Scattered showers and thunderstorms Tuesday

Monday has been mostly dry with falling dew points for most of Minnesota, but a few thunderstorms produced high funnel clouds in Dakota County in east central Minnesota during the afternoon.

These "cold air funnel clouds" often form behind a cold front when there is some atmospheric spin in the area. They are weak and rarely touch down. Other thunderstorms have popped up in southeastern Minnesota. And there have been isolated small showers in the northeast, as well.

The visible satellite showed a wide variety of cloud types this afternoon from many small cumulus clouds, to cumulonimbus thunderstorms to a deck of cirrus and cirrostratus streaming in from the southwest.

Tuesday will be a more unsettled day statewide as a weak cold front slides southward from Canada.

Scattered showers and some thunderstorms are on tap for Tuesday, beginning up north in the morning and then breaking out farther south in the afternoon. Fortunately for residents of waterlogged Iowa, the "No Precip" area will cover much of that state for the day.

Occasional showers are likely later this week. Strong to possibly severe storms are possible closer to the weekend, along with a return of significant humidity.

How lightning strikes people

I wrote about how lightning bolts form and flash to Earth in an instant in the Updraft blog this morning as part of Lightning Safety Awareness Week. Now let's take a look at ways that lightning strikes people outdoors, which is where nearly all lightning deaths and injuries occur.

Lightning tends to strike tall objects, especially pointy ones as they are effective at producing positive upward streamers to meet the stepped leader and complete the lightning channel. Trees and mountain tops, both rather good insulating materials, are struck frequently. So it is a myth that lightning targets metal objects such as flag poles and light towers.

The following animations from the National Weather Service illustrate some of the ways that a person can be in harm's way from a lightning strike. With any of them, once the stroke begins it will be over before you could observe it coming.

The first, most direct and usually the most devastating strike is called, appropriately enough, a direct strike. This is common in open fields and small boats where the person is the tall object where the lightning path to Earth is completed. If your hair stands on end in the vicinity of a thunderstorm, a direct strike can be short moments away.

Sometimes lightning will strike a tall tree and then have part of the current flash laterally to a person standing within a couple feet of the tree. This is called a side flash or splash and often occurs when people take shelter under a tall or solitary tree. The degree of bodily damage depends partly on how much of the current is diverted from the tree and through the person.

Once the current reaches the ground, it tends to spread out along the surface. This ground current injures or kills people and animals by going up a leg, damaging the body, often by stopping the heart but also potentially doing much other damage, and then down the other leg back to the ground. Ground current usually weakens with distance from the originally-struck object.

Conduction can cause serious injury or death far from the original lightning strike. Although lightning does not target metal objects, they are excellent conductors and can deliver a substantial charge far away if the lightning strikes a metal fence, guard rail, bridge structure, railroad tracks, plumbing or wires. In fact, striking telephone and electric wires is one way that lightning can reach people indoors, so avoid the use of corded phones and other items during thunderstorms.

So enjoy the great outdoors but head for the safe indoors if a thunderstorm approaches or develops.