FXUS65 KPSR 290323
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
820 PM MST SAT NOV 28 2009
.SYNOPSIS...
A STRONG LOW PRESSURE SYSTEM CROSSING THE DESERT SOUTHWEST IS
BRINGING COOLER WEATHER AND A CHANCE OF SHOWERS AND THUNDERSTORMS
ACROSS THE REGION ALONG WITH SNOW SHOWERS IN HIGHER TERRAIN THROUGH
SUNDAY. WARMER TEMPERATURES AND DRY WEATHER WILL RETURN EARLY NEXT
WEEK.
&&
.DISCUSSION...
A STRONG COLD WINTER-LIKE LOW PRESSURE SYSTEM CONTINUE TO SLOWLY
ADVANCE INTO AZ THIS EVENING AT 03Z SUN. THE 500 MB CENTER OF THE
TROF WAS LOCATED ABOUT 140 MILES SOUTH-SOUTHWEST OF LAS VEGAS AT
00Z...WITH MODELS FORECASTING THIS CENTER TO MOVE SOUTH INTO THE
NORTHERN GULF OF CA BY SUNDAY EVENING. DUE TO THE LARGE SIZE OF THIS
TROF...THE COLD UNSTABLE AIR HAD COVERED MOST OF AZ SATURDAY EVENING
...WITH FAIRLY STRONG DYNAMICS STILL NOTED ACROSS CENTRAL AZ AT
03Z...E.G. 500-300 MB HEIGHT FALLS OF 80 TO 120 METERS RESPECTIVELY
IN CENTRAL AZ.
DESPITE THE STRONG DYNAMICS...MOST OF THE MOISTURE SEEMED TO BE
CONCENTRATED IN THE BOUNDARY LAYER. SATURDAY MORNING SOUNDINGS AT
SAN DIEGO AND VANDENBERG SHOWED A FAIRLY NARROW PLUME OF HIGH
MOISTURE...6 TO 12 THSD FEET DEEP...THAT EVENTUALLY FLOWED OVER THE
COASTAL RANGE INTO THE DESERTS AND MOUNTAINS OF AZ. COUPLED WITH
STORM DYNAMICS...THIS RESULTED IN A FEW SHOWERS AND THUNDERSTORMS
OVER THE FORECAST AREA...SOUTHEAST CA TO SOUTH CENTRAL AZ. SMALL
HAIL WAS EVEN REPORTED IN NORTH PHOENIX SATURDAY AFTERNOON WITH A
FEW THUNDERSTORMS.
UPPER LEVEL STORM DYNAMICS WILL BE SHIFTING INTO SOUTHEAST AZ BY
EARLY SUNDAY MORNING...THEN INTO NORTHWEST MEXICO SUNDAY AFTERNOON.
THE BEST CHANCE OF MODERATE SHOWERS AND THUNDERSTORMS IN CENTRAL
AZ...INCLUDING THE PHOENIX AREA...WILL HAVE TO COME BEFORE MIDNIGHT
OR 07Z SUN. SNOW LEVELS IN SOUTH CENTRAL AZ WILL ALSO FALL TO NEAR
5000 FEET...INCLUDING SOUTHERN GILA COUNTY ZONE 24 BUT WITH VERY
LITTLE ACCUMULATION EXPECTED. SNOW LEVELS IN SOUTHEAST CA ARE NEAR
5000 FEET ...BUT SHOWERS HAVE BEEN SPOTTY THERE THIS EVENING.
AS DYNAMICS SHIFT SOUTH ON SUNDAY...THE DRIER AND COLDER AIR WILL
CHANGE THE CHARACTER OF THE PRECIP TO LIGHT SHOWERS IN SOUTH CENTRAL
AZ SUNDAY AFTERNOON AND EVENING. THEREFORE THE CHANCE OF SHOWERS
WILL CONTINUE OVER SOUTH CENTRAL AZ...INCLUDING PHOENIX THROUGH
EARLY SUNDAY NIGHT. OUT WEST IN SOUTHEAST CA AND SOUTHWEST AZ...
CLEARING SKIES ARE EXPECTED BY SUNDAY AFTERNOON.
ONE CAVEAT THOUGH...THERE IS A POSSIBILITY OF A BURST OF HEAVY SNOW
LATE SUNDAY NIGHT/MONDAY MORNING OVER THE EASTERN MOUNTAINS OF ZONE
24...SOUTHERN GILA COUNTY ON THE SAN CARLOS INDIAN RESERVATION.
WRAP AROUND MOISTURE...WITH INCREASED UPSLOPE SOUTHEASTERLY FLOW...
COULD PRODUCE BETWEEN 2 TO 4 INCHES OF DRY SNOW ABOVE 5000 FEET.
HOWEVER...A DEEPER MOVING TROF INTO MEXICO COULD NEGATE THE HEAVY
SNOW THREAT ON THE SAN CARLOS...THEREFORE ANY SNOW ADVISORIES WILL
BE DEFERRED TO THE SATURDAY MIDNIGHT OR SUNDAY DAY SHIFT AS THIS LOW
PRESSURE SYSTEM SLOWLY EVOLVES AND DEEPENS SOUTH.
OTHERWISE CURRENT FORECASTS OF A CHANCE OF SHOWERS THROUGH SUNDAY
EVENING IN SOUTH CENTRAL AZ...INCLUDING THE PHOENIX METRO AREA
LOOKS OK FOR NOW. THERE ARE NO CURRENT THREATS OF SIGNIFICANT
WEATHER THIS EVENING...AND...OTHER THAN A FEW GRID UPDATES MADE
EARLIER...FORECASTS LOOKS FINE FOR NOW. PREVIOUS DISCUSSION BELOW
STILL APPLIES.
PREVIOUS DISCUSSION...
COMPLEX WEATHER PATTERN IN THE SHORT TERM AS A STRONG LOW PRESSURE
SYSTEM LOCATED OVER THE MOJAVE DESERT IN SOUTHERN CALIFORNIA BRINGS
COOLER AIR AND HIGHER INSTABILITY TO THE SOUTHWEST U.S. THIS LOW IS
MOVING TOWARDS THE SOUTH AND WILL CROSS INTO MEXICO SOMETIME THIS
EVENING. A CHANCE OF SHOWERS AND A FEW THUNDERSTORMS WILL REMAIN
ACROSS THE CWA THROUGH SUNDAY MORNING AS THE LOW PRESSURE SYSTEM
MOVES AWAY FROM THE REGION. ALSO...THE COOLER AIR...ALONG WITH THE
HIGHER INSTABILITY...WILL LEAD TO SOME SNOW SHOWERS IN HIGHER
TERRAIN OF SOUTHERN GILA COUNTY WITH AMOUNTS UP TO ONE INCH ABOVE
5000 FEET TONIGHT. ATTM SNOWFALL AMOUNTS ARE NOT EXPECTED TO REACH
WINTER ADVISORY LEVELS. FREEZING TEMPERATURES CAN BE EXPECTED IN THE
HIGHER TERRAIN OF GILA COUNTY FOR THE NEXT TWO EVENINGS.
MODELS ARE IN AGREEMENT FOR NEXT 72 HOURS PULLING THE LOW ACROSS
NORTHERN MEXICO AND BACK UP INTO TEXAS. THIS WILL KEEP US IN A
NORTHWESTERLY FLOW ALOFT THROUGH WEDNESDAY...DRYING OUT THE
ATMOSPHERE AND BRINGING BACK CLEAR CONDITIONS AND A SLOW WARMING
TREND.
&&
AVIATION...
SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KIPL AND KBLH AIRPORTS...A
LOW PRESSURE SYSTEM MOVING SLOWLY MOVING THROUGH THE AREA. THROUGH
14Z SUN...SCT-BKN CLOUDS 6-8 THSD MSL WITH ISOLATED RAIN SHOWERS.
AFTER 14Z...CLOUDS CLEARING BECOMING SCT 8-10 THSD MSL. LIGHT WEST
TO NORTHWEST WINDS UNDER 10 KNOTS.
SOUTH CENTRAL AZ...INCLUDING KIWA AND KPHX...
A LOW PRESSURE SYSTEM SLOWLY MOVING INTO THE AREA. THROUGH 07Z
SUN...BKN CLDS 6 TO 8 THSD MSL...SCT RAIN SHOWERS AND AN ISOLATED
THUNDERSTORM. WEST WINDS 8 TO 12 KNOTS. FROM 07Z SUN TO 01Z
MON...BKN CLDS 6 TO 8 THSD MSL WITH A CHANCE OF RAIN SHOWERS. LIGHT
EAST TO SOUTHEAST WINDS 5 TO 10 KNOTS.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
THE DEEP LOW PRESSURE SYSTEM WILL MOVE OUT OF THE AREA WITH A
CLEARING TREND BY MONDAY. WEAK HIGH PRESSURE AND MOSTLY CLEAR SKIES
ARE EXPECTED TUESDAY THROUGH FRIDAY...WITH NEAR NORMAL TEMPERATURES
FOR LATE NOVEMBER. DRY CONDITIONS WITH LOW HUMIDITY CAN BE EXPECTED
ON WEDNESDAY IN THE WESTERN DESERTS...AND WINDS SHOULD REMAIN BELOW
CRITICAL FIRE WEATHER THRESHOLDS.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...VASQUEZ/WATERS
AVIATION...VASQUEZ
FIRE WEATHER...SIPPLE
