If Southern Illinois doesn’t get rain from Harvey this weekend, it may get rain from Canada.
Lewis Kanofsky, a meteorologist with the National Weather Service in St. Louis, said there are a number of reasons it’s “tough to pinpoint with a lot of accuracy” where the rain might come from. Either way, the greater St. Louis area is looking at rain starting with a slight chance early Friday morning and increasing until Saturday morning.
“Harvey is not moving very much,” he said, which is part of the reason it’s hard to forecast.
But lurking to the north is an “upper disturbance,” which “might push Harvey off” of the area.
“Eventually the remnants of that system (Harvey) are going ... northeastward,” he said, with some models suggesting it will move toward Southern Illinois and other models showing it heading more toward Tennessee.
The system in Canada is “way far back from where we have measurements,” Kanofsky said, which means what are tiny differences in model projections now become much larger as it moves.
“One way or the other, one of those ought to produce some rain,” Kanofsky said.
Hurricane Harvey prompted a change at the National Weather Service in how it colors maps.
Kanofsky said the service has been standardizing map colors for precipitation, but the common color table didn’t go high enough to accommodate the amount of rain Harvey is producing.
The NWS added shades of lilac and purple to show 15-20 inches, 20-30 inches, and greater than 30 inches of rain. Previous maps had a dark red that simply indicated greater than 15 inches of rain.