THERE'S hope for the United States's soggy Midwestern and sweltering Eastern regions. The stubborn atmospheric circulation that has brought this fierce weather may be changing.
"It's not the end of the tunnel," says National Weather Service meteorologist Edward O'Lenic. But the service's forecast for July 15-19 anticipates "a change for the better."
Meanwhile, the floods that have hit Mississippi Valley farms have not caused a national agricultural disaster. Agriculture Department meteorologist Norton Strommen notes that, while some low-lying lands are lost for this year, the weather has actually benefited many farmers around the corn belt's periphery. "We're not as far behind as some people think," he says. He still is planning on a record corn crop.
If the weather forecast holds true, it will be the first break in this air-circulation pattern, a pattern unusual for North America. Mr. O'Lenic's colleague, James Wagner, explains that this pattern is dominated by high pressure in the Southeast and an unusually persistent low-pressure region over the Rocky Mountains and the Pacific Northwest. Air circulation around these pressure features pumps moisture-laden air up from the Gulf of Mexico over the Mississippi watershed, while heat covers the East and S outheast with drought in Georgia and the Carolinas.
Now O'Lenic and his colleagues forecast that the low pressure will move just off the Pacific Northwestern coast while the high pressure moves more to the center of the country. The effect, O'Lenic says, would be to move precipitation and temperatures in the East and Midwest toward their normal seasonal values. He warns, however, that they may not fully attain those values.
It is hard to pin down causes for the unusual weather pattern. It reflects the position of the upper-air jet-stream wind flow. O'Lenic explains that, at this season, the "possible influences on its [jet-stream] position are myriad."
Once established, however, the pattern over the US has tended to be self-reinforcing. Southeastern dry soils are conducive to more hot, dry weather. Cooler wet soils in the Midwest favor more rainfall. Furthermore, the Mississippi Valley flooding reflects a history of above-normal precipitation going back to last fall, according to Mr. Wagner. The ground is so sodden that it can't absorb above- normal rains any more. "The sponge is full" and the result is flooding, says Illinois State Water Survey meteor ologist Stanley Changnon.
But the extra moisture will benefit farms on higher land and with sandy soil. Mr. Strommen expects the best crops to come from such lands this year. He adds that the outlook for a good harvest is bright.
He explains that "what interests me" is the fact that 54 percent of the corn crop still is listed as being in good condition. Last year at this time, the figure was only 52 percent. He notes, particularly, that 84 percent of the Kansas corn crop and 81 percent of the Texas crop is in "good to excellent" condition. Also 78 percent of the spring wheat planting and 64 percent of the winter wheat crop not yet harvested are in good-to-excellent condition. That's better than last year at this time, Strommen sa ys.
He notes that, while "it's a complicated picture, it's not quite what people think" when they see massive flooding of low-land farms.