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000
FXUS65 KPSR 252031
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
130 PM MST SAT MAY 25 2013

.UPDATE...UPDATED AVIATION DISCUSSION.

&&

.SYNOPSIS...
DRY AND WARM CONDITIONS WILL PERSIST ACROSS THE REGION THROUGH THE
MEMORIAL DAY HOLIDAY WEEKEND. A QUICK MOVING LOW PRESSURE SYSTEM IS
EXPECTED TO AFFECT THE DESERT SOUTHWEST NEXT TUESDAY AND WEDNESDAY
BRINGING COOLER THAN NORMAL TEMPERATURES AND BREEZY TO WINDY
CONDITIONS. A WARMING TREND WITH CONTINUED DRY AIR IN PLACE SHOULD
MOVE IN FOR LATE NEXT WEEK.

&&

.DISCUSSION...
VIS/IR SATELLITE REVEALS A FEW HIGH CLOUDS DRIFTING ACROSS THE
REGION THIS MORNING. SURFACE CONDITIONS REMAIN WARM AND DRY...DEW
POINT TEMPS IN THE 20S ACROSS THE SOUTHWEST AZ DESERTS...SOMEWHAT
HIGHER INTO THE 30S ACROSS SOUTHEAST CALIFORNIA. THE KTWC SOUNDING
PROFILES OVER THE PAST SEVERAL DAYS DO SHOW A REPEATED SHALLOW
MOISTURE SEEP IN THE 800-700MB LAYER DUE TO A STRONGER NOCTURNAL LOW
LEVEL SOUTHERLY FLOW...BUT OTHER THAN THAT...NOT MUCH IN THE WAY OF
ATMOSPHERIC MOISTURE FOR ANY CLOUD DEVELOPMENT TO MAR THE SUNNY
FORECAST ON TAP FOR OUR AREA. REGIONAL UPPER AIR PLOTS OVER THE PAST
24 HOURS SHOW A 20-30MB INCREASE IN 500MB HEIGHTS...AND WITH THE
DRY CONDITIONS...SUNSHINE AND MIXING POTENTIAL...AFTERNOON TEMPS
SHOULD HEAT UP ONCE AGAIN CLOSE TO THE CENTURY MARK FOR SOME OF OUR
WARMER DESERT SITES. THE INHERITED FORECAST GRIDS CAPTURE THE
CURRENT OBSERVATIONS AND MODEL TRENDS...NO CHANGES NEEDED TO THE
FORECAST AT THIS TIME.

PREVIOUS DISCUSSION...
A FEW MORE DAYS OF THIS BLOCKING WEATHER PATTERN IS EXPECTED AS
SOUTHWESTERLY FLOW ALOFT DOMINATES THE DESERT SOUTHWEST AND
SHORTWAVE ENERGY PINWHEELS AROUND THE LARGE STATIONARY LOW OVER THE
PACIFIC NORTHWEST. THE LAST COUPLE DAYS HAVE BEEN A DEGREE OR TWO
WARMER THAN FORECAST...MOST LIKELY DUE TO SLIGHTLY HIGHER HEIGHTS
ACROSS THE REGION AND EFFICIENT DAYTIME MIXING UNDER THE BREEZY
CONDITIONS. GIVEN THIS TREND...HAVE BUMPED UP HIGHS TODAY A BIT WITH
MOST LOWER DESERT SPOTS NEARING THE CENTURY MARK. THIS SHOULD BE THE
LAST DAY OF ABOVE NORMAL TEMPERATURES THROUGH MID NEXT WEEK AS THE
NEXT WEATHER SYSTEM WILL DIVE MUCH FURTHER SOUTH. A COUPLE MINOR
SHORTWAVE IMPULSES HELP TO BRING DOWN HEIGHTS AND TEMPERATURES
BEGINNING SUNDAY AND MONDAY...ONE TRACKING ACROSS THE GREAT BASIN ON
SUNDAY AND ANOTHER COMING ONSHORE IN SOUTHERN CALIFORNIA ON MONDAY.
THIS SHOULD ALLOW FOR AT LEAST SOME HIGH CLOUDINESS AND HIGHS 2-5
DEGREES COOLER THAN NORMAL WITH THE COOLEST TEMPERATURES ACROSS OUR
WESTERN ZONES.

THE TRACK AND STRENGTH OF THE MAIN WEATHER FEATURE THAT WE HAVE BEEN
FOLLOWING OVER THE PAST COUPLE DAYS IS STILL SOMEWHAT
UNCERTAIN...BUT OVERALL...MODELS ARE STARTING TO COME TO A
CONSENSUS. THE EUROPEAN IS SLIGHTLY STRONGER...FURTHER SOUTH...AND
MORE MOIST THAN THE GFS...BUT AT LEAST THE OPERATIONAL RUN AND EACH
MODEL/S ENSEMBLE MEMBERS SHOW LESS SPREAD THAN THE LAST COUPLE DAYS.
THE CURRENT FORECAST REFLECTS A FAIRLY EVEN BLEND BETWEEN THE TWO
SOLUTIONS WITH THE MAIN SHORTWAVE TROUGH TRACKING THROUGH THE
NORTHERN HALF OF ARIZONA TUESDAY NIGHT INTO WEDNESDAY MORNING. THIS
TRACK WILL DEFINITELY BRING IN COOLER AIR...BUT NOT QUITE AS MUCH AS
MODELS HAD BEEN SHOWING THE PAST SEVERAL RUNS. MOISTURE AVAILABILITY
WILL STILL BE ON THE FAIRLY LOW SIDE AND WITH A TRACK TO OUR
NORTH...ANY PRECIPITATION CHANCES WILL GENERALLY BE CONFINED TO THE
NORTHERN HALF OF THE STATE. FORECAST CONFIDENCE IN THIS SOLUTION IS
MUCH BETTER THAN THE SEVERAL DAYS...BUT THERE IS ALWAYS STILL ROOM
FOR ADJUSTMENTS TO BE MADE. THE SYSTEM WILL ALSO BRING INCREASED
WINDS...BUT CURRENT THINKING IS SPEEDS SHOULD REMAIN WELL BELOW
ADVISORY STRENGTH.

FOR LATE NEXT WEEK...A NORTHWEST TO WESTERLY UPPER FLOW IS LIKELY
ACROSS THE DESERT SOUTHWEST WITH A BROAD TROUGH ACROSS THE CENTRAL
UNITED STATES. THIS SHOULD LEAD TO A MODERATING OF TEMPERATURES FOR
THURSDAY AND FRIDAY WITH HIGHS RETURNING TO AROUND OR SLIGHTLY ABOVE
SEASONAL NORMALS.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA...INCLUDING KPHX...KIWA...KSDL...SOUTHEAST
CALIFORNIA/SOUTHWEST ARIZONA...INCLUDING KIPL AND KBLH...

FEW-SCT CIRRUS EXPECTED THROUGH SUNDAY AT ALL TAF SITES. IN THE
PHOENIX AREA...WIND GUSTS WILL REACH 20 KT LATE THIS AFTERNOON AND
EARLY THIS EVENING BEFORE DIMINISHING AROUND 03Z. TYPICAL DRAINAGE
FLOW LESS THAN 10 KT EXPECTED OVERNIGHT...FOLLOWED BY A
REDEVELOPMENT OF THE UPSLOPE FLOW SUNDAY AFTERNOON...THOUGH SOMEWHAT
WEAKER. TYPICAL SOUTHWEST AND WEST WINDS ANTICIPATED IN SE CA AS
WELL.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
LOW PRESSURE ALONG THE WEST COAST WILL BEGIN TO PUSH INLAND OVER THE
DESERT SOUTHWEST LATE MONDAY...THEN SLOWLY MOVE EASTWARD ACROSS THE
REGION ON TUESDAY AND WEDNESDAY. AS A RESULT...TEMPERATURES ARE
EXPECTED TO FALL FROM THE MID AND UPPER 90S ON MONDAY INTO THE UPPER
80S AND LOW 90S ON TUESDAY AND WEDNESDAY ACROSS THE LOWER DESERTS.
ALTHOUGH SOME INCREASE IN THE WIND SPEEDS CAN ALSO BE EXPECTED ON
TUESDAY AND WEDNESDAY AFTERNOON...SLIGHTLY HIGHER HUMIDITIES WILL
KEEP FIRE DANGER VALUES FROM REACHING CRITICAL LEVELS. TEMPERATURES
WILL THEN RECOVER TO NEAR-NORMAL VALUES ON THURSDAY AND
FRIDAY...WITH A RETURN TO SINGLE DIGIT DAYTIME HUMIDITIES...AND
LIGHTER WINDS AS A DRY WESTERLY FLOW RETURNS TO THE REGION.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...MEYERS/KUHLMAN
AVIATION...HIRSCH
FIRE WEATHER...PERCHA