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

Dry Sky Parties

One of the inside jokes of the meteorological profession is that summer in the Northwest begins on July 12. And usually that is about right. June often is cloudy and gloomy (but not this year!), and sometimes showers darken the skies around the fourth of July. But in the later portion of July the climatological probability of precipitation plummets to around 10% in the lowlands with many locations receiving less than an inch. Strangely, the lowlands of the Northwest are some of the driest locations in the entire U.S. in July and August. Drier even than the desert southwest, where "monsoonal" rainfall hits during the summer.
Take a look at the plot of the probability at Sea-Tac Airport of at least .01 inch of rainfall (.01 is the minimum required to call precip "measureable"). During July the probability drops from near 30% in the beginning of the month to LESS THAN 10% during the last few days. This is really extraordinary. The driest day of the year? July 29 gets the least on average.... .004 inches. For many meteorologists there is a tradition of having a "dry sky" party during that day or the closest weekend, with suitable libations that I won't discuss in this family-oriented blog. Want to plan a wedding? That is the weekend. Some wise people picked the first weekend of August for Sea Fair.
And you can see why July 12 is often suggested as the start of summer --this is just before the rapid drop off to dry conditions.
Talking about the forecast...a band of showers are now over NW Washington and the coast...and are headed for Puget Sound. But conditions should improve towards the weekend.

The Onshore Push has occurred

As predicted, marine air has surged into western Washington. I can hear the leaves blowing outside my window right now..and the wind chimes are ringing. Just heaven! A weaker onshore surge than June 4th and one that started in the mid-afternoon--which is unusual...most wait until the evening....

Firework Pollution? and a Major Change

Many times I have noticed that particles in the atmosphere tend to increase rapidly on July 4th...with a reduction of air quality. I took a look this morning...and it was there again..above is the trace at Puyallup and Queen Ann Hill from the excellent web site of the Puget Sound Clean Air Agency (http://www.pscleanair.org/airq/aqi.aspx). As you might suspect, fireworks probably has something to do with this (the pale of smoke is often profound after all the official and unofficial fireworks). According to Mike Gilroy, the chief meteorologist for the agency, July 4 brings the worst air quality of the year.



Today is the last warm day west of the Cascades. A look outside or the latest high-resolution image shows an obvious change...more clouds--both at low levels and aloft (see image). I plotted the temperatures the last few days (see plot)...temps have been 10-15F above normal. Last night had very high minimum temps--in the 60s in several locations.

The ridge of high pressure over us is in the process of shifting east and the clouds are associated with an approaching offshore trough (see upper level maps for situation this morning and tomorrow). This trough will initiate an onshore push tonight and marine air will fill the western lowlands. So boaters should be prepared for the influx of marine flow from the SW tonight! Today will not be cool...the temperatures aloft are just as warm as yesterday and the clouds will thin...getting back into the 80s. But tomorrow will be very different...highs near 70F. Lots of clouds and a few scattered light showers...particularly on the western slopes of the Cascades. The trough should stay in place the entire week...so expect temps a little below normal.

How Bad Has the Drought Been?

We have been in an extraordinary dry period--and this does not bode well for the summer. Here is some fascinating statistics given to me by Mark Albright (who used to be State Climatologist). For the period May 20 through the end of June, Sea-Tac this year was drier than ANY OTHER YEAR in the 116 yr record (see numbers below). On .18 inches of rain. I know...this is a somewhat artificial period...but the message is clear...we have been unusually dry.

Ten driest 20 May-30 Jun periods in Seattle:

2009 41 0.18
1934 41 0.28
1932 41 0.31
1925 41 0.36
1938 41 0.39
1924 41 0.50
1979 41 0.54
1911 41 0.55
1922 41 0.61
1918 41 0.63

What about June alone? This was the 7th driest June in 116 years.

10 lowest June precipitation amounts over the past 116 years from 1894 through 2009:

1922 30 0.03
1951 30 0.13
1908 30 0.15
1987 30 0.16
1925 30 0.16
1932 30 0.17
2009 30 0.18*
1934 30 0.23
1895 30 0.29
1940 30 0.34

The bottom line off all this is that we are going into the normal summer dry season with very low soil and surface "fuel" moisture values and the potential for big wildfires is greatly enhanced. The eastern slopes of the Cascades have also been dry and the climate prediction center is predicting increasingly severe conditions over eastern Washington (see graphic). This is really serious and people will have to be very careful with fire (and fireworks!).