High Diurnal Temperature Variances Yesterday
UPDATE: Manassass, Virginia had a 40-degree variation today (Thursday).
Temperatures warmed to 70 degrees at official stations in Washington, D.C. and Frederick, Maryland yesterday. Here in State College, Pennsylvania, home of AccuWeather HQ [Google Map] we warmed to 64, but what was more interesting was the morning temperatures. At my house, I recorded 22 degrees for a low, with heavy frost. This made for a 42-degree rise in 8 hours.
The difference between night and day temperatures is called "diurnal variation." Records aren't really kept of this data; Encylopedia Brittanica says "The diurnal range of temperature generally increases with distance from the sea and toward those places where solar radiation is strongest." I was taught in school that the desert southwest has the highest variation here in the United States, but normally here in the East, my experience has been that you don't see variations much over 30 degrees. A vague memory from my childhood in North Carolina indicates that I once saw a day with 29/72, or 43 degrees, and that was exceptional; thus I believe yesterday's 42-degree change here in Pennsylvania was also quite unusual.
Officially, the local NWS station at the airport only measured a 28-degree variation because they did not get as cold, but Williamsport had 33 degrees and Frederick, MD saw a 38-degree change. Below is a map of other lows and highs from Centre County:
I did spy two variations that beat mine at other amateur stations yesterday: 43 @DW1997 and 47 @DW2578, but their high temperatures seemed too high when compared to surrounding stations. One of the easiest biases that a weather station can have is a too-high maximum temperature bias, if the station is not sited correctly, away from non-grassy surfaces. I can personally vouch for my weather station (a Davis Vantage Pro) having proper sheltering (sensor has a shelter, station is over grass and high temperature matched other local stations). The reason that it obtained such a low reading is due to its placement in a dip in local elevation behind my house (photo below from Summer 2006).
