When to expect the warmest days of the year

When looking at temperatures from a climatological view, July is when we typically experience the warmest summer days.  Of course, growing up in northern Illinois and southern Wisconsin we know that this can happen really anytime during the summer months.  But on average, the beginning to middle of July is when we experience the heat with an average temperature of 85 degrees.

The National Climatic Data Center released some interesting information this week on when the United States, on average, experiences it's warmest temperatures.  This is looking at the average daily high temperature over a 30 year period; from 1981-2010.  Looking at the data, much of northern Illinois experiences the warmest temperature during the first to second week of July.  The further north you head into Wisconsin, the warmest temperature is experienced roughly a week later.

What's really interesting to note with the map on the left is how variable the climate is across the United States.  This is due to different factors influencing the temperature from coast to coast.

Here's the full article from NCDC:

Following the first official day of summer, many areas in the United States are approaching their highest temperatures for the year. To give you a better idea of the warmest time of year for your area, NCDC has created a new “Warmest Day of the Year” map for the contiguous United States. The map is derived from the 1981–2010 U.S. Climate Normals, NCDC’s 30-year averages of climatological variables including the average high temperature for every day. From these values scientists can identify which day of the year, on average, has the highest maximum temperature, referred to here as the “warmest day.”

Although the amount of solar radiation reaching the earth peaked at the summer solstice on June 21 in the Northern Hemisphere, temperatures for most of the United States tend to keep increasing into July. The temperature increase after the solstice occurs because the rate of heat input from the sun during the day continues to be greater than the cooling at night for several weeks, until temperatures start to descend in late July and early August.

But, this isn’t the case everywhere! The “Warmest Day of the Year” map shows just how variable the climate of the United States can be. For instance, the June values in New Mexico and Arizona reflect the North American Monsoon, a period of increased rainfall affecting the Southwest United States. Because these areas tend to be cloudier and wetter from July through September, the temperature is highest on average in June. Similarly, the persistence of the marine layer along the Pacific Coast leads to cool temperatures in early summer with the warmest days on average later in the season.

Temperature Normals are important indicators that are used in forecasting and monitoring by many U.S. economic sectors. Knowing the probability of high temperatures can help energy companies to prepare for rising electricity demand and farmers to monitor heat-sensitive crops. They are also useful planning tools for the healthcare, construction, and tourism industries. You may want to check the Normals before planning your next event or vacation.
While the map shows warmest days of the year on average throughout the United States, this year’s actual conditions may vary widely based on weather and climate patterns. For prediction of your actual local daily temperature, and to see how it matches up with the Climate Normals, check out your local forecast at Weather.gov.