July 22, 2015

Cooler, more seasonal weather for the next week

We are now entering a magical period for all Northwest residents:  the climatologically driest period of the year (last week of July and first week of August).

The time of year to schedule outdoor weddings and major outdoor receptions.

But ironically, we will cool down over the next week and showers will be felt by many.

Now, a bit of an admission...when I want to get a quick forecast without looking at any data, I often turn to weather.com.   They have a very sophisticated model post-processing system that combines a lot of model forecasts and observations using an advanced statistical system to provide a really excellent forecast for most locations.  The quality of their forecasts over the NW has been confirmed by verification at my department and by a firm that runs a web site:  weatheradvisor.com. Weather.com forecasts are generally more skillful than the National Weather Service (BUT KEEP IN MIND THEY HEAVILY USE NATIONAL WEATHER SERVICE MODELS AND DATA)

Here is their forecast for the next 10 days for Seattle.   For the next week, lots of temps in the 70s. Very typical, but the chances for showers increases late Friday and on into the weekend as an upper trough moves through.  My apologizes to all brides with outdoor weddings.

The second thing I often look at is the output from the joint U.S./Canadian ensemble (many forecast) system (NAEFS), which provides uncertainty and probabilistic information.  Here is the output for Seattle.  Cool the next week, plenty of clouds, and the chance of light rain.

Good weather to keep the fire danger down.

And then my next step is to look directly as a variety of model output, starting, of course, with the UW high-resolution WRF model.  Here is the forecasts of precipitation for the next two 72h periods.  With the east Pacific ridge replaced by upper troughs moving into BC, we see some rain extending from Seattle into British Columbia.  So you want cool and damp?-- go north. Warmer and drier, head to Portland and south.  California should dry out for a while.

So after endless heat and drought, some minor relief is in the bag.   But next week our old friend the ridge of high pressure rebuilds.  And temperatures back in to the 80s.

And what do I check after looking at more models?  That will be a future blog....


  1. The NWS at Sand Point wrote in their discussion (7/22) that the Seattle maximum this Saturday and Sunday might not reach 70 F. Ending SeaTac's streak of 70+ temperatures. Cliff's weather.com says 73 F for both days. I think if SeaTac gets a few sun breaks Sat and Sun afternoon the max will reach 70+.

    NOAA released Land and Ocean Temperature Percentiles, June 2015 and Global Land and Ocean Temperature Anomalies, July/June

  2. Curious -- what do you think of forecast.io? This is anecdotal, but I've noticed pretty accurate results by using apps that feed off of their data. Supposedly their forecasts are just aggregates of other weather sources, though I don't think they say which.

  3. Thanks, Cliff.

    I was hoping you could give your views on the Seattle School Board candidates as you have in the past. I value your thoughts on this.


    West Seattle

  4. Dr. Mass,

    Could you please comment on the reports of a "very strong" and possibly "record-breaking" El Nino forming? Is this going to be another flameout like last year?


  5. Read Dr Mass's July 20th blog, especially the last 2 paragraphs.

    As an aside, it's impossible for the el nino to fizzle out like last year. It's already been declared an el nino event, which never happened last year, and unless something extremely unusual happens, the el nino will continue at least until winter. NOAA says 90% chance of lasting thru winter, so it's possible that it will fizzle by ending early next year, but that will still be a lot more than last year.


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