Temperatures on Tuesday afternoon peaked at 98 degrees in Philadelphia - tying a record for the date from 2002 – and most other sections in the Mid-Atlantic region experienced high heat and humidity. Today will also be a day of high heat and humidity, but big-time relief is coming by Friday and it’s not out of the question that jackets may be required as we close out the work week (and begin the new month of August). A slow-moving cold frontal system will approach the area later tonight from the north and west, but then only be able to inch its way through the Mid-Atlantic region from tomorrow into tomorrow night as low pressure forms along its boundary zone.
Showers and thunderstorms are likely to be somewhat limited in coverage later today and tonight and then they should become more numerous and widespread on Thursday afternoon and night. Some of the rain will be heavy at times during the PM hours on Thursday, some of the storms can be strong-to-severe, and localized flash flooding is on the table. Showers may linger on Friday – the first day of August - and the day will feature a stiff east-to-northeast wind with low pressure pulling away from the east coast. Clearing skies will set in late Friday night and the first weekend of August may turn out to be the nicest weekend of the entire summer season with comfortable temperatures and low humidity levels.
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The Atlantic Basin tropical season typically reaches a peak around the middle of September and the preceding month of August usually features a steady ramp up in overall activity. Indeed, adhering to the climatological theme, it appears that tropical activity is about to pick up in the Atlantic Basin after we flip the calendar from July to August, and it could feature multiple systems. A teleconnection index known as the Madden-Julian Oscillation or MJO is providing support to this idea and suggests the time period from around August 5th to the 20th could be one to watch.
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High heat and humidity will persist in the Mid-Atlantic region through mid-week with high temperatures well up in the 90’s each afternoon, but there is significant relief in sight and the transition from here-to-there may feature some heavy rainfall and possible flash flooding conditions. A slow moving cold frontal system will approach the area late Wednesday and then only be able to slowly grind its way through on Thursday as low pressure forms along the frontal boundary zone. Showers and thunderstorms are likely to be scattered late Wednesday and Wednesday night and then they should become widespread on Thursday. Some of the rain can be heavy at times on Thursday with flash flooding conditions possible as part of the transition from the current high heat to the comfortable air mass coming at the end of week. The arrival of much cooler air on Friday will coincide with the calendar flip from July to August and the first several days of the new month look quite comfortable from the Midwest to the Mid-Atlantic. Showers may linger on Friday morning and the day will feature a stiff E-NE breeze with low pressure pulling slowly away from the east coast. Clearing skies will set in on Friday night and the first weekend of August may just turn out to be the nicest weekend of the entire summer season with comfortable temperatures and low humidity levels.
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Heat and humidity will increase today in the Mid-Atlantic region and temperatures should reach well into the 90’s on Friday along the I-95 corridor. It stays very warm and humid this weekend and through the first half of next week. In terms of prospects for rain, an approaching frontal system late tomorrow will increase the chance of showers and thunderstorms; especially, on the NW side of I-95. This front stalls out this weekend nearby and the result will be the threat of showers and thunderstorms from time-to-time.
Looking ahead, the pattern changes noticeably by later next week across the northeastern states with an upper-level trough of low pressure intensifying over southeastern Canada. Comfortable air is likely to drop south and east from Canada into the Northeast US and Mid-Atlantic region late next week and the first several days of August might be rather pleasant. It is at this time that conditions might change in the tropical Atlantic Ocean which can lead to a ramp up in activity by the middle of the new month and a teleconnection index (MJO) supports this notion.
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The last few days have been relatively quiet in the Mid-Atlantic region with dry and warm conditions dominating the scene. Heat and humidity will build up later in the week and an approaching frontal system could lead to showers and thunderstorms by Friday night. That front will stall-out nearby this weekend and likely result in a shower and thunderstorm threat on both weekend days.
The upper-level pattern next week will feature strong high pressure ridging over the south-central states and a northwest flow of air from the Great Lakes to the Northeast US. This kind of pattern sometimes produces complexes of thunderstorms that travel in the northwest flow from the Great Lakes/Midwest to the Mid-Atlantic/Northeast US...something to monitor during the next several days. Looking ahead, there are signs that a strong upper-level trough may become positioned over southeastern Canada at the end of next week potentially bringing a pleasant start to the month of August.
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The combination of a tropical air mass, a stalled-out frontal boundary zone, and an upper-level disturbance will “re-ignite” the atmosphere this afternoon and the result is very likely to be yet another round of heavy showers and strong thunderstorms for much of the DC-to-Philly-to-NYC corridor. With the likelihood of flooding downpours and the well saturated grounds, flash flood watches have been issued throughout the Mid-Atlantic region by the National Weather Service. This stalled-out front system will turn around by tomorrow and push to the north as a warm front and the heat and humidity should reach a peak in the afternoon with highs up in the 90’s in many places. A cold front then pushes through the northern Mid-Atlantic region later Thursday night into early Friday and it then stalls out across the southern Mid-Atlantic later in the day. As a result, the corridor from Philly to New York City will see a big break in the humidity on Friday, Friday night, and much of Saturday, but the stalled-out front will keep it unsettled and moderately humid in and around the DC metro area. The humidity does build back up again throughout the Mid-Atlantic region for the second half of the weekend and the chance of showers and thunderstorms will also make a return.
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The combination of a tropical air mass, a slow-moving surface cold front, and an upper-level disturbance raises the chance for afternoon and evening showers and thunderstorms in the Mid-Atlantic region. And, as has been the case quite often in recent days, some of the storms can be strong-to-severe and flooding downpours are on the table with a few inches possible in some spots in a short period of time. While flash-flooding is the greatest concern in this scenario, isolated damaging wind gusts are also possible later today associated with “downburst-type” thunderstorm activity. Looking ahead, while the threat of showers and thunderstorms may diminish on Tuesday, it is likely to rise again at mid-week as a stalled-out frontal system makes a turnaround and heads back to the north as a warm front.
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In general, it is much the same story as yesterday in the Mid-Atlantic region as far as the weather is concerned with the chance of late afternoon and early evening strong-to-severe thunderstorms along with possible flooding downpours. One minor difference from yesterday will be perhaps a bit later arrival time for the storms in the I-95 corridor as we’re looking at the late afternoon or early evening hours in many spots. Like yesterday, the ingredients are there for strong-to-severe thunderstorm activity and possible downpours including an upper-level trough, a slow-moving surface frontal system, and a humid air mass. The unsettled weather pattern continues from tomorrow through the upcoming weekend with a daily shot at showers and thunderstorms and much of next week looks unsettled as well.
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The combination of an upper-level trough, a slow-moving surface frontal system, and an extremely humid air mass will result in strong-to-severe thunderstorms later today and early tonight and there can be a repeat performance later tomorrow. Any shower or thunderstorm in this tropical air mass can produce flooding rainfall given the well saturated nature of the grounds in the Mid-Atlantic region. Temperatures today have soared to 90+ degrees all along the DC-to-Philly-to-NYC corridor and the high humidity is making for a very uncomfortable day. The unsettled weather pattern continues from Thursday into Sunday with a daily shot at showers and thunderstorms.
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A very unsettled stretch of weather is in store for the Mid-Atlantic region with a shot of showers and thunderstorms on a daily basis right into the upcoming weekend. The rainfall during the next few days will be enhanced by a tropical air mass that pushed northward this weekend along with the remnants of Tropical Storm Chantal. In addition, a slow-moving upper-level trough of low pressure now centered over the Great Lakes will enhance upward motion in the Mid-Atlantic region between now and mid-week. As a result, tropical downpours are possible during each of the next few days which can bring flash-flooding conditions to portions of the Mid-Atlantic region with today’s greatest concern centered around the Chesapeake Bay region. Any thunderstorm from later today into the mid-week can reach strong-to-severe levels with perhaps the highest risk of severe weather coming on Tuesday afternoon and evening.
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