FXUS65 KPSR 251638
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
935 AM MST FRI DEC 25 2009
.SYNOPSIS...
A DRY FLOW OF AIR ALOFT FROM THE NORTHWEST WILL RESULT IN SUNNY SKIES
TODAY. TEMPERATURES WILL BE BELOW AVERAGE FOR LATE DECEMBER WITH
FREEZING TEMPERATURES IN COLDER DESERT AREAS EARLY SATURDAY MORNING.
DRY WEATHER WILL CONTINUE BUT WITH HIGH CLOUDINESS FROM THE WEST
MOVING ACROSS THE AREA THIS WEEKEND. A PACIFIC LOW PRESSURE SYSTEM
WILL RESULT IN CONSIDERABLE CLOUDINESS AND A SLIGHT CHANCE OF
SHOWERS MAINLY IN SOUTH-CENTRAL ARIZONA MONDAY INTO TUESDAY. A DRY
FLOW OF AIR ALOFT FROM THE NORTHWEST IS EXPECTED TO RETURN WITH
MOSTLY CLEAR NIGHTS AND SUNNY DAYS BY THURSDAY.
&&
.DISCUSSION...
MOSTLY CLEAR SKIES ACROSS ARIZONA THIS MORNING. UNDER A DRIER
NORTHWESTERLY FLOW ALOFT...WOULD ANTICIPATE THAT UNDER MOSTLY
CLEAR/SUNNY SKIES...THE STRING OF COLDER BELOW NORMAL TEMPERATURES
WILL CONTINUE INTO THE WEEKEND. SURFACE CONDITIONS STILL GETTING
DRIER...DEW POINT TEMPS ABOUT 5-10 DEGREES LOWER THAN THIS TIME
YESTERDAY...GENERALLY IN THE TEENS AND LOW 20S. ALSO...A CHILLY
START TO OVERNIGHT LOWS/MORNING TEMPS...WITH SKY HARBOR BOTTOMING
OUT AT 37 DEGREES...AND OTHER OUTLYING URBAN AREAS JUST SHY OF THE
FREEZING MARK. MANY MESOWEST SITES --THOSE MORE RURAL AND SHELTERED
THROUGHOUT THE METRO AREA AND OPEN DESERTS-- REPORTED TEMPERATURES
THAT WERE AT OR BELOW FREEZING SINCE AROUND 2 AM. LOW TEMPERATURES
SATURDAY MORNING WILL BE JUST AS COLD...AND EVEN A FEW DEGREES
COOLER AT SOME SITES...GIVEN CLEAR SKIES/DRY CONDITIONS AND GOOD
RADIATIONAL COOLING. CURRENT MIN TEMP FORECAST TRENDS IN THIS
DIRECTION...BUT WILL CLOSELY ASSESS THE NEED FOR A FREEZE
WARNING--OR NOT--AND HAVE MORE TO OFFER IN THE AFTERNOON PACKAGE.
INHERITED GRIDS/SHORT TERM FORECAST LOOK GOOD...NO CHANGES MADE AT
THIS TIME. PREVIOUS DISCUSSION STILL APPLIES.
PREVIOUS DISCUSSION...
A DRY FLOW OF AIR ALOFT FROM THE NORTHWEST WILL CONTINUE OVER OUR
AREA TODAY BETWEEN A LARGE INTENSE COLD STORM SYSTEM OVER THE
CENTRAL UNITED STATES AND HIGH PRESSURE ALOFT ALONG THE WEST COAST.
THIS WILL RESULT IN SUNNY SKIES TODAY AND CLEAR SKIES TONIGHT. BELOW
AVERAGE TEMPERATURES ARE EXPECTED WITH FREEZING TEMPERATURES IN THE
COLDER DESERT AREAS EARLY SATURDAY MORNING.
THE HIGH PRESSURE SYSTEM ALOFT ALONG THE WEST COAST WILL WEAKEN AND
MOVE EAST ACROSS OUR AREA SATURDAY. A WEAK PACIFIC LOW PRESSURE
SYSTEM RIGHT BEHIND IT IS EXPECTED TO SPREAD HIGH CLOUDINESS FROM
SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA SATURDAY TO SOUTH-CENTRAL
ARIZONA BY LATE SATURDAY AFTERNOON AND EVENING.
ANOTHER AREA OF HIGH CLOUDINESS FROM THE PACIFIC IS EXPECTED MOVE
EAST ACROSS OUR AREA SUNDAY INTO SUNDAY NIGHT AHEAD OF A STRONGER
PACIFIC LOW PRESSURE SYSTEM. SOME RELATIVELY WARMER AIR AHEAD OF THE
LOW PRESSURE SYSTEM IS EXPECTED TO RESULT IN NOT QUITE AS COOL
WEATHER IN SOUTH-CENTRAL ARIZONA INCLUDING THE GREATER PHOENIX AREA
SUNDAY AND MONDAY.
THE PACIFIC LOW PRESSURE SYSTEM IS EXPECTED TO MOVE SOUTHEAST TO THE
SOUTHERN CALIFORNIA AND BAJA CALIFORNIA COASTS LATE MONDAY AND
NORTHEAST ACROSS OUR AREA BY LATE MONDAY NIGHT INTO TUESDAY. ENOUGH
MOISTURE AND DYNAMICS WITH THIS SYSTEM ARE EXPECTED TO WARRANT A
SLIGHT CHANCE OF SHOWERS MAINLY IN SOUTH-CENTRAL ARIZONA MONDAY AND
MONDAY NIGHT INTO TUESDAY. LITTLE OR NO RAIN IS EXPECTED FROM EL
CENTRO TO YUMA. LESS THAN A TENTH OF AN INCH OF RAIN IS EXPECTED IN
JOSHUA TREE NATIONAL PARK AND IN PHOENIX.
THE MAIN PART OF THE LOW PRESSURE SYSTEM MAY MOVE FAR ENOUGH SOUTH
OVER NORTHERN MEXICO THAT IT IS POSSIBLE THAT LITTLE OR NO RAIN WILL
OCCUR ANYWHERE IN OUR AREA. IF THE LOW PRESSURE SYSTEM DOES MOVE
CLOSE ENOUGH TO THE MEXICAN BORDER...UP TO 4 TENTHS OF AN INCH OR SO
OF RAIN IS POSSIBLE IN THE HIGHER TERRAIN NORTH AND EAST OF GLOBE.
COOLER AIR WITH THIS SYSTEM IS EXPECTED TO CAUSE TEMPERATURES TO
DROP BACK WELL BELOW AVERAGE FOR LATE DECEMBER IN SOUTHEAST
CALIFORNIA AND SOUTHWEST ARIZONA MONDAY AND SOUTH-CENTRAL ARIZONA
TUESDAY. IT IS ALSO EXPECTED TO CAUSE THE SNOW LEVEL IN THE HIGHER
TERRAIN EAST OF THE GREATER PHOENIX AREA TO DROP TO NEAR 5 THOUSAND
FEET MONDAY NIGHT AND 45 HUNDRED FEET TUESDAY.
ANOTHER AXIS OR RIDGE OF HIGH PRESSURE ALOFT FROM THE PACIFIC IS
EXPECTED TO MOVE EAST TO THE WEST COAST WITH A DRY FLOW OF AIR ALOFT
FROM THE NORTHWEST OVER OUR AREA BY THURSDAY. THIS IS EXPECTED TO
BRING A RETURN TO MOSTLY CLEAR NIGHTS AND SUNNY DAYS BY THURSDAY.
&&
.AVIATION...
SOUTH-CENTRAL AZ INCLUDING KPHX/KIWA...
CLEAR OR THIN CIRRUS TODAY AND TONIGHT AS NORTHWEST WINDS ALF WILL
REMAIN ACROSS THE REGION. LOOK FOR A LIGHT EAST BREEZE BECOMING WEST
AFT 20Z AT SKY HARBOR. A SFC INVERSION MAY LEAD TO SOME HAZE BUILDUP
ACROSS PARTS OF THE METRO AREA...BUT NO SIGNIFICANT VSBY
RESTRICTIONS ARE EXPECTED THRU 18Z.
SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING
KIPL/KBLH...CLEAR BLO 25 THSD FT TODAY. INCREASING SFC GRADIENT
ALONG THE LOWER COLORADO RIVER WILL GIVE OCNL GUSTY WINDS AT KBLH
BY THIS AFTERNOON. MAX GUSTS SHOULD STAY LESS THAN 25 KTS.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
GENERALLY INCREASING RH THROUGH THE PERIOD. THERE WILL BE A SLIGHT
CHANCE OF SHOWERS ON MONDAY AND TUESDAY AS A PACIFIC LOW PRESSURE
SYSTEM MOVES ONSHORE AND DRIFTS EAST. A CLEARING TREND WILL SWEEP
FROM WEST TO EAST ON WEDNESDAY WITH A SLOW WARMING TREND BY
THURSDAY.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...MEYERS/ELLIS
AVIATION...SIPPLE
FIRE WEATHER...SIPPLE
