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Rare Prolonged Excessive Heat Event (August 6-14)

Ask anyone in southeast California and southern Arizona about temperatures in the summer, and you'll likely get a similar response - it's always hot. And you're also likely to not get an argument. However, the first two weeks of August 2012 has brought back bad memories of the latter half of August 2011 - that is, almost unbearable heat. The biggest question is: How unusual has this first 2 weeks of August been? The answer: Very rare. And the remainder of this web page will summarize how rare, and list the multitude of records set in the first 14 days of the month.

Why has it been so hot for so long at the beginning of August? During the first week of the month, a strong ridge of high pressure aloft moved westward from the southern plains, and became parked over the Desert Southwest. This pattern has remained stagnant since the 6th of the month, and provided record breaking heat over a 9 day period. Presented below are average heights at the 500mb level during the Aug 1-11th period, as well as temperatures at the 850mb level during the same period. The bright pink color scheme depicts unusually high values, especially when considering these measurements were averaged over nearly a 2 week time frame.

500mb heights 850mb temps

Another way to view the rarity of the event is by the use of standardized anomalies. Presented below is a standardized anomaly plot from the morning of August 8th, where 500mb height anomalies equated to greater than 2 normalized standard deviations above normal (top plot), while the 850mb temperatures were at least 2-3 normalized standard deviations above normal (lower plot). These anomalies, while not remarkable in a sense of return period, have been persistent for a large part of the beginning of August.

standardized anomalies


The list of daily, weekly, and consecutive days records during the 9 day stretch from August 6-14 is most impressive. Here is a summary of some of these rankings and records:

Rankings for the first 2 weeks of August (1st-14th)

Year Avg Daily Temperature
2012
100.0
1995
98.1
2003
97.4
2011
96.5
1986
96.4
Year Avg High Temperature
2012
111.2
1995
110.4
1962
108.4
1975
108.3
2003
107.9
Year Avg Low Temperature
2012
88.8
2003
86.9
2011
86.4
1995
85.7
1986
85.7

 

 

 

 

 

Record High Temperatures

Date
Temperature
Old Record
Aug 7th
112
112 in 1905
Aug 8th
116
113 in 1991 & 1940
Aug 9th
114
112 in 2003, 1995 & 1933
Aug 12th
115
114 in 2007
Aug 13th
115
113 in 2003 & 1962
Aug 14th
113
113 in 1988

Record Warm Low Temperatures

Date
Temperature
Old Record
Aug 7th
90
89 in 2006
Aug 8th
93
93 in 2003
Aug 9th
93
91 in 2003

Most consecutive days with low temperature at least 90°

7 days (Aug 7-13) breaks the old record of 6 days ending 7/17/2003

Most consecutive days with the daily average temperatures at least 100°

8 days (Aug 6-13) ties the old record of 8 days ending 8/10/1995

 


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