Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 221541
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
840 AM MST TUE JUL 22 2014

.SYNOPSIS...
A STRONG HIGH PRESSURE SYSTEM IS FORECAST TO DEVELOP OVER THE REGION
THIS WEEK...RESULTING IN VERY HOT TEMPERATURES BY WEDNESDAY. AT THE
SAME TIME...MONSOON MOISTURE WILL SLOWLY INCREASE OVER THE AREA...
WITH OCCASIONAL CLOUDINESS AT TIMES. INCREASED MOISTURE LEVELS...
COMBINED WITH SEVERAL WEAK WEATHER DISTURBANCES FROM MEXICO...ARE
FORECAST TO INCREASE THE CHANCE OF AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS...MAINLY ACROSS ARIZONA.

&&

.DISCUSSION...
HIGHER ATMOSPHERIC HEIGHTS AND THICKNESS VALUES TODAY WILL TRANSLATE
INTO A MUCH WARMER DAY OVER YESTERDAY. HOWEVER THE CONCERN HAS BEEN
HOW MUCH CLOUDINESS WILL FLOW NORTH FROM MEXICO INTO CENTRAL AZ TO
REDUCE DAILY INSOLATION AND THE POTENTIAL HEATING CURVE...THE
EXCEPTION IS SOUTHEAST CA AND SOUTHWEST AZ WHICH WILL HAVE FULL
SUNSHINE TODAY.

THICK CLOUDINESS DID DEVELOP OVER SOUTH CENTRAL AND SOUTHEAST AZ
LATE LAST NIGHT DUE TO THE COMBINATION OF A WEAK MID LEVEL
DISTURBANCE...SEEN IN PLOT DATA...AND WEAK ENTRANCE REGION UPPER
LEVEL JET DYNAMICS. AND...MODELS FORECAST THE CLOUDS TO CONTINUE
THROUGHOUT THE DAY WITH EVEN A FEW SHOWERS AND THUNDERSTORMS OVER
THE EASTERN AZ MOUNTAINS...INCLUDING OUR SOUTHERN GILA COUNTY ZONE
24. HOW MUCH OF A REDUCTION IN INSOLATION WILL PREVENT THE FULL
SURFACE HEATING CURVE POTENTIAL IN SOUTH CENTRAL AZ...NOT SURE.
THEREFORE WE WILL CONTINUE WITH THE 109-110 DEGREE FORECASTS FOR
THE SOUTH CENTRAL AZ DESERTS TODAY.

WEDNESDAY...
ADDITIONAL MORNING AND AFTERNOON CLOUDINESS ARE EXPECTED ALONG WITH
HIGHER SURFACE HUMIDITY ON WED. AGAIN...INCREASED MOISTURE COULD
RETARD THE DIURNAL SURFACE HEATING CURVE IN SOUTH CENTRAL AZ
INCLUDING PHOENIX. CURRENT FORECASTS OF NEAR RECORD HEAT IN SOUTH
CENTRAL AZ ARE PREDICATED ON THE BEST PERFORMING MOS GUIDANCE...
WHICH MAY NEED TO BE ADJUSTED BASED ON THE ABOVE MOISTURE INCREASE
DISCUSSION. FOR NOW THE EXCESSIVE HEAT WATCH FOR A LARGE PART OF
SOUTHWEST AND SOUTH CENTRAL AZ ON WED AND THU WILL CONTINUE.

OTHERWISE FORECASTS LOOK OK FOR NOW. NO UPDATES PLANNED. PREVIOUS
DISCUSSION BELOW STILL APPLIES.


.PREVIOUS DISCUSSION...445 AM MST...
THE FOCUS OVER THE NEXT FEW DAYS THROUGH THURSDAY IS ON JUST HOW HOT
IS IS GOING TO GET. A BROAD UPPER LEVEL ANTICYCLONE IS CURRENTLY
PARKED OVER NEW MEXICO AND COLORADO...COMPLETE WITH A 596-600DM
HIGH CENTER. WITH THE INCREASE IN 500MB HEIGHTS...THIS WILL
DEFINITELY KEEP THE TEMPS OVER THE DESERT SOUTHWEST VERY HOT.

CURRENT IR/WATER VAPOR SATELLITE IMAGERY SHOWS A LIMITED SWATH OF
DEBRIS CLOUDS FROM EARLIER CONVECTION OVER SONORA AND CHIHUAHUA
MEXICO THAT IS BEGINNING TO STREAM NORTHWARD IN THE ANTICYCLONIC
FLOW ACROSS THE EASTERN HALF OF OUR CWA. PREVIOUS MODEL RUNS HAD
THIS MID-HIGH LEVEL CLOUD COVER CONSIDERABLY MORE OPAQUE AND THE
AMOUNT/EXTENT OF COVERAGE FURTHER WEST COVERING MOST OF SOUTH
CENTRAL ARIZONA BY THIS TIME.

HOWEVER...WITH THE CLOUD COVER LACKING...THE EXPECTED DAYTIME
REDUCTION IN DAYTIME IS NOW IN QUESTION. THERE IS NO DOUBT THAT
SOUTHEAST CA AND SOUTHWEST AZ WILL HAVE FULL SUNSHINE TODAY FOR A
SUBSTANTIAL WARM-UP...AFTERNOON TEMPERATURES RANGING 109-113 DEGREES
FOR THE LOWER DESERTS NEAR IMPERIAL/BLYTHE/YUMA. DEPENDING ON THE
AMOUNT OF HIGH CLOUDS THAT MATERIALIZE LATER TODAY ACROSS
SOUTH-CENTRAL ARIZONA...THERE COULD BE SUFFICIENT INSOLATION TO BUMP
FORECAST MAX TEMPS UP A COUPLE DEGREES. RIGHT NOW...109 IS FORECAST
FOR PHOENIX...BUT IT MIGHT ENDING UP TO BE A BIT WARMER AT MANY
LOCATIONS. THE AMOUNT OF CLOUD COVER...AND HOW HOT IT GETS TODAY
WILL INDICATE HOW EFFECTIVELY WE CAN COOL OFF OVERNIGHT INTO
WEDNESDAY MORNING...AND IT WILL DICTATE IF THE EXCESSIVE HEAT WATCH
SHOULD BE UPGRADED TO A WARNING FOR WEDNESDAY AND THURSDAY.

THE UPPER LEVEL FLOW IS ALSO PROGGED TO BECOME MORE EASTERLY TO
SOUTHEASTERLY WITH TIME...ALONG WITH A GRADUAL MOISTURE INCREASE.
THE 03Z KPSR RAOB FROM YESTERDAY EVENING REVEALED A SWITCH FROM
SOUTHWEST TO EAST HAS ALREADY TAKEN PLACE IN THE MID-LEVEL FLOW.
EVEN THOUGH THE SOUNDING SHOWED LITTLE CHANGE IN PRECIPITABLE WATER
AT 0.85 INCHES...MODEL FORECAST SOUNDINGS STILL SUGGEST THAT
ATMOSPHERIC MOISTURE WILL STEADILY INCREASE TO AROUND 1.30 INCHES
OVER THE SOUTHWEST DESERTS BY WEDNESDAY AFTERNOON. SOME LOW LEVEL
MOISTURE IS STARTING TO SNEAK BACK INTO THE AREA...AS SURFACE DEW
POINT TEMPERATURES ARE NOW 7-10 DEGREES HIGHER THAN THIS TIME
YESTERDAY MORNING ACROSS SOUTH-CENTRAL ARIZONA. YET...GIVEN THE SLOW
INCREASE IN MOISTURE...NOT EXPECTING MUCH TO CHANGE IN PRECIPITATION
CHANCES FOR LATER TODAY. STILL LOOKING AT THE BEST CHANCES OF
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS OVER EASTERN
ARIZONA...WITH ONLY ISOLATED STORMS WELL EAST OF PHOENIX OVER THE
HIGHER TERRAIN OF SOUTHERN GILA COUNTY.

WEDNESDAY AND THURSDAY...
AGAIN...THE BEST PERFORMING TEMPERATURE GUIDANCE CONTINUES THE
AFTERNOON WARM-UP INTO NEAR RECORD BREAKING TERRITORY WEDNESDAY
AND THURSDAY. THIS DESPITE MODEL GUIDANCE OF MORE CONVECTIVE DEBRIS
CLOUDS AND SLIGHTLY HIGHER HUMIDITIES. IN FACT...THE UPPER LEVEL
WIND FIELD ALONG WESTERN EDGE OF THE 300/250 MB ANTICYCLONES...OVER
CENTRAL AZ...INDICATE A LITTLE SPEED DIVERGENCE OR ACCELERATING
WIND FROM SOUTH TO NORTH THAT COULD SUPPORT A FEW LIGHT SHOWERS OR
SPRINKLES IN SOUTH CENTRAL AZ WED MORNING/EARLY AFTERNOON.

SINCE THERE IS A LOT OF VARIABILITY IN CLOUD FORECASTS...AND EVEN
PRECIPITATION CHANCES...AND THE BEST PERFORMING AFTERNOON TEMP
GUIDANCE IS STILL BULLISH ON HIGHER VALUES...THE EXCESSIVE HEAT
WATCH WILL CONTINUE FOR THIS TIME PERIOD. HOWEVER...THE WATCH COULD
BE UPGRADED TO A WARNING IF LESS CLOUD COVER ARRIVES TO MITIGATE THE
WARMTH. SOUTHEAST CA AND SOUTHWEST AZ WILL BE IN FULL SUNSHINE FOR
MUCH HIGHER AFTERNOON TEMPERATURES.

FRIDAY THROUGH EARLY NEXT WEEK.
A MUCH STRONGER EAST TO SOUTHEAST MID/UPPER LEVEL WIND FIELD IS
FORECAST TO DEVELOP...REPLETE WITH HARD TO TIME PERTURBATIONS OR
INVERTED TROFS FLOWING MAINLY ACROSS SOUTHERN AZ. THIS COULD PORTEND
AND UPSWING IN TYPICAL MONSOON DIURNAL CONVECTIVE ACTIVITY. PRECIP
PROBABILITIES WERE ADDED TO PORTIONS OF SOUTHWEST AND SOUTH CENTRAL
AZ.

&&

.CLIMATE...

RECORD HIGH TEMPERATURE FOR THE MIDDLE OF THE WEEK.

CITY        JULY 22       JULY 23      JULY 24
----        -------       -------      -------
PHOENIX   116 IN 2006   114 IN 2006  114 IN 2006
YUMA      116 IN 2006   115 IN 1959  117 IN 1943

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
MID AND HIGH CLOUDS WILL BE ON THE INCREASE THROUGH TONIGHT. GIVEN
THE RELATIVELY DRY CONDITIONS AT THE SURFACE...AREAS OF VIRGA ARE A
POSSIBILITY...WHICH MAY PRODUCE LOCALIZED GUSTY WINDS.
HOWEVER...WINDS WILL GENERALLY REMAIN LIGHT AND DIURNAL THROUGH THE
TAF PERIOD.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
NO AVIATION IMPACTS EXPECTED WITH LIGHT WINDS AND OCCASIONAL MID AND
HIGH CLOUDS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
STRONG HIGH PRESSURE WILL REMAIN THE PREDOMINANT WEATHER FEATURE
ACROSS THE REGION. BIGGEST IMPACT WILL BE THE HEAT...WITH ABOVE
NORMAL TEMPERATURES LIKELY THROUGH EARLY NEXT WEEK. THE TREND WILL
BE TOWARDS INCREASING MOISTURE EACH DAY...THOUGH THUNDERSTORMS WILL
MAINLY BE CONCENTRATED IN THE HIGHER TERRAIN OF EASTERN AZ. ACROSS
THE LOWER DESERTS OF AZ...ISOLATED THUNDERSTORMS WILL BE
POSSIBLE...PARTICULARLY DURING THE WEEKEND...THOUGH THE GREATER
THREAT IS FOR OUTFLOW BOUNDARIES CAPABLE OF PRODUCING STRONG WIND
GUSTS. FURTHER WEST ACROSS SE CA...THE CHANCE FOR RAIN AND
THUNDERSTORM IMPACTS WILL BE EVEN LOWER. MINIMUM HUMIDITIES WILL
GENERALLY FALL INTO A 15-20 PERCENT RANGE WITH GOOD OVERNIGHT
RECOVERY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...EXCESSIVE HEAT WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY
EVENING AZZ020>023-025>028.

CA...EXCESSIVE HEAT WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY
EVENING CAZ031>033.

&&

$$

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

DISCUSSION...VASQUEZ/MEYERS
CLIMATE...MO
AVIATION....HIRSCH
FIRE WEATHER...HIRSCH







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