'Hurricane’ Schwartz: We need rain

It's been nearly two straight weeks without measurable rain in Philadelphia. That's a long dry spell, especially for spring, and combined with unseasonably warm air, we end up with some problems.

Fire

Very dry ground combined with low humidity and high temperatures combine to produce the highest fire dangers. All it takes is a small ember to build into a dangerous forest fire. So, one reason we need the rain is simply to lower the fire danger. It's amazing how fast some fires can spread under ideal conditions.

Pollen

Many allergy sufferers can tell you just what days have high pollen counts just by the number of their sneezes. It's miserable. Some people can't even go outside without medication when the pollen level is high. And what is it that washes out the green stuff on your cars? Yes, it is rain, and a lot of people start praying for it when we have dry spells in the spring. Of course, not all allergy sufferers are affected the same. My allergies seemed to be worst when I was living in Cincinnati. I mowed the lawn one day, and was in bed for the next three, simply overwhelmed by my allergic reaction to the Ohio grass.

Farmers

Many farmers will tell you it's either too wet or too dry, or too hot or too cold. The weather is critical to them, and they are among the most dedicated weather watchers. Dry and hot weather are not very good conditions; ask the farmers in California.

In fact, the dry and hot weather affect each other. The heat helps dry the ground even more, since it causes more evaporation of the surface moisture.

Normally, some of the sun's radiation goes toward evaporating moisture. If it's dry, there's more radiation left to heat the ground.

During a dry spell, I have to sometimes add several degrees to my forecast to account for this. And the computer models don't handle this well, either.

Some people may notice that temperatures go higher than predicted during long dry spells or droughts. I also might lower my rain forecasts when the ground is unusually dry ahead of an approaching front.

We have had no measurable rain for 13 days. With an average of a little over .10" per day at this time of year, those 13 days would make us about 1.4" below average for that period. We did have some heavy rains in April, but much of that ran off. It wasn't a nice steady soak.

So it will take more than some scattered showers and storms to bring everything back to "normal." The dry weather and heat will start building again Thursday, and it looks like a hot Mother's Day weekend.

Glenn "Hurricane" Schwartz

Chief Meteorologist

NBC10 Philadelphia

You can watch Glenn "Hurricane" Schwartz every weekday on NBC10 at 11 a.m., 4 p.m. and 6 p.m. Follow him on Twitter @HurricaneNBC and stay informed when weather changes on the NBC10 app and the NBC10 First Alert Weather Team on Facebook: NBC10Weather