Eastern Washington Smoke

Today I flew to Cape Cod for a meeting on moving weather research to operations. I ALWAYS get a window seat. As we crossed the Cascades I was stunned on how murky it looked....there was clearly lots of smoke and it was pushed up against the eastern slopes of the Cascades.

Take a look at this satellite picture from this morning....there is a significant fire in southern BC and the smoke plume is heading south (see red arrow). Can you see the smoke entering eastern Washington?

You will also notice the extensive low clouds along the coast and the tendrils almost reaching the south Sound. Later on during the day the smoke plume was less distinct..the vertical mixing due to surface heating helps diffuse the smoke in the vertical.

There are going to be a lot more fires. In contrast, the people I talked to today here in New England were complaining about their cold, dreary summer.

When is the windiest time of the day?

This time of the year there are real differences in wind speed during various times of the day and in virtually all locations it is windiest during the late afternoon. Take a look at the above trace of weather observations at my department at the UW (you can click on it to see a bigger version). Note: times are in GMT/UTC... 00Z is 5 PM, 18Z is 10 AM, etc. Winds are light during the late evening and early morning, then pick up during the morning hours. You will also notice the wind shift...typically southwesterly in the morning and northwesterly during the higher wind period.

How about Hoquiam or Ellensburg over the past two weeks? See the attached graphics. You will see a strong daily (diurnal) variation in wind speed.
So why do winds vary during the day so much? A few reasons. The first is that winds generally increase with height in the atmosphere (since friction or drag is greatest near the rough surface). During the night when the surface cools, the atmosphere is more stable in the vertical (less mixing when cooler, dense air is low down). During the day, the surface warms and the air tends to mix in the vertical, as less dense, heated air rises. More mixing brings the winds down from aloft and thus the winds tend to be stronger.

But there is another reason...local, diurnal circulations like the sea breeze. At night land and water are similar in temperature around here, but during day, and particularly warm days, the land heats and pressure tends to fall over land compared to water. The result are sea breeze circulations that increase winds. On the coast near Hoquiam there is a classic sea breeze across the coast. Over Puget Sound there is the Sound breeze between the water-filled NW interior and central Puget Sound, which is mostly land. For Ellensburg, there is a huge "sea breeze" between the strongly heated eastern side of the state and the cooler west. If you want to learn more about these diurnal circulation, my book has a whole chapter on it.

Talking of weather, today (Saturday) is slightly cooler than Friday since there was more marine air moving in last night. Even more marine air will move into the western interior on Sunday. But temps will remain in the 70s and no precipitation is forecast. We have serious dry conditions, particularly east of the Cascade crest. The threat of major fires is quite real.

The highest clouds of the world over Seattle

Above is a picture taken after sunset at Seattle's Shilshole Bay Marina by Joseph Marsh on Tuesday evening. Just clouds? Not quite...these are very special clouds that are the highest clouds on earth...noctilucent clouds.

These clouds are most commonly seen on clear nights north of roughly 50N during the summer months. They are located in the mesosphere at heights of roughly 50 miles above the surface. (Remember...the layers of the atmosphere are troposphere, stratosphere, mesosphere). These are ice clouds that form on dust, probably produced by meteors. Such clouds often have a silvery or bluish color, and a ragged look.

Want to see the clouds in the department time lapse imagery? Check out the following and wait until the very end, after sunset:

http://www.atmos.washington.edu/images/webcam0/movies/20090714.mov

So on the next few clear nights take a look during twilight and see if you can spot them.

Amazing Amounts of Lightning

There were nearly 35,000 lightning strikes over the area over the 48h period ending this morning around 7:30 AM. Pretty amazing. The graphic above is from the national lightning network-- a series of sensors that can receive the electromagnetic pulses produced by lightning.

You will notice there is positive and negative lightning strikes indicated. Most cloud to ground strikes are negative, and only a small proportion are positive.

Thunderstorms

We have some potentially interesting weather coming up. But not tomorrow. Saturday will be beautiful...warm (into the lower 80s over much of the lowlands) and dry away from the mountains. Up in the Cascades there is a slight chance of some convective showers. But nothing serious.
And then there is Sunday. The air over us will be unstable, which means a little lift can release convection (i.e., thunderstorms). A measure that meteorologists look at to determine the potential for thunderstorms is CAPE--Convective Available Potential Energy. Sound impressive. Anyway, the values on Sunday will be high..particularly over the mountains (I have included a graphic of it that you can use to impress your friends). Normally we don't see CAPE of more than a few hundred here. But the CAPE tomorrow afternoon approaches 2000 over the northern Cascades, and over a thousand above all terrain. Something major is going to happen. In addition, an upper trough (which provides lift to release the instability) will move through on Sunday (see graphic). Between them, there is good chance of showers and thunderstorms over the mountains during the day and eastern Washington at night (see graphic of precipitation). Even a chance the lowlands could catch some of the action. Now a big worry is lightning caused fires...so we will have to watch this.

But wait! There's more! The trough will help incite an onshore push, which will bring cooler marine air into the region starting Sunday afternoon.

So enjoy a picnic tomorrow and enjoy the weather action on Sunday..particularly later in the day.

Also, If any of you are interested I will be giving a oublic talk in Leavenworth at 7 PM on July 31st and a book signing at 1 PM on August 1 (see more info to the right).

My Weather DVD

You have the book...now you can get the Northwest weather DVD! I am a strong supporter of Public TV and when they asked me to tape an introduction to Northwest Weather as a pledge gift, I was happy to do it. This hour-long presentation is a general introduction to Northwest weather and includes many of the graphics from the book. This was not easy for me...they even had me put on make-up. KCTS is asking for a donation of $50 to send it to you. Anyway, the funds go to a good cause, and if you are interested just click on the picture to the right or go to

https://secure.publicbroadcasting.net/kcts9/KCTSWeatherWisdom/form.pledgemain