A frequent complaint that I hear from blog readers is "It never rains/storms/snows at my house, it's like there is a protective shield over it!" I've been wanting to do a blog entry on this for a long time but recently some fellow weather enthusiasts have posted some explanations that I wanted to highlight.

1. Radar, Lies and Videotape: First and foremost, I believe it's a problem with the way radar works. As we've discussed before, local NEXRAD Doppler Radars show snow "going around" locations near their center. This is because the radar beam only covers a slice of the atmosphere and (because the radar is tilted up initially) this slice gets higher and higher as you move outwards (illustrated below by this NOAA graphic). What you see away from the radar is high in the clouds, where precipitation is heavier and things are more exciting. Because of evaporation, all that precipitation won't reach the ground.

As a result, as storms get closer to the radar center, they typically appear to weaken. And guess where most people are: Near a radar. Because they were meant to cover the populated areas, they are centered in populous regions. Below is a map of population from the U.S. census with radar locations overlaid.

Using a "radar composite" which takes multiple radars into account, such as the high-res Level II radar we have on MapSpace can mitigate that effect if you're within view of several radar domes. And yes, as you can see from the illustration above, radar covers multiple tilts but unless you're using 3D software, the average person looking at radar on television or the internet is looking at the lowest slice - even there, the beam is at over 10,000 feet near the edge of the scope! (Also if you get too close to the radar itself, it can't see above itself (this is called the "cone of silence" but we're talking a couple miles now so I don't think this is the primary factor).

2. Now It's Personal. I had this idea in my mind for a while but couldn't think how to explain it. Here in Central Pennsylvania we call it "The Central PA Storm Shield." It really does seem like storms go around us or disappear before getting here (see also #3 below). Adam from the Aerostorms Blog has explained this perceived effect well in a post entitled "The Storm Bubble", so I'll quote from it:

He also makes a great point which I have said in regards to East Coast chasing: You need to know your local vistas so that you can see storms as far away as possible, rather than being trapped at your house in the trees. Under the right conditions you can see lightning for hundreds of miles away at night -- so your bubble just got bigger.

3. But it Does Happen. Just Not Often. There are sometimes meteorological reasons for storms dying -- like the weekend rain that missed the Northeast. As chaser Scott M. said on Facebook, it seems to lend credence to "The NYC Split" where more stable ocean air sometimes punches inland, causing incoming storms to die before they reach the coast. Saturday, that stable air was pushed in by the subtropical storm offshore, an unusual situation where New York City was just in the wrong place at the wrong time. In that case, that lack of storms came on the heels of 1-2 weeks of rain so there did appear to be "holes" on the short-range accumulated precipitation map. In time thought, those holes fill in and if you look at a long-term precipitation map, there are not (repeatable) holes, shields or bubbles that storms have avoided.

I say "Eastern U.S." because mountains, especially the high ones out west, can cause more predictable precipitation effects and you often see enhanced amounts on western slopes while locations on the eastern side of mountains (assuming a west-to-east flow) get less rain and snow. This is because when air rises it becomes more moist, and the opposite happens when it descends. This is the primary reason that we often "get the shaft" with storms here in Central Pennsylvania as air goes down the mountains (mountains also disrupt thunderstorms' rotation which doesn't help, and heat over a wide area like Eastern Pennsylvania can regenerate storms, making it seemed as if they've "skipped over" us).

Got other reasons? Hit me up on Facebook.

Still think it doesn't storm at your house? Prove it. Find a map from a year or more of historical storm reports (yearly | since 1980) or yearly rainfall showing your "hole."

Jesse Ferrell