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Alaska is a big place, and the weather system affecting our state right now is even bigger, but I’m going to show you that is it the small scale that counts when it comes to winds of the south and southeast coasts. As I write this, virtually the whole state is under the influence of the strong pressure gradient between a large, deep low in the Northeast Pacific and strong but gradually weakening high pressure in Siberia and the Alaska interior. (The high was up to a crushing 1060 mb a few days ago, compared to the still hefty 1040 mb on this map) Here is the surface map from 3 pm/00z this afternoon from the GFS model (It’s the 12 hr forecast which is about as good as an analysis):

You probably know that where the isobars are drawn with the closest spacing is where the gradient is the strongest and therefore where the wind is supposed to be the strongest. (more…)

Polar lows are small, somewhat elusive, and usually quite potent…cool stuff for weather watchers. They are small compared to their more common, mid-latitude big brother lows, up to a few hundred miles across, compared to a thousand or more miles across for the later. They are more like the size of hurricanes. For that reason, and because they sometimes look a lot like hurricanes on satellite imagery, and because they do share some structural similarities, they are sometimes called arctic hurricanes. The Bering Sea is a hot spot (sorry for all the puns) for polar lows but certainly not the only area…the North Atlantic is a good place too. A interesting polar low recently tracked across the southern Bering, strongly affecting the Pribilof Islands: St. Paul and St. George, but each of the two in curiously differing ways, as we’ll see. Here’s the Infrared satellite image from 15 UTC  (6 am AST) on Jan 3rd. The polar low was still about 200 miles west of the Pribilofs. With most typical low pressure systems, they’d be in the thick of it, but this average-sized polar lows is not yet affecting their weather:

Polar lows often are most impressive on satellite images (many show a more “closed” look than this one) and less so on surface maps due to their size compared to the scale of the typical maps. (more…)