May 07, 2013

Hot Roads and Hot Records

Yesterday, Seattle Tacoma Airport hit 87F, the all-time record for the date and the warmest temperature in the ENTIRE continental U.S. (we tied Phoenix).    Pretty amazing.

But if you think the air temperatures were warm what about the roads?  The City of Seattle put in a number of road temperature sensors to allow it to be better prepared for freezing temperatures, and those sensors are still active in the summer.   Washington DOT also has road temperature sensors.  Let's see what they showed!  Here are the readings at 4 PM, near the time of maximum air temperatures for most sites (from the Seattle SnowWatch site).  Wow.  A number of road sensors (temps inside of rectangles) were in the 100s, with one near Southcenter (Renton) at 110F.   Not hot enough to fry an egg perhaps....but toasty.    During the summer, we should rename the web page, TarWatch.

Some interesting contrasts in air temperature, with some coastal locations in West Seattle only in the mid to upper 60s, while a few locations on the east side hit the upper 80s to lower 90s.

At night, road surfaces and other urban materials (e.g., stone, brick) don't cool off as fast as vegetation and thus are notably warmer.  Here is what the temperatures were like at 3 AM Tuesday.  The road temperatures had dropped to the mid 60s to lower 70s, while the air temperatures had declined into the mid-50s.  This retention and slow release of heat by roads are one contributor to the urban heat island effect in which urban cores (with lots of roads and buildings) stay warmer at night than rural areas.

UW undergraduate Jason Phelps did some climatology research and found that that maximum run of dry days at Seattle starting May first was 8, and we will clearly beat that this week (hasn't rain this month and won't start until late Saturday or Sunday).   And there are other records (consecutive days above 65F in the beginning of the month) that will will also clearly smash.

Tomorrow will be a cooler day as a minor marine push occurs.  Low clouds pushed up the clouds on Monday, and during the evening they began to extend into the Strait of Juan de Fuca and along the Washington coast (see visible satellite imagery at 6:10 PM Monday below).  Some low clouds might just reach the Puget Sound lowlands, but they will be thin enough to be burned back by the powerful May sun.

So enjoy a near perfect week and one suitable for putting in those tomato plants (I did so tonight).  But rain is on the horizon for Sunday.


  1. What's the 97 degree spot about near Battle Point on Bainbridge?

  2. hot roads are interesting and all, thankee; but we (the great unwashed) are hoping for an explanation from our meteorological priesthood! why was our blessed normally cool and gray zone threatened with Phoenix-like hell? were we bad? is this the shape of things to come? are broken records to become the norm (such that unbroken records are broken records)?? say us some sooth.

  3. KDLS was 91 and the hottest location on the classic NWS Difax map. KP69 in northern Idaho is also listed at 91, but that appears to be a bad ob.

  4. Indeed, Cliff.

    I believe this is the earliest that I have ever planted corn in West Seattle in 17 years...on April 30th. Hoping the forecast would be spot on...

    Today, the corn sprouts are emerging...

    Great job, meteorologists. Great job.

  5. You put in tomato plants! Now it's going to rain for sure :(


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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