Today I'm being shadowed by Christina, a 17 year-old young lady from South Allegheny High School.  I showed her my blog entries and asked her what I should write about.  She said she doesn't understand how it can be so cold one day, this time of year...and so warm the next.  My thought is that if that's what's on Christina's mind, it's probably on the minds of many others in the viewing audience.  So, let's address her question and hope it serves others, too.

October is a transition month, as we say goodbye to the summer months and prepare to say hello to the winter months.  It can literally feature a little of this and a little of that.  Part of the explanation for this has to do with the tilt of the Earth on its axis...23 1/2 degrees.  As we orbit around the sun, the angle of the sun gets higher in our sky as we approach the Summer Solstice (approximately June 21) and lower in the sky as we approach the Winter Solstice (approximately December 21).  We're heading into that lower angle sun time of year, obviously.  The lower angle sun gives an increasing glancing blow of incoming solar radiation, which doesn't warm us up as much...and of course, our days get shorter and nighttime lengths get longer...allowing for more cooling still.

As our source region for cold air (the arctic region) gets more active and sends more and more fronts at us from a northerly direction, the frequent blasts of air can have a pronounced cooling effect on our weather.  But we are just now splitting the difference between the arrival of autumn and the arrival of winter, so when the clouds clear up and winds come in from the southwest, we can still get a nice dose of warm air.  That's why we can have the phenomenon known as "Indian Summer," which we've been talking about, this week. 

So we can get frosted heavily, such as we did on Monday of this week.  And that can be followed by a day in the 60s, followed by two days in the 70s...as we saw on Tuesday, Wednesday, and Thursday.  To me, this is what makes Pittsburgh's weather some of the most enjoyable and interesting in the United States.  We get all four seasons and they are all beautiful.

Thanks for the question, Christina, and I hope you enjoyed your "shadowing" in the Weather Center.

D-Bow