Climatology 101: May 2015 Tucson’s coolest since 1998

Courtesy: NWS Tucson
Courtesy: NWS Tucson

Thanks to a series of troughs passing through the state, May 2015 goes down as one of the coolest & wettest we’ve seen in recent memory. With an average temperature of 73.4°, Tucson registered the 56th coolest May on record. Interesting to note that Tucson had a 15 day streak of below average highs, the longest such stretch since 1977.

While 0.09″ rain fell at Tucson International Airport last month, many Metro Tucson locations saw at least 0.25″. Casa de Beamish in Oro Valley picked up a whopping 0.62″ rain last month. That’s easily the most I’ve recorded during the month of May, dating back to 2011.

Below is the full climate report compiled by the National Weather Service forecast office in Tucson.

Longest stretch of below normal highs for May since early 1970s.
Rank
Year
# of days/Dates
Average
Normal
1)
2015
15 days (12th to 26th)
85.1°
92.6°
2)
1977
13 days (9th to 21st)
81.3°
89.3°
3)
1987
12 days (19th to 30th)
86.3°
92.8°
4)
1992
11 days (21st to 31st)
86.4°
93.3°
Normal periods: 1977 (1941-1970); 1987 (1951-1980); 1992 (1961-1990); 2015 (1981-2010)
The low temperatures also had an extended stretch of being below normal. The 13 days, starting on 16th and continuing through the 28th, was the longest in May since the early 1970s (see table below) and the longest since 18 days were recorded from late 2010 (December 30th) to early 2011 (January 16th).
Longest stretch of below normal lows for May since early 1970s.
Rank
Year
#of days/Dates
Average
Normal
1)
2015
13 days (16th to 28th)
57.5°
62.2°
2)
1987
11 days (20th to 30th)
55.3°
60.0°
3t)
2008
10 days (22nd to 31st)
56.4°
62.0°
1995
10 days (22nd to 31st)
58.0°
61.0°
Normal periods: 1987 (1951-1980); 1995 (1961-1990); 2008 (1971-2000); 2015 (1981-2010)
High pressure aloft built over the area as the month closed which ended the below normal high and low temperature streaks. The heat was then turned on with Tucson making its first run at triple digit highs for 2015 on the 30th with the ice breaking at 2:03 PM. The historical (1895-2014) first 100° date is May 26th.
Temperature extremes for the month ranged from a high of 104° on the 31st to a low of 50° on the 10th. The monthly average temperature of 73.4° is 2.6° below normal and ranks as the 56th coolest on record. Dating back to the the 1950s when the first climatic normals were published, this is the 7th May that ended up greater than 2° below normal. (see table below)
Average May temperature being greater than 2° BELOW normal
Rank
Departure from normal
Year/Avg temp
30 year normal period
Normal temperature
1)
– 4.3°
1953 (68.8°)
1921-1950
73.1°
2)
– 4.2°
1971 (69.3°)
1931-1960
73.5°
3)
– 3.8°
1975 (69.8°)
1941-1970
73.6°
4)
– 3.4°
1965 (70.1°)
1931-1960
73.5°
5)
– 2.8°
1977 (70.8°)
1941-1970
73.6°
6)
– 2.6°
2015 (73.4°)
1981-2010
76.0°
7)
– 2.2°
1980 (71.4°)
1941-1970
73.6°
A greater departure from normal occurred with the average high temperature. The 87.7°, which is the coolest since 1980, is 3.9° below normal and ranks as the 24th coolest on record for May. Dating back to the the 1950s when the first climatic normals were published, this is the 8th May that ended up greater than below normal. (see table below)
Average May HIGH temperature being greater than 3° BELOW normal
Rank
Departure from normal
Year/Avg temp
30 year normal period
Normal temperature
1)
– 4.6°
1975 (85.0°)
1941-1970
89.6°
2)
– 4.6°
1953 (84.6°)
1921-1950
89.2°
3)
– 4.3°
1977 (85.3°)
1941-1970
89.6°
4)
– 4.3°
1971 (85.1°)
1931-1960
89.4°
5)
– 3.9°
2015 (87.7°)
1981-2010
91.6°
6)
– 3.5°
1979 (86.1°)
1941-1970
89.6°
7)
– 3.4°
1957 (85.8°)
1921-1950
89.2°
8)
– 3.2°
1965 (86.2°)
1931-1960
89.4°
May 2015 daily high temperature departure from normal May 2015 daily low temperature departure from normal
Click on image above for larger view
Rainfall across the metro area, using several sources like rainlog.org and the Pima County Regional Flood Control District gages, varied widely from 0.05″ to 1″, with the highest amounts on the north and northwest side of the metro area. The International airport, which is the official recording location for Tucson, recorded just under a tenth of an inch /0.09″/ of rain. Funny to say that the 0.09″ ranks as the 49th wettest May on record, tied with 1895 & 1928. The last May that was above normal at the airport was in 2009 (0.67″).
May 2015 stats
Month
Normal
Departure
Average high temperature
87.7°
91.6°
– 3.9°
Average low temperature
59.1°
60.5°
– 1.4°
Average temperature
73.4°
76.0°
– 2.6°
Days with highs 100° or greater
2
4
– 2
Rainfall
0.09″
0.23″
– 0.14″

When did daily high/lows occur?
Month
Average
Departure
Average high temperature time
4:02 pm
3:50 PM
12 min. late
Average low temperature time
5:43 am
5:41 am
2 min. late
Average times based on data collected from 2001-2014

Spring 2015 Spring '15 climate recap for Tucson Arizona
13th warmest on record
52nd driest on record
10th straight Spring of below normal rainfall
Lowest 10 year Spring rainfall average on record
68% of the daily highs in May were below normal Click to enlarge
A most enjoyable May countered the warmer than normal March (2nd warmest) and April (18th warmest) to produce the 13th warmest Spring on record with an average Spring temperature of 69.6°. However this is the second straight spring that was cooler than the previous spring (2013 – 71.5°; 2014 – 70.3°). Temperature extremes ranged from 104° on May 31st to a low of 39° on March 5th.
Spring 2015 daily high temperature departure from normal Spring 2015 daily low temperature departure from normal
Click on image above for larger view
Precipitation amounts across the metro area for the spring season, using several sources like rainlog.org, thePima County Regional Flood Control District gages and CoCoRaHS, varied widely and mostly ranged from 0.30″ to 2″ with the highest totals on the north and northwest sides of the metro area. Officially, the airport recorded 0.75″ which is around a half an inch below normal and ranks as the 52nd driest Spring on record. This is also the 10th straight Spring with below normal rainfall at the International airport. Additionally when you look at the 10 year running averages, Spring’s 2006 to 2015 averaged only 0.59″. This is the lowest 10 year average for Spring on record. This is a dramatic drop from nearly 20 years ago when Spring’s 1986 to 1995 had a 10 year average of 1.55″. That equates to a 62% decrease.
Spring 2015 stats
Season
Normal
Departure
Average high temperature
83.9°
82.6°
+ 1.3°
Average low temperature
55.2°
52.9°
+ 2.3°
Average temperature
69.6°
67.7°
+ 1.9°
Days with highs 100° or greater
2
4
– 2
Rainfall
0.75″
1.27″
– 0.52″

2015
The first five months of 2015 goes into the record books as the 2nd WARMEST on record with an average yearly temperature to date of 65.3° which is 2.9° above normal. Rainfall is above normal for the first time through the end of May since 2010 with 3.70″ being recorded at the International airport. This ranks the 26th wettest January thru May period on record, tied with 1995.
2015 stats thru May
Year
Normal
Departure
Average high temperature
78.8°
76.6°
+ 2.2°
Average low temperature
51.7°
48.3°
+ 3.4°
Average temperature
65.3°
62.4°
+ 2.9°
Days with highs 100° or greater
2
4
– 2
Rainfall
3.70″
3.07″
+ 0.63″
2014-15 Water Year rainfall (Oct-May)
7.20″
5.46″
+ 1.74″
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