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How a little rain can drive folks crazy
Oct. 31st, 2012 10:26 pm
Currently at Toronto Pearson: 7. High today: 8. Got up to 20 in Ottawa yesterday, on the warm side of the post-Sandy circulation.
This whole complex weather event wins a prize for persistence, anyway: the last four days were the first set of four consecutive days on which Pearson recorded 10 mm or more of precipitation since Oct. 28-31, 1973. (The four-day total was higher then, 83.3 mm to 59.8. We get more than 60 mm of rain in a day probably something around once a decade. The Toronto area's most famous weather event, Hurricane Hazel in 1954, dropped 156 mm on Pearson over three days, with 121.4 mm of that coming on Oct. 15. I'm actually surprised to see that it was that much, since, long ago, I read that Toronto didn't nearly get its biggest one-day rainfall from Hurricane Hazel. This, it turns out, is true for the Toronto Downtown weather station, where 86.9 mm fell on Oct. 15, but--by the looks of it--probably not for Pearson (though Pearson is, after all, actually just off the edge of Toronto). Poking through a bunch of other Toronto weather stations that were operational at the time, only one of them shows as much as 100 mm of rain on 15/10/54.) The barometric pressure has been below 100 kPa at Pearson since Oct. 29 at 8 p.m., so, fifty straight hours so far, and it's been steady at 99.7 for the last six hours. (At the end of October and beginning of November in 1973, it stayed below 100 kPa for about 56 consecutive hours.) Interesting that the pressure started rising, though very slowly and irregularly, at around 5 a.m. yesterday (when it bottomed out at about 99 even; by way of comparison, it got down to about 97.6 as the remnants of Hazel passed through on Oct. 15, 1954), with the deteriorating centre of Sandy still approaching. (Judging from the radar and wind reports, it appears that the main centre of circulation passed over the north shore of Lake Ontario early this afternoon.) Looking back through the records, another odd thing jumps out about the passage of the front last Friday: by the time the cloud band and the rain showed up, the air pressure at Pearson had been rising through the previous fourteen hours. (For all the archival air pressure numbers here, I'm relying on this calculator to produce the standard sea-level normalizations, since the EC archives just give the raw numbers at the station. In case you didn't know: 100 kPa of reported air pressure in Toronto is less air pressure than 100 kPa of air pressure in New York City, but it's way more air pressure than 100 kPa of reported air pressure in Denver. 100 kPa of normalized air pressure on top of Mt. Everest would be as much actual air pressure as 37.2 kPa at sea level.)
One thing I've learned from everything that's gone on with the weather lately: sometimes you really can't tell what's driving the weather by looking at surface weather charts, because what's driving the weather is going on at what meteorologists call the 500-millibar level--the layer of the atmosphere where the air pressure is in the 500-millibar range (1 kPa = 0.1 mb), which averages around 18 000 feet above sea level--and while the surface and 500-mb charts often look the same, sometimes, like when Sandy was about to make a sharp left turn into New Jersey, they look very different. Another thing I have learned lately is that the National Weather Service has vastly more informative weather maps on its website than either EC or the Weather Network does, including 500-mb charts for previous days (though not, as far as I can see, 500-mb forecasts). Here you can see how different the surface and 500-mb charts look for 6 a.m. on Monday, with Sandy sitting just off the coast. On the surface chart, there's nothing to indicate any way for Sandy to turn westward, but on the 500-mb chart, you can see that Sandy has a high immediately to its north and a low immediately to its west--it has just gotten caught between a couple of rollers that are about to shoot it onshore.
Today I harvested my broccoli crop. Here it is!
This whole complex weather event wins a prize for persistence, anyway: the last four days were the first set of four consecutive days on which Pearson recorded 10 mm or more of precipitation since Oct. 28-31, 1973. (The four-day total was higher then, 83.3 mm to 59.8. We get more than 60 mm of rain in a day probably something around once a decade. The Toronto area's most famous weather event, Hurricane Hazel in 1954, dropped 156 mm on Pearson over three days, with 121.4 mm of that coming on Oct. 15. I'm actually surprised to see that it was that much, since, long ago, I read that Toronto didn't nearly get its biggest one-day rainfall from Hurricane Hazel. This, it turns out, is true for the Toronto Downtown weather station, where 86.9 mm fell on Oct. 15, but--by the looks of it--probably not for Pearson (though Pearson is, after all, actually just off the edge of Toronto). Poking through a bunch of other Toronto weather stations that were operational at the time, only one of them shows as much as 100 mm of rain on 15/10/54.) The barometric pressure has been below 100 kPa at Pearson since Oct. 29 at 8 p.m., so, fifty straight hours so far, and it's been steady at 99.7 for the last six hours. (At the end of October and beginning of November in 1973, it stayed below 100 kPa for about 56 consecutive hours.) Interesting that the pressure started rising, though very slowly and irregularly, at around 5 a.m. yesterday (when it bottomed out at about 99 even; by way of comparison, it got down to about 97.6 as the remnants of Hazel passed through on Oct. 15, 1954), with the deteriorating centre of Sandy still approaching. (Judging from the radar and wind reports, it appears that the main centre of circulation passed over the north shore of Lake Ontario early this afternoon.) Looking back through the records, another odd thing jumps out about the passage of the front last Friday: by the time the cloud band and the rain showed up, the air pressure at Pearson had been rising through the previous fourteen hours. (For all the archival air pressure numbers here, I'm relying on this calculator to produce the standard sea-level normalizations, since the EC archives just give the raw numbers at the station. In case you didn't know: 100 kPa of reported air pressure in Toronto is less air pressure than 100 kPa of air pressure in New York City, but it's way more air pressure than 100 kPa of reported air pressure in Denver. 100 kPa of normalized air pressure on top of Mt. Everest would be as much actual air pressure as 37.2 kPa at sea level.)
One thing I've learned from everything that's gone on with the weather lately: sometimes you really can't tell what's driving the weather by looking at surface weather charts, because what's driving the weather is going on at what meteorologists call the 500-millibar level--the layer of the atmosphere where the air pressure is in the 500-millibar range (1 kPa = 0.1 mb), which averages around 18 000 feet above sea level--and while the surface and 500-mb charts often look the same, sometimes, like when Sandy was about to make a sharp left turn into New Jersey, they look very different. Another thing I have learned lately is that the National Weather Service has vastly more informative weather maps on its website than either EC or the Weather Network does, including 500-mb charts for previous days (though not, as far as I can see, 500-mb forecasts). Here you can see how different the surface and 500-mb charts look for 6 a.m. on Monday, with Sandy sitting just off the coast. On the surface chart, there's nothing to indicate any way for Sandy to turn westward, but on the 500-mb chart, you can see that Sandy has a high immediately to its north and a low immediately to its west--it has just gotten caught between a couple of rollers that are about to shoot it onshore.
Today I harvested my broccoli crop. Here it is!
