Last week, a two day storm event brought rough weather first to the Twin Cities on Wednesday, followed by this howling, apocalyptic dust storm to Sioux Falls. There were tornadoes in Minnesota, South Dakota, Nebraska and Iowa, but the real show were a couple of bowing lines of thunderstorms that rolled through each town.

There was more severe weather on Thursday in the Upper Midwest and into the Great Lakes. Severe watches were out from Missouri to Kentucky, and also popped up from Minnesota into Wisconsin and Iowa. There was a particularly different feel to these storms than the ones last week, though, and much of it has to do with the orientation of the upper level pattern.

Last week, the upper level pattern featured a brisk south to north jet streak butting against a stout ridge in the east and situated on the eastern flank of the trough that was allowing the storm system to develop. One of the results was a very narrow opportunity for a warm sector of any consequence, but a lingering “warm front” boundary was the perfect environment for bowing lines and derechos, which is what we got, twice, last week.

This week, the system brought a wider warm sector, and was able to advance cold air. Initially, on Thursday, it lead to some significant hail, such as what I saw in downtown St. Paul Thursday afternoon.

As the storm moved on, the progressive low with access to warm moist air was a ripe environment for tornadoes, of which one struck Gaylord, Michigan. This storm was an EF-3 tornado, which is quite strong in general, but in particular for northern Michigan.

The wave, which again, because it was more open than the one from last week, has continued it’s course, and has allowed the parent area of low pressure into Canada. But again, because it is advancing, has brought cold air in on the back side. Even tonight, there is an ongoing threat of some severe weather thanks to a ranging cold front from the eastern Great Lakes to Texas.

Clashing air masses and strong jet streams are good environments for severe weather. Differing patterns and flows might lead to different results, but as the last couple of weeks have shown, they can all be dangerous.