Saturday, September 12, 2009

24 Minnesota Tornadoes in '09

The National Weather Service just released the latest rundown on tornadoes so far this year: 24 and counting. That's pretty close to average, but a little on the low side, the result of our cool, relatively dry summer. The same Canadian breeze that kept us 2-4 degrees cooler than average in July and August also pumped low dew point air into Minnesota, meaning less moisture, less fuel, for severe thunderstorm development.

For a great rundown on Minnesota's tornado season click here.

Wisconsin had its fair share of twisters, 16, which is also fewer than average (normal is closer to 21 tornadoes/year). Here is a list of the tornadoes that formed east of the St. Croix.

Minnesota tornadoes since 1950. The potential for tornadoes generally increases the further south and west you travel across Minnesota. The North Shore of Lake Superior saw the fewest tornadoes (the result of persistently cool breezes coming off the lake). As you might expect, the larger counties experienced more tornadoes than the small counties (29 for Hennepin Co. vs. 7 in Ramsey Co).

82 yesterday in the Twin Cities - September temperatures are running 3.5 degrees above average. At this rate we may actually see more 80-degree days in September than we did back in July! I know - very strange. A few isolated showers and T-showers popped up Saturday, mostly south and west of the Minnesota River Valley, where the atmosphere was most unstable. Weather systems will remain in a holding pattern this week, dominated by two stalled "cut off" lows, one over the western Plains, the other over the northeastern USA. A weak bubble of high pressure will keep Minnesota mostly sunny and unseasonably warm for the next few days - I see low to mid 80s into Tuesday, possibly Wednesday. BTW every computer run is progressively milder (and drier). Earlier it appeared we might see some 60s by the end of the week, now I'm not so sure. Some of the long range (GFS) guidance is bringing noticeably cooler air south of the border between September 23-26 - the timing is still very much up in the air, but there's little question we're about to enjoy another unusually balmy week. Forget September, as far as the atmosphere is concerned it's the third week of August out there.

Minor weather headache: morning fog. With our long nights (and dew points flirting with 60 - a fair amount of moisture in the air) the potential for ground fog is going to be fairly high this week. The risk is greatest in Minnesota's river valleys, water adding more moisture to the air. With clear skies and little or no wind the temperature can more readily fall to the dew point, resulting in 100% relative humidity, "saturation" and a (lazy) cloud forming on the ground. There should be enough sun, and enough of a breeze to burn off most ground fog by 9 am most mornings.

End of the World? I know, welcome to the Apocalypse. Good grief. This has NOTHING to do with our weather, but I stumbled across this and had to include this in my weather report. This image was taken from the ISS, the International Space Station, passing over an active volcano on the island on Matua. The pyroclastic flow of ash, steam and noxious gases is being ejected upward at close to 130 mph (!) Click here for an amazing video of the volcanic eruption as the ISS passed overhead. Good stuff.

Paul's Outlook

Today: Hazy sun, warm and humid. Feels more like mid August out there. Winds: S/SW 4-8. High: 83

Tonight: Mostly clear, patchy ground fog. Low: 59

Monday: Warm sunshine, still summerlike. High: 84

Tuesday: Blue sky, but hazy - sticky, distractingly nice. High: 83

Wednesday: Our balmy September hangs on. Plenty of sun, hard to concentrate. High: 81

Thursday: Mix of clouds and sun, dry. High: 77

Friday: Patchy clouds, but still rain-free. Temperatures a bit closer to average. High: 75

Saturday: Partly sunny, more comfortable. High: 73

Sunday: Warm winds, hazy sun - another summer rerun. High: 81

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