State climatologist Bruce Watson explains the concept of wet-dry cycle and how recent heavy rains are part of a long term weather cycle. 8 inches of rain fell in the metro area on the night of June 24, 2002. Watson says the month ranks among the top ten soggiest on record.
On June 9-10, 2002, 48-hour rainfall totals topped 12 inches in some areas of Roseau and Lake of the Woods counties, one of the most significant precipitation events in Minnesota's post-settlement history. That was followed by heavy rains again drenching northern Minnesota on June 22-23, 2002.
Transcripts
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SPEAKER 1: Right now, we're right at the peak of the 20-year wet dry cycle, which begins in years ending with a 7 and ends in years beginning with a 6. So that the current wet cycle where it began in 1997, it will continue until 2006. So you can see the 2002 is right plunk in the middle. And of course, on top of that, June is the wettest month on the average. So we have all those things operating. And it just turns out that this June, we've had this very unusual flow of air off the Gulf of Mexico, which has resulted in a great deal of rain.
SPEAKER 2: So, Mr Watson, are you saying that perhaps for the next four Summers we'll also be getting a lot of rain?
SPEAKER 1: Well, in the wet decades, most of the months are wet, but you usually get one or two that aren't. And in the dry decades, you get one or two months that are on the West Side, but most of them aren't. So it's not a perfect fit.
SPEAKER 2: OK, so it's sort of a cumulative effect then?
SPEAKER 1: Exactly. Right. Incidentally, this wet dry cycle has been known since at least the 1920s. People already had identified it. And it centered on Manitoba, but it includes all of Minnesota, Iowa, Wisconsin, the Dakotas, Nebraska, Saskatchewan.
SPEAKER 2: How unusual is it for us to have such consistent heavy rains in June?
SPEAKER 1: Well, it happens. We've had June's that it has had over 7 inches of rain, although this June will probably, at least at my weather station, easily top 9 inches and very likely 10 inches. And I do expect I'll have the wettest June I've ever had.
SPEAKER 2: We have received quite a bit of rain this June, as you mentioned. What would happen if it was snow? How much snow would we actually have on the ground?
SPEAKER 1: Well, actually it all is snowing. All, or virtually all the precipitation we get in the summertime starts as snow in the clouds. And of course, it melts on the way down. But you're talking right now about, if we get 90, or if we get inches of rain, that would come out to about 90 inches of snow.
SPEAKER 2: Really. So it's like a 10 to 1 ratio then?
SPEAKER 1: Right.
SPEAKER 2: Why isn't the Western United States seeing much rain this summer?
SPEAKER 1: The thing is, if we're getting wet, somebody has to be extraordinarily dry. In other words, if you have a lot of rain, that means that the air is generally rising in your place. Well, in the atmosphere, the amount of air rising has to be balanced by the amount of air that's sinking. And where you get the sinking air, of course, you get dryness.
SPEAKER 2: What can we expect for the rest of the summer in minnesota?
SPEAKER 1: I expect it's going to be a fairly wet summer, although I'm sure we're going to dry out quite a bit in July, especially after the old, say, the 8 or 9th of July, we should get a lot drier.