The AccuCam shows another dreary, cold November day here in State College, Central Pennsylvania, home of AccuWeather HQ [Google Map].

The StarDot NetCam AccuCam

A quick look at the last 3 days of hourly observations from our local airport shows it's been "mostly cloudy" to "overcast" for 93% of the time.

One thing that I noticed when I moved to Central Pennsylvania from eastern North Carolina in 1997 is that it seems to be a lot colder, cloudier and windier up here. Especially this time of year, it's tough to find the will to go outside and get some exercise because it's usually cloudy, cold, AND windy (any of those could be excused individually). It seems like it's "always" windy here, no matter whether it's 100 degrees or 0. This is something that I wasn't used to in North Carolina; it seemed like it was always calm there unless there was a hurricane or a big front coming through in the winter.

But I wanted to quantify that, because people's memories, especially about long-term things like the weather, tend to flounder. Cold is easy; we're at a higher elevation here and much further north. But how can you quantify average wind or cloudiness over time? Enter the NCDC Climate Atlas, which has national maps of average climate data for a 30-year period.

Here's a look at the Annual Sky Cover -- what percentage of the sky is covered with clouds on average, if you add up the hourly observations.

While Raleigh, NC was about 59%, here in State College the clouds cover the sky about 67% of the time, a significant difference. Although much of this generally cloudiness extends up into western New England, it gets worse as you move towards Lake Erie, so much so that Buffalo and Erie are essentially the same as "typically dreary" Seattle! The same goes for "hours of sunshine" (which is slightly different because it doesn't include the overnight hours):

There, Pittsburgh is essentially equivalent to Seattle. It is seasonal, however. I notice more cloudy days here in the Spring, Fall and Winter than Summer. And sure enough, if you take a look at July's Percentage of Sunshine...

...it's not that different between North Carolina and Pennsylvania.

Wind isn't as significant, but it does average higher here than in North Carolina. This really doesn't match my memory though, and I think I may know why. The documentation says that this data is only for 230 stations nationwide (and more of those are disqualified if they have more than a few days of missing data). Here in Pennsylvania, it's probably just Pittsburgh, Harrisburg, and Philadelphia, (maybe Williamsport) -- none of which are near enough to State College to be representative of our wind speeds because of the local effects of the mountains which essentially "start" here and build to our northwest. (Even in this modern era, there are still only two official climate stations east of Pittsburgh - Williamsport and Harrisburg).

RED = OFFICIAL CLIMATE STATIONS IN EASTERN OHIO AND CENTRAL PA (NWS)

But I believe the overall reason for the cloudiness (and perhaps to a lesser extent, the windiness too) on the maps above (precluding the aforementioned local effects) are threefold:

MAP BY FERMI

1. The Appalachian mountains. When air moves from the west up the mountains, clouds form, and they may not disappear until the air descends the eastern slopes (generally east of here). When the wind is from the east instead, they can also block the westward movement or dissipation of clouds.

2. The Great Lakes, which provide amply moisture to form clouds as winds move (generally) southeast across them.

3. The Jet Stream. The jet stream retreats to the Northeast U.S. in the Summer, which means that we're under its influence more on average and we get a greater chance for (windy) low pressure systems to move through with clouds that may interrupt our outside plans.

Posted by Jesse Ferrell on Sunday, November 22, 2009 9:52 AM
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