November 17, 2009
Code Orange PM2.5 in California's Central Valley due to Haze; Conditions Improve in East
Air quality conditions in the Eastern United States improved to Code Green (Good) today, with a few areas of Code Yellow (Moderate) in the Ohio River Valley and Southeast, as shown by the loop of preliminary PM2.5 AQI values (below on upper left, courtesy of AIRNow). The haze that Nikisa and Ruben tracked for the past few days has dissipated under the influence of northerly flow generated by an area of high pressure centered over Quebec and an extra-tropical cyclone (low pressure system) over the Midwest. The location of the extra-tropical cyclone is evident in today's Aqua MODIS true color image, overlaid with the synoptic analysis and AQI values (below on upper right in Google Earth). Note that the cloud shield of the system forms a perfect, text-book "comma" shape that is typical of mature extra-tropical systems. The "comma" shape of the system really stands out in a GOES visible image of the US from this afternoon (below on lower left, courtesy of the College of DuPage). Generally Good air quality should continue for the rest of the week in the East, as the low pressure system is expected to move slowly through the area, and the Canadian high pressure system will continue to bring clean, northerly, on-shore flow to the Northeast and northern Mid-Atlantic regions.
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PM2.5 conditions are in the Code Orange (Unhealthy for Sensitive Groups) range in several isolated areas of the West today, including Hanford in California's Central Valley, as shown in the loop of preliminary PM2.5 AQI values (below on upper left). Haze is the likely culprit for the elevated PM2.5 values - current weather station observations from the ASOS network (Automated Surface Observing Systems) report haze at Merced and Lemoore, California, with reduced visibility. Smoke has been reported all afternoon at Monterey, but I can't confirm reports of a fire there, or any other source of smoke. Light haze in the Central Valley is apparent in today's Terra MODIS true color image (below on upper right, overlaid with AQI values in Google Earth). NOAA's Hazard Mapping System reports an unusually high concentration of fires in North Dakota and southern Saskatchewan and Manitoba (below on lower left), which they suspect are agricultural fires. So far the fires do not appear to be impacting air quality at the surface. Otherwise, fire activity is relatively quiet this week.
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