What is a Normal Summer?

We talk about summers being warm or cool, wet or dry. In practice, this is generally in comparison to what we perceive as normal for our particular locality. Precisely defining a "normal" summer, however, is a bit more complex: the one thing we can be sure of is that any particular summer will not be exactly normal.

In practice, a "normal" summer would be one in which the temperature and precipitation for each day corresponded to the average values for that date over a number of years. It would be a dreary season, with a little rain every day, and no very hot or cold days. Such an imaginary summer, however, makes a useful ideal for comparing summers across Alaska, or for looking at how a particular summer differs from the normal a given place. Here at the Geophysical Institute, we have charted these precipitation and temperature averages for a number of Alaskan stations.

You might think that the farther north you go, the colder the summer. This, however, is only part of the story. Oceans store cold from the previous winter, and warm up only slowly. Thus the warmest summer temperatures, with average daily highs in July around 70 degrees and records approaching 100 degrees, are found in the Interior, well north of the southernmost -- and more oceanic -- parts of the state. The coldest summer temperatures are found on the Arctic coast, where a day with a 50 degree high is warm, and 70 degrees has a good chance of setting a record. Seventy degrees could set a record much farther south, in the Aleutians, too, though the average high is warmer. The Southeastern islands and the Southcentral coast are warmer, but still rarely approach the warmth of the Interior. One additional difference between coastal and inland stations is that inland areas are warmest around late June and early July, while coastal areas are likely to be at their warmest in August.

Precipitation changes with the seasons in Alaska, too. For most of the state north of the Alaska Range, April is the driest month of the year. Thunderstorms start bringing rain to the Interior in May and more strongly in June, while the larger frontal storms begin affecting the area north of the Range in July. Almost all stations in these parts of Alaska are wettest in August, but the average daily precipitation during this wet season is still only about four to seven one-hundredths of an inch a day. In practice, this is likely to mean one or two days a week with a few tenths of an inch of rain. By September the precipitation is starting to decrease, and occasional freezing temperatures are widespread. Between the Alaska Range and the Coast Range complex, the greatest precipitation occurs in late August or even September, and the amount is a little greater -- around nine one-hundredths of an inch a day in Anchorage in September, for instance.

The amount and timing of precipitation south of the Coast Range complex is quite different. The driest month in most Southcentral, Aleutian, and southeastern stations is in June or even July, but in most southern areas these months are still wetter than they are in the Interior. Ketchikan, for instance, averages about a quarter of an inch a day in its driest month, June. At Kodiak and in the Aleutians, the precipitation seasons are not very pronounced, though the wettest months tend to be in the fall. Southcentral and Southeastern stations, however, remain "dry" through mid-August, when the precipitation begins to climb very rapidly. The wettest month in these areas is usually October, when precipitation in some parts of Southeast exceeds an inch a day on the average.

Added July 13, 1996: When this article was originally released to newspapers across Alaska, a chart was included for each local area. Today, charts of this kind are available on the Internet, for instance at http://www.cdc.noaa.gov/~cas/Climo/polys/alaska.html