News & Events

Air Quality Action Day Forecast for Sunday, April 26

Friday, April 24, 2009

Sunday, April 26:
Ozone – Code ORANGE - Air Quality Action Day
Fine Particulates (PM 2.5) – Code YELLOW

** Special Note from the Air Quality Partnership of the Lehigh Valley / Berks Area: The Air Quality Partnership of Lehigh Valley - Berks encourages residents to consider using public transit or other forms of alternative transportation on Air Quality Action Days for Ozone.

Short-Term Discussion: Currently, mostly sunny skies persist across the region as a ridge of high pressure builds in across the eastern US. The actual high pressure system which is driving this ridge is actually off the Carolina coastline. Therefore, we are now to the west of this high, which is why our winds have turned out of the south. These southerly winds have allowed for temperatures to climb into the 70s this early afternoon. In addition, we have seen air quality levels rise into the low moderate range (for both ozone and PM 2.5). Over the weekend, we expect ozone and PM 2.5 to climb even further. The combination of warmer air and limited mixing during the morning hours will allow ozone levels to reach Code ORANGE at least on Saturday into Sunday. PM 2.5 levels should remain in the mid moderate range, rising to the upper moderate late in the period. Now onto the day-to-day details…

On Saturday, expect mostly sunny conditions to continue to persist across the region as we remain under the influence of the ridge of high pressure centered across the eastern US. This high will keep our winds out of the south, which should force temperatures closer to mid 80s. With this warmth over the region, expect ozone levels to rise into the upper moderate threshold. PM 2.5 levels should rise in the morning (thank you morning inversion) but should fall as winds increase in the afternoon. Levels should average in the moderate range.

By Sunday, the sun should continue to be the primary feature in the sky thanks to the ridge of high pressure over the eastern US. This ridge will continue to pump in very warm temperatures to the region (high temperatures will once again reach into the upper 80s). The combination of abundant sunshine and warm temperatures should help to ozone levels rise further into the Code ORANGE threshold. PM 2.5 levels will continue to be on the rise. However, increased mixing in the afternoon will limit the rise of the fine particulate concentrations to the moderate category.

Extended: As we take a peek at next week, we notice that the warm conditions will continue through the early part of the week. A cold front pressing through the middle of the week will not only put an end to the very warm temperatures but should also force air quality levels to drop as well. So here is how things are shaping up… Early in the week, the weather across our region should continue to be influenced by the broad ridge of high pressure off the East Coast. This system will keep our flow out of the south, allowing temperatures to rise into the 80s. In addition to the warmth, we should see air quality levels rise into the Code ORANGE threshold for a day or two. During the same time, we will watch a storm system makes its way out of the Midwestern US. This system will help to drive more clouds into the region by late Monday into Tuesday. By Wednesday, we should see this frontal system push through our area. Once it does, expect to see a drop in temperatures. In addition, the higher air quality levels from earlier in the week should push off to the east ahead of the front. Expect a much more seasonable pattern set up by the end of the week as the flow turns more zonal. Air quality levels by this time should be in the upper good to low moderate range.