The heat will stay on, possibly becoming warmest September ever

Sep 9, 2011

We’ve got one more weekend of great hot weather before we begin to see temperatures more normal for September, says Cliff Mass, KPLU’s weather commentator and University of Washington Professor of Atmospheric Sciences.

Look for temperatures to be in the lower 80s today with another five to seven degrees higher on Saturday. Sunday will peak at nearly 90. If these temperatures hold out through Monday, we could set a record for number of days in September that have reached or exceeded 80. The record is eight days.

“I think we’re going to definitely tie it and we may in fact exceed it, especially if Monday stays warm,” Mass says.

He adds that if you want cooler temps, you just need to go to the coast … but it will be getting warmer there as the weekend progresses since warm air from inland will be moving off shore.

Or, just wait for the sun to go down.

Outside of the city, temperatures at night have been dropping anywhere from 30 to 50 degrees, with the widest ranges occurring in eastern Washington. If you’re in the city, the temperatures stay warmer.

“It makes a big difference where you are. If you live in the city where there is an 'urban heat island effect,' that tends to keep the minimum up. So, if you want to get those really cool temperatures at night you want to get out of the city because the city has all this brick and stone that holds heat and releases it during the night.”

On his blog, Mass explained the temperature swings this way:

  • We start with fairly warm aloft and the sun being still fairly strong....that allows warming.
  • We have weak offshore flow aloft...that keeps the low clouds and marine influence at bay.
  • We have clear or nearly clear skies...that allows good infrared radiational cooling to space--and thus good temperature falls at night.
  • And nights are getting longer--that gives more time for nighttime cooling.  And the relatively equal time for heating and cooling at this time of the year is helpful

Put this all together and you get one big temperature range.

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.