Research Measurable Precipitation

When will the rain end and summer begin? Consider looking at climate maps from the National Climatic Data Center in order to find out about days with precipitation.

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!