FXUS65 KPSR 222202 AAA
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
302 PM MST TUE DEC 22 2009
.SYNOPSIS...
A STRONG LOW PRESSURE SYSTEM AND ASSOCIATED COLD FRONT WILL BRING
COLDER AND BREEZY TO WINDY WEATHER INTO THE REGION THIS
EVENING...WITH THE STRONGEST WINDS EXPECTED IN SOUTHEAST CALIFORNIA
AND SOUTHWEST ARIZONA PRODUCING AREAS OF BLOWING DUST. AS THE SYSTEM
MOVES THROUGH THE AREA...THERE WILL ALSO BE A CHANCE OF SHOWERS AND
THUNDERSTORMS...MAINLY ACROSS SOUTH-CENTRAL ARIZONA...AND
ACCUMULATING SNOWFALL IN THE HIGHER ELEVATIONS OF SOUTHERN GILA
COUNTY. MUCH COLDER WEATHER IS EXPECTED WEDNESDAY THROUGH
SATURDAY...WITH FREEZING TEMPERATURES EXPECTED IN COLDER DESERT
AREAS THURSDAY MORNING...CHRISTMAS MORNING AND AGAIN SATURDAY
MORNING.
&&
.DISCUSSION...
A POTENT WINTER STORM IS CURRENTLY MOVING THROUGH THE
SOUTHWEST...BRINGING STRONG GUSTY WINDS...BLOWING
DUST...CONVECTION...AND EVENTUALLY SNOWFALL TO ARIZONA. SHOWERS
BEGAN DEVELOPING ALONG THE APPROACHING SURFACE TROUGH EARLY THIS
MORNING AND HAVE INCREASED IN COVERAGE AND INTENSITY AS THE DAY
PROGRESSED. RADAR CURRENTLY SHOWS A BROAD AREA OF CONVECTION
EXTENDING FROM GILA COUNTY SOUTHWEST TO SOUTHERN MARICOPA COUNTY. A
FEW LOW TOPPED THUNDERSTORMS HAVE DEVELOPED IN EASTERN MARICOPA AND
SOUTHWEST GILA COUNTY. REPORTS OF SMALL HAIL HAVE BEEN RECEIVED FROM
NWS STORM SPOTTERS.
THE STRONG GUSTY WINDS HAVE RESULTED IN AREAS OF BLOWING DUST ACROSS
OUR SOUTHERN ZONES. A WIND ADVISORY AND DUST STORM WARNING ARE IN
EFFECT FOR PORTIONS OF THE PHOENIX FORECAST AREA THROUGH THIS
EVENING.
AS THE STORM SYSTEM PROGRESSES EAST SNOW LEVELS WILL LOWER TO LESS
THAN 4000 FEET OVER GILA COUNTY AND ACCUMULATING SNOW WILL BEGIN
FALLING THIS EVENING INTO WEDNESDAY MORNING. A WINTER WEATHER
ADVISORY HAS BEEN ISSUED FOR THIS EVENING THROUGH WEDNESDAY
MORNING...WITH ACCUMULATIONS OF 3 TO 5 INCHES EXPECTED ABOVE 5000
FEET AND 1 TO 3 INCHES EXPECTED AT ELEVATIONS ABOVE 3800 FEET AND AT
AND BELOW 5000 FEET.
BOTH THE GFS AND ECMWF KEEP SOME MOISTURE OVER EASTERN ARIZONA
THROUGH WEDNESDAY AFTERNOON...SO KEPT POPS GOING IN OUR EASTERN
ZONES THAT WERE IN THIS MORNINGS FORECAST PACKAGE. LIKELIHOOD OF
PRECIPITATION WILL GRADUALLY DIMINISH THROUGH WEDNESDAY EVENING.
BOTH THE ECMWF AND GFS SHOW THE UPPER LEVEL TROUGH AXIS RAPIDLY
SWINGING THROUGH THE REGION AND EXITING OVER THE MID-WEST US BY
THURSDAY MORNING. ARIZONA WILL REMAIN HOWEVER IN A COLD NORTHWEST
FLOW THROUGH THE EARLY PART OF THE WEEKEND. THIS WILL MEAN VERY COLD
MORNING TEMPS IN THE LOWER DESERTS THURSDAY...FRIDAY...AND SATURDAY.
ALTHOUGH FREEZING TEMPS WILL LIKELY BE REACHED IN SOME OF THE COOLER
LOCATIONS...AREAL COVERAGE AND DURATION OF SUB-FREEZING READINGS
DOES NOT CURRENTLY MEET FREEZE WARNING CRITERIA. IT IS POSSIBLE THAT
A FREEZE WARNING MAY BE DEEMED NECESSARY SHOULD MINIMUM TEMPERATURES
BE ADJUSTED BY SUBSEQUENT SHIFTS.
BY SUNDAY THERE IS QUITE A BIT OF DISPARITY BETWEEN THE GFS AND
ECMWF...WITH THE MODELS COMPLETELY OUT OF PHASE WITH ONE ANOTHER.
THE ECMWF SHOWS A WEAK TROUGH LOCATED OVER THE FOUR CORNERS REGION
WITH A TROUGH LOCATED UPSTREAM OFF THE CALIFORNIA COAST. THE GFS HAS
A MORE ZONAL PATTERN OVER SOUTHERN ARIZONA...BUT DOES PICK UP ON THE
SAME APPROACHING TROUGH IN THE EASTERN PACIFIC. BIG DISCREPANCY IS
THE AMOUNT OF PRECIPITATION GENERATED BY EACH MODEL. THE ECMWF
BRINGS AN AREA OF PRECIPITATION BACK INTO THE SOUTHWEST BY SUNDAY
EVENING...WHILE THE GFS LAGS PRECIPITATION 12 TO 24 HOURS AND SWINGS
IT TO THE SOUTH ACROSS BAJA AND NORTHERN MEXICO.
WITH THE BIG EMPHASIS TODAY ON THE FIRST TWO FORECAST PERIODS...AND
THE CURRENT UNCERTAINTY IN THE MODEL SOLUTIONS IN THE EXTENDED PART
OF THE FORECAST PACKAGE...DECIDED TO LEAVE FORECAST BEYOND SATURDAY
AS INHERITED THIS MORNING. EXISTING GRIDS AND FORECAST PACKAGE BEGIN
RAMPING UP PRECIP CHANCES...MAINLY IN OUR EASTERN ZONES...BEGINNING
SUNDAY EVENING.
&&
.AVIATION...
SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
A STRONG COLD FRONT WILL MOVE THROUGH THE AREA. INCREASING WESTERLY
SURFACE WINDS...STRONGEST AT KIPL...25 TO 40 KNOTS. MOSTLY CLEAR
SKIES. FROM 22Z TUE TO 06Z WED...CLEARING SKIES BUT WESTERLY GUSTS
IN THE 20 TO 35 KNOT RANGE. AFTER 06Z WED...WEST TO NORTHWEST
SURFACE WINDS 10 TO 15 KNOTS. CLEAR SKIES.
SOUTH CENTRAL ARIZONA INCLUDING KPHX AND KIWA...
BETWEEN 20Z TUE AND 02Z WED. COLD FRONT APPROACHING. 21Z TUE...
CLOUDS THICKENING AND LOWERING WITH A CHANCE OF SHOWERS AND
THUNDERSTORMS. CLDS BKN AT 6 THSD AGL. TSTM GUSTS TO 35 KTS
POSSIBLE. FROM 02Z WED TO 07Z WED...WEST WINDS 10 TO 20 KNOTS...SCT
CLDS NEAR 6 THSD FT AGL...WITH BKN CLDS AOA 10 THSD. ISOLATED RAIN
SHOWERS.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
TONIGHT...
A COLD FRONT WILL MOVE THROUGH THE AREA. INCREASING HUMIDITY IS
EXPECTED THROUGH WEDNESDAY MORNING...WITH A FEW SHOWERS POSSIBLE IN
SOUTHWEST AND SOUTH CENTRAL AZ. VERY WINDY THROUGH LATE NIGHT
TUESDAY ALL ZONES.
WEDNESDAY...
CLEARING WITH A SLOW DECREASE IN HUMIDITY...FOLLOWING THE COLD
FRONT. GUSTY NORTHWEST WINDS DIMINISHING MORNING HOURS AND BECOMING
LIGHT...WITH THE EXCEPTION OF NORTH WINDS TO 25 MPH DOWN THE
COLORADO RIVER VALLEY.
THURSDAY THROUGH SUNDAY...
MUCH LOWER HUMIDITY SPREADING ACROSS THE REGION FROM THE NORTH.
OTHERWISE DRY WEATHER WITH BELOW NORMAL TEMPERATURES.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...DUST STORM WARNING UNTIL 5 PM MST THIS AFTERNOON FOR
AZZ020-025>028.
WIND ADVISORY UNTIL MIDNIGHT MST TONIGHT FOR AZZ020>028.
WINTER WEATHER ADVISORY UNTIL 5 AM MST WEDNESDAY FOR AZZ024.
CA...DUST STORM WARNING UNTIL 4 PM PST THIS AFTERNOON FOR CAZ031.
WIND ADVISORY UNTIL 11 PM PST THIS EVENING FOR CAZ030>033.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...MCLANE
AVIATION...VASQUEZ
FIRE WEATHER...VASQUEZ
