July of 2009 was one of the hottest months on record in the Desert Southwest and Death Valley. The NWS in Phoenix
http://www.wrh.noaa.gov/psr/pns/2009/July/Brief3.php
and Las Vegas
http://www.wrh.noaa.gov/total_forecast/getprod.php?wfo=vef&sid=VEF&pil=PNS
have prepared interesting summaries for the month.
According to the summary from the Las Vegas office, the station at McCarron AP (LAS) came in with an average of 94.7F for July 2009 (106.0/83.4), which is 3.5 degrees above normal. July 2009 is now the 4th warmest month on record for Las Vegas, behind July 2007, July 2005, and July 2003. Records here began in 1937. The growing city has resulted in higher and higher minimum temperatures, and this is in large part why the five warmest months have been in the last decade at Las Vegas. At Needles AP, a station not affected by urbanization, July 2009 was the 3rd warmest month on record (ave 99.4F, records since 1948). The five warmest Julys have all been since 1996 at Needles AP.
This page is concerned primarily with the temperature record for Death Valley, California. The summary prepared by NWS LAS for July 2009 contains the following for Death Valley:
...DEATH VALLEY... THE AVERAGE TEMPERATURE FOR JULY 2009 WAS 105.2 DEGREES AT THE OFFICIAL WEATHER STATION AT FURNACE CREEK IN DEATH VALLEY NATIONAL PARK IN CALIFORNIA. THIS RANKS AS THE 8TH WARMEST JULY ON RECORD AND TIES WITH JULY 2008. THE WARMEST JULY EVER IN DEATH VALLEY WAS 107.0 DEGREES SET IN 1917. RECORDS AT DEATH VALLEY DATE BACK TO 1911. IN ADDITION...THERE WERE 8 DAYS WITH A HIGH TEMPERATURE OF 125 DEGREES OR BETTER IN DEATH VALLEY IN JULY 2009 INCLUDING A HIGH OF 128 DEGREES ON THE 18TH. THIS IS THE SECOND GREATEST NUMBER OF SUCH DAYS FOR ANY MONTH AND IS ONLY EXCEEDED BY JULY 1913 WHEN THERE WERE 10 SUCH DAYS. THAT JULY HOLDS IN THE DISTINCTION OF THE ALL-TIME DEATH VALLEY RECORD HIGH OF 134 DEGREES.
Let’s take a closer look at the temperature data for July 2009 at Death Valley. Here is a list of the daily maximum and minimums (these were retrieved from the daily “RTP” summaries issued by NWS LAS, and should be considered as preliminary data):
1 119/93
2 119/94
3 118/88
4 116/91
5 120/85
6 120/87
7 119/86
8 117/85
9 117/85
10 116/84
11 120/91
12 122/89
13 119/84
14 120/83
15 123/88
16 125/88
17 126/90
18 128/90
19 126/93
20 125/92
21 120/85
22 122/86
23 122/93
24 120/94
25 119/93
26 122/91
27 125/92
28 125/92
29 125/91
30 122/84
31 122/91
Frequency of maximums:
116 2
117 2
118 1
119 5
120 6
121 0
122 6
123 1
124 0
125 5
126 2
127 0
128 1
Average maximum 121.26F (ranging from 116F to 128F)
Average Minimum 88.97F (ranging from 83F to 94F)
Average 105.11F
The average that I computed is slightly lower than the 105.2F given in the NWS LAS summary. A value of 105.15F is obtained if one rounds off the above average values to 121.3 and 89.0, so perhaps NWS LAS used those values and rounded 105.15 up to 105.2. The July 2009 averages of 121.3/89.0/105.1 compare to 1971-2000 normals of 114.9/86.3/100.6 at Death Valley. So, the month was 4.5 degrees warmer than normal, and its average maximum was 6.4 degrees above normal. With maximums ranging from 116F to 128F, all maximums were above normal. (By the way, Death Valley maximums have been 116F or greater from June 24th through August 4th.)
Death Valley’s average maximum of 121.3F this past July is the hottest yet for any month at the “Death Valley” cooperative station, which was established at the Visitors Center in Furnace Creek in April, 1961.
http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca2319
(click on the “average maximum” link under “monthly temperature listings” to review the average monthly data)
July 2002 and July 2003 both had average maximums of 120.6F at Death Valley. From 1911 through 1960, the cooperative station in Furnace Creek was “Greenland Ranch”. The highest average maximum on record at Greenland Ranch was 121.9F in July 1917.
http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca3603
However, the max temp data from this month are highly suspect (all of the maximums ranged from 119F to 125F; the ave max was much warmer than expected compared to surrounding stations, a prominent cool-down in the desert late in the month was not apparent in the Greenland Ranch data, etc.). Second highest at Greenland Ranch is 120.5F in July 1930. The hottest average maximum at Cow Creek, which was a few miles north of Furnace Creek and operated from 1935 to 1960, was 120.2F in 1959.
http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca2092
Thus, the average maximum of 121.3F in July 2009 is the hottest on record for stations in and near Furnace Creek in Death Valley, if one discards the untrustworthy data from Greenland Ranch in July 1917.
Given the above, one can state that the average maximum temperature of 121.3F for Death Valley in July 2009 is the hottest (reliable) average maximum at any officially recognized temperature station to date for the United States. (A temporary station was set up at Badwater in Death Valley during the summers of 1959, 1960, and 1961…the average maximum in July 1959 was 122.4F at Badwater!)
If the untrustworthy data from July 1917 are discarded, July 2009 is the first month where all maximums were 116F or hotter (all maximums in July 1931 were 115F and up).
In July 1913, Greenland Ranch had an average maximum of 116.4F, and reported three days with maximums of 130F and above (including the record 134F on July 10). However, these and other maximum temperatures from Greenland Ranch in July 1913 are not supported by data from the closest surrounding stations (nor are the 130-plus temperatures supported by nearly 100 years of temperature measurement in Death Valley!) . The hottest trustworthy maximum temperature on record from a Furnace Creek-area station is 129F.
Stay tuned for much more on Death Valley temperature records on Stormbruiser!
Bill Reid
bill@stormbruiser.com