The workweek started off relatively calmly in the areas west of Minneapolis. It was partly cloudy and 80 degrees. By lunchtime, softball-size chunks of ice were dropping from the clouds.

"We got pounded" by the enormous hail, laughed Joe Checkal, owner of J.C.'s Auto Body and Paint in Franklin Township, Minnesota. "I've been in business 46 years and have never seen that before. They were as big as tennis balls." Despite the wallop, Checkal is relieved to have somehow escaped significant damage. "Even with all the cars outside, I didn't lose any glass."

At the Pioneer Creek Golf Course in Maple Plain, Minnesota, the hail wasn't quite as hefty - but there was plenty of it.

"We had them bigger than our golf balls," said Lisa Koenecke, who works in the Pro Shop. "It came out of the blue. We heard the storm would have hail, but this was a lot."

Thunderstorms had been in the forecast, but they weren't really anticipated until the afternoon.

"The atmosphere had a strong cap," said Tyler Hafenstein, a meteorologist at the National Weather Service office in the Twin Cities. A cap is a layer of warm air above the ground that limits storm growth. It's like covering a pot of boiling water with a lid, preventing plumes from rising. He explained that high-resolution models didn't predict storm cells to develop until the late afternoon. Attention instead was focused on a clustering of storms farther north that was being watched for gusty wind potential.

"We launched a special weather balloon around noontime, though," Hafenstein said. "It showed the cap had eroded earlier than expected. We were warming quickly at the surface. But with the storms farther north, there were no reports of large hail."

One storm managed to develop to the west, remaining just strong enough as it approached the area to thrive despite a subtle lingering cap. "It rode along the cold front," Hafenstein said.

The Storm Prediction Center hadn't been anticipating colossal hail, either; the primary threat simply seemed to be damaging winds along the leading edge of "bowing" storms.

"The main concern will remain damaging gusts," wrote the Storm Prediction Center. "Isolated large hail events to 1.5 inches in diameter [are] possible."

The center's early morning outlook emphasized wind hazards instead, although it correctly nailed the early timing of the storms. "There is an enhanced risk of severe thunderstorms by midday," the center wrote.

National Weather Service hail report from Aug. 5.  https://www.weather.gov/source/crh/lsrmap.html?zoom=7&lat=44.99&lon=-93.83&hr=24&severe=1&winter=1&flooding=1&other=1
National Weather Service hail report from Aug. 5. https://www.weather.gov/source/crh/lsrmap.html?zoom=7&lat=44.99&lon=-93.83&hr=24&severe=1&winter=1&flooding=1&other=1

The local National Weather Service office issued a severe thunderstorm warning for Wright, Hennepin and Carver counties at 12:19 p.m., highlighting the potential of "half dollar size hail." That was upped to golf ball-size hail 12 minutes later. The public reported tennis ball-size hail in Watertown at 12:40 p.m.

The most intense hail core passed about 35 miles west of downtown Minneapolis, dumping 4-inch ice chunks between Watertown and Delano along the South Fork Crow River. The cell drifted over U.S. 12, where stones still larger than baseballs came down.

Corey Mitteness owns the Oakwood Insurance agency in Watertown, which received the hail core more directly than downtown Delano. "We're rocking and rolling here," he said. "There have been more than a hundred claims. We're busy." The two cities have a little under 10,000 residents combined.

Several neighborhoods north of downtown Minneapolis reported hail, but the storm had tempered a bit by then - the hail tamed to about an inch or so.

Hailstorms in Minnesota aren't terribly rare, but only 36 days since 1950 have featured hail four inches in diameter or greater. The Upper Midwest and Northern Tier see their hail season stretch a bit longer than the Southern Plains and Tornado Alley. It's not terribly uncommon for large hail to fall there anytime between May and August.

In the meantime, more tranquil weather is in the offing, with cool air filtering in. Highs this week will be in the 70s.

This article was written by Matthew Cappucci, a reporter for The Washington Post.