FXUS65 KPSR 030458 CCA
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
955 PM MST WED DEC 2 2009
CORRECTED TYPO
.SYNOPSIS...
A DRY FLOW ALOFT FROM THE NORTHWEST WILL RESULT IN CLEAR SKIES
TONIGHT AND SUNNY SKIES THURSDAY WITH TYPICAL TEMPERATURES FOR EARLY
DECEMBER. A DRY COLD FRONT FROM THE NORTH WILL BRING BREEZY WEATHER
TO SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA THURSDAY INTO FRIDAY
AND SOUTH-CENTRAL ARIZONA BY FRIDAY ALONG WITH COLDER AND VERY DRY
AIR. SOME FREEZING TEMPERATURES ARE EXPECTED IN COLDER DESERT AREAS
THURSDAY NIGHT WITH MORE WIDESPREAD FREEZING TEMPERATURES FRIDAY
NIGHT. HIGH CLOUDINESS IS EXPECTED TO INCREASE FRIDAY NIGHT INTO
SATURDAY...FOLLOWED BY UNSETTLED WEATHER AND A CHANCE OF RAIN NEXT
WEEK AS PACIFIC STORMS MOVES INTO OUR AREA.
&&
.DISCUSSION...
CLEAR SKIES PREVAIL ACROSS THE FORECAST AREA THIS EVENING UNDER
NORTHWESTERLY FLOW ALOFT. THE DESERT SOUTHWEST LIES BETWEEN AN UPPER
LOW CENTERED OVER THE NORTH-CENTRAL STATES AND A HIGH AMPLITUDE
RIDGE WITH AN AXIS NEAR THE WEST COAST. SOUTHERN BRANCH FLOW
UNDERCUTTING THE RIDGE SEEMS TO BE DIMINISHING THOUGH THERE IS ALSO
A SUBTROPICAL JET EMANATING FROM SOUTHWEST OF HAWAII WHICH IS
MERGING WITH THE UNDERCUTTING FLOW OFF THE CALIFORNIA COAST.
IN THE SHORT TERM...MODELS CONTINUE TO SHOW A SOUTHWARD MOVING WAVE
ON THE WESTERN PERIPHERY OF THE UPPER LOW THAT WILL PASS OVER
ARIZONA TOMORROW AND TOMORROW NIGHT. IT WILL LEAD TO BREEZY TO
LOCALLY WINDY CONDITIONS AT TIMES TOMORROW AFTERNOON TO FRIDAY
MORNING...MOST NOTICEABLE ALONG THE LOWER COLORADO RIVER VALLEY AND
THE HIGHER TERRAIN OF SOUTH-CENTRAL ARIZONA. THERE WILL ALSO BE SOME
COOLING OVER EASTERN PORTIONS OF OUR FORECAST AREA...MAINLY EAST OF
PHOENIX. ANOTHER NOTABLE CHANGE WILL BE THE EXTREMELY DRY
CONTINENTAL AIR BROUGHT THE DISTURBANCE USHERS IN. ANTICIPATE
SUB-ZERO DEW POINTS FRIDAY. MODELS CONTINUE TO SHOW ANOTHER WAVE
APPROACHING FROM THE NORTH ON FRIDAY.
NO CHANGES TO THE FORECAST AT THIS TIME OTHER THAN SOME MINOR GRID
UPDATES.
PREVIOUS DISCUSSION...
A FLOW ALOFT FROM THE NORTHWEST IS EXPECTED TO BE DRY WITH MOSTLY
CLEAR SKIES TONIGHT AND SUNNY SKIES THURSDAY. TYPICAL TEMPERATURES
FOR EARLY DECEMBER ARE ALSO EXPECTED.
THE VERY DRY FAR SOUTHWEST END OF A VERY LARGE LOW PRESSURE SYSTEM
ALOFT CENTERED OVER THE UPPER MIDWEST AND ASSOCIATED COLD FRONT WILL
MOVE SOUTHEAST ACROSS OUR AREA THURSDAY AFTERNOON AND THURSDAY NIGHT.
STRONG SURFACE HIGH PRESSURE BEHIND THIS SYSTEM IS EXPECTED TO BUILD
OVER NEVADA AND UTAH WITH BREEZY WINDS FROM THE NORTH IN SOUTHEAST
CALIFORNIA AND SOUTHWEST ARIZONA THURSDAY INTO FRIDAY...ESPECIALLY
DOWN THE LOWER COLORADO RIVER VALLEY. ALSO...AN INCREASE IN
BREEZINESS FROM THE NORTHEAST IS EXPECTED IN SOUTH-CENTRAL ARIZONA
BY FRIDAY MORNING AND EARLY AFTERNOON. THESE WINDS WILL BRING COLDER
AND VERY DRY AIR INTO OUR AREA WITH SINGLE DIGIT MINIMUM AFTERNOON
RELATIVE HUMIDITY FRIDAY.
SOME FREEZING TEMPERATURES ARE EXPECTED IN COLDER DESERT AREAS
THURSDAY NIGHT WITH MORE WIDESPREAD FREEZING TEMPERATURES FRIDAY
NIGHT. PROTECTION FOR THE MORE FROST SENSITIVE PLANTS WILL BE
NECESSARY PERHAPS EARLY FRIDAY MORNING...BUT MORE LIKELY BY LATE
FRIDAY NIGHT AND EARLY SATURDAY MORNING.
A WEAK PACIFIC LOW PRESSURE SYSTEM FROM THE WEST IS EXPECTED TO
SPREAD CONSIDERABLE HIGH CLOUDINESS OVER OUR AREA FRIDAY NIGHT AND
SATURDAY.
A HIGH PRESSURE SYSTEM ALOFT IS EXPECTED TO BECOME ANCHORED OVER THE
GULF OF ALASKA AND ALASKA THIS COMING WEEKEND AND MUCH OF NEXT WEEK.
AT THE SAME TIME A STRONG AND COLD LOW PRESSURE SYSTEM IS EXPECTED
TO DEVELOP NEAR THE PACIFIC NORTHWEST COAST BY SUNDAY INTO MONDAY.
THERE IS MUCH UNCERTAINTY REGARDING WHAT TRACK THIS LOW PRESSURE
SYSTEM WILL TAKE. IT COULD MOVE SOUTHEAST AND RESULT IN MOST OF THE
RAINFALL THAT OCCURS NEXT WEEK ON MONDAY NIGHT AND TUESDAY. HOWEVER
A LOW PRESSURE SYSTEM FROM THE WEST AND MOISTURE ASSOCIATED WITH THE
SUBTROPICAL JET STREAM WILL PROBABLY BRING MOST OF NEXT WEEKS
RAINFALL SOMETIME BETWEEN WEDNESDAY NIGHT AND FRIDAY. IN OTHER
WORDS...AS IS TYPICAL THAT FAR OUT IN TIME...THE TRACK AND TIMING IS
UNCERTAIN...BUT IT DOES LOOK AS IF OUR WEATHER WILL BECOME UNSETTLED
WITH A CHANCE OF RAIN NEXT WEEK. THE SNOW LEVEL IS EXPECTED TO MOSTLY
BE ABOVE 7 THOUSAND FEET.
THERE IS A POTENTIAL FOR SIGNIFICANT RAIN IN OUR AREA NEXT WEEK...
ESPECIALLY IN SOUTH-CENTRAL ARIZONA NORTH AND EAST OF PHOENIX.
HOWEVER...THERE IS STILL MUCH UNCERTAINTY THIS FAR OUT IN TIME. FOR
THE TIME BEING...HAVE KEPT THE PRECIPITATION FORECAST INHERITED BY
THE PREVIOUS SHIFT. STAY TUNED.
&&
AVIATION...
SOUTHEAST CALIFORNIA...SOUTHWEST AND SOUTH-CENTRAL AZ...INCLUDING
KPHX...KIWA...KIPL...AND KBLH.
ANTICIPATE LIGHT WINDS THROUGH 18Z THURSDAY BEFORE MORE NOTICEABLE
WINDS DEVELOP AFTER 20Z AS A DRY WEATHER DISTURBANCE ENTERS THE
STATE FROM THE NORTH. ANTICIPATE TYPICAL WIND DIRECTIONS THURSDAY
AFTERNOON OVER THE PHOENIX AREA...BUT WITH A BIT STRONGER SPEEDS.
LOOK FOR NORTHERLY WINDS TO DEVELOP OVER SOUTHEAST CALIFORNIA AND
THE LOWER COLORADO RIVER VALLEY THURSDAY AFTERNOON...WITH GUSTS OF
15-20 KNOTS AFTER 21Z. OTHERWISE...SKIES WILL BE CLEAR.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
A LOW PRESSURE SYSTEM WILL MOVE THROUGH THE SOUTHERN ROCKIES BY
FRIDAY. THE ASSOCIATED COLD FRONT WILL BRING AN INCREASE IN THE WIND
LATE THURSDAY...AND INTO FRIDAY. MUCH DRIER AIR WILL SPREAD ACROSS
ALL ZONES ON FRIDAY...WITH MINIMUM RH VALUES DROPPING INTO THE
SINGLE DIGITS THROUGHOUT THE DESERTS. AT THIS TIME...CRITICAL FIRE
WEATHER THRESHOLDS ARE NOT EXPECTED TO BE REACHED.
INCREASING CLOUDS AND HUMIDITY ARE EXPECTED LATE IN THE WEEKEND...AS
A MAJOR CHANGE IN THE PATTERN DEVELOPS. A SERIES OF PACIFIC STORMS
ARE EXPECTED TO MOVE ACROSS THE REGION...FOR AN INCREASING CHANCE
OF SHOWERS PARTICULARLY MONDAY AND TUESDAY.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...AJ/ELLIS
AVIATION...AJ
FIRE WEATHER...SIPPLE
