Low pressure will slide across southeastern Canada today and whip a strong cool front across our area later tonight. As a result, there are likely to be numerous showers later today into early tonight and perhaps multiple lines of convection (i.e., thunderstorms) passing through the region. Any shower or storm that forms later today could bring downpours to the region with the chance for localized flash flooding and there can be frequent lightning, small hail and damaging wind gusts as well in some spots. The front clears the region by early tomorrow morning setting us up for a much nicer air mass in the Wednesday-to-Friday time period, but an unusually strong summertime upper-level trough promises to bring us unstable weekend weather.
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Showers and embedded strong thunderstorms in the overnight hours were associated with the passage of a warm frontal system that has resulted in noticeably warmer and more humid air for the Mid-Atlantic region; especially, when compared to the last few comfortable cooler-than-normal days. Today’s temperatures will climb well into the 80’s and the humidity levels have climbed to uncomfortable levels and these harsh conditions will only intensify over coming days. In fact, temperatures should easily reach the 90 degree mark for highs on Friday in the DC-to-Philly-to-NYC corridor and then climb well into the 90's on Saturday, Sunday and Monday - perhaps even a flirtation with the 100 degree mark in some spots on those three days. This stretch of hot and humid weather will likely last for a week or so from its beginning on Friday. The good news is that this extended stretch of heat and humidity could very well be the worst of the summer in the Northeast US as there are signs for more comfortable weather conditions during the second half of July and during the month of August.
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The summer solstice has just passed and the days will grow shorter and shorter from here on out until the winter season gets underway. While winter is still a long way off, there are already some clues that can provide some insight as to what kind of weather we can expect around here in the Mid-Atlantic region. First, signs point to the formation of warmer-than-normal sea surface temperatures by the upcoming winter season in two key areas of the Pacific Ocean: 1) the central equatorial region and 2) the Gulf of Alaska. Second, there is little doubt that solar activity will remain on the low side through the upcoming winter season as we are rapidly approaching the next solar minimum phase from an already historically weak solar cycle #24. Finally, one important wintertime cold air source region for the Mid-Atlantic is Greenland and it is currently experiencing above-normal snow and ice cover. While this is in the speculation phase, all of these factors point to the possibility of cold and snowy conditions in the Mid-Atlantic region during the upcoming 2018-2019 winter season.
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In about ten days, signs point to strong upper-level ridging to be positioned over the Northeast US and this would likely result in above-normal temperatures for the DC-to-Philly-to-NYC-to-Boston corridor as the month of July gets underway. In addition, with upper-level ridging centered over the Northeast US, the chances for tropical mischief will increase from the Caribbean Sea to the Gulf of Mexico. This particular location of upper-level ridging this time of year often leads to low-level convergence in the Atlantic Basin and it promotes the westward movement of tropical waves.
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The Atlantic Basin tropical season is still rather young having “officially” just begun a few weeks ago on June 1st, but there have been two factors so far that have suppressed activity and they may not let up anytime soon. First, sea surface temperatures have been running at below-normal levels in the all-important "breeding grounds" region of the tropical Atlantic Ocean in the region extending from the west coast of Africa to the Caribbean Sea. Second, there has been a persistent flow of dry air moving westward from the Sahara Desert region of Africa into this same "breeding grounds" region of the tropical Atlantic Ocean. Both of these factors tend to inhibit the formation of tropical storms or the intensification of storms that actually do manage to form.
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So far this year, 90 degree days have been relatively few and far between in the I-95 corridor. The highest temperature of the year in Philly and DC actually came in early May with 91 degrees measured at Reagan National Airport (DCA) on May 2nd and 91 degrees at Philly Airport (PHL) on May 3rd. These high temperature marks of the year should easily be surpassed on Monday, June 18th, with 95-100 degrees on the table from DC-to-Philly-to-NYC. The good news is that the excessive heat looks like it’ll be a one-day affair on Monday with somewhat cooler conditions likely on Tuesday and Wednesday.
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**An important note on the weather web site: there will be some big news tomorrow as Vencore Weather is moving to a new home...stay tuned**
Overview
It has been a hard year to cut the grass. The I-95 corridor has had five weekends in a row with rain and this upcoming one will become the sixth. Tropical moisture is entrenched in the eastern US and multiple disturbances in the upper atmosphere will head our way from the Midwest over the next few days and “squeeze out” this abundant moisture in the atmosphere likely resulting in some tropical downpours.
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The grounds are already well saturated in the DC-to-Philly corridor after recent soaking rains and there is more significant rainfall on the way. Tropical moisture is riding northward from the Caribbean Sea and Gulf of Mexico and it is now firmly entrenched in the eastern third of the nation. Disturbances in the upper atmosphere will head our way from the Midwest over the next several days and tap into this abundant moisture and the result is likely to be downpours later this week and during the upcoming weekend.
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The overall numbers are likely to be near normal this year in terms of the number of tropical storms and hurricanes in the Atlantic Basin (includes the Caribbean Sea and Gulf of Mexico). In a normal Atlantic Basin tropical season, there are about 12 named storms with 6 reaching hurricane status and only 2 or 3 actually reaching major status (i.e., category 3, 4 or 5). Last year's tropical season was hyperactive with 17 tropical storms, 10 hurricanes and 6 majors and it followed an above-normal year in 2016. The major factors involved with this year’s tropical outlook include the likely transition of La Nina in the equatorial Pacific Ocean to El Nino conditions by later this summer. The Atlantic Ocean is sending mixed signals in terms of the prospects for tropical activity this season with some sections featuring (unfavorable) colder-than-normal sea surface temperatures and others featuring (favorable) warmer-than-normal waters. The sea surface temperature pattern in the Caribbean Sea, Gulf of Mexico and western Atlantic Ocean makes the southern and eastern US somewhat vulnerable to what I like to call “home-grown” tropical hits during this upcoming tropical season.
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The grounds are already well saturated in the DC-to-Philly-to-NYC corridor after recent soaking rains and there is more significant rainfall on the way. As a result, localized flash flooding will become an increasing concern over the next few days as we’ll continue to get hit by rounds of showers and thunderstorms. In fact, many spots in the I-95 corridor may receive 3-5 inches of rain between this afternoon and Saturday night and this is on top of all of the recent rainfall.
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