Does storm seasonality vary with latitude?

Question

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?

Answer 1

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.

• Latitude- Needs to be small, but not 0
• Instability- there needs to be a good amount of instability for convection
• Vorticity - No vorticity= no spin
• (thermal) Energy - The water needs to be warm enough to sustain a tropical cyclone
• Relative Humidity - A (typical) tropical cyclone is moist. While a dry tropical cyclone is theoretically possible, it is not common, and the barrier for formation is much smaller for a wet tropical cyclone.
• (little) Shear - An ideal tropical cyclone is symmetrical. Shear disrupts the symmetry (among other issues). That being said, it might be easy to overestimate the impact that shear has on weakening an already strengthened tropical cyclone.

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.

Answer 2

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.