Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 020305
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
805 PM MST MON SEP 1 2014

&&

.SYNOPSIS...
ABOVE NORMAL TEMPERATURES WILL CONTINUE THROUGH THE MAJORITY OF THE
WEEK UNDER MOSTLY DRY CONDITIONS. MOISTURE WILL MAKE A GRADUAL
RETURN INTO THE REGION DURING THE LATE WEEK...SUPPORTING INCREASING
CHANCES FOR AFTERNOON AND EVENING THUNDERSTORMS OVER THE HIGHER
TERRAIN OF EASTERN AZ. BY THE WEEKEND...A DEEPER TROPICAL MOISTURE
PROFILE MAY BEGIN TO WORK INTO THE REGION BRINGING INCREASING
HUMIDITIES AND CLOUD COVER WITH SLIGHT STORM CHANCES BACK IN THE
FORECAST OVER THE LOWER DESERT ELEVATIONS OF ARIZONA AND TOWARDS THE
LOWER COLORADO RIVER VALLEY.

&&

.DISCUSSION...
LIGHT...AND DEEP WESTERLY FLOW ACROSS THE REGION ALONG WITH HIGH
PRESSURE ALOFT IS KEEPING SKIES CLEAR AND TEMPERATURES ABOVE NORMAL
ACROSS OUR CWA THIS EVENING...WITH PHOENIX SKY HARBOR REPORTING A
HIGH OF 108 TODAY. THE LATEST NAM CONTINUES TO SHOW LITTLE CHANGE IN
THE SENSIBLE WEATHER THROUGH MID-WEEK...WITH MAINLY CLEAR SKIES AND
ABOVE NORMAL TEMPERATURES TO CONTINUE THROUGH THE PERIOD. AS FAR AS
THE VERY SHORT TERM IS CONCERNED...OTHER THAN SOME VERY MINOR
ADJUSTMENTS TO THE TEMPERATURE AND DEWPOINT GRIDS...INHERITED
GRIDDED AND ZONE FORECAST PRODUCTS ARE HOLDING UP QUITE WELL...AND
NO UPDATES ARE PLANNED.

&&

.PREVIOUS DISCUSSION...
CLEAR SKIES PREVAIL ACROSS THE DESERT SOUTHWEST THIS AFTERNOON AS
DRY NORTHWESTERLY FLOW ALOFT REMAINS IN CONTROL FROM THE PAC NW TO
THE MISSISSIPPI RIVER. PWATS ACROSS THE REGION RANGE FROM APPROX 0.4
TO 0.7 INCHES WHICH IS ABOUT HALF OF WHAT SHOULD BE OBSERVED IN
EARLY SEPTEMBER. NOT SURPRISINGLY THIS HAS ALLOWED TEMPERATURES TO
WARM UP ONCE AGAIN...WITH EARLY AFTERNOON READINGS /LOWER 100S/
ALREADY EXCEEDING CLIMATOLOGICAL NORMALS FOR 1 SEPTEMBER.

THE FORECAST THROUGH MID WEEK WILL REMAIN ONE OF DRY CONDITIONS AND
ABOVE NORMAL TEMPERATURES AS DRY NORTHWESTERLY FLOW REMAINS IN
PLACE. H5 HEIGHTS WILL VARY LITTLE FROM DAY TO DAY AND A BLEND OF
THE BEST PERFORMING BIAS CORRECTED GUIDANCE CONTINUES TO YIELD HIGHS
IN THE 105-110 RANGE THROUGH WEDNESDAY. THUS...VERY FEW CHANGES WERE
MADE TO THE FORECAST THROUGH MID WEEK. THERE WILL BE A GRADUAL
INCREASE IN MOISTURE ACROSS ARIZONA LATE WEDNESDAY NIGHT INTO
THURSDAY WITH TODAYS 12Z GFS INDICATING SOME SHOWERS BREAKING OUT
ACROSS THE DESERTS EARLY THURSDAY MORNING. NOT BUYING INTO THIS
SOLUTION AS POINT SOUNDINGS ACROSS THE DESERTS DEPICT A VERY
UNFAVORABLE DRY LAYER BELOW 500MB. MORE FAVORABLE BL DO NOT
MATERIALIZE UNTIL THURSDAY AFTERNOON...WHICH IS WHEN CLIMO-LIKE POPS
WERE INTRODUCED INTO THE FORECAST.

MOISTURE LEVELS SLOWLY RETURN TO A MORE MONSOON LIKE PROFILE WHERE
AFTERNOON AND EVENING THUNDERSTORMS WILL BE POSSIBLE ACROSS THE
CENTRAL AND EASTERN AZ HIGHER TERRAIN...INCLUDING SOUTHERN GILA
COUNTY...FOR THURSDAY AND FRIDAY AFTERNOONS. MOST OF THE ACTIVITY
WILL REMAIN NORTH-EAST-SOUTH OF THE PHOENIX AREA...WITH GREATER
CHANCES OF SEEING STORM OUTFLOW INTRUSIONS AND THE EVER-PRESENT
THREAT FOR BLOWING DUST ALONG THOSE BOUNDARIES ACROSS THE LOWER
DESERT ELEVATIONS.

ALONG WITH ADDITIONAL GULF MOISTURE SPREADING OVER NORTHERN
MEXICO...FORECAST MODELS CONTINUE TO DEPICT THE FORMATION OF A
TROPICAL SYSTEM OFF THE CENTRAL MEXICAN COAST AND ANYWHERE FROM
300-500 MILES SOUTH OF THE BAJA TIP BY LATE WEDNESDAY. WHERE EARLIER
NHC FORECASTS HAD A 50 PERCENT PROB FOR DEVELOPMENT IN THE NEXT 5
DAYS...THEIR LATEST FORECASTS ARE NOW IN THE HIGH CHANCE RANGE AT 70
PERCENT. BY THE LATE FRIDAY/SATURDAY TIME PERIOD...THE TROPICAL
SYSTEM COULD BE TRACKING UP ALONG THE SOUTHWESTERN BAJA COAST.
ALSO FAR TO OUR NORTHWEST...RENEWED TROUGHING DEVELOPS OVER THE
PAC NORTHWEST COAST...EVENTUALLY SLIDING DOWN THE CA COAST BY THE
LATE WEEK. THE COMBINATION OF INCREASING HUMIDITIES AND CLOUDINESS
FROM THE POTENTIAL TROPICAL MOISTURE TAP ALONG WITH FALLING UPPER
HEIGHTS WILL ALLOW DAYTIME TEMPERATURES TO COOL DOWN BY THE LATE
WEEK/WEEKEND.

LATE FRIDAY THROUGH THE COMING WEEKEND...DISAGREEMENTS BETWEEN THE
MEDIUM RANGE OPERATIONAL AND ENSEMBLES MEMBERS CONTINUE WITH HOW THEY
HANDLE 1) THE TROPICAL SYSTEM AND 2) THE STRENGTH...EVOLUTION AND
RESIDENCE TIME OF THE TROUGHING TO OUR NORTHWEST. THE TROPICAL
SYSTEM IS BROUGHT NORTHWARD AND QUICKLY MOVES INTO THE BROAD MEAN
TROUGH FLOW OVER THE REGION IN THE GFS BY EARLY NEXT WEEK...THE
ECMWF KEEPS THE SYSTEM COMPACT AND TRACKS IT WEST OUT INTO THE OCEAN
BEFORE ATTEMPTING TO TURN IT BACK TOWARDS THE SOUTHWEST U.S. DURING
THE SAME TIME FRAME. TROUGHING OVER THE WEST COAST FOR THE WEEKEND
IS STRONGER WITH THE GFS SOLUTION BUT STRONG FOR EARLY NEXT WEEK
WITH THE ECMWF. WHILE THE PATTERN CONTINUES TO DEVELOP MADE MINOR
ADJUSTMENTS TO THE POP FORECAST...INTRODUCING SOME SLIGHT CHANCE
COVERAGE TOWARDS THE COLORADO RIVER VALLEY AND SOUTHEAST CA FOR
SUNDAY AND NUDGING POPS FROM PHOENIX EASTWARD UPWARDS A BIT AS THERE
IS SOME MODEL CONSENSUS ABOUT THE DEEP MONSOON MOISTURE PROFILE AND
ENERGY EXPANDING INTO THE REGION FROM THE GULF OF CA. TEMPERATURE
FORECAST FOR THE WEEKEND AND EARLY NEXT WEEK BECOMES TRICKY WITH THE
RETURN OF MOISTURE AND STORM CHANCES...BUT ALL THE CONSENSUS AND
BEST PERFORMING EXTENDED TEMPERATURE GUIDANCE WERE INDICATING A
SIGNIFICANT COOL DOWN BY EARLY NEXT WEEK...WITH WELL-BELOW NORMAL
TEMPERATURES AND SOME LOWER DESERT ELEVATIONS POSSIBLY STRUGGLING TO
HIT THE 100F MARK.

&&

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

CLEAR SKIES WILL CONTINUE THROUGH TUESDAY. LIGHT DIURNAL WIND
PATTERNS WILL CONTINUE WITH OCCASIONAL AFTERNOON GUSTS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
MONSOON MOISTURE RETURNS TO THE REGION DURING THIS PERIOD ALONG WITH
AN UPTREND IN SHOWER AND THUNDERSTORM CHANCES. ACCORDINGLY
HUMIDITIES TREND UPWARD AND HIGH TEMPERATURES TREND DOWNWARD. OVER
THE WEEKEND MINIMUM HUMIDITIES CLIMB WELL ABOVE 20 PERCENT AND HIGH
TEMPERATURES DIP BELOW NORMAL. WITH THE RETURN OF THUNDERSTORMS TO
THE AREA...THE POTENTIAL FOR STRONG AND ERRATIC WINDS FROM DISTANT
STORMS ALSO RETURNS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...PERCHA/LEINS/NOLTE
AVIATION...AJ
FIRE WEATHER...AJ





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