September 21, 2012

Wildfire and Air Quality and When is a Drought NOT a Drought?

Lets begin with an amazing MODIS satellite image showing the extensive smoke over eastern WA yesterday.  The densest smoke is being produced by the fires near Wenatchee, but you can see another fire south of Mount Rainier--which is spreading NW over the southern Sound.  Most of the eastern Washington smoke was spreading for northwestward into BC. At the same time, the eastern Pacific is full of low clouds, with some of it pushing into the Strait and southwest Washington.

 The smoke in eastern Washington is producing extraordinarily bad air quality near Wenatchee and Cashmere.  Let illustrate by showing you a measure of particulates (PM2.5) in the air at Wenatchee (red line) and Seattle (blue line).  Seattle stays relatively low, but you can see the impact of the Wenatchee fires, with huge peaks, some exceeding 500 micrograms per cubic meter.  That is really high.

Professor Dan Jaffe of the UW reports incredible pollution levels at his measuring site at Mt. Bachelor...and here is a picture he sent showing the fires near the Sisters in Oregon.  Not only is there smoke, but some pyrocumulus (cumulus produced by the heat of the fire)

Photo credit: Jonathan Hee of the UW


We have been very dry the last two months, but are we in a drought?  The NOAA Drought Index says NO! (see below)....and they are correct (who am I to doubt the U.S. government?).

Yes, we are breaking all kinds of records for lack of rain in August and September, and consecutive days of rain, but quite frankly, even in a normal year we don't get that much in these months and lack of rain has little impact, particularly since our rain over the past year, and the snowpack starting the summer was normal, or even a bit above normal.

Lets illustrate.  Here is a plot of the cumulative precipitation over the past 12 weeks (blue is normal, red is observed) at Sea Tac.  You can see how the observed (red) precipitation is flat lined, while normal precipitation is increasing rapidly.  Over the past 12 weeks we should have had 3 inches, but only had about 1 inch--thus about 2 inches below normal.  Considering Seattle normally receives about 38 inches a year, this is no big deal, and could be made up quickly when storms return.
But what about the same plot over the past year?  Take a look!   We end up with almost exactly normal precipitation, in fact a bit over because of the wet spring we had.
Obviously, the surface conditions are dry and the wildfires are a problem, but our precipitation situation over the past year and the subsurface moisture situation is fine.  We are not Texas...and you can all be happy about that.


  1. Cliff,

    The storms arent coming back.

    Ill make sure you get that memo.

  2. Yeah. Just noticed on the NWS water year chart last night how we are above average on precipitation for the year. Forgot how wet our spring was.

    At the sametime though, droughts have to start in one fashion or another so what a way to start. If a drought indeed occurs, we will look back and call this a drought.

    Probably nothing to unusual, but on the WV today, there's some cirrus that essentially originate around the equator and 180'W and the flow today brings them all the way into Canada. Pretty cool.

  3. What's up with Tillamook County? Looks like they have their own little drought going on from the map.

  4. The western slopes of the Olympics are showing our expected precip in the months of July and August in the lower 20%. This does not mean drought, it means outdoor BBQ in September.


  5. Focus on the pyro-cumulus, Cliff.

    — What is it up there, the WFD. — Looks like a fuller sweep, eay. .. From the Eastern slope of the Rockies, through CA, and [then] north.

  6. We have not had about an inch of rain here on Maury Island directly across from SeaTac. Total so far has been about .011 inches for the last 12 weeks. The trees are showing signs of stress. This is the driest period that I can recall in 18 yrs of living here.

  7. I have been thinking the same thing Cliff, this is not a drought here on the West side.

    If there were a couple of months to get above normal temps and below normal precip, I think late Aug through October has perhaps the least impact.

    Record heat in mid July is like 100 degrees and with long days and short nights. Now in September, record heat is what 80 degrees, with long cool nights.

    If we had a low snow pack winter, a relatively dry late spring, and a serious blast of heat from early July through the end of August, that would be a real mess. And that could easily happen. Each of those do hit here from time to time, we just haven't gotten them all together...yet...and I sure hope we don't!


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