An upper-level low continues to meander over the Northeast US and showers and thunderstorms will again “pin wheel” around this system during the afternoon and evening. Some of the thunderstorms will reach strong-to-severe levels with highly unstable conditions given the cool air aloft combined with warm lower levels of the atmosphere. Any thunderstorm that forms today can include heavy downpours and perhaps small hail as the freezing level is rather low in this pattern. The upper-level low will finally slide to the southeast by tomorrow and this will reduce the chances for showers and thunderstorms.
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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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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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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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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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There are two important weather stories here at the end of the work week with continued very unsettled weather conditions in the Mid-Atlantic region and also tropical depression Cristobal which remains just inland over the Yucatan Peninsula region of Mexico at mid-day. The surge of summer-like heat and humidity into the Mid-Atlantic region on Wednesday was accompanied by severe thunderstorm activity and a stalled out frontal boundary zone will remain the focus area for showers and thunderstorms over the next 24 hours or so. Any rainfall in the Mid-Atlantic region can be heavy at times with the potential of localized flash flooding and any thunderstorm that forms can be strong-to-severe with gusty winds.
Meanwhile, tropical depression is parked inland over Mexico, but it is likely to move back out over the open warm waters of the Gulf of Mexico and take a turn to the north this weekend. There is a chance that Cristobal – the third named tropical system of this young tropical season – will close in on the north-central Gulf coastal region by the end of the weekend and all eyes from the Panhandle of Florida to Texas should remained focused on this threat.
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There are two important weather stories here at mid-week with a sudden surge of summer-like conditions into the Mid-Atlantic region and the development of a tropical storm in the southwestern Gulf of Mexico. The surge of summer-like heat and humidity into the Mid-Atlantic region will be accompanied by some strong-to-severe thunderstorm activity in some spots later today and tonight as a cold front approaches from the northwest. The highest probability of the severe storm activity will be to the north of the PA/MD border with one shot around mid-day and then another shot from later this afternoon into tonight. This front stalls nearby on Thursday and this could result in some heavy rain bands tomorrow and tomorrow night in the Mid-Atlantic region.
Meanwhile, Tropical Storm Cristobal has intensified in the overnight hours, but it may very well weaken over the next couple of days as it moves inland over Mexico. However, by the end of the week, TS Cristobal is likely to move back out over the open waters of the Gulf of Mexico and take a turn to the north this weekend. There is a chance that Cristobal – the third tropical storm of this young tropical season – will close in on the central Gulf coastal region by the end of the weekend and all eyes should remained focused on this threat from the Panhandle of Florida to Texas.
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A pre-frontal trough of low pressure will become the focal point for showers and thunderstorms late this afternoon and early tonight in the Mid-Atlantic region and some of the storms can reach strong-to-severe levels as they approach the I-95 corridor. A strong surface cold front will arrive in the same corridor late tonight, but it will encounter a more stable atmosphere likely not resulting in additional showers or storms. A much cooler air mass will arrive in the Mid-Atlantic region tomorrow night and Sunday and the month of June could actually begin with temperatures in the 40’s early Monday in some of the northern and western suburbs in the I-95 corridor. Elsewhere, unsettled weather continues across the Southeast US over the next couple of days and there can be some shower and thunderstorm activity in Florida on Saturday, but prospects for the 3:22 PM SpaceX launch at Cape Canaveral are perhaps a bit higher than they appeared yesterday. Looking ahead, there are indications that tropical activity may develop over the Gulf of Mexico in about a week to ten days and we’ll monitor those prospects in coming days.
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The “official” Atlantic Basin tropical season begins on Monday, June 1st, but nature itself has, of course, gotten off to an early start. This actually continues a trend for a pre-June 1st start to the tropical season as there has been a named tropical (or sub-tropical) system in each of the last five years. Tropical Storm Arthur brushed the North Carolina coastline about ten days ago and Tropical Storm Bertha became the second storm of this young season and came ashore on Wednesday in South Carolina. There are signs that the active and early start to the 2020 tropical season will continue as we transition into the month of June which begins on Monday. In fact, there are reasons to believe that the Gulf of Mexico region could feature a tropical storm or even a hurricane by late next week or during the following (second) week of June.
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The east coast of the US will be an interesting area to monitor over the next week or so in terms of the weather as we’ll see a tropical system just east of Florida in the near term and then perhaps a coastal low by the end of next week which could impact the Mid-Atlantic. Low pressure is now forming over the Florida Straits and it’ll intensify over the next 24-48 hours as it makes a move to the northeast over the relatively warm waters of the southwestern Atlantic Ocean. This system may come uncomfortably close to the US east coast in coming days and may play a role in the development of a coastal low by the end of next week in the Mid-Atlantic region.
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