When is the warmest time of year?
Summer has arrived, and with the season comes the warmest days of the year. Depending on where you live, the hottest day of the year may occur earlier or later in the summer than in other locations in the United States.
Using weather data averaged over many years, we can determine the expected time of the warmest time of the year for each region of the country.
The map below shows the date on which the hottest day of the year typically occurs, according to the latest 30-year climate averages (1991-2020) from NOAA’s National Centers for Environmental Information.
However, keep in mind that the weather does not always follow what is considered average. A strong area of high pressure can provide warmer temperatures days or even weeks earlier or later than shown on the map below.
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For most people, the hottest day is after the summer solstice
Almost the entire country is expected to experience the hottest day after the summer solstice in a normal year.
Although the Sun is highest in the sky and provides the most direct solar radiation on the first day of summer, it takes time for the Earth’s surface and the air above it to warm up. This creates a seasonal gap between the summer solstice and the average warmest day of the year.
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The desert southwest is the main exception
Blame the North American monsoon.
Many areas in Arizona, New Mexico, and far western Texas see temperatures peak in June before the start of the monsoon season. The monsoon brings more frequent rains and thunderstorms to the region, especially by July.
Relatively cool temperatures usually accompany the southwest monsoon due to increased cloud cover, so most of the region tends to see the warmest days of the year by the middle or end of June.
According to FOX Weather’s Senior Weather Data Specialist Shane BrownFort Stockton, Texas, reaches its average hottest day before any other city in the United States — on June 11, about 10 days before the summer solstice.
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July is generally the warmest month for the United States
For the United States as a whole, July is the hottest month of the year.
According to Brown, if you combine the warmest days of the year in each location in the Lower 48, July 26 is the average hottest date in the country.
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The South waits until August
Daily rain and thunderstorms are the norm throughout the South in early summer.
Later in the summer, high pressure visits the southern states more frequently, providing brighter, drier days but driving temperatures to the highest values of the year.
Many locations from the eastern half of Texas to parts of the Southeast typically record their warmest days of the year in August.
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West coast wait until fall?
It takes until September, the first month of meteorological fall, for some parts of the West Coast to experience the hottest days of the year.
Onshore winds dominate coastal areas of the western United States during most of the summer due to a weather pattern caused by a combination of hot inland deserts and cool air over the Pacific Ocean. Winds off the water often create low clouds and fog, making temperatures cooler near the coast.
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But as summer cools down in much of the country with September, the hot weather is just beginning along the West Coast due to the change in wind direction.
Instead of winds blowing onshore, the winds shift offshore and send warmer, drier air from inland deserts toward the coast. These winds are called Santa Ana winds in Southern California or Diablo winds in Northern California.
According to Brown, San Simeon, California, doesn’t see its hottest day until October 7 on average, later than any other location in the country.