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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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 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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My fellow Pennsylvania prognosticator, Punxsutawney Phil, and I have a little bit of a disagreement about the coming six weeks as he has predicted an early spring while I believe there is plenty of winter left across much of the nation and it will not be an early spring for most…hopefully, he turns out to be right. In terms of temperatures, after a very cold middle of the month of January, a “January thaw” developed that brought temperatures to above-normal levels for much of the last ten days or so. The month of February is likely to start off warmer-than-normal across much of the central and eastern US and colder-than-normal out west. However, the overall temperature pattern looks to change by the middle of the month to colder-than-normal for much of the nation and that change can take us right into the middle of March. Support for this kind of pattern change comes from an on-going stratospheric warming event and numerous teleconnection indices which can provide clues as to future weather patterns across the US based on what is trending in other parts of the world.
In terms of precipitation, an “El Nino enhanced” southern branch of the jet stream has already resulted in one powerful storm system for California that will now slide across the Rocky Mountain States to the southeastern US. A second and perhaps even more powerful Pacific Ocean storm will slam into the Golden State later this weekend and into the early part of next week. Several inches of rain will accumulate in California across low lying areas and tremendous snowfall in the higher elevation locations such as the Sierra Nevada Mountains. The Deep South and southeast US can experience severe thunderstorms later this weekend.
El Nino conditions in the tropical Pacific Ocean have gotten a “jolt” in recent days due to a burst of westerly winds and this sudden surge in strength will play a big role in the intensification of the southern branch of the jet stream. The phrase “atmospheric river” or “pineapple express” will be used quite often during the next couple of weeks as a powerful and relentless jet stream over the Pacific Ocean continues to inundate the US west coast with copious amounts of moisture.
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The weather stays on the chilly side in the Mid-Atlantic region into the upcoming weekend, but becomes milder by the time we get to early next week with afternoon highs on Monday, Christmas Day, likely at or above the 50 degree mark in much of the I-95 corridor. By the next Tuesday and Wednesday, the mild weather pattern will likely result in more rain for the area as a low pressure system pulls out of the southern US and heads towards the Great Lakes. By the time we get to the end of the next week and following weekend, important upper-air changes across North America will become more evident and they should lead to colder, more winter-like, conditions in the eastern and southern US as the new year gets underway. An update is given in this posting on the teleconnection index known as the Madden-Julian Oscillation (MJO) and a stratospheric warming event that continues to unfold which could impact US temperatures in the month of January.
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The remainder of this week and the upcoming weekend are likely to be seasonably cold-to-slightly below-normal in the Mid-Atlantic region and Northeast US, but much of the rest of the nation should be warmer-than-normal. The return to seasonal cold in the Mid-Atlantic/NE US follows what has been a very mild few days that culminated with a major rainstorm up and down the eastern seaboard. There are signs that the overall pattern will change by later next week that can result in more sustained cold for the eastern and southern states. A look at some teleconnection indices tends to support the notion of a change in the pattern that would favor more colder-than-normal air for the eastern and southern US - and potentially, an increased chance for snow as well.
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