Air pollution episode over western U.S.

By: Dr. Jeff Masters , 2:19 PM GMT on December 14, 2005

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Particle pollution in the western U.S. has reached Unhealthy for Sensitive Groups and Unhealthy levels on the U.S. EPA's Air Quality Index (AQI) due to a stagnant weather pattern impacting the region. Some regions of California have reported unhealthful levels of particle pollution ten straight days; on Tuesday, Bakersfield, Fresno, and Sacramento all reported Unhealthy AQI levels. The unhealthful conditions are expected to continue today, and Bakersfield, Fresno, Hanford, and Visalia, in California, and Phoenix, Arizona have all declared air quality Action Days.

Figure 1. Winds over the western U.S. have been light the past ten days, generally less than 10 mph.

Figure 2. Visibility has been reduced below seven miles in many regions of Califonia due to air pollution and fog today.

The jet stream has been locked in place the past two weeks with a ridge of high pressure over the western U.S., and a trough of low pressure over the eastern part of the country. This pattern has steered cold air and storms into the eastern U.S., but left the western U.S. under high pressure with light winds and no rain. With no wind to flush the stagnant air out, and no rain to deposit the pollutants to the ground, particles of air pollution have built up to unhealthful levels. This weather pattern is expected to continue for at least another week. Beginning December 22 or 23, long range computer models are showing a major shift in the jet stream pattern, which may allow rain and wind to return once more to the western U.S.--and bring the eastern U.S. out of its deep freeze.

Check your local air quality forecasts and conditions by visiting the EPA AIRNow website at and selecting Local Forecasts and Conditions. If you are under an air pollution action advisory, limit prolonged or heavy exertion, reduce your activity time or substitute another activity that involves less exertion. Plan outdoor activities for days on which particle levels are lower. Reduce particle levels in the atmosphere by reducing your use of electricity and other particle sources such as automobiles, wood-burning stoves, and fireplaces.

Jeff Masters

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33. TampaSteve
6:40 PM GMT on December 15, 2005
Yeah...nice full moon last night...big, bright halo, too!

La Niña = more hurricanes = time to stock up on water and canned goods!
32. Inyo
7:57 AM GMT on December 15, 2005
La Nina's actually don't have that strong of a connection to dry years in southern California... nothing like El Nino and wet years. The effects aren't just opposite each other. It does tend to be cold in La Nina, and it generally isn't unusually wet. I still don't care much for it but it is interesting nevertheless.
Member Since: September 3, 2002 Posts: 42 Comments: 916
31. jorick
6:22 AM GMT on December 15, 2005
Here in Ft. Lauderdale, we had the farthest north full moon in many a year. In fact, not only did it pass pretty much directly overhead, it actually passed over to the north of us by about a degree and a half.

The Tropic of Cancer at around 23 1/2 degrees N latitude is the northern limit of the sun in the summer, but is also approximately the northern limit of the full moon in winter. But since the moon strays from the ecliptic by a few degrees, it can get pretty far north of that. And this full moon, Ft. Lauderdale was lucky to be south of it.

Here are the specs on the northernmost pass, thanks to Astronomy Lab 2:

Date: 12/14/2005
Time: 23:50 EST
My location:
Latitude: 26º 9' 55"
Longitude: 80º 10' 30"
Moon's location:
Altitude: 88º 40' 17"
Azimuth: 0º 0' 0" (passing through true North)

What does this have to do with weather? Nothing. But it's interesting enough and I'm bored enough so I thought I'd post it.
Member Since: September 15, 2005 Posts: 0 Comments: 3
30. windcast
6:18 AM GMT on December 15, 2005
29. KatrinaRitaWilmaZeta
5:31 AM GMT on December 15, 2005
well timmy i am of to bed and well see what kind of blog dr m will have i hop the next blog will be a good one there has been no one on her in the past 2 night now and this to tell you if we had a cat 4 or cat 5 storm to talk about then there would be a lot on the blog but there not
28. KatrinaRitaWilmaZeta
5:26 AM GMT on December 15, 2005
timmy did you no that ca can get hurricane
27. KatrinaRitaWilmaZeta
5:25 AM GMT on December 15, 2005
timmy would it be like a hurricane that would be cool for ca
26. timmy
5:23 AM GMT on December 15, 2005
KRWZ, I don't think that I can write what CA's going to see. It would be reported as obscene. I can tell you that it's another kind of storm, though...

(It's at the end of the Onion article if you want to see for certain.)
25. KatrinaRitaWilmaZeta
3:28 AM GMT on December 15, 2005
24. KatrinaRitaWilmaZeta
3:26 AM GMT on December 15, 2005
23. KatrinaRitaWilmaZeta
2:31 AM GMT on December 15, 2005
timmy i live in ca what is ca going to see
22. timmy
2:28 AM GMT on December 15, 2005
Yeah, I can't tell which would be worse, a category 5 bloodstorm or what the Pacific Northwest is going to receive...
21. haydn
2:12 AM GMT on December 15, 2005
What is a bloodstorm? I've never heard that before. Does it relate to the current jetstream pattern or ....?
20. Trouper415
2:03 AM GMT on December 15, 2005
haha, i like the bloodstorms. sound pretty nasty with those bullet piercing winds and clot sized hail
Member Since: September 22, 2005 Posts: 5 Comments: 704
19. KatrinaRitaWilmaZeta
1:31 AM GMT on December 15, 2005
i i am thinking that next ywar will be like this year

wit K R and W be comeing cat 5 storm like this year
18. theboldman
1:23 AM GMT on December 15, 2005
hmm im up in the foothills in northern ca does this affect me as well
Member Since: September 8, 2005 Posts: 25 Comments: 2
17. timmy
1:13 AM GMT on December 15, 2005
Hey, at least we're not seeing blood storms.
16. lightning10
1:00 AM GMT on December 15, 2005
La Nina makes me sad. So does Homework.
Member Since: November 24, 2005 Posts: 41 Comments: 630
15. ForecasterColby
11:54 PM GMT on December 14, 2005

To add to the endless fun for next year, here comes La Nina!
14. lightning10
11:07 PM GMT on December 14, 2005
I would love another rainy season like last year. Something that I will always remember.
Member Since: November 24, 2005 Posts: 41 Comments: 630
13. seflagamma
10:58 PM GMT on December 14, 2005
excuse me, it took me so long to finish typing my posts because of interruptions that by the time I posted it; others are talking about the polution subject.
I'm sorry!
Member Since: August 29, 2005 Posts: 307 Comments: 41073
12. seflagamma
10:55 PM GMT on December 14, 2005
Doc Masters,
More good info...I guess no one in the above posts are from the areas out west being polluted because of the jet stream's position!!! LOL

One thing about SE Florida; we rarely get bad air because of the sea breezes we usually get from the ocean...
However, Tropical storms are another matter all together!
take care and thanks again for the info.
Member Since: August 29, 2005 Posts: 307 Comments: 41073
11. Inyo
10:48 PM GMT on December 14, 2005
oh yes, i should clarify, when i say " It had only rained 2 or 3 inches that year, " i mean the rain year which had started the previous July
Member Since: September 3, 2002 Posts: 42 Comments: 916
10. Inyo
10:47 PM GMT on December 14, 2005
In the early 90s (93?), the drought was heading into its 8th year, and not looking good. It had only rained 2 or 3 inches that year, going into March. Then, the jet stream shifted south, dropping 12 or 14 inches (i don't remember the exact amount) of rain around LA, with massive snows in the mountains. Since the average rainfall for the entire year is only 12-14 inches in the lowland LA area, it basically put a 'miraculous' end to the drought. Since then it has been relatively wetter, although some very dry years (including the driest on record, 01-02), and the second wettest on record, 04-05. Unless climate change is a factor, as some speculate, we won't expect to see another year like 04-05 in our lifetimes.
Member Since: September 3, 2002 Posts: 42 Comments: 916
9. lightning10
10:17 PM GMT on December 14, 2005
Sorry for the Double post. I wanted to ask a question. I herd on the news a while back ago that the LA area had a March merical. Does anyone know how much rain we had up tell March and how much rain fell that month?
Member Since: November 24, 2005 Posts: 41 Comments: 630
8. lightning10
9:44 PM GMT on December 14, 2005
I live in the Vallie Whittier, CA. My school is on top of a hill. Today looking out the air quality is horrable. I havnt sceen it this bad in years.
Member Since: November 24, 2005 Posts: 41 Comments: 630
7. haydn
7:52 PM GMT on December 14, 2005
To clarify a statement above.

We rarely get snow in the midlands. I do like snow, but not ice. Here the snow melts in one day. messy salt and dirt on the car...
6. haydn
7:47 PM GMT on December 14, 2005
In SC we're finally getting some rain though we don't have a problem with smog. Couldn't imagine not lighting a fireplace to keep down particles if I had one. Great for smores. We have another system rolling in from the gulf with rain late tonight and tomorrow. No white stuff. I prefer snow to ice.

The days are full of hot herbal tea and wassil. Hurricane season has endeds. That means hot tea season begins and lasts through the winter. Also time for movies new and old...King Kong, Narnia, Miracle on 34th Street. I do believe Dr Masters is right about the season
5. jorick
6:42 PM GMT on December 14, 2005
Hey squeak! I know how you're feeling. I just finished shovelling 6 inches of sunshine off my walk. They're expecting another foot before it ends this evening around sunset. And the tropical breezes don't help either. All they do is pile it up even deeper.

Last Sunday I fell asleep in my deck chair right in the middle of a sunstorm. When I woke up an hour later, the sun was just piled all over my body and drifted around my legs. And for some strange reason, it has a tendency to turn my skin brown on contact.

The forecast is calling for another three feet of drifting sun tomorrow, with a possibility of heavy sunshowers mixed with sunflakes on Friday. *Sigh* Oh, well...
Member Since: September 15, 2005 Posts: 0 Comments: 3
4. jorick
6:35 PM GMT on December 14, 2005
Hmm... South Florida.

Nice and warm so no need for wood burning stoves or fireplaces.

Only 3.5 miles to work so it's actually quicker to ride my bike there than drive a car through the bumper to bumper traffic.

In a 15 foot travel trailer, all the lignts are 12 volt, and all I run is a battery charger, fridge, microwave and computer. Only $20 a month for electricity.

Smog? Naaah! Tropical breezes blow it all to Los Angeles.

Hey! I'm APC (Accidentally Politically Correct)!
Member Since: September 15, 2005 Posts: 0 Comments: 3
3. squeak
6:23 PM GMT on December 14, 2005
Just found out after talking to our admin at work...the snow is going to continue off and on until Friday! It is about to end here for today though; the reason we got so much in the south metro is because some of the heavier bands came in from the SW on their way to Wisconsin. The next round is forming in North Dakota, along with more temps in the single digits, and on its way here. They're forecasting what is a conservative amount for this area: 2 more inches followed by another day of flurries; but I have a feeling I'll easily be seeing a foot of snow outside my front door by Friday (we already had 2-3" on the ground).

Let it snow, let it snow, let it snow! Good day for cross country.
2. Inyo
5:12 PM GMT on December 14, 2005
The weather pattern indeed has been rather stagnant and boring and disgusting in California.. the San Gabriel Mountains where i work stick up enough to be out of the smog invasion, but the general condition around here is pretty depressing. Los Angeles is having a typical amount of smog but usually this time of year we can scour some of that out. I'm glad to not be in the Central Valley!

I'm hoping for some good storms and another wet year... although southern California rarely has two wet years in a row, things clearly have been anything but 'normal' lately anywhere. The southern jet stream has certainly seemed active but it is useless to us while the high pressure is locked in.
Member Since: September 3, 2002 Posts: 42 Comments: 916
1. squeak
4:35 PM GMT on December 14, 2005
Already about 5 inches of snow in MSP today, and we'll see close to 10 inches by the time the storm ends tomorrow.

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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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