Indian summer! (Plus, how your forecast has been sharpened by the new coastal radar)

Oct 14, 2011

A gray day today, but some perfect fall days are in store, according to KPLU and UW weather expert Cliff Mass.

"Tomorrow (Saturday), we are going to have actually quite a nice day. A weak ridge builds over the region. So we are going to have sun with temperatures getting up perhaps into the lower 60's and really a decent sunny day."

Mass sees a mix of sun, clouds and possibly a  shower on Sunday. The sun doesn't bring much warmth this time of year, unless it gets a little help.

"That help is coming up during the next few days," he says.

"We are going to have a high pressure building up inland, off-shore flow,and when the air sinks in the mountains it’s going to warm up further. So on Monday we are going to start seeing sun coming out and temperatures rising and on Tuesday going to see a tremendous warming."

By "tremendous" he means temperatures getting up into the 70's. In other words, an "Indian Summer," which Mass also describes on his blog:

In France the term is "St. Martin's Summer," while in eastern Europe "Old Ladies Summer" and "Gypsy Summer" are often used.  All of these names describe a warm period in the autumn that follows a period of cool weather....  

Technically, he explains to KPLU's Keith Seinfeld, many weather scientists define Indian Summer as requiring a freezing frost before the temps rise, but this is close enough.

We don't get too many killing frosts west of the Cascades in autumn, so the term Indian Summer here is usually reserved for periods in mid-fall when the temperature rise to summer-like levels.

Mass answers question about the new coastal radar:

Two people have asked about the new coastal radar, via KPLU's Facebook page. Tamara Pickrell was wondering if the radar has made a difference in any forecasts. And Bryan McClullan asks:

"How is the new coastal radar? What has improved since its implementation?"

Mass says it's making a difference regularly, in pinpointing where and when the rain will fall:

"Yesterday (Thursday) the coastal radar really proved itself, because we could see this band of rain … coming in and that gave us confidence to note that there is going to be some showers today in the central part of Western Washington."

Mass' blog offers some detail about how the coastal radar is enhancing forecast detail.

Ask Cliff Mass a question: go to our Facebook page and post a question for Cliff or join the conversation on someone else’s question. Cliff says he will jump into our Facebook page from time to time to answer some of those questions.

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. You can also listen to a podcast of this and previous "Weather with Cliff Mass" shows.