Recent NWS Phoenix - Public Information Statements

Pepper Ridge Weather Station


The Monsoon has Ended Officially in Phoenix

PUBLIC INFORMATION STATEMENT...UPDATED
 NATIONAL WEATHER SERVICE PHOENIX AZ
 540 AM MST THU SEP 13 2007
 
 ...MONSOON 2007 ENDED SEPTEMBER 11TH...
 
 THE OFFICIAL ONSET FOR THE MONSOON OCCURS WHEN THE AVERAGE DAILY DEW 
 POINT TEMPERATURE...AS OBSERVED AT PHOENIX SKY HARBOR INTERNATIONAL 
 AIRPORT...REACHES OR EXCEEDS 55 DEGREES FOR THREE CONSECUTIVE DAYS. 
 HOWEVER...THE ENDING DATE OF THE MONSOON REQUIRES MORE OF A 
 SUBJECTIVE DETERMINATION...AND IS GENERALLY DEDUCED BY LOOKING AT 
 UPPER LEVEL WIND PATTERNS. IF FORECAST MODELS CONTINUE TO DEPICT A 
 PERMANENT TRANSITION TO DRIER WESTERLY FLOW ACROSS THE REGION BEYOND 
 SEVEN DAYS...AND THE FLOW IS EXPECTED TO RESULT IN A PROGRESSIVE 
 DOWNWARD TREND OF AVERAGE DEW POINT TEMPERATURES BELOW 55 DEGREES 
 ...A DATE CAN BE DETERMINED FOR THE EXODUS OF MOISTURE AND THE END 
 OF THE MONSOON.
 
 SEPTEMBER 11TH WILL MARK THE END OF THE 2007 MONSOON SEASON FOR 
 PHOENIX. A BRIEF SUMMARY IS LISTED BELOW.
                      
 
 START DATE     END DATE      MONSOON DAYS*   PRECIPITATION (INCHES)  
 
   JUL 19        SEP 11            48            0.67 (7/19-9/11)
 
 *(MONSOON DAY...A DAY WHERE THE AVERAGE DAILY SURFACE DEW POINT      
   TEMPERATURE REACHED OR EXCEEDED 55 DEGREES. AVERAGE IS 55 DAYS.)
 
 HOW DID THIS SEASON COMPARE TO PREVIOUS YEARS? THIS YEAR TIED AS THE 
 EIGHTH DRIEST ON RECORD...AND WAS THE DRIEST SINCE 1993 WHEN 0.61 
 INCHES OF RAIN FELL. THE WETTEST PERIOD OCCURRED IN 1911 WHEN 8.58 
 INCHES OF RAIN FELL...THE DRIEST BEING 1932 WHEN 0.21 INCHES FELL. 
 THE LONG TERM AVERAGE FOR THIS PERIOD IS 2.35 INCHES. THIS 
 COMPARISON IS BASED ON DATA FROM JULY 1ST THROUGH SEPTEMBER 15TH FOR 
 PHOENIX...WITH RECORDS DATING BACK TO 1896.
 
 DUE TO THE SOMEWHAT CHAOTIC NATURE OF THUNDERSTORMS ACROSS THE 
 VALLEY...RAINFALL AMOUNTS ACROSS THE METRO AREA CAN VARY GREATLY 
 EACH YEAR. SOME RAINFALL AMOUNTS FROM AROUND THE AREA INCLUDE... 
 4.01 INCHES AT APACHE JUNCTION...3.38 INCHES AT CASA GRANDE...4.13 
 INCHES AT CAREFREE...0.42 INCHES AT PHOENIX DEER VALLEY AIRPORT... 
 0.94 INCHES AT FOUNTAIN HILLS...AND 1.22 INCHES AT YOUNGTOWN.
 
 A COMMONLY ASKED QUESTION IS WHETHER OR NOT RAINFALL DURING THE 
 MONSOON IS CHANGING /OR BECOMING LESS/. BASED ON THE LONG TERM TREND 
 FOR PHOENIX THE ANSWER IS NO. THE DATA SHOW THAT THERE IS GREAT 
 VARIABILITY FROM ONE YEAR TO THE NEXT...AND EVEN ONE DECADE TO THE 
 NEXT. THERE IS ALSO A LONG TERM OSCILLATION WHICH APPEARS IN THE 
 DATA SET...WITH PEAKS IN RAINFALL AMOUNTS /WET/ DURING THE 
 1910S...1950S AND 1980S...AND TROUGHS /DRY/ DURING THE 1930S...1970S 
 AND THE 2000S.
 
 $$
 
 MEYERS/INIGUEZ 

Monsoon Rainfall in Phoenix 1896 - 2007

Monsoon Rainfall for Phoenix

The Hot Summer of 2007 in Phoenix - Sky Harbor Statistics


NOUS45 KPSR 111342 CCA
 PNSPSR
 
 PUBLIC INFORMATION STATEMENT
 NATIONAL WEATHER SERVICE PHOENIX AZ
 640 AM MST TUE SEP 11 2007
 
 ...A LOOK AT HOT TEMPERATURES IN PHOENIX...
 
 MAXIMUM TEMPERATURES HAVE BEEN WELL ABOVE NORMAL SINCE LATE SPRING. 
 SINCE MAY 1ST...THE AVERAGE HIGH TEMPERATURE IN PHOENIX HAS BEEN 
 104.1 DEGREES. THIS IS THE SECOND WARMEST ON RECORD /RECORD IS 104.3 
 DEGREES IN 1989...NORMAL IS 102.2 DEGREES/. LOW TEMPERATURES SINCE 
 MAY 1ST HAVE BEEN BY FAR THE WARMEST ON RECORD AT AN AVERAGE OF 81.1 
 DEGREES /PREVIOUS RECORD 80.4 DEGREES IN 2003...NORMAL IS 77.0 
 DEGREES/.
 
 THE TABLES BELOW DISPLAY DATA ON MAXIMUM AND MINIMUM TEMPERATURE 
 DISTRIBUTIONS FOR PHOENIX. COLUMN 1 INDICATES THE TEMPERATURE STEP 
 BEING EVALUATED. COLUMN 2 DISPLAYS THE AVERAGE NUMBER OF OCCURRENCES 
 PER YEAR BASED ON 1896 THROUGH 2006 DATA. COLUMN 3 IS THE AVERAGE 
 NUMBER OF OCCURRENCES BASED ON 1977 THROUGH 2006 DATA. COLUMN 4 IS 
 THE RECORD NUMBER OF OCCURRENCES FOR EACH STEP AND THE YEAR THE 
 RECORD OCCURRED. COLUMN 5 DISPLAYS THE NUMBER OF OCCURRENCES FOR 
 EACH STEP SO FAR THIS YEAR AND HOW THAT NUMBER RANKS IN THE 
 HISTORICAL RECORD.
 
 FOR EXAMPLE...THE FIRST LINE IN THE TOP TABLE INDICATES THAT FOR 
 MAXIMUM TEMPERATURES OF 100 DEGREES OR GREATER THE LONG-TERM AVERAGE 
 IS 91 OCCURRENCES PER YEAR. THE AVERAGE SINCE 1977 HAS BEEN 109 
 OCCURRENCES PER YEAR. THE MOST 100 DEGREE OR GREATER DAYS OCCURRED 
 IN 1989 WHEN THERE WERE 143. SO FAR THIS YEAR THERE HAVE BEEN 106 
 DAYS WITH A MAXIMUM TEMPERATURE OF 100 DEGREES OR GREATER...WHICH 
 TIES AS THE 24TH MOST ON RECORD.
 
 
  (1)       (2)         (3)          (4)            (5)
  MAX    1896-2006   1977-2006                   2007 COUNTS
  TEMP    AVERAGE     AVERAGE       RECORD        AND RANK#
  100+       91         109       143...1989     106...24TH%
  101+       82         100       129...1989     101...15TH%
  102+       73          92       118...1989      89...25TH%
  103+       64          83       108...1989      80...22ND
  104+       55          74        95...2002      74...15TH%
  105+       46          65        87...2002      70... 9TH%
  106+       37          54        78...2002      69... 3RD%
  107+       28          43        68...2002      60... 2ND%
  108+       22          34        54...2002      52... 2ND 
  109+       15          25        43...2007      43... 1ST
  110+       11          18        32...2007      32... 1ST
  111+        7          12        24...2007      24... 1ST%
  112+        4           8        18...1985      14... 4TH%
  113+        2           5        12...1995@      9... 8TH%
  114+        1           3         9...1974       4...11TH%
  115+        1           2         7...1974       2...13TH%
 
  MIN     1896-2006   1977-2006                  2007 COUNTS
  TEMP     AVERAGE     AVERAGE      RECORD        AND RANK#
  80+        35          66        88...2001      81... 3RD%
  81+        28          59        77...2003      71... 6TH
  82+        23          52        72...2001      67... 5TH
  83+        18          44        63...2003@     59... 4TH
  84+        13          36        56...1981      54... 3RD
  85+        10          28        51...1981      47... 2ND
  86+         7          21        40...2007@     40... 1ST%
  87+         5          15        37...2007      37... 1ST
  88+         3           9        29...2007      29... 1ST
  89+         2           5        22...2007      22... 1ST
  90+         1           3        15...2003      14... 2ND
   @ AND PREVIOUS YEARS
   # THROUGH 10 SEP 2007
   % TIED WITH ONE OR MORE YEARS
 
 CLEARLY BOTH HIGH AND LOW TEMPERATURES HAVE BEEN INCREASING IN 
 PHOENIX DURING THE PAST CENTURY. MUCH OF THIS INCREASE...ESPECIALLY 
 IN THE LOW TEMPERATURES...CAN BE ATTRIBUTED TO THE URBAN HEAT 
 ISLAND. OTHER FACTORS THAT INFLUENCE TEMPERATURE RECORDS MAY INCLUDE 
 CLIMATE VARIABILITY...REGIONAL CLIMATE CHANGE...AND CHANGES IN 
 INSTRUMENTATION TYPE AND LOCATION. THE PRECISE AMOUNT OF VARIABILITY 
 THAT CAN BE ATTRIBUTED TO EACH OF THESE POSSIBLE FACTORS IS 
 CURRENTLY UNKNOWN...THOUGH THE URBAN HEAT ISLAND IS VERY LIKELY THE 
 DOMINANT FACTOR.
 
 THERE HAVE BEEN SEVERAL FACTORS THAT HAVE MADE 2007 PARTICULARLY 
 WARM BESIDES THOSE MENTIONED ABOVE. PRECIPITATION FOR THE SUMMER HAS 
 BEEN BELOW NORMAL. HIGH PRESSURE IN THE MID LEVELS OF THE ATMOSPHERE 
 WAS ABNORMALLY STRONG THIS SUMMER...RESULTING IN VERY WARM MID-LEVEL 
 TEMPERATURES. DESPITE ABOVE NORMAL MOISTURE LEVELS IN THE LOW LEVELS 
 OF THE ATMOSPHERE...THE WARM MID LEVEL AIR ACTED TO SUPPRESS 
 THUNDERSTORM DEVELOPMENT. THE LACK OF PRECIPITATION IN THE VALLEY 
 MEANT LESS OF THE SUNS ENERGY WAS CONSUMED IN THE PROCESS OF 
 EVAPORATING RAINFALL...AND INSTEAD WENT DIRECTLY IN TO WARMING THE 
 AIR IN THE LOW LEVELS. IT IS UNKNOWN AT THIS TIME WHY THESE FACTORS 
 CAME TOGETHER AS THEY DID...THOUGH IT REMAINS AN AREA OF ACTIVE 
 RESEARCH.
 
 &&
 
 ALL TEMPERATURES IN DEGREES FAHRENHEIT. RECORDS FOR PHOENIX DATE 
 BACK TO 1896.
 
 $$
 
 INIGUEZ

Page Last Updated Sept 14th, 2007

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