FXUS65 KTWC 090945
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
245 AM MST WED DEC 9 2009
.SYNOPSIS...WESTERLY FLOW ALOFT WILL BRING QUIET WEATHER TO
SOUTHEAST ARIZONA...WITH OCCASIONAL HIGH CLOUDS FROM TIME TO TIME.
A SERIES OF WEAK DISTURBANCES WILL BRING MOSTLY CLOUDY SKIES
THURSDAY INTO THE WEEKEND. EXPECT ONLY A SLIGHT CHANCE OF SHOWERS ON
THE MOUNTAINS THURSDAY EVENING THROUGH SATURDAY. A STRONGER WEATHER
SYSTEM WILL BRING A BETTER CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW
SHOWERS ON SUNDAY.
&&
.DISCUSSION...A MUCH QUIETER MORNING BEHIND YESTERDAY'S STORM. STILL
PLENTY OF CLOUDS TO CONSIDER...WITH SOME LOW CLOUDS PERSISTING
ACROSS MUCH OF SOUTHEAST ARIZONA...AND PLENTY OF CIRRUS APPROACHING
FROM THE WEST IN NEAR ZONAL FLOW ALOFT. EXPECTATION IS FOR THESE
CIRRUS TO THIN AS THEY ENTER THE DESERT SOUTHWEST...AND RETAINED
PARTLY CLOUDY WORDING IN THE SKY GRIDS FOR TODAY. DAY SHIFT MAY HAVE
TO CHANGE TO MOSTLY CLOUDY IF CIRRUS IS THICKER. TEMPERATURES
CONSIDERABLY BELOW NORMAL AGAIN TODAY...BUT A BIT WARMER THAN
YESTERDAY WITH MOST LOWER ELEVATIONS IN THE UPPER 50S.
FAST WESTERLY FLOW ALOFT WILL BRING A PARADE OF WEAK DISTURBANCES
INTO ARIZONA OVER THE COMING DAYS...BUT NONE ARE LOOKING IMPRESSIVE
AT THIS TIME. THE FIRST DISTURBANCE IS SHOWN BY 00Z NAM/GFS/ECMWF TO
ZIP THROUGH ON THURSDAY. SHOULD BE PLENTY OF HIGH AND PERHAPS MID
CLOUDS WITH THIS...FOR MOSTLY CLOUDY SKIES. MODEL GUIDANCE CONTINUES
TO NOT SUPPORT POPS FOR THURSDAY...AND AGAIN KNOCKED MOST EVERYTHING
BELOW MENTIONABLE LEVELS. ISOLATED POPS MAINTAINED FOR THE MOUNTAIN
TOPS THURSDAY NIGHT...NOT EXPECTING MUCH. MORE DISTURBANCES ARRIVE
FRIDAY...CONTINUING THE MOSTLY CLOUDY SKIES AND THE SLIM SHOT FOR A
SHOWER ON THE HIGHER TERRAIN NORTHEAST OF TUCSON. AGAIN...NOT
EXPECTING MUCH BUT CAN'T ZERO OUT THE POPS EITHER. 00Z GFS SHOWS YET
ANOTHER WEAK DISTURBANCE SATURDAY...AGAIN MOSTLY CLOUDY SKY GRIDS
SATURDAY AND SLIGHT CHANCE POPS FOR THE HIGHER TERRAIN NORTHEAST OF
TUCSON...MATCHING WITH PHOENIX AND FLAGSTAFF. FINALLY...A STRONGER
MORE NOTEWORTHY SYSTEM ARRIVES IN CALIFORNIA SUNDAY MORNING. MODELS
ARE CONVERGING SUGGESTING THIS SYSTEM WILL BRING OUR NEXT ROUND OF
SENSIBLE WEATHER TO SOUTHEAST ARIZONA. CONTINUED MOSTLY CLOUDY...BUT
GFS AND ECMWF AGREE THIS WAVE WILL BE SLIGHTLY MORE AMPLIFIED. IN
THIS PACKAGE...TRIED TO HONE IN ON THIS TIME PERIOD OF SUNDAY
THROUGH MONDAY MORNING FOR OUR NEXT NOTEWORTHY CHANCE OF PRECIP. AT
LEAST 20% POPS FOR ALL ZONES DURING THIS TIME...WITH 30% CHANCE
POPS FOR THE HIGHER TERRAIN. THIS FOLLOWS THE 00Z MEX GUIDANCE WELL.
WOULD LIKE TO GO HIGHER ON POPS FOR SUNDAY/MONDAY...BUT TIMING WAVES
IN THIS FAST FLOW 5 DAYS OUT IS FAR FROM PERFECT AND WILL BE
CONSERVATIVE FOR NOW. MEDIUM RANGE MODELS DO AGREE RIDGING WILL
FOLLOW THIS WAVE FOR A WARMING TREND TUESDAY AND WEDNESDAY OF NEXT
WEEK.
&&
.AVIATION...BROKEN CLOUD BASES BETWEEN 035-050 AGL WITH PERIODS OF
MVFR BASES AROUND 025 AGL THROUGH 16Z AT THE TERMINAL SITES. THIS
WILL LEAD TO MOUNTAIN TOP OBSCURATIONS NEAR THE TERMINAL SITES.
THESE BROKEN BASES WILL BECOME SCATTERED AFTER 16Z AND CONTINUE
THROUGH TONIGHT ALONG WITH CONSIDERABLE CIRRUS CLOUDS STREAMING
THROUGH ON FLAT ZONAL FLOW ALOFT. WINDS GENERALLY LIGHT AND DIURNAL
IN NATURE THIS MORNING...THEN BECOMING WEST TO SOUTHWEST AT 10 TO 15
KTS THIS AFTERNOON AND CONTINUING INTO THE EARLY EVENING. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
&&
.FIRE WEATHER...NO FIRE WEATHER CONCERNS AT THIS TIME.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...NONE.
$$
TURNER
WEATHER.GOV/TUCSON
