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04 October 2002 — Weather Watcher (1)

The coming of autumn, like the arrival of spring, causes me to become more aware of the weather.

Generally, I notice the weather only passively; much of my time is spent indoors and I fail to notice whether it's warm or it's cool or it's wet or it's windy. This is especially true in the summer and winter when the weather remains relatively constant from one day to the next. (The exception, of course, is on days that I bike; when I bike, I'm keenly aware of the weather.)

In the spring and in the autumn, however, as days warm or cool, the weather becomes more interesting to me. And, apparently, to those around me.

When I get to work, Jeff and I compare notes: there was frost on the windshields in Canby -- what happened in Molalla? Goods Bridge was a little slick -- how was Whiskey Hill Road? When Nick arrives, he adds his two cents: things were fine in Portland, maybe, but the stretch of 99E between Oregon City and Canby was a little dicey.

Over the years, we've found a couple of handy web sites for answering questions regarding Portland-area climate and weather:

  • Historic storms of Oregon
    The top ten Oregon weather events of the 1900s, as determined by the National Weather Serviced. I'm not sure a forest fire can properly be classified as a weather event, but this is still interesting reading. The winter of 1995/1996 was certainly memorable: a strong wind storm swept through in December (December 12th, Jeff remembers -- he had taken the day off to move into his new house); there was a great deal of snow at the end of January (though I can't find actual data for this); this snow was followed by a cold snap that lasted from the end of January until the beginning of February; the cold snap ended with freezing rain and then warm weather and rainfall. This winter culminated with the worst flooding I've ever seen in the area (photos). Actually, the local news stations kept calling it a "one hundred year flood".
  • Portland temperature log
    A data-filled page recording the daily high and low temperatures in Portland since 1940. This is a handy reference for old-timers: Just how cold was the cold snap in February 1989? (Answer: nine degrees farenheit, but colder in Salem.) How hot did it get on Mother's Day 1987? (Answer: low nineties, but that's plenty hot for early May.)
  • Climate of Portland
    This is the best page of the bunch, filled with links to data and information about Portland-area climate. This is the page that I've archived to my hard drive for fear that it will vanish. Here one can find standard climate data (high and low temperatures, rainfall, etc.), but also find more unusual information such as monthly dense fog records, frequency of wind direction based on time of day, etc. Awesome!
  • Weather Channel forecast
    Though this site is less useful than it might be, it's a good reference for upcoming weather. The site contains some basic climate statistics.
  • Weather Underground
    Nick is partial to this weather site. It contains more detailed data regarding current weather conditions, as well as detailed forecasts. One great feature is the site's "personal weather stations" section in which weather data is collected from weather watchers from around the area and posted for comparison to the offical data. When we were comparing notes on yesterday's frost, we could tell from the "personal weather stations" list that the cold temperatures were more prominent in southwest Portland; Sherwood was colder than Gresham, for example.
  • The National Weather Service
    The official site of the National Weather Service's Portland bureau contains great information regarding current weather and past climate data.
One fun fact: there's only a 50% chance that we'll experience a temperature of 24 degrees or below each winter, and only a 30% chance of a temperature 20 degrees or below.

One site says that from 1941-1999 the average last frost in Portland was March 30th and the average first frost was November 8th. The average frost-free period was 223 days. Another site says the average time between last frost and first frost is about 191 days. Average last frost: about April 21st. Average first frost: about October 21st. Those are easy extremes to remember: the average frosts occur a month after each equinox.

Nearly all snow in the Portland area falls between December 1st and February 1st, with peaks around the end of December, the middle of January, and the beginning of February. So little snow falls in the area, though, that I'd be willing to bet that these averages are skewed by once-in-a-lifetime snow events; the big February 1st storm of 1989 is enough to throw off the entire average. Interestingly (to me), the entire first two weeks of December have an above average chance for some good snowfall.

When was the latest snowfall in Portland? That's easy: we had snow this past St. Patrick's day. We were at the yurt with Mac and Pam and woke up Sunday morning to a light dusting of snow. (Was it a sign? A portent?) The earliest snowfall is a trace on Halloween.

There is almost no chance of a White Christmas in Portland; since 1940, only five Christmases have had snow, and those were all trace amounts. Christmas Eve has a three or four snowfalls of half inch or more, though.

Portland's record high temperature is 107 degrees; its record low is -3 degrees.

On this day at foldedspace.org

2005At a Loss for Words   I'm experiencing one of those periods of life during which I find I haven't much to say. I've been contemplating a massive restructuring of this weblog. Another fine evening at Monday Night Football.

On 06 October 2002 (03:59 PM), tammy jata said:

Hey what an informative webpage!Enjoyed reading it thanks

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