While quite warm this week in places like Washington, D.C. and Philadelphia, the worst of the heat and humidity is still to come. In fact, humidity levels have been rather manageable in these areas during the past few days limiting “heat indices” which are meant to reflect how weather conditions “feel” to humans given the heat and humidity. Large-scale upper-level ridging has been centered overhead during the past few days allowing for a bit of an onshore flow of air in places like D.C., Philly, and southern New Jersey, but that pattern will change in the Friday, Saturday, Sunday time frame resulting in higher heat and humidity. In addition, the chance of showers and storms will increase beginning later tomorrow and the threat of rain will continue this weekend and any storm that forms can produce locally heavy rainfall and damaging wind gusts.
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Washington, D.C. reached the 90 degree mark on Thursday for only the first time this month, but that is about to change in a big way as an extended hot spell is coming to the Mid-Atlantic region. The hot stretch begins early next week, but before we get there we’ll have to deal with possible strong-to-severe thunderstorms later today and early tonight and these will be followed by a comfortable Father’s Day weekend with lower humidity.
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Numerous signs point to an active tropical season this year in the Atlantic Basin with more tropical storms, hurricanes, and “major” hurricanes compared to the long-term averages. The average number of named tropical storms in an Atlantic Basin tropical season is 14.4 with 7.2 of those reaching (minimal) hurricane status, and 3.2 becoming “major” (1991-2020 baseline period).
Based on my overall analysis of current and forecasted atmospheric and oceanic conditions, I expect around 16 named storms this season with around 9 reaching hurricane status and of those perhaps as many as 4 to achieve “major” classification level. Another metric to use in the assessment of overall tropical activity is known as the accumulated cyclone energy or ACE which utilizes both strength and longevity of tropical storms in its calculation and I expect this to be 150-160% of normal in the Atlantic Basin this tropical season.
The two most important parameters that have been factored into the “2024 Tropical Outlook” include: (1) the development of La Nina in the equatorial part of the Pacific Ocean and (2) warmer-than-normal sea surface temperatures in much of the breeding grounds region of the tropical Atlantic Ocean and Caribbean Sea…both of which are favorable for the development and intensification of tropical activity. I believe the most vulnerable areas to be directly impacted this upcoming tropical season include those in and around the Caribbean Sea, Gulf of Mexico, and Southeast US.
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A spurt of tornadoes since late April has put levels well above normal as we reach the end of May and the overall active weather pattern of recent weeks looks like it’ll continue into the month of June. One of the key ingredients to this on-going active weather pattern has been the steady influx of colder-than-normal air masses from Canada into the US at the same time increasingly warm and humid air has been flowing northward from the Gulf of Mexico. The main area of concern for severe weather and tornadoes over the next few days will be across the Plains states all the way from Texas (today/tonight/tomorrow) to the Dakotas/Minnesota (on Sunday).
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There have been occasional cold air outbreaks from Canada into the Northeast US and Mid-Atlantic region during the month of April and this week will be no exception. In fact, low temperatures this morning were in the 30’s across many suburban locations along the DC-to-Philly-to-NYC corridor with scattered frost in some areas. Another chilly air mass will push into the northeastern states at mid-week following the passage of a strong cold front and early Thursday morning is likely to feature more low temperatures in the 30’s with patchy frost again on the table.
Next week, however, will feature a big-time warmup across the eastern half of the nation coinciding pretty well with the transition from April into May. Temperatures can climb well up into the 70’s by Sunday afternoon in places like DC, Philly, and New York City and 80+ degrees is possible for highs on Monday and the upcoming pattern change will result in far less frequent outbreaks of chilly air from Canada into the US.
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A double-barreled storm system will impact a large part of the nation from today through Thursday with an initial (primary) low located over the Upper Midwest and a secondary is to form later tomorrow near the Mid-Atlantic coastline. The initial system is producing severe weather today across the Ohio Valley and there are waves of heavy rain running all along the “I-80” states from Illinois-to-Pennsylvania with “flash flood watches and warnings” issued in most areas. The severe weather threat will shift to the east on Wednesday raising the chances for strong-to-severe thunderstorm activity in the southern Mid-Atlantic and eastern Carolinas.
Farther north, it is cold enough for accumulating snow today across portions of Minnesota and Wisconsin and some spots will get dumped on over the next 24 hours. The accumulating snow threat will shift a bit to the east to Michigan by later tonight and perhaps to the south on Wednesday into Iowa and Illinois. Once the secondary storm gets going near the east coast later tomorrow, the accumulating snow threat will shift from the Upper Midwest to the interior Northeast US and some spots in interior New York State and New England will get dumped on by the time Thursday evening rolls around.
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The 2024 baseball season gets underway in just two weeks on Thursday, March 28th, and a sneak peek at the weather from this long-range vantage point suggests there certainly can be additional cold air outbreaks to deal with in many areas. If indeed a sustained colder-than-normal weather pattern were to set up by April, this would follow a recent trend for the month which has been colder-than-normal on average across much of the nation.
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A very cold low pressure system that is currently rotating around the Gulf of Alaska is already impacting the region from northern California to Washington and it has the rest of California in its sights. This cold storm system promises to be long-lasting and it is very likely to produce tremendous snowfall amounts in the higher elevations of the Sierra Nevada Mountains with as much as 11 or 12 feet on the table. The air mass sliding into the western US will become increasingly colder-than-normal over the next few days and this will allow snow to fall at relatively low elevations in the state of California.
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Above-normal sea surface temperatures continue this month across most of the equatorial part of the Pacific Ocean, but there are signs that this El Nino episode which began about a year ago will flip to La Nina conditions (colder-than-normal) by the early part of the 2024 summer season in the Northern Hemisphere. A flip from El Nino to La Nino across the equatorial Pacific Ocean can have big implications on the upcoming 2024 Atlantic Basin tropical season. In fact, this expected dramatic change in sea surface temperatures across the Pacific Ocean may be a major contributor to a very active tropical season in the Atlantic Basin as atmospheric conditions are typically more favorable (lower wind shear) during La Nina episodes for the development and intensification of tropical storms. A second favorable factor for a very active tropical season in the Atlantic Basin is the likely continuation there of widespread warmer-than-normal sea surface temperatures. Finally, as oceanic cycles play a critical role in global temperatures, a flip from El Nino to La Nina in the world’s largest ocean could mean a return to closer-to-normal levels following a spike during the past year or so.
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Temperatures will climb to well above-normal levels in the central US during the next couple of days and then in the eastern US this Friday and Saturday. However, a pattern change to colder-than-normal begins next week in the central and eastern US and this change looks like it will have some staying power. Numerous teleconnection indices point to an upcoming change in the temperature pattern and an on-going stratospheric warming event supports the idea.
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