WeatherWeather Blog


"Fair Weather" Funnel Clouds Explained

The science behind this phenomenon
Osceola Funnel Cloud.jfif
Posted at 4:39 PM, Jul 09, 2022

Over the last couple of days the region was inundated with showers and thunderstorms. Some locations saw up to 6" of rainfall, while others got next to none. These storms were not severe, contained little damaging winds or hail, yet a few of these storms produced funnel clouds? Over the past two days a few thunderstorms produced small funnel clouds. These were reported in northern Polk County, near Clay Center east of Hastings, in Carroll County Iowa, and a few other locations. Why did they occur? Are they dangerous? Why were they not tornado warned? Keep reading to find out

If you have been to the beach near an ocean on a partly cloudy day, there is a chance you might have seen a water spout off shore. These water spouts are often called "fair weather waterspouts" for their relatively harmless nature. Fair weather water spouts are not formed by traditional means of funnel cloud formation, hence why they are weak and off-shore.

Although formed in different conditions, the funnel clouds sighted over the past couple of days share similar traits. They often develop on small showers or even just cumulus clouds, and rarely touch the ground.

These funnel clouds can often form when there is enough instability, the energy needed for clouds to rise, is present to support the development of cumulus clouds. These cumulus clouds then begin to form and become small showers, or just remain clouds. When one of these cumulus clouds interacts with a weak front or wind shift boundary, it can manipulate the wind within the cloud, often causing a little bit of rotation. That rotation can develop in the form of a funnel cloud which is weakly rotating.

These fair weather funnel clouds very rarely touch the ground. If they do, it is typically a weak land spout tornado with winds no more than 50-60 mph. These can still do minor damage, but they are typically weak. Due to the rarity of touchdowns and the often weak nature, the National Weather Service typically does not issue tornado warnings on these funnel clouds. In rare instances, like near Clay Center on Thursday, a tornado warning can be warranted if there is a higher chance of one reaching the ground.

Another reason they are not warned is because they are nearly impossible to detect on radar. Traditional tornadoes often have strongly rotating storms, thus a radar signature is apparent and can be warned. However, fair weather funnel clouds are formed on small showers or sometimes no rain at all. This means radar will not detect them due to their weak rotation or accompanied with little rain.

What the National Weather Service does do for these is issue a "Special Weather Statement" when conditions for these funnel clouds are apparent. If you have the Storm Shield App downloaded and notifications turned on, you likely got the "Special Weather Statement" alert depending on where you live. This lets you know that the conditions for funnel clouds are there, but when/where they will appear is unclear.

If you spot one of these funnel clouds, contact your local National Weather Service immediately. This lets them know one is occurring and can monitor for any changes. Sometimes, county officials will sound tornado sirens for these to alert the public as well.

The best course of action is to stay away from the funnel cloud. Despite them rarely touching the ground, they still can. Just go inside and stay away from windows if one is spotted and moving towards you. Often times they only last a few minutes so stay indoors for 5-10 minutes or after it has dissipated.