MEMPHIS, TN (WMC) - July in the Mid-South typically involves unbearable heat, but there was an abnormal drop in temperatures at the end of July and early August.
We typically see our hottest temperatures of the year during those two months and cool downs are rare. Temperatures for the 30th and 31st of July 2018 were the coolest since July 4, 2015. We only topped out in the lower 80s at the end of July and early August, which is about 10 degrees below average. However, the most notable difference was the drop in humidity. Our typical late summer pattern involves high humidity and a heat index near 100.
The jet stream was the reason for the dramatic shift in temperatures. The upper level winds moving from west to east, known as the jet stream, guide our weather pattern every day. If you've ever been on an airplane, you've likely been in the jet stream and not even known it. This level of the atmosphere is where planes cruise. The jet stream serves as a divide between cooler and warmer air, so a north or south shift can cause major changes in our weather in the Mid-South.
In the Summer, the jet stream usually sits near the Great Lakes. However, at the end of July and early August, the jet stream took on a more winter-like position (see image above). This allowed for cooler, drier air from the north to grace our area and bring relief from the typical sweltering summer heat.
This abnormal pattern usually only lasts for a few days and then goes back to normal. This means that August temperatures will return to the lower 90s and the humidity will increase once again.