After a comfortable and rain-free day on Wednesday, the chance of showers and thunderstorms will increase again later today and early tonight as a weak frontal system approaches the area. The work week will end on another pretty comfortable note as high pressure centered over the Southeast US extends its reach into the Mid-Atlantic region. On the backside of this high pressure system, warmer and more humid air will push into the Ohio Valley and Mid-Atlantic regions this weekend and the chance of showers and thunderstorms will increase along with the heat and humidity. Some of the storms that form late Saturday into Sunday can be on the strong-to-severe side; especially, north of the PA/MD border. One final note, some of the very dry and dusty Sahara Desert air that has now pushed into the southern US can make it into the Mid-Atlantic region over the next few days possibly resulting in more colorful sunrises and sunsets.
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A cool front passed through the region in the overnight hours and its passage will result in much more comfortable conditions today and eliminate the chance of showers and thunderstorms. Another frontal system will approach late Thursday and it could bring us a shower or thunderstorm, but Friday looks to be a rain-free day with comfortably warm conditions. It'll turn quite warm over the upcoming weekend and the threat of showers and thunderstorms will increase by the time we get to later Sunday. One final note, there is a chance that some of the very dry and dusty desert air mass that pushed across the Atlantic Ocean in recent days makes it all the way into the Mid-Atlantic region by later this weekend. If so, it could result in much more colorful sunrises and sunsets for a couple of days with an enhanced orange or reddish tint to the skies.
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An unusually large and intense outbreak of dry, dusty air from northern Africa has crossed the Atlantic Ocean and is now turning skies brownish in the Caribbean Sea. There is a possibility that some of this dusty air mass makes it all the way into the Ohio Valley and Mid-Atlantic later this weekend after first moving over the southern US. This layer of dust is commonly referred to as the Saharan Air Layer (SAL) which is a mass of very dry, dusty air that forms over the Sahara Desert in northern Africa during the late spring, summer, and early fall and it can move westward over the tropical North Atlantic on a regular basis during the Atlantic Basin tropical season. SAL activity usually ramps up in mid-June and peaks in mid-August and sometimes the individual outbreaks can cover vast portions of the Atlantic Ocean and reach as far west as the central US and Central America.
The SAL has unique properties of dry air, strong winds and warmth that can have a significant inhibiting effect on the formation and/or intensification of Atlantic Basin tropical systems - at least on a temporary basis. In addition to its potential inhibiting effect on tropical activity in the Atlantic Basin, dusty air masses that travel over the Atlantic Ocean from Africa can actually have long term impacts on beaches in the Caribbean and soils in the Amazon. This particular outbreak of dry, dusty air is more widespread than usual - perhaps one of the most massive in several decades - and it likely formed during mid-June when strong winds from thunderstorms kicked up dust to an altitude of about 20,000 feet or so over the Sahel region of northern Africa.
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It stays quite warm and humid today in the Mid-Atlantic region and there will be plenty of sunshine. A cold front will arrive tonight and this system will enhance the chances of showers and thunderstorms; especially, during the late afternoon and evening hours. Any storm that forms late in today or early tonight can be strong-to-severe and produce heavy rainfall. High pressure will reduce the threat of showers and thunderstorms on Wednesday and Thursday and then another high pressure system will build into the region this weekend resulting in very warm conditions and an increasing shot at showers and thunderstorms by later Sunday.
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A warm and unsettled pattern is in store for the region for the first half of the week as waves of low pressure will move through the Great Lakes and drag frontal systems into the Mid-Atlantic. The next few days will feature high temperatures not far from 90 degrees and there will be a continued shot at showers and thunderstorms. The strongest frontal passage of the week is likely to come through by Thursday when a cold front drops southeast across the Great Lakes and into the eastern US with additional showers and thunderstorms likely in this area.
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The official Atlantic Basin tropical season was barely underway in June of 1972 when a polar front interacted with an upper-level trough of low pressure over the Yucatan Peninsula. Within a few days, a tropical depression formed and the system moved slowly eastward and emerged in the western Caribbean Sea by the middle of the month. The depression began to intensify over the warm waters of the Caribbean Sea and soon became Tropical Storm Agnes – the first named storm of the 1972 tropical season. Ultimately, Agnes would reach hurricane status, grow to a diameter of about 1000 miles, and become the costliest hurricane at the time to hit the US and the Commonwealth of Pennsylvania was the prime focus of its wrath.
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An upper-level disturbance continues to have an impact on the region as it slowly pushes to the north over the western part of the Mid-Atlantic. This system is combining with higher moisture levels to produce bands of showers and thunderstorms and this threat of rain will stick around into at least the middle of next week. The rain chances over the next several days will be highest during the afternoon and evening hours as it will tend to be “diurnally-driven” with daytime heating playing an important catalyst type of role. Any shower or storm that forms over the next few days can produce heavy rainfall and localized flooding conditions. Another strong upper-level low pressure system may impact our region by the latter part of next week.
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The Saharan Air Layer (SAL) is a mass of very dry, dusty air that forms over the Sahara Desert in northern Africa during the late spring, summer, and early fall and it can move westward over the tropical North Atlantic on a regular basis during the Atlantic Basin tropical season. SAL activity usually ramps up in mid-June and peaks in mid-August and sometimes the individual outbreaks can cover vast portions of the Atlantic Ocean and reach as far west as the central US and Central America. The SAL has unique properties of dry air, strong winds and warmth that can have a significant inhibiting effect on the formation and/or intensification of Atlantic Basin tropical systems - at least on a temporary basis. This outbreak of dry, dusty air is more widespread than usual and appears to have formed when strong winds from thunderstorms kicked up the dust to an altitude of about 20,000 feet in mid-June over the Sahel region of northern Africa.
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High pressure that has been to our north in recent days has shifted off the east coast and this new positioning has opened the door for more humid air to push into the region. In addition, an upper-level disturbance that has been spinning over the Carolinas in recent days is now making a move to the north and this combined with the higher humidity has increased our chances for showers and thunderstorms. Indeed, this threat of rain will stick around not only for the rest of the work week, but also for the weekend and at least the first half of next week. The rain chances over the next several days will be highest during the afternoon and evening hours as it will tend to be “diurnally-driven” with daytime heating playing an important catalyst type of role. Another strong upper-level low pressure system may impact our region by the latter part of next week.
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There is a surface low pressure system this morning near the Outer Banks of North Carolina and satellite imagery clearly shows an upper-level low spinning over the central part of the same state. This upper-level has resulted in substantial rainfall in recent days across the Carolinas and westward to West Virginia and southwestern Virginia and it is about to finally make a move to the next. As a result of this movement, showers will move into the DC metro region later today and likely edge into Philly later tonight or early Thursday and once the threat of rain arrives, it’ll likely stick around all the way into next week. In fact, another significant upper-level trough of low pressure is likely to push into the Great Lakes/Mid-Atlantic/NE US by the middle of next week and this will more than likely continue the wet pattern that is unfolding for this part of the nation.
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