA
ADDING TO THE SUBTROPICAL FEED COMING OFF THE MEXICAN PLATEAU.
THIS MOISTURE ARRIVES OVER THE AREA THURSDAY AFTERNOON AS THE
PACIFIC TROUGH CONTINUES TO THE WESTERN GREAT BASIN BRINGING
SHOWERS AND THUNDERSTORMS TO THE AREA. STORMS INCREASE IN COVERAGE
AND INTENSITY THURSDAY NIGHT INTO FRIDAY AS THE MAIN TROUGH SHIFTS
OVER THE AREA. GIVEN INPUT FROM HURRICANE ODILE...ECMWF FAVORS
ANOTHER SIGNIFICANT OUTBREAK OF HEAVY RAIN FOR THE LATTER PART OF
THE WEEK.

IN CONTRAST...THE GFS WAS SLOWER TO BREAK DOWN THE RIDGE AS THE
EASTERN PACIFIC TROUGH NOT AS PROGRESSIVE. IN ADDITION...HURRICANE
ODILE REMAINS STALLED OFF TO SEA WEST OF THE BAJA PENINSULA. A
SHALLOWER EASTERN PACIFIC TROUGH EVENTUALLY SWEEPS ACROSS THE
GREAT BASIN THURSDAY NIGHT THEN MOVES OVER THE AREA FRIDAY. AS A
RESULT...SHOWERS AND THUNDERSTORMS HOLD OFF UNTIL LATE THURSDAY
NIGHT WITH BEST CHANCES FRIDAY. ODILE REMAINS SEPARATED FROM
SUBTROPICAL MOISTURE FEEDING INTO THE AREA SO IN THIS SCENARIO
LESS MOISTURE AVAILABLE FOR HEAVY RAIN.

IN SUMMARY...APPEARS THE END OF THE WEEK WILL BE ACTIVE WITH SOME
QUESTION AS TO THE ONSET OF SHOWERS AND THUNDERSTORMS. ALSO IN
QUESTION IS HOW MUCH QPF THIS SYSTEM WILL BRING...WITH ECMWF
FAVORING A SIGNIFICANT OUTBREAK OF HEAVY RAIN.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 411 AM MDT SAT SEP 13 2014

VFR CONDITIONS WILL PERSIST AT TAF SITES THROUGHOUT THEN NEXT 24
HOURS. ISOLATED THUNDERSTORMS ARE EXPECTED OVER THE SOUTHERN
MOUNTAINS FROM 18Z THROUGH 03Z. THESE STORMS WILL GENERATE STRONG
OUTFLOW WINDS RESULTING IN LOCALIZED TURBULENCE.


&&

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

$$

UPDATE...BEN
SHORT TERM...NL/EH
LONG TERM...EH/NL
AVIATION...NL



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