...July 2009 Finishes as the 3rd Coldest on Record...

A persistent weather pattern throughout the majority of the month has produced the 3rd coolest July on record for the local area. Not only was the month characterized by a lack of 90 degree heat, but also by refreshingly cool overnight temperatures. Numerous daily records were approached and/or broken during July 2009. Here is a chronological look at the cool temperatures this month, and a summary of the records that have been broken in Kansas City.  For a more in depth look at the record breaking low temperatures during the middle of the month, please visit our summary page at:  Record Breaking Low Temperatures 

July 3: 10th coldest high temperature for the date (77 degrees)
July 17: Morning record low (55 degrees) followed by the 4th coldest high temperature for the date (76 degrees)
July 18: Morning record low (56 degrees) followed by the 4th coldest high temperature for the date (78 degrees)
July 19: Morning record low (54 degrees)
July 21: 3rd coldest high temperature for the date (73 degrees)
July 28: 2nd coldest high temperature for the date (74 degrees)
July 29: 8th coldest high temperatures for the date (79 degrees)
July 30: 6th coldest high temperatures for the date (76 degrees)

Below is a listing of the new top 10 coldest months of July in the recorded history of Kansas City, with July 2009 now the 3rd coolest July on record. 

 

Days: 7/1 - 7/31
Length of period: 31 days
Years: 1888-2009

Rank Value Ending Date
1 72.4 1891
2 72.5 1950
3 73.5 2009
4 74.2 1895
5 74.3 1905
6 74.4 1992
7 74.5 1924
8 74.6 1915
9 74.9 2004
10 75.0 1904


This same weather pattern affected St. Joseph (and all other surrounding communities for that matter), such that  July 2009 now ranks as the 3rd coolest July on record. Here are the monthly stats for St. Joseph for the all-time July records:

 

Days: 7/1 - 7/31
Length of period: 31 days
Years: 1908-2009

Rank Value Ending Date
1 71.9 1971
2 72.1 1950
3 72.9 2009
4 73.3 1915
5 73.5 1967
6 73.6 2004
7 73.9 1924
8 74.9 1958
9 75.1 1959
10 75.3 1979


Where have all the 90s gone?

One very unique statistic for the month of July 2009 has been the lack of warm days or days at or above 90 degrees. There have only been 3 days where the high temperature reached at or above 90 degrees in Kansas City this month.  In Kansas City history, there have only been three other Julys on record with 3 or less 90 degree days.  Here is a listing of the top 6 lowest number of 90 degree July days on record:

Number of 90+ Degree Days
July 1891 0
July 1915 1
July 1950 2
July 2009 3
July 2004 4
July 1899 4


 So, why was July so abnormally cool?

A very persistent flow pattern took shape at the beginning of the month, and maintained its structure through the end of the month. This type of pattern is much more typical during the winter months, and is only occasionally seen during the summer (and typically only holds for a few days versus weeks). This pattern is described as a negative version of the North Atlantic Oscillation/Arctic Oscillation (NAO/AO) teleconnection. Below is the mean 500 mb flow across the northern hemisphere during the past 30 days, along with the anomaly versus climatology. Note how these anomalies are nearly opposite of the positive phase of the NAO/AO teleconnection presented below.

               500 mb heights and anomalies
                                                    (click on image for larger version)

      Positive Phase of the NAO                  Positive Phase of the AO
NAO Corrolation loading pattern  AO Corrolation loading pattern

This persistent teleconnection pattern led to an expansive area of below average temperatures across the upper Midwest through the East Coast of the United States and southern Canada. Conversely, much above average temperatures were experienced over northeast Canada and Greenland, as well as the Pacific Northwest through western Canada and throughout Alaska. Below is a map of temperature anomalies over the past 30 days.

       July Temperature anomalies
                                             (click on image for larger version)

Perhaps, the most amazing statistic for the month of July is to compare the average temperature from Kansas City versus the average temperature from Portland, Oregon. On average, the difference in the average July temperature between the two cities is over 10 degrees (78.5 degrees in Kansas City versus 68.1 degrees in Portland). However, for the first time ever (or at least since 1948), Portland, Oregon actually had an average July temperature warmer than Kansas City. In fact, only once before did the range between the two cities ever fall below 3 degrees!

Year

Kansas City
Average Temperature

Portland, Oregon
Average Temperature

Difference

2009

73.5

73.6

-0.1

1985

77.0

74.1

2.9

1996

75.2

72.0

3.2

2004

74.9

71.5

3.4

1992

74.4

70.2

4.2

 



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