Fall into ... Summer?

September has arrived, which means fall is upon us. Whether you believe the season begins on September 1st (meteorological fall) or the 22nd (autumnal equinox), the return of pumpkin spice, apple picking, and changing leaves are just a few signs of fall. Another signal is the gradual decline of summer like temperatures through the month.

This doesn’t seem to be the case in 2018.

For those that know me, I hate the heat, and I cannot stand it. Fall is one of my favorite seasons, and when the cooler air arrives, it feels so refreshing. However we are near the end of September, and it hasn’t happened yet. So what gives?

There are a few factors, but one of them lies within the jet stream, which is an area of really fast winds in the upper atmosphere. Usually this time of year, the jet stream, located up in higher latitudes, begins to slowly move southward. This begins the transport of cooler air down into the midwestern and eastern parts of the United States. Unfortunately, the jet stream has not begun to swing southward yet, so it leaves the ability for warm, moist air to travel up from the Gulf of Mexico. For the better part of September 2018, temperatures remained summer like.

In fact, numerous records have been tied or broken for the month. Below is an image of weather stations in the United States that either met or exceeded its daily maximum temperature value for a particular day. There were 623 stations that had at least one record for the month of September 2018, and the month isn’t even finished yet. 38 stations have had at least 5, with most of them occurring in Colorado, Wyoming, and Florida.


What is even more striking are the record warm overnight temperatures. In September 2018 alone, there were 1,027 stations that had at least one record tied or broken overnight. 131 experienced at least 5 record nights, and 9 has had at least 10. While people might associate heat as a daytime issue, it can cause numerous problems at night as well. Although most people are sleeping, air conditioners are not. In fact, in some cases, they are running all night because of these warmer than normal temperatures, which creates a demand for electricity that energy companies need to satisfy. Something they may not have considered a decade ago.


Taking another look at the minimum temperature map, there appears to be a bullseye right over the western parts of Virginia and North Carolina. Asheville, North Carolina, located in the Blue Ridge Mountains, was one of the stations with 10+ overnight records for September. Below provides current and climatological temperature information for the weather station located at Asheville’s Regional Airport. Daytime maximum and minimum temperatures are plotted for 2018, and are compared against the climatological average (1981-2010), along with daily records. If a value meets or exceeds its extreme, it is given a colorized dot. The yellow dots (warm overnight records) are prominent in the area from May to September. Not only were there 11 overnight records in September 2018 (so far), there have been 44 overnight records for the entire year. 265 days have occurred in 2018 (at the time of writing) which means about 17% of nights have been warm enough to be records. This certainly puts a strain on someone’s air conditioner (can you guess where I’m currently writing this?)


The crazy thing is the month is not even over. At the time of writing, data was only up to September 22nd. so there are 8 more days to go for records to be set.

So when will relief come? There is some hope according to the Climate Prediction Center. Their 3-4 week outlook shows most of the eastern United States will experience below normal temperatures during the mid to late parts of October. This can only mean one thing…

…Winter is coming.