FXUS65 KPSR 090437
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
935 PM MST TUE DEC 8 2009
.SYNOPSIS...
WEAK HIGH PRESSURE IN PLACE OVER THE DESERT SOUTHWEST...WITH
INCREASING CLOUDS EXPECTED OVERNIGHT. TEMPERATURES WILL REMAIN COOL
WEDNESDAY...FOLLOWED BY A COUPLE OF FAST MOVING LOW PRESSURE SYSTEMS
THURSDAY THROUGH SATURDAY...WITH A SLIGHT CHANCE FOR VALLEY RAIN AND
MOUNTAIN SNOW. A MUCH STRONGER AND COLDER LOW PRESSURE SYSTEM WILL
MOVE THROUGH SUNDAY AND MONDAY...INCREASING THE THREAT FOR
PRECIPITATION...WITH A BETTER CHANCE FOR VALLEY RAIN AND HIGHER
TERRAIN SNOW.
&&
.DISCUSSION...
SAT IMAGERY THIS EVENING SHOWS MID AND HIGH LEVEL CLOUDS HEADING
TOWARD OUR CWA...FOR PARTLY CLOUDY SKIES OVERNIGHT. WITH THE
INCREASING CLOUD COVER...OVERNIGHT LOWS WILL BE A BIT MORE MILD THAN
OTHERWISE THOUGHT GIVEN THE COLD AND DRY AIRMASS IN PLACE. INHERITED
MIN TEMPS FOR WED MORNING ALREADY REFLECTING THIS...SO TWEAKED THE
SKY GRIDS JUST A BIT TO BETTER MATCH LATEST SAT TRENDS. OTHERWISE...
FORECAST APPEARS TO BE IN GOOD SHAPE...WITH NO OTHER UPDATES PLANNED
FOR TONIGHT.
THE SYNOPTIC PATTERN FOR THE NEXT SEVERAL DAYS IS PROBABLY BEST
DESCRIBED AS UNSETTLED...MEANING A COUPLE OF MINOR SHORTWAVE
TROUGHS WILL QUICKLY MOVE THROUGH THE MOSTLY ZONAL FLOW...BEFORE
BOTH THE GFS AND ECMWF DEVELOP A HIGHLY AMPLIFIED RIDGE OF HIGH
PRESSURE OVER THE PAC NW...WITH A MUCH STRONGER/COLDER LOW PRESSURE
SYSTEM DIVING DOWN THE FRONT SIDE OF THE RIDGE...AND THROUGH
SOUTHEAST CA AND ARIZONA...SUN/MON TIME FRAME. WILL HAVE A SLIGHT
CHANCE FOR VALLEY RAIN AND MOUNTAIN SNOW THU/FRI...INCREASING
CHANCES LATE IN THE WEEKEND/EARLY NEXT WEEK WITH THE STRONGER LOW
PRESSURE SYSTEM.
CURRENT FORECAST TRENDS AND DIGITAL DATABASE LOOK ON TRACK FOR
NOW...TAKING A BROADBRUSH APPROACH WHILE THE DETAILS OF THESE
UPCOMING EVENTS BECOME MORE CLEAR.
PREVIOUS DISCUSSION...
12Z GFS SHOWS A FLAT RIDGE AXIS COMING ONSHORE AND INTO AZ WED NIGHT
AND EARLY THURSDAY...BUT UNTIL THEN OUR MINIMUM TEMPERATURES ARE
LIKELY TO BOTTOM OUT EARLY WEDNESDAY WITH SOME COLDER VALLEY
LOCATIONS DROPPING INTO THE LOWER 30S TONIGHT UNDER CLEAR SKIES.
MODELS SINGING THE SAME TUNE WITH REGARD TO A SERIES OF UPPER LEVEL
TROUGHS MOVING ONSHORE BEGINNING THURSDAY. THESE ARE RATHER
FAST-MOVING SHORT WAVES AND THE TIMING OF THE ASSOCIATED SHOWERS
WILL LIKELY CHANGE FROM RUN TO RUN. BUT AT THIS TIME...NAM APPEARS A
LITTLE DEEPER ON THE FIRST ONE...WHILE THE GFS INTRODUCES LIGHT
SHOWERS A BIT FARTHER EAST. BUT A DEEPENING MARINE LAYER ALONG THE
CALIFORNIA COAST WILL NEED TO BE MONITORED. GFS SHOWS A STEADY
INCREASE IN THE MOISTURE. THE 1000-700MB MIXING RATIOS PICK UP MID
DAY THURSDAY INTO MID DAY FRIDAY. THEY WILL DROP OFF A BIT ON
SATURDAY...AND PICK UP AGAIN ON SUNDAY...AS THE LAST IN THE SERIES
OF SHORT WAVES SWEEP ACROSS THE AREA. TEMPERATURES ARE NOT LIKELY TO
WARM VERY MUCH BY SATURDAY/SUNDAY WITH VARYING AMOUNTS OF CLOUDS AND
THE SLIGHT CHANGES TO HEIGHTS/THICKNESSES. FINALLY...WINDS ARE
NOT EXPECTED TO PICK UP SIGNIFICANTLY DURING THE PERIOD.
&&
AVIATION...
NO AVIATION CONCERNS EXPECTED UNDER INCREASING MID AND HIGH LEVEL
CLOUDS...WITH WEAK HIGH PRESSURE IN PLACE.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
AN UNSETTLED WEATHER PATTERN AS A SERIES OF WEATHER DISTURBANCES
MOVE ACROSS THE REGION. ANTICIPATE COOLER TEMPERATURES...LIGHT WINDS
AND ELEVATED HUMIDITY LEVELS THROUGH THE PERIOD...WITH ANOTHER SHOT
AT PRECIPITATION ACROSS THE AREA CONTINUING INTO THE WEEKEND.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...WANEK/SIPPLE
AVIATION...WANEK
FIRE WEATHER...MEYERS
