The mid-week warm weather has been replaced by a cool swath of marine air that will linger for the early weekend and then dissipate into warmer temperatures come Sunday and Monday, said KPLU weather expert Cliff Mass.
Expect temperatures in the upper 60s to the low 70s with morning clouds for Saturday and early Sunday, Mass said. The warmer temperatures -- potentially into low 80s -- will return briefly later Sunday and Monday. Cooler weather then will reassert itself late Monday.
"Nothing extreme but we're going to that normal situation this time of year," he said. "This back-and-forth."
The cooler shift will make it ideal for runners in the weekend's Rock 'n' Roll Marathon in Seattle, Mass said. "So if you are going on a long run or a fun run, it will be quite decent this weekend," he said.
The Blob Is Back
Mass said the weather variations can be blamed -- or credited -- on what he calls a "blob" of warm marine water in the northeast Pacific Ocean stretching for 1,000 to 2,000 miles.
The blob ebbs and flows, he said, and as it does, it act like a giant thermostat. Air moving inland over the Pacific passes over the blob and heats up. This means that for the summer, weather will be warmer than average while the blob lingers.
Mass estimated that the temperature could climb, on average, two- to three-degrees above normal.
"The blob is there. It doesn't change very rapidly," Mass said. "It's like a science fiction movie."
And like a science fiction movie, if there is a blob, there is a blob-beater. It arrives in the fall in the form of El Nino, Mass said. Come September, Mass expects the blob to be pushed away when the surge of warm, equatorial Pacific water arrives from the south.
"I don't think we'll see the blob as we get into the fall and the winter," he said. "I think we'll get solidly into an El Nino pattern."
The weekly KPLU feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KPLU Environment Reporter Bellamy Pailthorp. Cliff Mass is a University of Washington Professor of Atmospheric Sciences, a renowned Seattle weather prognosticator, and a popular weather blogger. You can also subscribe to a podcast of “Weather with Cliff Mass” shows.