Tuesday, August 21, 2007
Action Day?: No
Temperature: Near 70
Short-Term Discussion: On Tuesday, expect mostly cloudy skies to persist for much of the day as we still contend with a stalled out frontal system to our south. In addition, thanks to the cooler air to the north, warmer air to the south couplet, rain is likely to continue to fall at times throughout the day. This rain is also likely to be heavy at times as the best dynamics remain across Pennsylvania. Thanks to the area of high pressure to our north, temperatures will remain a bit on the cool side, with highs ranging around the 70 degree mark. Air quality levels will also remain rather low. During the day, we expect easterly winds to prevail. Onshore flow like this tends to clean out the higher air pollutants and shift them west. Therefore, we expect PM 2.5 levels to range in the good (GREEN) range. As is the case with many rain events, ozone will stay confined to the good (GREEN) category.
Extended: For the rest of the week, we notice that conditions will be getting progressively warmer and possibly even drier as the frontal system, which plagued our weather early in the week, finally moves off to the north. The heaviest rain should fall on Tuesday as the main tropical flow combines forces with the frontal system to our south. For the most part, Wednesday should be a transition day. The model guidance is still conflicting on the exact timing of when the warm air advection will commence across the region. This all has to do with the timing of the frontal passage as it passes off to our north. We do think that this will definitely happen by Thursday. Therefore, expect much warmer and more humid conditions to return to the region at this time. As the temperatures warm, we will have to be concerned once again with the air quality across the region. Ozone and PM 2.5 levels will likely be on the increase as the weather conditions become more favorable for higher air pollution. Depending on how bad conditions get, we could be issuing another round of Air Quality Action Days for the region. This warm and more humid air mass will be in place across the region until the next frontal system passes through the region on Sunday. At this time, we expect another round of showers to break out across the region before passing off to our east and allowing a seasonably cool and dry air mass to return early next week. We will continue to keep our eyes open for the developing air quality situation later this week.
