FXUS65 KPSR 262146
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
240 PM MST SAT DEC 26 2009
.SYNOPSIS...
DRY CONDITIONS AND BELOW NORMAL TEMPERATURES WILL CONTINUE THROUGH
THE WEEKEND...BEFORE ANOTHER PACIFIC LOW PRESSURE SYSTEM MOVES INTO
THE REGION MONDAY. THIS NEXT SYSTEM WILL BRING A SLIGHT CHANCE OF
SHOWERS TO OUR FORECAST AREA...THE BEST CHANCES OVER THE HIGHER
TERRAIN OF SOUTH-CENTRAL ARIZONA THROUGH MID-WEEK.
&&
.DISCUSSION...
MID-HIGH LEVEL CLOUDS CONTINUE TO OVERSPREAD THE REGION THIS
AFTERNOON AHEAD OF THE NEXT UPPER LEVEL DISTURBANCE NEAR THE PAC NW
COAST. THE CLOUDINESS IS EXPECTED TO PERSIST THROUGH SUNDAY MORNING
...AND WILL HELP KEEP OVERNIGHT TEMPS SEVERAL DEGREES WARMER...THUS
AVOIDING THE NEED FOR A FREEZE WARNING IN THE PHOENIX METRO AREA...
ALTHO SOME SHELTERED SITES WILL STILL BE CLOSE TO FREEZING.
AFTERNOON TEMPS HAVE WARMED UP NICELY...RUNNING ABOUT 2-3 DEGS
WARMER THAN THIS TIME YESTERDAY. THIS SLIGHT WARMING TREND IS
EXPECTED TO CONTINUE SUNDAY INTO EARLY NEXT WEEK...WITH TEMPS
TOPPING OUT NEAR 60 DEG/LOW 60S EACH DAY.
MONDAY AND TUESDAY...ENERGY CONTINUES TO SPILL INTO THE TROF...AND
THE SYSTEM DROPS SOUTH ALONG THE WEST COAST. CURRENT RUNS OF THE
GFS/ECMWF/NAM12 ARE IN BETTER AGREEMENT...AND PLACE THE TROF AXIS AS
FAR SOUTH AS THE NRN BAJA PENINSULA MONDAY AFTERNOON/EVENING. THIS
TRACK OF THE LOW SHUNTS THE BEST MOISTURE AND DYNAMICS TO THE SOUTH
AND EAST OF OUR FORECAST AREA...BUT WITH FORECAST SOUNDINGS SHOWING
SIGNIFICANT MOISTENING OF THE MID-UPPER LEVELS OF THE ATMOSPHERE FOR
OUR FORECAST AREA...IT IS NOT OUT OF THE QUESTION TO HAVE SOME LIGHT
SHOWERS CWA-WIDE THROUGH TUESDAY. WILL CONTINUE TO MAINTAIN SLIGHT
CHANCE POPS ACROSS ALL ZONES...THE BEST CHANCES OVER THE HIGHER
TERRAIN OF SOUTH-CENTRAL AZ--SOUTHERN GILA COUNTY.
WEDNESDAY...MODELS ARE IN DISAGREEMENT WITH A SECONDARY IMPULSE THAT
MOVES OVER CENTRAL AND EASTERN ARIZONA WEDNESDAY. THE ECMWF HAS
DROPPED THIS FEATURE ALTOGETHER FROM PREVIOUS RUNS...AND NOW THE
GFS/CANADIAN BOTH HINT AT THIS ROGUE DISTURBANCE...THUS INCREASING
MOISTURE AND POP CHANCES OVER OUR EASTERN ZONES. BASED ON THIS
UNCERTAINTY...TOOK A BLEND OF THE MODEL SOLUTIONS AND ELECTED TO
CONTINUE TO INTRODUCE A SLIGHT CHANCE OF SHOWERS...MAINLY OVER
SOUTH-CENTRAL ARIZONA THROUGH WEDNESDAY EVENING.
THURSDAY THROUGH SATURDAY...A BRIEF PERIOD OF DRIER NORTHWESTERLY
FLOW AS THE EASTERN PACIFIC RIDGE STRUGGLES TO BUILD ALONG THE WEST
COAST. MODELS SUGGEST THAT ANOTHER LOW PRESSURE SYSTEM COULD PREVENT
THE RIDGE FROM RE-ESTABLISHING...LEAVING THE WEATHER PATTERN
UNSETTLED OVER THE DESERT SOUTHWEST THROUGH THE WEEKEND.
&&
.AVIATION...
WEAK RIDGING ALOFT WILL MEAN QUIET WEATHER AND LIGHT WINDS FOR THE
REGION TODAY. AT KPHX/KIWA...WINDS WILL BE LIGHT WITH NO DOMINANT
WIND DIRECTION. GRADIENT SHOULD FAVOR NORTHERLY COMPONENT TO WINDS
THROUGH LATE MORNING/EARLY AFTERNOON. EASTERLIES WILL SET UP BY LATE
EVENING. BAND OF HIGH CLOUDS WILL STREAM IN FROM THE PACIFIC
TODAY...LEADING TO BKN LYR AOA 20 THSD FT.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
A LOW PRESSURE SYSTEM WILL MOVE EASTWARD FROM THE PACIFIC...BRINGING
A SLIGHT CHANCE OF SHOWERS TO THE AREA AND INCREASED HUMIDITY MONDAY
AND TUESDAY. TEMPERATURES ARE EXPECTED TO REMAIN BELOW SEASONAL
NORMALS.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...MEYERS
AVIATION...ROGERS
FIRE WEATHER...ROGERS
