An upper-level low is spinning over the Northeast US and showers and thunderstorms are pin wheeling around this system. Some of the thunderstorms will reach strong-to-severe levels over the next few hours with highly unstable conditions given the chilly air aloft combined with the rather warm lower levels of the atmosphere. Any thunderstorm can contain gusty winds, heavy downpours and small hail as the freezing level is rather low in this scenario. The best chance for the shower and thunderstorm activity will be north and east of the PA/MD border to northern New England, but a few storms can make it all the way down into northern Maryland, northern Virginia, and the Washington, D.C. metro region.
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It stays somewhat unsettled in the Mid-Atlantic region for the next few days as an upper-level low spins around over New England. This feature will drop southeastward by the end of the week and a cold front should arrive in the area on Friday night. High pressure should push in behind the front as we begin the weekend with another cold frontal pushing towards us by Sunday night.
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Temperatures will spike on Saturday in the Mid-Atlantic region after a comfortably warm day on Friday and the sudden warm up will be accompanied by plenty of instability in the atmosphere. Multiple waves of energy in the upper part of the atmosphere will shift eastward on Saturday from the Northern Plains across the Ohio Valley and into the Mid-Atlantic/Northeast US. In addition, there will be a frontal boundary zone extending all the way from the Northern Plains into the eastern Great Lakes and this too will help to create some instability. As a result, strong-to-severe thunderstorms will be possible in the Mid-Atlantic region on Saturday afternoon and evening; especially, to the north of the PA/MD border.
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High pressure will build into the region today and provide us with some sunshine, warm temperatures and comfortable humidity levels. On Saturday, high pressure in the Southeast US will funnel hot and humid air into the Mid-Atlantic region and temperatures could spike into the lower 90’s for afternoon highs. In addition, a frontal boundary zone will approach later in the day and it could result in some shower and thunderstorm activity in the Mid-Atlantic region. Some of the storms that form on Saturday and Saturday night in the Mid-Atlantic can reach strong-to-severe levels with heavy rainfall and damaging winds; especially, to the north of the PA/MD border. It stays very warm on Sunday – though likely not quite as hot as on Saturday – and there will be the chance of additional showers and thunderstorms as another frontal system arrives. Following the front, high pressure will build into the Mid-Atlantic region early next week and it is likely to become unsettled once again by the middle of next week.
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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 evening hours. Any storm that forms late in the day 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 quite 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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