It's no secret that Portland's summer has been on the cool side, especially when compared to last years record heat. To date, we have had 24 cloudy mornings since July 1st, which is 10 days above average.
The lack of heat is also making news headlines. Portland has only reached 90 degrees four times this summer. The usual average through September is 13 days.
New research links last winter's warm weather, caused by a warming of Pacific waters known as El Nino, and the cooler oceanic pattern currently in place, called La Nina. Scientist believe when a rapid transition between the two takes place during the early summer months, the result is a trough pattern of low pressure over the Northwest.
A persistent trough produces a northwesterly flow and is linked to marine clouds and cool days.
So, the next time we are coming off of an El Nino winter and a La Nina is developing going into the early summer, forecasters will be talking about the likely hood of cool, cloudy summer days.