Anatomy of a big winter storm

If not a legendary perfect storm, it was at least “a near-perfect heavy snow and wind event.”

That's the description a meteorologist at the National Weather Service's Davenport office used for the meeting of weather systems over the Midwest that produced this week's blizzard.

“It was just the right ingredients together at the right time and in the right place,” NWS meteorologist Andy Ervin said Wednesday afternoon.

The setup: “Very cold arctic air over the northern Plains and, at the same time, very mild, springlike air over the Southern states,” Ervin said. “This sets up a very impressive frontal boundary,” the transition between air masses.

The final ingredient: “A very strong piece of energy in the upper atmosphere off the West Coast,” Ervin said. “An upper-level storm system off the Rockies (moved) right in to that contrast between the very cold arctic air and that warmer air. The phasing (merging) of those different elements went just about perfectly to create a very significant winter storm system, and a very large system.”

Thanks to the upper-atmosphere low pressure system off the Rockies, “this one just had the right stuff to be much stronger than what we typically might see,” Ervin said.

Forecasters' work was complicated by a “dry slot,” a relatively small area of dry air dragged along with the high-level low. That prevented heavier snows over an area southwest of Cedar Rapids on Tuesday night and early Wednesday.

Temperatures plunged Wednesday as the low-pressure area moved east, its counterclockwise flow bringing more arctic air to Eastern Iowa.

“We should be below zero (Wednesday) evening and overnight” and again tonight, Ervin said.

A modest warming should bring temperatures into the 20s this weekend.

“We may even get near 30 degrees,” Ervin said. “But the main story is, we're not looking to melt this snow soon.”