December 08, 2010

Squall Line!

Taking a look at the radar this morning was sort of like listening to shark theme from JAWS---you knew something intense was about to happen and it was time to take cover. Take a look at the radar graphic from the Camano Island radar at 7:26 AM:

Wow . An intense line of convective cells....sometime known as a squall line... was moving towards us. Green indicate moderate rain and yellow is heavy rain. This line was accompanied by lightning, a shift in wind direction, a burst in wind speed, a drop in temperature, a rapid increase in humidity and a jump in pressure.

Many locations had gusts to 30- 40 mph and at Paine Field in Everett the winds gusted to 58 mph! Several thousand people lost their power as trees hit power lines. Seeing what was happening the National Weather Service put out a severe thunderstorm warning at 8:15 AM.

Here is what happened at the UW today (click on the image to expand)--look at just after 15 at the bottom (that is 7 AM our time). The graph shows changes in wind speed (top), wind direction (second row), then temperature, relative humidity, pressure and precipitation.

A number of locations got .25 to .35 inches of rain as this line passed. Considerable street flooding occurred here in Seattle. The satellite imagery showed the line approaching the coastline a few hours earlier.

The eastern Pacific is full of convective clouds (cumulonimbus) associated with an unstable atmosphere. This complex array of lines and convective areas are not well forecast by current computer models. When the radar is installed on the coast at least we will be able to see them coming.

Talking about convective lines, several of you sent me this cartoon today, which is amazingly appropriate!

Image courtesy of

Here is the precipitation map for much of western Washington from the Rainwatch Web site. A swath of 1-1.5 inches was found over Puget Sound. But what has been really exceptional has been the rain stretching from the north Olympic Peninsula into the San Juans. Strong radar echos were locked over that region for hours and rainfall totals of 2-3 inches have occurred in some locations (the pink colors).Talking about rain... a LOT is coming starting Sunday, with the establishment of a significant pineapple express event. And a super warm front. More on that later.


  1. So, here is a question. Is it unusual to have thunderstorms early in the day like this in the Pacific Northwest? It seems like logically there would be no reason why thunderstorms wouldn't come any time of day, but I just could not remember lightning in the morning like that ever in my life living here. Unlike the Southeast when thunderstorms or other extreme weather (like hurricanes ...) seemed to hit any time of day.

  2. It rained like heck at times up here on the west side of San Juan Island (500' above the County Park). Unfortunately, the rain gauge was not working correctly, so I can't say just how much.

  3. The rain was intense driving this evening on Fidalgo Island near Anacortes. Heaviest I've seen in a while. Windshield wipers were on high setting!

    Cliff... any thoughts on the possibility of lowland flooding from the incoming pineapple express?

  4. Amazing December weather, what a frontal passage up here in the North Sound! Thanks for your excellent blog Cliff! I am a United airline pilot who lives in Bellingham and mostly flies to the Hawaiian islands on my trips.Your blog and direct observation on my part is really helping make the connection on mid Pacific and NW weather patterns, like most local's I have always understood the North pacific and Aleutian low, but an earlier blog on how a typhoon in the South pacific morphed into the super low pressure system off our coast was awesome. Keep up the good work, and I can't wait for that coastal radar!

  5. So is this "Pineapple Express" a quick hit and then a cool down? I'm just asking because the NWS posted the following on their 9:15 pm update tonight:

    "After the cold front passes there is some pretty cold air over
    Washington Tuesday and Wednesday. Temperatures will be lower. Highs
    will likely not get higher than 40s with lows in the 30s. There is
    still some southerly flow at the surface through Wednesday but later
    periods could have some offshore flow. Burke"

  6. We saw the mountlake terrace flash from here in Bothell, and it had just started to sprinkle a few minutes before my son stepped outside to walk to the bus stop, he got no more than 50 paces when the rain just started to DUMP. Poor guy. (So I grabbed the car and drove him the rest of the way).

    My wife was worried about the lightning and him waiting outside, and I was all, "oh lightning only strikes once during these quick-moving storms, so its already done", but as we waited in the car, lo and behold, lightning hit Cedar Park Christian School not more than a 2000 feet away. I won't live that one down.

  7. psst, Cliff, might do to recognize Randall at xkcd for his fine cartoonery.

  8. Hi Cliff,

    I noticed yesterday on the visible satellite that one could see these weird lines of convection aimed NE, and today there are more of these on the visible 1KM. These almost look like plumes from a fire or a volcanic eruption What causes this particular pattern?


  9. Cliff, I know you probably don't have time to answer every question but I have one about the upcoming pineapple express. I wondered what sort of dynamics cause all the rain? When one looks at the model's depiction, one sees primarily strong SW surface flow with a warm air mass. What is missing is any kind of upper or surface trof (other than the initial front) to indicate the potential for precipitation. So is all the precipitation primarily the result of wind interacting with the terrain? I have your book, so will probably look there for an answer also. Thanks, Seattle

  10. On the way into work, saw 2 flashes of lighting over Seattle. Time was about 8am. Rain on the I-90 bridge was truly miserable with white caps on the water from the W which is amazing because there is just over a mile and a half for these waves to build. (not much distance)


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

More Typical Spring Temperatures Will Save Washington and California's Cherry Crop this Year

Last year was a cherry disaster for the West Coast and the key driver was the cool/wet weather late last winter and spring in California.   ...