Tuesday, June 30, 2015

2015 Summer Weather Pattern Bucking the Trend?

According to the Missouri Climate Center, precipitation for the month of May seems to be the harbinger of summer temperatures.

"It is evident summers tend to be more seasonable or cooler as well as experience near average to wetter conditions following an unusually wet May. The rationale behind these occurrences are that May can be considered a transition month into the summer season, where weather patterns in the Midwest tend to be more stagnant. An established or recurring weather pattern in May could stick around for the summer. Additionally, wet soil moisture conditions at the onset of summer can act to suppress maximum temperatures when more of the sun's energy will be used in evaporating available moisture."
Pat GuinanState ClimatologistCommercial Agriculture/University of Missouri Extension
Courtesy Missouri Climate Center

The pink shaded cells represent a higher than normal temperature average and blue below normal, with white being within the margin of error for normal temperatures.  As we can see, 7 out of 20 wettest months were followed by below normal temperatures for June, July, and August, with another 8 following the average. Only four times has a wet May been followed by above average temperatures and only one of those with higher precipitation than average as well.  It can also be pointed out that in half of the times when summer temperatures were seasonal or below average, the following summer rainfall totals tended to be completely average while three out of the four hotter seasons showed rainfall well below average.

Below is the graph provided by NOAA for temperature and precipitation outlook for Summer 2015 indicating they were already predicting mild temperatures and above average precipitation for our area.
With June 2015 ending we can look at the average temperature and rainfall for the month to see if this is indeed the trend.  My guess is that with a sampling of only 120 years worth of data there is not enough sample points to make for any meaningful correlation.  Indeed we see temperatures and precipitation are not supporting the historical trend indicated by the Missouri Climate Center. It may be, due to climate change, and entirely new trend is developing.
The following graphic is for precipitation above or below average for the month of June.
Courtesy Missouri Climate Center
The above indicates that for the month the average departure from the mean statewide was anywhere from 1-10 inches above normal.  For the tri-county region of Lake of the Ozarks, it was 4-6 inches, well on its way to a record of some kind I'm sure.

Below is a similar graph indicating temperature deviation for the month of June. Here we see a above average data for the Lake area by 1-2 degrees.

Courtesy Missouri Climate Center

So far this summer has started off warmer and wetter than average, contrary to the conditions predicted by the data. In fact, this summer is on track to being only the second time where a wet May was followed by warmer temperatures and higher precipitation. The other season of wetter and warmer weather occurred only five years ago, in 2010, and may represent a more important trend to be aware of happening. Whether temperatures and precipitation follow for the remainder of the summer remain to be seen, but if they do this summer will likely be making a new mark of its own in the top 20 wettest Mays in Missouri.