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Anecdotally, where I live in northern Europe, the weather seems to be stormier in winter, and this seems to be backed up by hard data. For example, https://www.sciencedirect.com/science/article/pii/S0078323411500193?via%3Dihub discusses the meteorology of the North Sea, confirms storms are more prevalent in winter because of stronger winds. And https://journals.sagepub.com/doi/full/10.1177/0022526619886061 analyzes British coastal trade over the last few centuries, confirms this pattern historically.

But looking at weather patterns in other temperate regions, I seem to be seeing different results; Virginia and Japan are both said to have peak storm season in late summer, August-September.

What's the reason for this difference? I can think of a few possible explanations:

  • The seasonality of storms is different at latitudes 35-40 compared to 50-55.
  • It's different if you're on the west side of a large continent versus the east side.
  • It's influenced by quirks of local geography such as the layout of the North Sea versus the Sea of Japan.
  • The sources are talking about different things. Virginia and Japan are indeed stormiest in winter just like northern Europe if you talk about midrange storms driven by local meteorology; the peak in August-September is not for those kind of storms at all, but for hurricanes that come up from the tropics.

What is the explanation for the differing patterns?

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  • $\begingroup$ Hurricanes/Taifuns. $\endgroup$
    – Erik
    Jul 13 at 7:29
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It really depends on how you define storms. For tropical storms, there are some regions where they are not usually a threat. Likewise, for extratropical storms, there are latitudes where such things are not a concern (such as the tropics). The key to understanding the seasonality to such storms is to understand what controls the seasonality of what drives each.

Thunderstorms (broadly speaking) rely on a warm air over cooler air. During spring and summer that is more likely to happen. More in the spring, as the land and air near the land responds pretty quickly to the increase in radiation, whereas the air further away from the land takes some time to adjust. Air that moves over a cool ocean current will tend to be cooler, so less thunderstorms will usually occur where land is downstream of cool water.

Extratropical cyclones rely on sharp changes in temperature, which is enhanced during winter. That is, the tropics maintain the amount of radiation that they get, while the higher latitudes get less incoming radiation (0 past the Ant/arctic circle). Large change in radiation means large change in temperature which means more extratropical storms in the winter.

For tropical storms, there is an acronym that I memorized for the necessary (but not sufficient) ingredients for them to develop (the technical term is tropical cyclogenesis): LIVERS.

If you consider all of the climate controls for those factors, then you will have a decent grasp of the seasonality of tropical cyclones.

Certainly, storms that are unique to their own locale, such as haboobs or the Meiyu front, have their own causes and their own seasonality. But in general, if you understand what drives the weather systems, then you can generate how they fluctuate by the season and latitude. Of course, there are exceptions, such as the snowfall in Baghdad.

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  • $\begingroup$ So according to that link, extratropical cyclones form between 30-60 latitude, preferentially in December-January for the strongest ones. How does that square with other sources' claims that peak storm season for Japan and Virginia is August-September? Those are both north of 30 degrees. $\endgroup$
    – rwallace
    Jul 14 at 4:49
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    $\begingroup$ Because, the term ‘storm season’ is quite ambiguous. For example, the North Atlantic hurricane season goes from June 1 to November 30., with it peaking between August and October. The peak distribution of typhoons occur in August. And that doesn’t count the Mesoscale Convective Systems/squall lines/derechos, that could contribute to ‘storminess.’ $\endgroup$ Jul 14 at 14:04
  • $\begingroup$ So comparing e.g. Virginia to Britain, would it be accurate to say that Britain doesn't care about peak hurricane season in August because it's too far north for many hurricanes to reach that far north; Britain thinks peak storm season is December because that's peak for extratropical cyclones... $\endgroup$
    – rwallace
    Jul 14 at 15:12
  • $\begingroup$ but then does Virginia not think of December as peak storm season because a) they get fewer/weaker extratropical cyclones, or b) they get just as many, so just as much December hazard therefrom, but they don't pay so much attention because hurricanes are so much bigger a threat? $\endgroup$
    – rwallace
    Jul 14 at 15:13
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    $\begingroup$ I wouldn't say that they don't care about hurricane season, as the UK Met Office does have information about them and makes seasonal hurricane outlooks. Having lived, not in Virginia (VA), but both North and South of there, it is more terms of what sort of form will the precipitation take. If you consider precipitation as a measure of storminess, [Norfolk VA](en.wikipedia.org/wiki/Norfolk,_Virginia#Climate) gets more annual precip than [Plymouth, UK](www.plymouth.climatemps.com/precipitation.php). $\endgroup$ Jul 14 at 16:39
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Yes, In he tropics where humidity is more ubiquitous moist air currents feed systems that allow for storms. In temperate climates these storms proliferate where it's warm and humid and die off in winter.

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