Why So Cool? Updated for Latest First 90 Degree Day Stats

Has it seemed like it's been a cool summer so far? Although June was generally 0.4 to 2 degrees below normal and July is averaging 2 to 3 degrees below normal so far,  what we have lacked has been the July heat....

Typically Omaha has 6 days in June that have a high temperature of 90 degrees or warmer and in July, Omaha has on average 12 days or more with highs 90 degrees or warmer.  This year Omaha has had 5 days in June with 90 degrees or warmer and 0 in July.  Note, we are only half way through July, but expect to be in a cooler pattern for at least the next week or so.

Station Years of Record June/July Days =>90 degrees - Normal June/July Days => 90 degrees - 2009
Omaha 1871-2008   6 / 12   5 / 0
Lincoln 1887-2008   8 / 15   9 / 1
Norfolk 1893-2008   7 / 13   4 / 0
Source:  xmACIS    

There are many variables that can affect temperature; wet or dry soil conditions, vegetative state and season, clouds, winds and weather patterns.  This year, all three sites are in the top three for the latest first 90 degree day.

OMAHA - July Latest First 90 Degree Day

#1 7/30/1993
#2 7/21/1906
#3 2009  so far

LINCOLN - July Latest First 90 Degree Day

#1 7/16/1924
#2 7/15/1915
#3 7/14/1902 and 2009

NORFOLK - July Latest First 90 Degree Day

#1 1992 never made 90
#2 7/23/1994
#3 2009 so far 

Over the July 4th weekend, Norfolk recorded their coldest 4th on record with a high of 69 degrees and now this week we are looking to tie or break record lows. 

Here are the record lows for July 17th, 18th, and 19th:

July  Records 17th    18th   19th  
Omaha    55  1885  57  1873 51 1873
Lincoln    54  1900  55  1992 53 1947
Norfolk    46  1906  49  1992 48 1947

The mid level steering flow as depicted by the forecast 500 mb height chart forecast valid for 7am Friday has a ridge over the western U.S. and a closed low over the Upper Great  Lakes.  This pattern will bring cool (cold) weather to the Great Lakes and Mississippi and Missouri Valleys.  Surface high pressure is forecast to extend across much of the Central Plains.


500 mb ht fcst
Forecast surface pattern for Friday morning (cyan) in millibars and 500 heights (pink) in decameters.  Ridge amplifies over the western United States with the trough deepening over the Great Lakes to the Missouri River Valley.
July 13th height pattern
Composite Mean of 500mb heights from June 13th to July 13th with the mid level ridge over the southern Plains.
500 mb patter May 1st
Composite mean of 500mb heights on May 1st, 2009

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