A frequently used metric for describing the continental or marine characteristic of the climate for a location is the annual temperature range. Stations near an ocean have their temperatures significantly modefied by the air over the adjacent water. Ocean water heats up and cools down much slower than land. When a landmass is close to an ocean, modified air from the ocean can quickly replace continental air as it heats up or cools down; thereby minimizing the extremes in temperature. Conversely, stations in the interior of a continent are sufficiently far removed from the moderating influence of the water and their temperatures vary greatly.
In this blog post, I pulled daily temperature readings for the 1981-2014 time period and computed the coldest temperature each winter (not calendar year) and the hottest temperature each summer. The data were obtained from the National Center for Environmental Information's (NCEI) Global Historical Climatology Network (GHCN) database. Only WBAN ("first order") stations were used due to computational and computer memory limitations (note: in Alaska, Cooperative stations were also utilized).
To be included in the analysis, a complete year of data must be present (no more than 10 missing observations). In addition, a station must have a minimum of 10 complete years since 1981. A total of 1,049 stations met the inclusion criteria. The following sets of maps show the typical warmest temperature of the year, the typical coldest temperature of the year, and typical annual temperature range. Importantly, the median value for each station was used – not the average. In some cases, extreme outliers or even bad data make it into the GHCN database. Using median values prevents those suspect values from overwhelming a station's true value.
Figures 1, 2, and 3 show the annual warmest temperature, annual coldest temperature, and annual temperature range. These are not all time extremes. They represent the median value from the list of annual extremes.
While no one should be surprised that it is hottest in the desert southwest and coldest in Alaska, what might surprise some people is that interior Alaska has the greatest annual temperature extremes in the U.S. The town of Eagle, Alaska, near the Canadian border, leads the way with a 145°F temperature swing from winter to summer in an average year. At the other end of the spectrum, several stations in Hawaii only have a 27°F change in temperatures from the low in winter to the max in summer!
Figure 1. Median value for the hottest temperature in a given year.
Figure 2. Median value for the coldest temperature in a given year.
For my Alaska readers, here are the same figures but reconfigured so that Alaska is the focus of the maps.
Figure 4. Median value for the hottest temperature in a given year (Alaska-centered)
Figure 5. Median value for the coldest temperature in a given year (AlasKa-centered)
Figure 6. Median value for the range in temperature between the coldest winter temperature and the hottest temperature the following summer (Alaska-centered).