Research Measurable Precipitation

Posted by Aurae Beidler Jun 4, 2008

As the rain falls in early June in Western Oregon, I am reminded of a local saying. We have a saying in Oregon that summer doesn’t start until July 5th. Most years this proves to be true, as some 4th of July celebrates are spoiled with rain. This week, I decided to investigate this urban legend or old wives tale, to see how true it is. I searched online for climate data on precipitation.

I found the NCDC or National Climatic Data Center’s website and searched for precipitation data. Using the NCDC’s Climate Maps of the United States, I was able to pull up maps featuring any climate data from temperature to precipitation. I used the Quick Search feature, selected the Lower 48 states and Precipitation. Choosing these options, I was then able to view a full-color climate map showing the Mean Number of Days with Measurable Precipitation, organized by Annual or Monthly totals.

Comparing the precipitation maps for the months of May, June and July, I found it is true that in Western Oregon, the mean number of days in July with measurable precipitation is between 0.5 to 3.4. June records a mean number of days with measurable precipitation as 5.5 to 7.4, with some areas up to 10.4. May’s map shows a mean number of days with measurable precipitation as 7.5 to 10.4 and some areas up to 13.4.

So, the data shows that the transition from spring to summer is a gradual change but that July definitely does have a significant lower amount of days with measurable rain. Check it out for your area to see when you can expect the rain to end and summer to begin!