The overall numbers are likely to be slightly below-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) with around 11 named tropical systems, 5 hurricanes and 2 majors. In a normal Atlantic Basin tropical season, there are about 12 named storms with 6 reaching hurricane status and 3 actually reaching major status (i.e., category 3, 4 or 5 on the Saffir-Simpson Hurricane Wind Scale).
The major factors involved with this year’s tropical outlook include the likely continuation of El Nino in the equatorial Pacific Ocean. In addition, 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 (i.e., warmer-than-normal) makes the southern and eastern US somewhat vulnerable to what I call “home-grown” tropical hits during this upcoming tropical season.
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According to the latest “US Drought Monitor” report, the long-term drought in California is now “officially” over following the very wet winter season of 2018-2019. For the first time since 2011, the state has no region suffering from prolonged drought and the vast majority of the state California is “normal”. The reservoirs are full, the lakes are full, and there is a ton of snow in the higher elevation locations. In fact, the snow pack in the Sierra Nevada – a major source of California’s water supply – has reached incredible amounts by doubling in the month of January and then doubling again in February and more snow is coming this week.
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Four extreme cold air outbreaks in recent history have been analyzed in order to determine if there were similar atmospheric signals in the weeks prior to these events. The four extreme cold air outbreaks examined here include the most recent one that took place across parts of Canada and much of the eastern half of the US during late January 2019 (Figure 1). This analysis shows that there were strikingly similar characteristics in all four of the extreme cold air outbreaks with the roots of each traced to the tropics and to the upper part of the atmosphere known as the stratosphere. In all four cases, a recurring tropical disturbance known as the Madden-Julian Oscillation (MJO) contributed to a major stratospheric warming event which ultimately led to the extreme cold air outbreaks into the middle latitudes.
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As the year winds down, it appears this will be another down year for tornadoes in the US and likely the first one in recorded history without any classified as “violent”. The preliminary tornado count in the US for the year places 2018 in the lowest 25th percentile and this will likely become the first year since modern records began in 1950 with no tornadoes ranked as EF4 or EF5 (i.e., “violent”). The great news here is that the number of tornado-related deaths in the US during 2018 is near record low levels. As far as hurricanes are concerned, the Atlantic Basin tropical season was above-normal for the year, but about half as intense as last year. Unfortunately, the 2018 Atlantic tropical season will be remembered for two deadly and damaging hurricanes – Florence which generated tremendous flooding over the Carolinas and Michael which made landfall in the Florida Panhandle as one of the strongest ever in that part of the country.
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One of the ways to monitor the potential for wintertime Arctic air outbreaks in the central and eastern U.S. is to follow what is happening in the stratosphere over the Northern Hemisphere. Sudden Stratospheric Warmings (SSWs) are large, rapid temperature rises in the winter polar stratosphere, occurring primarily in the Northern Hemisphere, and these events have been found to set off a chain of events in the atmosphere that ultimately can lead to polar vortex disruptions and Arctic air outbreaks for the central and eastern US. Indeed, there is a significant stratospheric warming event now unfolding and it raises the chances for more frigid weather during the middle and latter stages of January.
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The month of December is well underway and there have already been some impressive snow accumulations for the month in such places as the Upper Midwest, western US and, most recently, in a large swath from Texas to North Carolina/Virginia with the very latest major winter storm. As it turned out, the month of November ended up with the most snowfall ever recorded in North America during the satellite era which goes back to the 1960’s. Unusual cold for the month from Mexico-to-US-to-Canada contributed to this snowfall record in North America. The November snowfall extent in the Northern Hemisphere was the third highest ever recorded in the satellite era and continues an upward trend in recent years.
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The winter has gotten off to a fast start across much of the nation and it looks like the overall cold and stormy weather pattern will continue as we head through the first half of December. Colder-than-normal conditions have been widespread through the month of November so far and snowfall has been unusually early and unusually high in many places. Signs point to more widespread cold across the US during the first couple weeks of December and the next ten days may feature copious amounts of snow in many of the same areas that received snow earlier this month.
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It’s not too often that still-falling leaves can be seen on top of snow in the Mid-Atlantic/Northeast US as that would require an early snowfall during the latter part of October or November which is certainly less likely than during the winter season. This week’s abnormally cold and stormy weather pattern across the much of the eastern half of the nation has resulted in some unusual snowfall observations for the month of November. In fact, wintertime snowfall has actually been in a relatively long-term upward trend across the entire Northern Hemisphere with some of the snowiest winters recorded taking place during just the last decade.
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The sun is blank again today and has been without sunspots about 60% of the time this year as the current historically weak solar cycle heads towards the next solar minimum. Solar cycle 24 is currently on pace to be the weakest sunspot cycle with the fewest sunspots since cycle 14 peaked in February 1906. Solar cycle 24 continues a recent trend of weakening solar cycles which began with solar cycle 21 that peaked around 1980. The last time the sun was this blank in a given year on a percentage basis was 2009 during the last solar minimum when 71% of the time was spotless. That last solar minimum actually reached a nadir in 2008 when an astounding 73% of the year featured a spotless sun - the most spotless days in a given year since 1913. All indications are that the fast-approaching next solar minimum may be even quieter than the last one which was the deepest in nearly a century.
One of the natural consequences of a solar minimum is for the upper part of the Earth’s atmosphere to cool down. Another natural impact of decreasing solar activity is the weakening of the ambient solar wind and its magnetic field which, in turn, allows more cosmic rays to penetrate the solar system. The intensification of cosmic rays can have important consequences on such things as the safety of airline passengers and astronauts in space, Earth’s cloud cover and climate, and possibly even on lightning.
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Hurricane Lane weakened some in the past 24 hours as it has encountered increased southwesterly wind shear, but it remains a “major” category 4 storm as it slowly closes in on the Hawaiian Islands from the south. There is still a good chance that Hurricane Lane will not make actual landfall on any of the island chain; however, it'll still generate tremendous amounts of rainfall on parts of the state and some sections can experience hurricane conditions (e.g., Maui, Oahu). The fact that it is a slow mover and will come close to the island chain will allow for a prolonged period of torrential rainfall, especially, on windward facing slopes with up to two or three feet possible on the Big Island. This is very likely not going to be the last tropical threat for Hawaii this season as warmer-than-normal sea surface temperatures and a developing El Nino in the central Pacific Ocean will likely aid in the formation of additional systems in coming days.
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