Spring

In the United States and the rest of the northern hemisphere, the first day of the spring season is the day of the year when the Sun crosses the celestial equator moving northward (on March 20^th or 21^st). This day is known as the Vernal Equinox.

A common misconception is that the earth is further from the sun in winter than in summer. Actually, the Earth is closest to the sun in December which is winter in the Northern hemisphere.

As the Earth travels around the Sun in its orbit, the north-south position of the Sun changes over the course of the year because of the changing orientation of the Earth's tilted rotation axes. The dates of maximum tilt of the Earth's equator correspond to the Summer Solstice and Winter Solstice, and the dates of zero tilt to the Vernal Equinox and Autumnal Equinox.

The reason for these changes has to do with the Earth's yearly trip around the sun. For part of the year the Earth's North Pole points away from the sun and part of the time toward it. This is what causes our seasons. When the North Pole points toward the sun, the sun's rays hit the northern half of the world more directly. That means it is warmer and we have summer.

The declination of the Sun on the vernal equinox is 0° 00'. On the day of the vernal equinox, day and night are nearly the same amounts of time. In the United States, there are about 12 hours of daylight on this day.

Tornado Season

March is the traditional start of tornado season in the United States. Although tornadoes can occur at any time throughout the year, the peak activity period is March through early July, according to the National Weather Service (NWS).

An average of 1,200 tornadoes touch down in the United States each year, and most of them form during this tornado season. Because these storms kill about 70 Americans annually and injure some 1,500 others, disaster experts urge families to be prepared — particularly those who live in Tornado Alley.

Tornado Alley is roughly defined as the area of the Central Plains from Texas to Nebraska. This is where most tornadoes form each season. Much of the damage that tornadoes inflict each year occurs in this region of the country. Texas has the highest number of tornadoes, with an average of 124 each year.

Tornado map courtesy U. S. Geological Survey