WeatherWatcher: April 2011 in review

Saturday, May 21, 2011

Information gathered from Carl's Shoreline Weather Station

Did April seem cold to you? 
If so, that is probably because the month of April was the coldest April recorded since record keeping begin in Seattle, based on Seattle records from the Columbia tower, then later the Sea-Tac station. 

It was certainly the coldest in the last three years I’ve been tracking data in Shoreline. The average temperature for the month of April in 2010 was 47.8ºF. Average April temperature this year was 44.1ºF.

April temperature chart from Carl Dinse.

Now, it doesn’t seem like four degrees is a lot, but in averages it is. We had many occurrences where wet snow flakes were seen mixing with the rain. In the past, it has snowed significant amounts here during the month of April, but only for a day, and it was usually only in the instance of a convergence zone storm. In other words, when the snow stopped, it would all melt quickly, and temperatures were moderated, usually by the next day.

So despite one or two days that may have dipped to near freezing, because the other 28 days were at normal temperatures it all averaged close to normal. This April, we averaged on our low temperatures, so the month averaged at 38.1ºF. The overall average would have been lower if it weren’t for our two days topping at or near the 70’s.

Three years of April rainfall.  Carl Dinse.

April also reinforced the La Nina expected effects with having the most rainfall compared to April of 2010, or 2009. April 2009 had 2.39 inches of rain, April 2010 had 2.08 inches of rain, and this April (2011) had 3.49 inches of rain.

This graph shows that the majority of rainfall in April this year and the last two have a pretty consistent pattern of falling in the first half of the month, and the second half of the month seems to taper down. Of course this year, our La Nina is also settling down to a neutral state towards the later half of May, and into June, so our weather should return to a more normal pattern. 


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