Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 021120
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
420 AM MST TUE SEP 2 2014

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.

&&

.SYNOPSIS...
ABOVE NORMAL TEMPERATURES WILL CONTINUE THROUGH AT LEAST WEDNESDAY
UNDER MOSTLY DRY CONDITIONS. MOISTURE WILL MAKE A GRADUAL RETURN INTO
THE REGION BEGINNING THURSDAY...SUPPORTING INCREASING CHANCES FOR
AFTERNOON AND EVENING THUNDERSTORMS OVER THE HIGHER TERRAIN OF AZ. BY
FRIDAY...A DEEPER TROPICAL MOISTURE PROFILE WILL CONTINUE TO WORK
INTO THE REGION RESULTING IN INCREASED HUMIDITIES...CLOUDINESS AND
COOLER TEMPERATURES. SLIGHT STORM CHANCES RETURN TO THE FORECAST OVER
THE LOWER DESERT ELEVATIONS OF ARIZONA AND TOWARDS THE LOWER COLORADO
RIVER VALLEY FOR THE WEEKEND.

&&

.DISCUSSION...
ANOTHER QUIET EVENING CONTINUES INTO THE EARLY MORNING HOURS WITH
CLEAR SKIES AND MOSTLY LIGHT WINDS OBSERVED ACROSS THE FORECAST AREA.
COMPARING DEWPOINT READINGS FROM THOSE 24 HRS AGO IT IS HARD TO
DISCERN ANY SORT OF TREND...WITH VALUES HIGHER OR LOWER BY ONLY A FEW
TO UP TO 20 DEGREES OF DIFFERENCE AT VARYING SURFACE SITES. LOOKING
HIGHER THROUGH THE WHOLE ATMOSPHERIC COLUMN...MEASURED/OBSERVED PWATS
LAST EVENING WERE HOLDING BELOW NORMAL VALUES - AT 67 PERCENT NORMAL
IN FLAGSTAFF WITH 0.45 INCHES AND FAIRING A BIT BETTER DOWN TUCSON-
WAY AT 85 PERCENT WITH 0.82 INCHES. WATER VAPOR AND 02/00Z UPPER AIR
ANALYSIS SHOWED THE HIGH PRESSURE CENTER TO OUR SOUTH WITH CONTINUED
DRY WESTERLY FLOW MOVING INLAND OFF THE PACIFIC. FAIRLY STEADY STATE
FORECAST IN STORE FOR TODAY AND WEDNESDAY...WITH LITTLE CHANGES
EXPECTED IN THE BROADER MEAN WIND FLOW AND TEMPERATURES THROUGH THE
COLUMN OVER WHAT WE`VE SEEN THE LAST FEW DAYS. THIS WILL RESULT IN
ANOTHER ROUND OF ABOVE NORMAL TEMPERATURES AND MOSTLY CLEAR SKIES.

UPPER RIDGE CENTER IS EXPECTED TO DEVELOP/RELOCATE TO OUR EAST BY
LATE WEDNESDAY...GRADUALLY BACKING WINDS TO MORE FAVORABLE
MONSOON HEADINGS. EARLY THURSDAY MORNING THE GFS...AND TO A LESSER
EXTENT THE NAM...STILL TRIES BRINGING IN SOME LIGHT PRECIP OVER THE
SOUTH-CENTRAL DESERTS. WHILE THE GFS HAS HAD SOME RUN-TO-RUN
CONSISTENCY WITH THIS SOLUTION...STILL NOT SOLD WE`LL SEE WETTING
PRECIP ON THE DESERT FLOORS THAT EARLY IN THE FORECAST PERIOD.
INCREASING CLOUD COVER AND MAYBE SOME VIRGA SHAFTS COULD BE
POSSIBLE...BUT MOISTURE REMAINS LIMITED BELOW 500MB. WHEN EVALUATING
THE COLUMN AS A WHOLE...1 INCH AND ABOVE PWATS RETURN TO AREA
OVERNIGHT WEDNESDAY ACROSS MUCH OF CENTRAL AND SOUTHERN AZ. AFTERNOON
AND EVENING THUNDERSTORMS WILL BE POSSIBLE ACROSS THE CENTRAL AND
EASTERN AZ HIGHER TERRAIN...INCLUDING SOUTHERN GILA
COUNTY...BEGINNING THURSDAY AFTERNOON. MOST OF THE ACTIVITY WILL
REMAIN NORTH-EAST-SOUTH OF THE PHOENIX AREA THURSDAY...WITH GREATER
CHANCES OF SEEING STORM OUTFLOW INTRUSIONS AND THE EVER-PRESENT
THREAT FOR BLOWING DUST ALONG THOSE BOUNDARIES ACROSS THE LOWER
DESERT ELEVATIONS.

FORECAST FOR FRIDAY IS A BIT TRICKIER...AS WE SEE A DECENT RETURN OF
MOISTURE BUT NOT MUCH BY WAY OF UPPER LEVEL SUPPORT OR ENERGY TO SEE
ORGANIZED STORM DEVELOPMENT. FORECASTS REMAIN GENERALLY CONSISTENT
WITH THE BEGINNINGS OF A DEEPER MOISTURE SURFACE MOVING IN FROM THE
SOUTH...WITH 850MB DEWPOINTS APPROACHING 10-12C READINGS HEADING INTO
THE AREA LATER IN THE DAY FRIDAY. FELT INTRODUCING AT LEAST 10
PERCENT POP/SLIGHT CHANCE MENTIONING DOWN THROUGH MARICOPA
COUNTY...INCLUDING THE PHX METRO...WAS WARRANTED. WHILE ORGANIZED
STORMS ARE NOT EXPECTED...TRAVELING OUTFLOW BOUNDARIES COULD SUPPORT
ISOLATED PULSE STORM ACTIVITY. DURING THIS SAME PERIOD...TROUGHING
WILL DEVELOP DOWN FROM THE PAC NW OFF THE NORTHERN CA
COAST...MAINTAINING DRIER FLOW OVER MOST OF SOUTHEAST CA...WITH A
SHARP MOISTURE GRADIENT ALONG THE LOWER COLORADO RIVER VALLEY. THE
RETURN OF INCREASING HUMIDITIES AND CLOUDS WILL HELP REIGN IN OUR
ABOVE NORMAL TEMPERATURES...COOLING TEMPERATURES TO MORE NORMAL
READINGS FOR THE LATE WEEK.

SATURDAY INTO EARLY NEXT WEEK...TROPICAL INFLUENCE IS LOOKING MORE
LIKELY FOR THE WEEKEND AND EARLY NEXT WEEK AS THE CURRENT AREA OF
INTEREST OFF THE CENTRAL MEXICAN COAST IS EXPECTED TO DEVELOP WITHIN
THE NEXT 2 TO 5 DAYS INTO A TROPICAL STORM WHILE MOVING CLOSER
TOWARDS THE BAJA PENINSULA. WITH CONTINUED ADJUSTMENTS TO THE
TROPICAL STORM TRACK ALONG WITH THE STRENGTH AND RESIDENCE TIME OF
THE WEST COAST TROUGH...FELT A BROAD BRUSH FORECAST APPROACH FOR THE
WEEKEND WAS WARRANTED. PRECIP CHANCES WERE INCREASED GIVEN DECENT
EXTENDED MODEL CONSENSUS ON MOISTURE AND CAPE/OMEGA FIELDS FOR SUNDAY
AND MONDAY...WITH SLIGHT CHANCES HOLDING EVEN DURING THE OVERNIGHT
HOURS ACROSS MUCH OF THE FORECAST AREA. SOME DISCREPANCIES REMAIN IN
MOISTURE PLACEMENT AND INFLUENCE OF DRY AIR INTRUSION FROM THE TROUGH
TO OUR NW...WITH THE LATEST EURO SOLUTION IS MORE AGGRESSIVE WITH THE
MOISTURE EXPANSION ACROSS SOUTHEAST CA. BOTTOM LINE...POTENTIAL IS
THERE AND CONFIDENCE HAS BEEN STEADILY INCREASING FOR A RETURN OF
SEVERAL STORMY DAYS AND EVENINGS THAT MAY LAST INTO IN THE MIDDLE
PART OF NEXT WEEK. LONGER RANGE PROBABILITIES CALL FOR AN EXTENDED
WINDOW OF ABOVE NORMAL PRECIP ACROSS THE SOUTHWEST REGION. WITH THE
UPTICK IN STORM ACTIVITY AND EXPECTATION OF MOSTLY TO CONSIDERABLY
CLOUDY SKIES...A COOL DOWN OF WELCOME PROPORTIONS WILL RESULT FOR THE
WEEKEND...WITH SEVERAL BEST PERFORMING AND CONSENSUS TEMPERATURE
FORECASTS COOLING MUCH OF THE FORECAST AREA BELOW 100F BY MONDAY AND
BEYOND.

&&

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

THROUGH 04Z WED...VERY DRY WESTERLY FLOW ALOFT PROVIDING CLEAR SKIES
AND LIGHT WIND UNDER 8 KNOTS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
MONSOON MOISTURE WILL RETURN TO THE REGION THIS PERIOD ALONG WITH AN
INCREASING THREAT OF SHOWERS AND THUNDERSTORMS. HEAVY RAIN IS A
POSSIBILITY IN SOUTH CENTRAL ARIZONA SUNDAY AND MONDAY. HUMIDITIES
WILL TREND HIGHER WITH A CORRESPONDING DOWNWARD TREND IN AFTERNOON
TEMPERATURES. MINIMUM RELATIVE HUMIDITIES WILL RANGE FROM NEAR 20
PERCENT THURSDAY...TO 30 TO 35 PERCENT BY MONDAY. DIURNAL AFTERNOON
WINDS EACH DAY WILL RANGE FROM 10 TO 15 MPH. RECOVERY AT NIGHT WILL
BE A FUNCTION OF NOCTURNAL SHOWERS AND THUNDERSTORMS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...NOLTE
AVIATION...VASQUEZ
FIRE WEATHER...VASQUEZ/AJ






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