FXUS65 KPSR 051709
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1005 AM MST SAT DEC 5 2009
.SYNOPSIS...
DRY WEATHER WITH BELOW AVERAGE TEMPERATURES FOR EARLY DECEMBER IS
EXPECTED THIS WEEKEND. A WET PACIFIC STORM WILL RESULT IN THE
LIKELIHOOD OF RAIN MONDAY AND MONDAY NIGHT. CLEARING IS EXPECTED
TUESDAY...FOLLOWED INCREASING CLOUDINESS WEDNESDAY AND A CHANCE OF
RAIN THURSDAY THROUGH EARLY FRIDAY. DRY WEATHER WITH NEAR AVERAGE
TEMPERATURES FOR MID DECEMBER IS EXPECTED TO RETURN NEXT WEEKEND.
&&
.DISCUSSION...
A THICK LAYER OF HIGH CLOUDINESS WAS MOVING EAST ACROSS THE AREA
THIS MORNING. AS A RESULT...HAVE INCREASED THE FORECAST CLOUD COVER
TO CONSIDERABLE CLOUDINESS EAST OF THE LOWER COLORADO RIVER VALLEY
FOR SOUTHWEST AND SOUTH-CENTRAL ARIZONA THROUGH THIS AFTERNOON.
MOSTLY CLOUDY SKIES OVER SOUTHEAST CALIFORNIA AND THE LOWER COLORADO
RIVER VALLEY INCLUDING YUMA ARE EXPECTED TO GIVE WAY TO DECREASING
CLOUDINESS FROM THE WEST THIS AFTERNOON BEHIND A VERY WEAK AXIS OR
TROUGH OF LOW PRESSURE. TEMPERATURES WILL PROBABLY BE SLIGHTLY LOWER
THAN FORECAST BUT STILL CLOSE. OTHER THAN THE INCREASED CLOUD COVER
TODAY...NO OTHER IMMEDIATE UPDATES ARE PLANNED.
PREVIOUS DISCUSSION...
NOTE...SIGNIFICANT RAIN IS LIKELY LATE MONDAY AND MONDAY NIGHT OVER
THE MOUNTAINS NORTH THROUGH EAST OF PHOENIX...FROM WICKENBURG TO
CAVE CREEK...AND GLOBE/MIAMI.
TODAY AND SUNDAY...
NUMERICAL MODELS...NAMELY THE GFS AND EUROPEAN ARE COMING AROUND TO
NEARLY THE SAME SOLUTION. A SERIES OF VERY COLD AND DYNAMICAL TROUGHS
OUT OF WESTERN CANADA WILL SETTLE OVER THE WESTERN STATES THIS
WEEKEND. ONE DRY DISTURBANCE WILL MOVE ACROSS NORTHERN AZ SATURDAY
NIGHT BUT WITH LITTLE EFFECT DUE TO THE BONE DRY AIRMASS CURRENTLY
OVER THE REGION. THEREFORE EXCEPT FOR HIGH CLOUDS AND SLIGHTLY
BELOW NORMAL TEMPERATURES...DRY WEATHER IS EXPECTED THIS WEEKEND
ACROSS THE FORECAST AREA...SOUTHEAST CA TO SOUTH CENTRAL AZ.
MONDAY THROUGH EARLY TUESDAY MORNING...
BOTH THE GFS AND EUROPEAN MODELS AGREE THAT A VERY COLD AND
DYNAMICAL TROUGH WILL MOVE SLOWLY INTO THE REGION MONDAY THROUGH
EARLY TUESDAY. THIS SYSTEM WILL TAP LOTS OF PACIFIC MOISTURE...
RESULTING IN A GOOD CHANCE OF SHOWERS THIS PERIOD.
58 MPH 850 MB SOUTHERLY WINDS...WITH STRONG WARM ADVECTION AND
INCREASING UPPER LEVEL DYNAMICS...WILL RESULT IN A GOOD CHANCE OF
SHOWERS OVER SOUTHEAST CA AND THE COLORADO RIVER VALLEY MONDAY.
PRECIP AMOUNTS HAVE THE POTENTIAL TO RANGE FROM 1/4 TO 1/2 INCH ON
THE DESERTS...TO 3/4 INCHES MAYBE MORE OVER THE MOUNTAINS OF JOSHUA
TREE NATIONAL PARK. PRECIP CHANCES WILL ABRUPTLY END MONDAY EVENING.
SNOW LEVELS WILL REMAIN NEAR 6000 FEET MONDAY...BUT FALL
DRAMATICALLY MONDAY NIGHT TO NEAR 4000 FEET...HOWEVER PRECIP ENDS BY
THEN.
FOR SOUTH CENTRAL AZ MONDAY AND MONDAY NIGHT...INCLUDING PHOENIX
AND VICINITY...LIGHT RAIN SLOWLY DEVELOPS DURING THE DAY. BY
EVENING...A BELT OF STRONG LOW LEVEL 50 MPH 850 MB WINDS...WITH DEEP
LOW LEVEL MOISTURE AND POSSIBLE THUNDERSTORMS...HAVE THE POTENTIAL
TO PRODUCE PERIODS OF VERY HEAVY RAIN...UPSLOPE RAIN MONDAY NIGHT.
BASED ON A LOCAL QPF STUDY...WHETHER ONE USES THE GFS OR EUROPEAN
MODEL...PRECIPITATION COULD RANGE FROM 3/4 OF AN INCH AT SKY HARBOR
AIRPORT...TO AROUND 2 INCHES OVER THE MOUNTAINS JUST NORTH AND
NORTHEAST OF CAVE CREEK/CAREFREE. THIS IS THE TYPE OF SETUP THAT
COULD REQUIRE A FLASH FLOOD WATCH FOR THE FLOOD PRONE
MOUNTAIN/DESERT INTERFACE AREAS NORTH THROUGH EAST OF PHOENIX.
AND...THUNDERSTORMS COULD EXACERBATE RAINFALL. SNOW LEVELS WILL
REMAIN NEAR 6000 FEET MONDAY NIGHT.
TUESDAY...
THE AIRMASS BEGINS TO DRY OUT TUESDAY MORNING WITH RAIN TAPERING OFF
DURING THE MORNING HOURS. SNOW LEVELS TUESDAY MORNING WILL FALL
SIGNIFICANTLY...TO NEAR 4000 FEET...HOWEVER PRECIPITATION ENDS BY
THEN. FLURRIES ARE LIKELY OVER THE MOUNTAINS OF SOUTHERN GILA COUNTY
ABOVE 4000 FEET TUESDAY.
LATE TUESDAY THROUGH WEDNESDAY...
A MUCH DRIER PATTERN DEVELOPS...A PERIOD BETWEEN STORMS. A SLIGHT
CHANCE OF SHOWERS WILL REMAIN OVER THE HIGHER TERRAIN OF SOUTH
CENTRAL AZ.
THURSDAY THROUGH EARLY FRIDAY...
A STRONG AND MOIST PACIFIC WESTERLY FLOW WILL RESULT IN ANOTHER
CHANCE OF SHOWERS REGION WIDE.
NEXT WEEKEND...
A SLIGHT CHANCE OF SHOWERS DEVELOP OVER SOUTHERN GILA COUNTY...
OTHERWISE DRY WEATHER IS EXPECTED ACROSS THE LOWER DESERTS OF
SOUTHEAST CA...SOUTHWEST AND SOUTH CENTRAL AZ.
&&
AVIATION...
LIGHT WINDS...WITH INCREASING MID AND HIGH LEVEL CLOUDS EXPECTED
THROUGH 06Z SUNDAY....AHEAD OF THE WELL-ADVERTISED APPROACHING LOW
PRESSURE SYSTEM THAT WILL MOVE INTO THE REGION LATE SUNDAY INTO
EARLY NEXT WEEK.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
A SERIES OF LOW PRESSURE SYSTEMS WILL MOVE ACROSS THE REGION...
BRINGING INCREASED MOISTURE THAT WILL LEAD TO CHANCES OF DESERT RAIN
AND MOUNTAIN SNOW. BREEZY CONDITIONS...WITH GUSTS UP TO 30 MPH...ARE
EXPECTED AREA-WIDE LATE MONDAY INTO TUESDAY...AND LIGHTER WINDS THE
REST OF THE PERIOD. ANTICIPATE COOLER TEMPERATURES AND ELEVATED
HUMIDITY LEVELS ALL WEEK.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...ELLIS/VASQUEZ
AVIATION...MEYERS
FIRE WEATHER...MEYERS
