90-Degree Days or Here Comes Summer
- Becky Bolinger
- May 31, 2019
- 12:35 pm
The impending heat of summer means the start of 90° days for some; for others it’s the continuation of the heat that’s already started. Let’s take a closer look at where we see those 90° temperatures – up until now, and into the first month of summer (June).
Although June 21 is considered by many to be the start of summer (with the occurrence of the summer solstice), meteorologists and climatologists consider the beginning of June to be the beginning of summer. A closer look at the climatological data, and you might be able to figure out why.
Average maximum temperatures in June are largely between 70° and 90° for most of the country (maroon dots). For the desert southwest, most of Texas, and the southeast, average maximum temperatures are mostly over 90° (pink dots). For isolated locations in the north, the Pacific Northwest, and some high elevation locations of the Rockies, average June maximum temperatures stay below 70° (yellow dots). Looking at this map, it seems it could be a useful tool in helping those in the south know where to go to cool off for the summer!
Despite the fact that most of the country averages temperatures below 90° in June, many of these locations will actually see their first 90° day in – you guessed it – June. Check out this map that shows stations that typically observe their first 90° day in June. Pretty much all of the locations that don’t average temperatures above 90° will still see a 90° day this month.
While a lot of these areas in gray are anticipating their first really hot day of the year, there are other areas that have already become familiar with the heat. This last map shows the number of 90° days already experienced across the country. Not surprising that most of the regions that average very hot temperatures in June have already seen several 90° days before the official start of summer. Following a line around Interstate-10 from southern CA all the way to Florida, many stations have observed more than ten 90° days. Some of these hot days have even extended north into the High Plains and the Midwest.
90° is a pretty important metric for determining how “hot” a location is. At 90°, vegetation begins to show signs of stress. It’s widely considered fact that the growth of some crops is inhibited during these hotter days. When the temperature tops out above 90°, heat stress is also more common for people and animals. Over the last couple of decades, summer trends have seen an increasing number of these very warm temperatures. For example, in Colby, Kansas, average number of 90° days has increased from around 50 in the 1970s to around 60 in the 2010s. On a positive note, thanks to increased irrigation through many areas of the High Plains, the number of 90° days has actually decreased (take Seward, Nebraska for example). Still, it’s safe to assume that we’ll have a number of uncomfortable days ahead of us as we head into summer. Be prepared, and find ways to help your family (and your livestock!) keep cool on those particularly hot summer days.