A Tour of US Temperatures

By Barry A. Klinger, George Mason University
Questions and Comments: bklinger@gmu.edu
Return to Weather and Climate Page

This page presents a snapshot of climatological temperatures in the Contiguous United States (CONUS). Climate often refers to time-average quantities, but it also includes the seasonal cycle and day-to-day weather.

Sections
What We Are Looking At
What It Tells Us
Global Heating
What About My City?
Details

Click Here for Higher Resolution PDF of Figure (new tab or window)

What We Are Looking At

The figure shows daily maximum temperature statistics for 8 large cities widely distributed across CONUS, from 30 years (1990-2019) of weather station data. For each city, for each day of the year, I found the median and a measure of the range of values (10th percentile to 90th percentile) from the 30 measurements (1 for each year) on that day. See Details for more information.

The right panel of each pair shows another way of looking at the temperatures: the percentage of all days in the 30 year record that fall in each temperature range. The bars are subdivided into 4 "seasons", consisting of DJF (December-January-February), MAM, JJA, and SON. The subdivisions have the same color as the corresponding months in the left panel. The distribution graph also lists percentages of the days falling into three broad categories, "hot" (> 77^oF, 25^oC), "cold" (< 50^oF, 10^oC), and moderate.

What It Tells Us

As you might expect, temperatures are generally colder in more northerly locations, warmest in July and coldest in January, but the plots of seasonal variations reveal many different patterns as well. Boston, Chicago, Denver, and Washington (BCDW) share many similar features.

1. The seasonal temperature range (measured by daily medians) is < 20^oF for LA and Miami, about 30^oF for Seattle and Houston, and 45-55^oF for BCDW.
2. Generally cities in the middle of the continent, including Houston, have a larger seasonal cycle than coastal cities at the same latitude. Houston is also a coastal city, but its location in middle longitudes exposes it to a more continental climate.
3. The wintertime weather range (as measured by 10th/90th percentiles) is about half the seasonal range for all except LA and Miami - for which the weather range is almost as large as the seasonal range. If day-to-day temperature changes feel like you are lurching between different seasons, you are right!
4. Warmest months range from under 77^oF (Seattle) to over 95^oF (Houston), and coldest months range from under 32^oF (Chicago) to almost 77^oF (Miami).
5. Weather range in the summer is about half that of the winter. This is because much of weather is due to the daily drift of warm and cold air masses, and the geographic range of temperatures is greater in the winter (see #4 above).

The distribution plots offer an interesting alternative view of the same temperature data:

1. For BCDW, each of about 5-6 neighboring 9^oF temperature ranges occur on about the same number of days per year. For instance, in Boston, about 13% of daily highs are 77-86^oF and 16% are 41-50^oF.
2. In other cities, the distribution has a more prominent peak. For Seattle the peak is 50-59^oF, closer to the cold end of its range. In Houston it is 86-95^oF, near the upper end of its range. Thus a "typical" day is colder than its average in Seattle and warmer than its average in Houston.

I defined "moderate" temperatures to range from "light jacket" to "short sleeves" weather (50-77^oF), which I personally find optimum. Others may prefer a slightly warmer range (59-77^oF or even 59-86^oF). The distribution plots tell us how often a city spends in moderate, hot, and cold ranges:

1. LA is the king of moderate weather - moderate 85% of the time, mostly 59-77^oF.
2. Seattle is pretty moderate (64%), but mostly on the cold side of moderate.
3. BCDW are each moderate about 40% of the time, but with the remainder skewing cold in the northern two and hot in the southern two.
4. Miami and Houston are both hot. Miami has the most hot days, but mostly in the lowest category (77-86^oF). Houston is above 95^oF almost 40% of the time. Their coastal locations make both quite humid on hot days as well. This has not stopped people moving there - population grew by about 20% in Houston and 10% in Miami in the last decade.

Global Heating

Global temperatures are already about 1 C higher than a century ago due largely to humans pumping carbon dioxide into the atmosphere and is likely to get a few degrees warmer over the next century if we don't reduce emissions soon. What will this do to future temperatures at the cities discussed here?

Temperature in most locations already ranges over tens of degrees, and will continue to do so in the future. One way it will impact people is in the distribution of extremes. In Washington DC over the last 30 years, about 220 days (2% of the total) have warmed to over 95^oF, but a much greater number, 1530, reached 86-95^oF. A little bit of warming will push some of the 86-95^oF days above 95, and since there are so many of them, the number of extremely hot days may change by a lot. Thus rather than feeling a general rise in temperature, people will experience global heating as a new climate with more very hot days and fewer very cold days. Similarly, seasonal distributions will change. Recently in Washington, summer has typically included a few days of 77^oF or lower, but in the future, the entire summer may be above 77^oF.

Of course climate change will be felt in many other ways as well, including changing vegetation, changing times for leaves to bud and to fall, and changes in rainfall.

What About My City?

If you are not among the 50 million or so people living in the 8 urban areas listed here, you are probably between two of them, and can estimate your city or town's statistics by averaging the statistics of the two. If you email me at bklinger@gmu.edu, I can also provide the Matlab software for creating the plots and/or the plots themselves for a weather station near your home.

Details

Data is from https://ncdc.noaa.gov, under link "Data Access". Stations are:
Boston: Logan Airport, GHCND: USW00014739
Chicago: O'Hare Airport, GHCND: USW00094846
Denver: Stapleton, GHCND: USW00023062
Houston: Houston Intercontinental Airport, GHCND: USW00012960
Los Angeles: Airport, GHCND: USW00023174
Miami: Miami Beach, GHCND: USW00092811
Seattle: Seattle Tacoma Airport, GHCND: USW00024233
Washington: National Airport (Arlington, VA), GHCND: USW00013743

For the monthly data, I plotted the 15 day running mean (that is, average for the period from 7 days before to 7 days after) for the 15th day of each month (left panel of the pair for each city). For the distributions, each range excludes the bottom of the range (for instance, 30-35 means > 30 up to 35).