Weak fronts mean sun, but the coming strong front will bring clouds

Sep 30, 2011

Weak weather fronts mean the sun should stick around through the weekend, with temperatures in the lower 70s and mid-60s and some occasional light showers. Then, a stronger front moves in late Sunday that will seal our fate for next week – at least when it comes to no sun.  

“The pattern of the atmosphere is shifting,” Cliff Mass told KPLU’s Keith Seinfeld, “so we are going from a ridge-like pattern to a trough-like pattern, which means that for much of next week we are going to be stuck in a cloudy, wet situation with highs getting up to only around 60.”

If you’ve noticed how chilly it’s been lately in the morning, there’s a good reason. The coldest time of day is right after sunrise, says Mass, not during the middle of the night. 

“This time of the year, it’s more like 7 o’clock or 7:30, and during the winter, the coldest time could be 8 o’clock or even 8:30,” he says.

The reason is the atmosphere is cooling all night long, as the heat escapes to space. And even when the sun rises, there’s still more heat leaving than there is solar radiation coming in.

The weekly KPLU feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and repeats twice on Friday afternoons during All Things Considered. The feature is hosted by KPLU’s Health and Science reporter Keith Seinfeld. Cliff Mass is a University of Washington Professor of Atmospheric Sciences and renowned Seattle weather prognosticator.