LThe sun will rise this morning at 6:19, and set 15 hours 6 minutes later at 9:25 this evening. At is highest it will be 34.8° above the southern horizon, and civil twilight does not start until 10:23 in the evening.

At least it’s beginning to warm up. Last week was really cold — well below zero at night, and often near freezing in the daytime. Yesterday things took a sudden turn for the better — or at least warmer — it actually reached above 50°F according to the thermometers along the road. And it looks like it may stay that way.

Lightning storms aren’t quite here yet, but the thunderstorm season is definitely approaching.

Lightning is caused by particles of different sizes and compositions striking each other in strong updrafts. These collisions often transfer charge between the particles, and if they are falling through the updraft  at different rates (as would be the case for light ice crystals and heavy, often wet hailstones) the result will be the buildup of charge of one sign (usually negative) near the bottom of the cloud, and the other near the top. The charge near the bottom of the cloud will induce a charge of the opposite sign in the ground, and a transfer of charge occurs during a cloud-to-ground lightning strike.

Strong updrafts require heating near the ground, which can occur in volcanic eruptions (common in the Alaska Peninsula and the Aleutian Islands) or by strong solar heating of the ground. This is common during early summer in Interior Alaska, and in fact most of the wildfires here are caused by lightning strikes. The worst of the lightning (and the forest fires) are generally in June, but there is nothing unusual in thunderstorms from May through July. August thunder and lightning are rarer, and the ground is generally still too wet and snow-covered in April for the sun to heat it adequately. It certainly is this year!

 

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