Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 241159
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
459 AM MST SUN MAY 24 2015

.UPDATE...UPDATED AVIATION DISCUSSION...

&&

.SYNOPSIS...
A SERIES OF LOW PRESSURE SYSTEMS MOVING THROUGH ARIZONA WILL KEEP
TEMPERATURES BELOW NORMAL THROUGH THE REMAINDER OF THE MEMORIAL DAY
WEEKEND. ISOLATED SHOWER AND THUNDERSTORM ACTIVITY IS POSSIBLE OVER
PARTS OF SOUTHWEST AND SOUTH-CENTRAL ARIZONA TODAY...THOUGH
MEASURABLE PRECIPITATION WILL GENERALLY REMAIN NORTH AND EAST OF
PHOENIX. A GRADUAL WARMING AND DRYING TREND IS EXPECTED EARLY THIS
WEEK...WITH TEMPERATURES RETURNING TO THE UPPER 90S AND EVEN
EXCEEDING THE 100 DEGREE MARK BY THE WEEKEND.

&&

.DISCUSSION...
LATEST STREAMLINE ANALYSIS SHOWS A WEAKENING UPPER LOW ACROSS WESTERN
CO WITH ANOTHER COMPACT VORT MAX DIVING SOUTHEASTWARD THROUGH
SOUTHERN CA. MODELS CONTINUE TO INDICATE THAT VORTICITY AND JET-FORCED
ASCENT WILL BE PREVALENT ACROSS SOUTHERN AZ TODAY AS THE LOW SLIDES
EASTWARD. WEAK WV TRANSPORT WILL BE AN INHIBITING FACTOR TO
WIDESPREAD PRECIPITATION. HOWEVER...A FEW NCEP NMM-BASED WRFS
SUGGEST THAT INSTABILITY ASSOCIATED WITH THE MID-LEVEL COLD POOL WILL
BE SUFFICIENT TO GENERATE ISOLATED THUNDERSTORMS ACROSS PORTIONS OF
SOUTHWESTERN AZ THIS AFTERNOON. MEASURABLE PRECIPITATION REMAINS
UNLIKELY IN THESE AREAS BUT A FEW LIGHTNING STRIKES ARE POSSIBLE.

IN TERMS OF PRECIPITATION...MODEL CONSENSUS SUGGESTS THE BEST CHANCE
WILL AGAIN BE WELL NORTH AND EAST OF PHOENIX. ACROSS THE LOWER
ELEVATIONS...A DRY SUB-CLOUD LAYER WILL LIKELY RESULT IN AREAS OF
VIRGA WHERE CU FIELDS ARE THE MOST ORGANIZED. WITH ONE LOW EXITING
THE WEST AND ANOTHER MOVING THROUGH AZ...TEMPERATURES WILL AGAIN BE
BELOW NORMAL...BUT A FEW DEGREES WARMER THAN THOSE OBSERVED SATURDAY.

EARLY THIS WEEK...THE MEAN FLOW WILL BECOME MORE ZONAL AND
ULTIMATELY SOUTHWESTERLY WHILE THE PERSISTENT NEGATIVE HEIGHT
ANOMALY MIGRATES EASTWARD AND DISSOLVES. HEIGHTS ACROSS THE REGION
WILL RISE STEADILY THROUGH THE WEEK...HERALDING A RETURN TO WARMER
AND DRIER CONDITIONS. GFS/ECMWF INDICATE THAT A WEAK PACIFIC TROUGH
WILL MOVE THROUGH THE DESERT SOUTHWEST WEDNESDAY...BUT THIS SYSTEM
WILL DO LITTLE TO TEMPER THE BUILDING HEAT. FORECAST IS WEIGHTED
HEAVILY TOWARDS THE OPERATIONAL AND ENSEMBLE-BASED ECMWF...WHICH ARE
EXHIBITING VERY LOW SPREAD AND ARE OFTEN TOP PERFORMERS IN THESE
TYPES OF SCENARIOS. WHAT THIS EQUATES TO IS LOWER DESERT HIGHS RISING
THROUGH THE 90S THROUGH MIDWEEK. HIGH TEMPERATURES MAY EXCEED THE 100
DEGREE MARK AS EARLY AS FRIDAY IN PHOENIX BUT WILL REMAIN WELL BELOW
RECORDS.

&&

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

NO AVIATION IMPACTS EXPECTED INTO MONDAY. CLEAR SKIES THIS MORNING
WILL GIVE WAY TO SOME FEW TO SCT AFTERNOON MID AND HIGH CLOUDS
MAINLY TO THE NORTH OF THE PHOENIX AREA. SOME HIGH BASED CU IS
PROBABLE ALSO OVER HIGH TERRAIN AREAS THIS AFTERNOON AS A WEAK UPPER
LEVEL DISTURBANCE PASSES THROUGH SOUTHERN ARIZONA. A VERY WEAK
PRESSURE GRADIENT WILL KEEP WINDS LESS THAN 10 KTS THROUGH THE
PERIOD WHILE FOLLOWING TYPICAL DIURNAL PATTERNS IN THE PHOENIX AREA.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
DRIER AND WARMER CONDITIONS WILL DEVELOP INTO THE REGION OVER THE
COMING WEEK AND RESULT IN OUR WARMEST TEMPERATURES SO FAR THIS YEAR
BY NEXT WEEKEND. THE WEATHER PATTERN WILL STILL REMAIN SOMEWHAT
ACTIVE OVERHEAD...AS A FEW WEAK DISTURBANCES BRUSH PAST OR THROUGH
THE AREA. HOWEVER...THESE WILL BE ON THE DRY SIDE. TEMPERATURES WILL
GRADUALLY WARM CLOSER TOWARD SEASONAL NORMALS. AS A RESULT...
AFTERNOON RELATIVE HUMIDITY VALUES WILL FALL BACK INTO THE TEENS
FOLLOWING FAIR TO GOOD OVERNIGHT RECOVERY. HOWEVER...WINDS WILL
GENERALLY REMAIN LIGHT FOLLOWING TYPICAL DAILY PATTERNS LEADING TO
MINIMAL FIRE WEATHER CONCERNS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&

$$

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

DISCUSSION...HIRSCH
AVIATION...KUHLMAN
FIRE WEATHER...NOLTE/MO



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