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Sunday, October 31, 2010

Extra-Tropical Low

An extra-tropical low is just a fancy name for any cyclone which forms north or south of the Tropics. I've heard them described as "cold hurricanes", which is somewhat true, except that they are typically much larger in area than hurricanes tend to be. This one in particular that is slowly marching our way is currently 938mb, certainly as low as the eyes of many hurricanes or typhoons. Out at sea, this thing is already spawning 50' significant wave heights, which means that statistically some of the waves are 100'. That's a lot of water.

As you can see, the cold front has already occluded the warm front, and the occluded front is wrapping around the low. All other things being equal, this would bring a LOT of rain to the Salish Sea basin.

However, there's more to the story. The low will follow the Rossby waves at the 500mb level. Here's the 500mb map:

Even though the jet stream is way down around Cape Mendocino, the 500mb contours appear to be steering the low even more northward into the Gulf of Alaska. So, we won't expect to see even the backwash of this until Friday (the rains tonight and tomorrow are from another cold front), and depending on how things shape up we may get no more than a typical late-autumn occluded front out of it at this latitude.

Will post more when I know more.

Have a happy and safe Halloween!!

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