FXUS65 KPSR 272201
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
255 PM MST FRI NOV 27 2009
.SYNOPSIS...
A STRONG PACIFIC LOW PRESSURE SYSTEM WILL MOVE THROUGH ARIZONA THIS
WEEKEND. THE THREAT FOR VALLEY RAIN AND MOUNTAIN SNOW SHOWERS WILL
BEGIN EARLY SATURDAY...TAPERING OFF WEST TO EAST AS THE SYSTEM MOVES
TO OUR EAST MONDAY. DAYTIME TEMPERATURES WILL DROP BACK INTO THE MID
TO UPPER 60S FOR THE LOWER DESERTS SUNDAY AND MONDAY...WITH WARMER
AND DRIER CONDITIONS EXPECTED THROUGH THE MIDDLE OF NEXT WEEK.
&&
.DISCUSSION...
VIS/IR SATELLITE REVEAL BANDS OF HIGH LEVEL CLOUDS AHEAD OF OUR NEXT
POTENT LOW PRESSURE SYSTEM PASSING THROUGH CNTRL AND SO CA THIS
AFTERNOON. CLOUDS WILL THICKEN AND OVERSPREAD THE REGION LATER
TONIGHT. A MODEST TAP OF MID LEVEL MOISTURE IS ALSO SNEAKING INTO
SOUTHEAST PORTIONS OF THE STATE...EVIDENT FROM THE CUMULUS THAT HAVE
FORMED ACROSS SE AZ...SONORA AND CHIHUAHUA MEXICO. TEMPERATURES HAVE
WARMED UP NICELY TO FORECAST HIGHS ACROSS MUCH OF OUR CWA...SOME
SITES IN SOUTHEAST CALIFORNIA RUNNING ABOUT 3 DEGS COOLER IN
RESPONSE TO HEIGHT FALLS OF THE APPROACHING SYSTEM. SFC DEW POINTS
REMAIN IN THE 20S TO NEAR 30 DEGREES ACROSS SW AND S-CENTRAL AZ...
ABOUT 10-15 DEGREES HIGHER THAN YESTERDAY. PROGS AND GUIDANCE
SUGGEST THAT THE GRADUAL MOISTENING TREND WILL CONTINUE AND EXPAND
CWA-WIDE IN ADVANCE OF THE LOW AS IT DROPS SOUTHWARD ALONG THE WEST
COAST DURING THE NEXT 12-18 HOURS. THE PREVIOUS DISCUSSION THAT
FOLLOWS SUMMARIZES THE EXPECTED WEATHER VERY WELL AND IS STILL
REFERENCED.
PREVIOUS DISCUSSION...
TRAJECTORY OF THE LOW IS FAVORABLE FOR IMPORTING A DECENT AMOUNT OF
MOISTURE...BUT MORE SO...MODELS ARE INDICATING A VERY STRONG JET MAX
(+120KT) TO DEVELOP ON THE SOUTH SIDE OF THE LOW FRIDAY NIGHT
...ROTATING AROUND THE FRONT SIDE OF THE TROUGH AND THROUGH SOUTH
CENTRAL AZ BY EARLY SATURDAY. OVER THE ERN ZONES...OROGRAPHICALLY
ENHANCED PRECIP IS EXPECTED STARTING EARLY SATURDAY UNDER A STRONG
SWLY FLOW...WITH SLIGHT CHANCES ACROSS THE ENTIRE CWA. MEANWHILE...
THE COLD CENTER /700MB TEMPS AROUND -7C/ WILL MOVE INTO THE WESTERN
ZONES OVERNIGHT SATURDAY INTO SUNDAY. AS SUCH...THE SNOW LEVEL IS
EXPECTED TO DROP TO AROUND 4500/5000 FEET...WITH SNOW FLURRIES
POSSIBLE OVER THE HIGHEST TERRAIN OF CA ZONE 30...JOSHUA TREE
NATIONAL PARK...BY EARLY SUNDAY. THE PRECIP OVER THE ERN HALF OF THE
CWA FOR THE FIRST PART OF THE WEEKEND WILL MAINLY BE WARMER/UPSLOPE
ENHANCED...WITH THE SNOW LEVEL REMAINING ABOVE 6000 FT THROUGH
SATURDAY. BY EARLY SUNDAY...THE COLD POOL MOVES EASTWARD...WITH SNOW
LEVELS LOWERING TO NEAR 5000 FEET...WITH SNOW ACCUMULATION POSSIBLE
ACROSS THE HIGHER TERRAIN OF SOUTHERN GILA COUNTY...EAST OF THE
POPULATION CENTERS OF GLOBE/MIAMI. ACROSS THE VALLEY FLOORS...THE
THREAT FOR RAIN SHOWERS WILL CONTINUE THROUGH SUNDAY...WITH THE BEST
CHANCE LOOKING LIKE SUNDAY DAYTIME HOURS. DIFFICULT TO TELL JUST
WHEN THE PRECIP THREAT WILL END...WITH MODELS INDICATING WRAP AROUND
MOISTURE OVER THE ERN HALF OF OUR CWA INTO EARLY MONDAY.
AS FOR TEMPS...DAYTIME HIGHS SHOULD COOL INTO THE MID 60S BY SUNDAY
AND INTO MONDAY -- A FEW DEGREES BELOW CLIMO FOR THIS TIME OF YEAR.
SIGNIFICANT CLOUD COVER OVER THE WEEKEND SHOULD KEEP OVERNIGHT LOWS
FROM GETTING TOO CHILLY...MID TO UPPER 40S ACROSS THE WARMER DESERT
SPOTS. BY TUESDAY...LESS CLOUD COVER WILL ALLOW FOR MAXIMUM
RADIATIONAL COOLING...WITH DESERT LOWS EXPECTED TO BE IN THE MID TO
UPPER 30S. MODELS ARE INDICATING SHORTWAVE RIDGING TO BUILD IN
BEHIND THE DEPARTING TROUGH TUE AND WED...FOR MOSTLY CLEAR SKIES AND
DAYTIME HIGHS WARMING BACK TO NEAR AVERAGE FOR EARLY DECEMBER.
&&
.AVIATION...
A COLD FRONT WILL MOVE WEST TO EAST ACROSS THE FORECAST AREA SAT
MORNING. BIGGEST IMPACT FROM THIS SYSTEM WILL BE AN INCREASE IN WIND
SAT AFTERNOON AS A WEAK LOW LEVEL JET DEVELOPS AHEAD OF THE FRONT.
GUSTS TO 25KT WILL BE POSSIBLE AT KPHX/KIWA. AN INCREASE IN LOW
LEVEL MOISTURE IS ALSO ANTICIPATED SAT AFTERNOON...RESULTING IN SOME
STRATOCU/ALTOCU AT ALL TAF SITES AND AREAS OF SHOWERS...MAINLY
ACROSS THE HIGHER TERRAIN EAST OF PHOENIX.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
A LOW PRESSURE SYSTEM WILL MOVE THROUGH THE AREA LATE THIS WEEKEND
...WITH A CHANCE OF SHOWERS ON SUNDAY. DRY AND BREEZY CONDITIONS
CAN BE EXPECTED IN SOUTHEAST CALIFORNIA...AND A DECREASING CHANCE
OF SHOWERS IN SOUTH-CENTRAL ARIZONA ON MONDAY. MOSTLY CLEAR SKIES
WITH NEAR NORMAL TEMPERATURES ARE FORECAST FOR THE ENTIRE AREA
TUESDAY THROUGH THURSDAY.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...MEYERS/WANEK
AVIATION...HIRSCH
FIRE WEATHER...SIPPLE
