While global sea surface temperatures continue to run at above-normal levels, there has been a rather dramatic cooling trend across tropical regions all around the world. During the past year or so, water temperatures in the Indian Ocean have dropped to nearly neutral levels around India and well above-normal levels immediately east of Africa have moderated to only slightly above-normal conditions. In the central part of the tropical Pacific Ocean, relatively neutral water temperatures have replaced the El Nino conditions of a year ago when water temperatures were as much as two degrees higher than normal. Perhaps the most dramatic change in water temperatures has taken place in the tropical Atlantic Ocean where much warmer-than-normal conditions of a year ago are virtually normal as we approach the end of April and there is even a pocket of colder-than-normal water just off Africa’s west coast. The tropics are a critically important part of the world with respect to the total energy budget and cooling trends can certainly have an inhibiting impact on the upcoming tropical season.
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It has been unusually dry across much of the Mid-Atlantic region during the past several months, but prospects for getting back to normalcy are looking better and better in what has become an overall wetter weather pattern. In fact, today features an impressive plume of tropical moisture that is flowing right into the Mid-Atlantic region from the southwestern Atlantic Ocean and beneficial rain is falling in most areas. This widespread area of moisture is supported aloft by a vigorous and slow-moving upper-level trough of low pressure and, as such, the threat of showers and thunderstorms will continue through Thursday. After a brief lull in the action later this week, another low pressure system will head towards the Great Lakes and it’ll renew the threat of showers and thunderstorms in the Mid-Atlantic region from later Friday into Saturday. This active weather pattern looks likely to continue through the remainder of the month of May and there will be additional cold air outbreaks as well including potentially one for the Mid-Atlantic region during the Memorial Day weekend.
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It has been unusually dry across much of the eastern US during the past several months with a focus on the Florida Peninsula, but we have been chipping away at these conditions in recent weeks and there are likely to be additional beneficial rainfall events during the new couple of weeks. Rain is falling today throughout much of the Mid-Atlantic region and Northeast US – the second bout of rain this week – and rain is currently falling across portions of the northern Gulf region. This area of Gulf moisture will push east during the next few days and then take a turn to the north early next week and ride up slowly along the Atlantic seaboard. As a result, it appears there will be more beneficial rainfall in the Mid-Atlantic region and Northeast US from later Tuesday into Thursday further alleviating the dry conditions and additional rain threats exist later this month in an on-going active pattern.
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The change of calendar to the month of May is bringing a changing weather pattern that is likely to result in a prolonged and significant rain event for the Mid-Atlantic region...something not seen in these parts in quite awhile. While there can be scattered showers and thunderstorms between tonight and late Saturday, the main event is likely to begin on Saturday night with widespread showers and thunderstorms and occasional rain will be a threat on Sunday, Monday, Tuesday and perhaps Wednesday as well in the Mid-Atlantic region to go along with cooler conditions. The upper part of the atmosphere is evolving into a classic “omega-block” pattern which will allow for cooler and rainy weather to stick around for several days in the Mid-Atlantic region, and this should alleviate drought and fire-hazard conditions endured during the past several weeks.
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There have been numerous colder-than-normal air masses in recent weeks pushing into the central and eastern US from Canada and also into the western US from the eastern Pacific Ocean. The continuing influx of these colder-than-normal air masses along with an active jet stream has led to numerous severe weather outbreaks in recent weeks. Indeed, severe weather is likely later today and tonight with a focus on the Upper Midwestern states of Minnesota, Wisconsin, Iowa and Illinois though some severe thunderstorm activity can extend all the way south and west to the south-central states of Texas and Oklahoma. The overall pattern that has produced these occasional cold air and severe weather outbreaks in the US looks quite likely to last at least into the first part of May with a risk next Monday and Tuesday in the nation’s mid-section.
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We’re not quite done yet with the cold air intrusions into the northeastern part of the nation and the next strong cold front can produce some strong-to-severe thunderstorm activity tonight in portions of the southern Mid-Atlantic region with downpours, vivid lightning and damaging wind gusts on the table. Following the passage of a strong cold front, the winds will become a big factor on Tuesday and Tuesday night with gusts of 40 mph or so from a west-to-northwest direction. The risk of severe weather will increase this weekend across the nation’s mid-section as another clash develops between incoming cold, dry air to the west and warm, humid air to the east.
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The risk is high today for a severe weather outbreak across the Tennessee Valley, Mississippi Valley, Ohio Valley, and Mid-South and this threat includes the possibility of multiple strong (EF-3+) tornadoes. Numerous ingredients are coming together to result in a widespread severe weather outbreak later today and tonight including strong jet streaks at multiple levels of the atmosphere, a clash of air masses with cold, dry air to the north and west and warm, humid air to the east and south, and a strong surface low pressure system with its attendant cold front. In addition to the severe weather, it appears that a multi-day extreme rainfall event is on the way for much of this same part of the nation from later today through the first half of the weekend with widespread flooding a serious concern.
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An on-going active weather pattern will result in strong-to-severe thunderstorms later today and tonight across the middle of the country and there can be isolated tornadoes as well. On Wednesday and Wednesday night, the severe weather threat will become enhanced across the Middle Mississippi Valley/Tennessee Valley and Ohio Valley and, this time, multiple strong tornadoes will be on the table. In this same part of the nation, it appears that a multi-day extreme rainfall event is on the way from later tomorrow through the upcoming weekend with widespread serious flooding a real concern.
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Strong-to-severe thunderstorms are a threat later today and tonight across much of the eastern US including in the DC-to-Philly-to-NYC corridor as a strong cold front pushes eastward towards the Atlantic seaboard. This same frontal system resulted in numerous damaging wind gusts on Sunday across the Midwest/Mississippi Valley with a few tornadoes reported there as well and that same part of the nation will likely have a repeat performance of severe weather on Wednesday. In fact, numerous severe weather outbreaks are on the table for the month of April largely as the result of a recent stratospheric warming event which, in turn, enhances the likelihood for additional cold air outbreaks into the central and eastern states setting up “battle zone” regions. Finally, we’ll revisit the passage of a “back door” cold front this weekend that impacted the northeastern states and, in some locations, there were record-breaking temperature swings.
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Any long-time weather forecaster in the northeastern part of the nation knows quite well to be fearful of the “back door” cool front this time of year as it can make a forecast of summer-like temperatures look rather foolish with winter-like reality instead. Indeed, the “back door” cool front is rather common in the northeastern part of the US during the months of March and April, and it can mean the difference of 30-40 degrees over a short distance, and the difference between summer and winter weather conditions over a short period of time.
In fact, there can be winter-like temperatures this Saturday in Boston, Massachusetts while a summer-like feel is as close by as Harford, Connecticut, and summer-like temperatures in New York City and New Jersey on Saturday can drop significantly by Sunday after the passage of a “back door” cool front from northeast-to-southwest. The key factor in the potential dramatic impact of the passage of a “back door” cool front this time of year is that the western Atlantic Ocean is still quite cold so a switch of low-level flow of air from a warmer continental direction to an ocean flow can result in substantial temperature swings.
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