A Nail Biter: Will Seattle Beat the All-Time Record Dry Streak?

Today (Tuesday) brings Seattle to 44 days without rain.  Impressive!

Tomorrow will be dry, allowing us to tie the second longest dry-spell (45 days), and we will certainly beat it, with dry conditions guaranteed through Saturday (48 days!)

But will we beat the all time record---51 days-- which we will tie on Tuesday (Sept. 11th) if it doesn't rain?

Folks...it is going to be close.  Lets start with one of the best long-range forecasting tools, the output from the North American ensemble forecasting system, in which many forecasts are considered.  Consider the second panel down.  The bracket shows the range of the forecasts and the colored lines show two particular forecasts--the single forecasts used in most weather forecasts (the control members).  The bracket show that some members are going for rain on the 10th and 11th, with one control member giving measurable precipitation.

This increase in precipitation threat is associated with a trough passing by just to our north.  Here is the upper-level (500 hPa)  map for Sunday at 5 PM that illustrates this.

Take a look at  the 24 hr precipitation forecast from the UW WRF system for the period ending 5 AM on Monday.  Precipitation in the area, but Sea-Tac looks like it is rain shadowed by the Olympics.  VERY, VERY close.

And the precipitation for the next 24-h is negligible:

Who says meteorology isn't exciting?  I bet the Weather Channel sends Jim Cantore here to cover it. And I expect KING-TV's Jim Forman to be stationed at the airport all day looking for the rain (perhaps without his famous parka).

 This is going to be closer than the Presidential election.  You will tell your grandchildren that you lived through this.

For those interested in going to the Columbus Day Storm gathering on Oct 11th, you need to register...see information on upper right of this blog.

Olga 2SE

 (Note:  A blog was accidentally put on line before it was ready (Climate Tribes)....I took it off...will be finished later....cliff)

Last week, I was up on Orcas Island giving a talk on climate change in the Northwest.  While on Orcas, there was one place I was really interested in seeing...and it wasn't Mt. Constitution.  Rather, I wanted to check out an extraordinarily long-lasting observation site (122 years) that has been run by the Willis family the entire time:  Olga 2E.  You can imagine my delight when during the questions and answers, I found John Willis--the current keeper of the observing flame--right in front of me. 

An observing site like Olga 2SE (meaning it is found roughly 2 miles southeast of the town of Olga) is meteorological gold.   First, it is very long lasting, so we can really see the trends.  Second, it is in a rural area, so urban development is not an issue.  We owe John and his family a great deal for taking the time to provide this invaluable service to the region and the nation.

Just to orient you...here is a large map, followed by a closer in view, both using Google maps, that shows you the location of this site:

The green arrow is close to the location, but off by a few feet.  To really see it, here are some photos from the ground.  (I got these images from a really excellent site created by Anthony Watts and associates:   surfacestation.org -check WA sites here).  One close image and the other a bit back.  The temperature sensor is in the white housing, just north of the stairs.  A bit close to the porch, but that is probably consistent with the exposure over the last century.

What has this observing site told us about changes in the local climate for over a century?  Let me show you a few plots I made using the nice facility available at the Office of the Washington State Climatologist (found here).   First, annual  precipitation (blue line).  The state average is shown in green and the trend in red.  On average about 28.68 inches a year (roughly ten inches less than Seattle).  Really very little long-term trend:  a small downward tendency of .13 inches per decade.  Less precipitation extremes lately.  The State average is more...and not much trend in that either.

How about annual average maximum temperature at Olga?  Max temperatures appear to be cooling weakly...by about .05 F per decade.  This is consistent with other rural sites around the region--there is really very little sign of maximum temperature warming.

But annual average minimum temperature is a different story.  Virtually no trend until 1975 and then a jump in temperature.  As first I was suspicious of this jump, but checked out other local stations and many of them had a similar feature.

For example, consider Blaine or Port Angeles (you can click on them to enlarge).   Both show the warming after 1975.

 OK,  I believe that there was a warming in the minima at Olga 2E....but why?  One possible contributor to this might be the profound change in the Pacific Decadal Oscillation (PDO) at that time.  We believe the PDO is a form a natural variability for the Pacific basin, shifting from warm to cool phases over a period of roughly 30 years. Around 1975 the PDO transitioned quickly from a cool to warm phase.    So that is origin of the warming  and probably the best one. Or perhaps it is some influence of increased greenhouse gases--more moisture or greenhouse gases in the air keeping up minimum temperatures.  At Olga it is certainly  not local urbanization.

With cooling maxima and rising minima, the total (or mean) temperature change is a slight trend upward. Roughly 1F since 1955 (after which greenhouse gases increased more rapidly), less or even warming if you pick other periods.  Bottom line:  no significant changes in temperature over the period of record.

 Here are the extreme daily temperatures during the year at Olga.  Notice the interesting cold excursions (green lines)  during the winter..some even going below zero!  These are associated with strong northeasterly flow bringing arctic air through the Fraser River Valley.  Never go above the low 90s there for the extreme max.

Observing sites like Olga 2E give us important insights into long-term climatic trends unavailable from shorter lived stations.   They also identify earlier warm periods (like the 1930s), that are not included in the records of most climatological stations, many of which started in the 1940s and 1950s.

Orcas Island has a fascinating meteorology that includes blasts of northeast winds from Fraser River Valley, strong southeasterlies during the winter, a large contrast of precipitation due to it proximity to the Olympic rain shadow, and much more....perhaps in a future blog I will talk about it.