LAST December was the coldest for the United States since the National Weather Service began keeping reliable records for the country as a whole in 1931. Moreover, last summer brought a record-hot August, following one of the warmest winters in 52 years.
Such swings between weather extremes are beginning to seem almost ''normal.''
Meteorologists have seen nothing to suggest a significant climatic shift. But it does appear that the US, and perhaps the world generally, has had a long run of unusual weather.
In summarizing last year's weather, the specialist magazine Weatherwise recently noted that six US winters in the past decade ran to extremes. Three of them averaged temperatures far below normal, while the other three had temperatures much above normal. That's almost three times the number of extremely cold and extremely warm winters expected in a 10-year period, to judge from meteorological records.
Whether or not the underlying climate is shifting, this experience points up the need for nations, local communities, and individuals to be prepared for extremes of weather. Devastating drought, extreme and persistent cold, or other unusual weather cannot safely be considered a ''fluke'' that is unlikely to recur. Failure to prepare for extreme weather leaves communities unnecessarily exposed.Failure to provide for the related expenses in community or personal budgets is fiscally foolish.
According to the US National Oceanic and Atmospheric Administration (NOAA), December's cold snap added a hefty $1.76 billion to the nation's heating expenses. This showed up directly on consumers' fuel bills, and it drained public budgets. For example, NOAA estimates that heating costs rose 35 to 135 percent above normal for the average consumer in the northern Rocky Mountains and the Mississippi River Basin, the areas hardest hit.
Looking back at last summer, July and August brought one of the worst droughts on record to the US east of the Rocky Mountains. This was in spite of winter, spring, and fall storms that made 1983 an extremely wet year on average for many parts of the country.
The drought involved crop loses of nearly $10 billion. Commenting on this, NOAA climatologist Douglas Lecomte has noted that there were similar loses in 1980. But, he said in a review in Weatherwise, the 1983 costs were especially remarkable because ''planted acreage in 1983 was already sharply reduced by the government's payment-in-kind (PIK) program.''
Taking a larger view, 1983 brought extreme weather to many parts of the world. For example, Argentina, Brazil, Ecuador, Paraguay, and Peru had massive floods, as did Australia, where flooding ended the worst drought in a century. The message from the weather records seems clear. No one can forecast where climate may be trending. But extreme weather is occurring often enough to be a prominent factor in routine national, community, and individual planning.