In my previous column I wrote about this transition time of year. Nature is caught somewhere between winter and spring, and many of us are in the same quandary. People are beginning to come out of their winter doldrums and part of that is due to the Sun. There is more of that bright object shining in the sky than there was just a few weeks ago.

Consider the earlier sunrises and the later sunsets. It all adds up to more bright hours. The amount of daylight in mid-March is approximately 12 hours, a vast improvement over the measly nine hours of daylight in late December. Here's something to look forward to: by the beginning of April our daylight increases to 12 hours, 44 minutes; by May 1 it grows to 14 hours, 7 minutes!

I also mentioned in my previous column the increased severe weather this time of year, especially to our south. The more active jet stream and the return of warmth and humidity to the southern states add up to an active weather pattern that features almost daily severe weather events.

Our country is designed for severe weather in the spring. As moisture begins to move north from the Gulf of Mexico, the Rocky Mountains to the west and the Appalachian Mountains to the east prevent it from spreading too far. So high humidity and high dew points tend to stay trapped in the southern states. Warmer weather and a higher sun angle heat the Earth's surface and cause that moisture to rise. As it reaches higher into the atmosphere, a roaring jet stream overhead creates even more lift. The result can be explosive thunderstorm development and severe weather.

Another mechanism for lifting the moisture is a cold front. Cold fronts come in a variety of strengths, but a spring front tends to be strong. Imagine cold air in the northern Plains being shoved south and ramming head-on into warm and moist air in Kansas, Oklahoma, and Texas.

Cold air is heavier and denser. As it slams into the less dense warm and humid air, it plows it up like a snowplow pushes aside a fresh snowfall. The result is rapid lifting of the moisture. Combine that with the lift provided by a fast jet stream overhead and severe weather is the result.

Imagine if your job was to watch over the entire United States and look for potential severe weather explosions. You would scour the national weather picture and check the hourly surface weather observations looking for strong cold fronts. You would also need to dissect the upper air wind information that comes in twice a day from weather balloons. These balloons carry radiosondes (weather instrument packages) that measure conditions above the Earth's surface. They would help you spot the jet stream and the fastest core of winds aloft.

Is there a place where all of the right conditions come together to form the potential for severe weather? If you found such a place, you would probably issue a severe thunderstorm or tornado watch. You would be employed by the Storm Prediction Center in Norman, Oklahoma. Perhaps it's appropriate that this place is located right in the center of "tornado alley," right in the heart of where severe weather takes place in spring and early summer.

Meteorologists at the Storm Prediction Center (SPC) are like detectives. They look for clues to severe weather. The challenge for them is to spot the potential for strong storms hours before they can produce tornadoes, hail, or high winds. It is SPC that issues the severe weather watches. These watches are areas they believe may produce severe storms in the near future. While the watch area covers hundreds of square miles, it is up to the local National Weather Service office to issue severe weather warnings. The warnings are based on actual severe weather occurring while the watches are based on severe weather potential.

To check out SPC in action, go to their Web site at spc.noaa.gov/. On that site you will get a hint of the various things they look for when it comes to spotting severe weather. This is the time of year when they really get busy. And the challenge doesn't stop until well into next autumn.