Thursday, August 28, 2014

The Sign of Fall

After a beautiful summer, with warmth and relatively dry conditions from mid-July to mid-August, a reminder that we are living in the Northwest often comes in late August:  the first passage of the first fall-like system, usually a weak frontal passage.  And just on schedule, one is now approaching us.   As proof here is an infrared satellite image for 9:15 PM, Thursday.

You can see the frontal cloud band stretching from the central Pacific into British Columbia, with the swirl of a low pressure center off of SE Alaska.   A visible satellite view of the frontal cloud band at 5 PM is shown below. Looks impressive!

The fact that the clouds are quite white in the infrared suggests the cloud tops of the band are fairly cold and high.  Our coastal radar at Langley Hill, near Hoquiam, clearly delineated the rain within the front (at around 5 AM on Friday).

The latest forecast models suggest this band will spread over us Friday afternoon and Saturday.   So Saturday should be the worst day of the holiday weekend.

Here is the forecast 24-h precipitation ending 5 AM on Saturday.  Avoid British Columbia...that is where most of the rain will be.  Washington and Oregon are generally dry except for some light showers on the windward slopes of the Cascades.  True Northwesterners laugh at such light precipitation.   But temperatures on Friday won't get much above 70F.

The next 24-h (ending 5 AM on Saturday) will be wetter, particularly over western Washington.  But cross the Cascades and you will be out of it and most of Oregon should be dry, except its far NW corner.

For the 24h ending Monday at 5 AM, precipitation is mainly limited to BC and NW Washington.  Again, heading to eastern WA or Oregon is the ticket to a dry outing.  A Vancouver or Whistler trip could be wet, although a stop for dim sum in Richmond, BC. always good.  Most of the rain comes in late Sunday and

thus most of the day will be dry. That is illustrated by the 3-h precipitation forecast ending 2 PM on Sunday. So Sunday is better than Saturday for most of western WA.

Monday will have light showers over western WA.  Here is the forecast precipitation for the 3-h ending 2 PM.

So to reiterate my advice for enjoying dry outdoor activities this weekend:

Head to eastern WA or all of Oregon (except the far NW coast).
Sunday afternoon looks like a gap between weak systems.
Take your Gore-tex garments out of deep storage.

Tuesday, August 26, 2014

The Hazy Pacific Northwest

More than one person has commented to me about about how hazy the skies have been lately.  In contrast, early in the summer, the skies were often starkly blue with the mountains sharply silhouetted on the horizon.

Want to see the difference between early July and now?  Look at these samples from the Puget Sound Clean Air Agency visibility cameras, one from July 7th and the other from yesterday morning:

The reason for the loss of visibility?

Smoke from wildfires all around us.  There are many fires in British Columbia to our north (see map)

And lots of fires over Washington, Oregon,  Idaho, and California (see image)

So if the winds are from North to East to South, smoky air is moving over us.  During the past few days we have gotten smoke from British Columbia fires, smoke that first moved west and then south.   Here is the MODIS satellite imagine on Monday...can you see the smoke over the interior of BC that is moving towards the coast?

We can run a trajectory calculation (Hysplit) to see where the air over us Monday night came from (see graphic)...yep...from coastal British Columbia.

The wildfire smoke has caused the air quality in a number of Northwest locations to decline to moderate.  Here is an example from Seattle...Queen Anne Hill.

This is not the only summer we have experienced worsening visibility from regional wildfires and won't be the last.

Sunday, August 24, 2014

Yakima and and Central/Southern WA Cascades Gets Hit by Thunderstorms

This is really getting to be an amazing year for thunderstorms over the Cascades and the eastern Cascade slopes.   It just doesn't stop!

Today's storms were focused from Yakima into the central and southern Washington Cascades.  The 24-h rainfall ending 7:30 PM Sunday is shown below: 1/2 inch in Yakima, with as much as .80 inches near Snoqualmie Pass and .5-1 inch over the eastern slopes of the northern Oregon Cascades.

Rain gauges can, of course, miss some significant rain features, particularly from thunderstorms.  Here are the "storm totals"--mainly for this afternoon-- from the Pendleton, Oregon radar.  In limited areas along the eastern slopes of the WA Cascades there was 1-2 inches.

The National Weather Service had a flood warming out this afternoon for the Yakima area and there was some localized flooding over roadways.  Here is a report from a NWS spotter near Tampico (east of Yakima, see map below).  The spotter estimated 2 inches of rain (consistent with radar) and water running over Ahtanum Rd.

Time:0340 PM
Magnitude:E2.00 INCH
Location:2 E TAMPICO

A storm-total precipitation map from the Portland radar shows the Yakima precipitation and the heavy rainfall south of Hood River.

The thunderstorms today brought lots of is the lightning strike map for the 24h ending 9 PM Sunday.  Lots of lightning over the central and southern WA Cascades, as well as eastern Oregon. Some new fires have been reported.

For example, one small fire started near Selah, Washington, but was quickly extinguished (see picture)

Picture courtesy of MASON TRINCA/Yakima Herald-Republic

It looks like the lightning and thunderstorms will take a break for a few days, staring tomorrow (Monday)

Friday, August 22, 2014

Thunderstorms and Flooding in Northeast Washington

This is turning out to be the summer of thunderstorms in parts of eastern Washington and yesterday was no different.  Strong thunderstorms hit Okanogan County, including much of the area of the Carleton fire, resulting in mudslides and flooding.  At least ten homes were destroyed and both SR 20 and 153 were closed (see pics from Methow Valley News and Wenatchee World).

Take a look at the "storm total" of the precipitation from Thursday to Friday morning based on the Spokane National Weather Service radar:  1-1.5 inches fell, with most of that happening within an hour or so.

The thunderstorm tops were so tall (about 35,000 ft) that they were picked up by the Camano Island radar (see image at 5:08 PM yesterday).

As an aside, I should note that radar coverage is very poor over the eastern slopes of the Cascades, with the radar beams from the Seattle, Spokane, and Pendleton radars being quite high (about 6000 ft!) by the time they get to say Wenatchee.   Thus, shallow rain can be missed by these radars. The solution to this problem would be to secure smaller, gap-filler radars.   Folks in Wenatchee, Ellensburg, and Yakima might lobby for decent coverage.

The heavy precipitation caused some of the rivers to rise very fast;  here is an example of the river stage of the Methow River near Pateros.  Nice spike from a passing thunderstorm.

Why the thunderstorms?  Same old story...a weak upper trough moved through when potentially unstable air was over Washington (see upper level map for 5 PM Thursday below)

Let me give you an idea about how unusual things have been.  Here is the departure from normal of precipitation over the last month.  Except for the Olympic Peninsula, it has been wetter than normal and MUCH wetter than normal over the Cascades and eastern slopes of the Cascades.

 Want to be impressed?  Here is the percentage of normal for the same period. Much of eastern Washington has received 300+% of normal (but keep in mind that normal is modest this time of the year).

 It looks like things will dry out this weekend as the trough moves eastward.  Nice weekend.

Wednesday, August 20, 2014

Will this be the warmest summer in Northwest history?

Although summer still has one more month to run, the extraordinary warmth of the past two months is putting us on a track whereby we might achieve that record.  Here is the average departure of the maximum temperature from normal from June 21st until now.  The Northwest is well above normal, particularly over and east of the Cascade crest.

Minimum temperature?  Same picture.

We can compare the temperatures at Seattle Tacoma Airport, Yakima, and Spokane against the normal highs and lows (see figures).  For roughly 2/3 of the days, the max temperatures are higher than  normal (the red line), with many days 5-10F warmer than normal.
July was the first or second warmest for many stations around the Northwest and, as shown above, August was even more anomalous.

The latest Climate Prediction Forecast for the next 6-10 days is...  you guessed it.  Warmer than normal over Washington and Oregon.

Temperatures this summer are running roughly 3F above normal.  Following the median global warming scenario, this is like advancing 30-50 years into the future.  So this summer you are getting an idea of the conditions you or your children will experience in approximately 2050.