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Long odds
No matter what you see on TV or read on the Internet, it's not easy
to predict the weather, according to meteorology's William Gallus.
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If this were Vegas, it's doubtful that many would place bets on the weather
forecasts in Iowa or anywhere else for that matter.
The odds are definitely in the house's favor when it comes to predicting
the weather.
That's even more the case when it comes time to predict rainfall during
the summer months in Iowa.
"Warm season rainfall is generally agreed to be one of the most difficult
weather parameters to predict and forecasts of it are often terrible,"
says William Gallus, associate professor of geological and atmospheric
sciences.
In the past 10 years, the National Science Foundation has established
the United States Weather Research Program. One of the program's goals
is to improve rainfall forecasting.
It's an effort that Gallus has been a part of since day one and he says
he has found it a problem not likely to be solved in the near future.
"My research has generally shown the problem to be a very difficult
one to solve," he said, "and I think my results generally match
those of other researchers - there is no silver bullet to solve the problem."
Weather forecasting is accomplished through computer models. The models
rely on information provided by weather stations, typically at airports
throughout the nation. Weather balloons are also utilized, but those are
limited as well. In Iowa for instance, the two nearest weather balloons
are sent up at 7 a.m. and 7 p.m. each day in Omaha and Davenport.
"Forecasting models have improved drastically in recent years,"
Gallus said. "But we're still a long ways away from being totally
accurate."
So why is it so difficult?
Gallus says the latest computer models will look at weather information
obtained from grid points eight miles apart. This is a vast improvement
from the older models that looked at grids around 50 miles apart.
"Everybody thought this was the answer to our prayers," he said.
"But improvement was limited - a thunderstorm cell is still just
too small. Everything generally may look right on the computer model but
the storm just won't happen at the right grid point."
That explains why a forecast can say it's going to rain up to 2"
in Boone and Marshall Counties but instead those counties remain relatively
dry while Story County gets the 2" rainfall.
Gallus says Iowa receives 70-80% of its rainfall during the warm season,
typically within small, intense thunderstorms. While the prediction of
whether or not it will rain is easier, the amount of rainfall a community
can expect is much harder to predict.
"In the winter months I would say we can accurately predict precipitation
amounts 50 percent of the time," he said. "In the summer it's
closer to 10 percent accuracy."
And Gallus doesn't see a lot of improvement on the horizon either.
"It appears almost impossible to design one particular model that
will clearly stand out as being better than others," he said. "A
more reasonable approach is to run multiple versions of models and use
all of that information in some way. With rainfall, the best way may be
to issue probabilistic forecasts."
But Gallus says that's probably not going to cut it with the populace,
especially in Iowa.
"When I first came here, I expected people to be concerned with what
the weather was going to do the next day," he said. "But many,
especially farmers, want to know what the weather is going to do in the
next week or so.
"Some mathematical formulas used to grade forecasts suggest there
is some accuracy out to seven days," he continued. "At least
it's better than the almanac, but any forecast skill really drops off
after three or four days."
Around LAS
April 25 to May 8, 2005
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