IN THE LAST week, we have had lots of reports around the country of the appearance of funnel clouds. There even unconfirmed reports of touchdowns in parts of the country classing them as tornado albeit weak in nature with little damage.
This is not uncommon to Ireland. They are well documented nowadays as most of us have camera phones and other form of professional camera equipment and of course being in the right or wrong place at the right time helps.
Funnels clouds can form from different set-up in the atmosphere. They are best known for forming in turbulent skies near thunderstorms from cumulonimbus clouds. In the Plains of the US, they form from supercell thunderstorms. What’s that? A vast rotating storm that can produce a violent life-threatening tornado. But funnels can also form in fair weather when the skies are relatively calm under harmless cumulus clouds.
In Ireland, there have been reports of several touchdowns in recent years with damage done to buildings and also leaving a trail of destruction which is often the only evidence of a tornado passing through an area if not caught on camera. A tornado is classed as such when a funnel touches down on the ground. If they touch down over water, they are known as water spouts. The term ‘mini tornado’ is a misinterpretation of a tornado. It’s either a tornado or a funnel, or else it is simply squally and gusty winds which can be associated with thunderstorms or heavy showers.
What we usually get in Ireland are cold air funnels. These can occur from cumulonimbus or a smaller cumulus cloud. A small vortex occurs at the base of the cloud and this will have the appearance of rotating slowly in a tight circle.
The Cause
Directional wind shear in the atmosphere: that is the change of wind direction through the atmosphere at height coming in contact with winds blowing in the opposite direction from near the ground surface. This creates vertical speed shear with a vortex or rotation in the base of the cloud. The presence of this vertical speed shear, which is wind gaining speed with height can be nudged off the horizontal axis at the base of the cloud by an updraft in a cumulus cloud. Vertical speed shear with a cone can extend from beneath this rotation – it can just hang from the base of the cloud which can dissipate soon after.
Now and again, a rope-like feature extends towards the ground, giving the appearance of bending and twisting as it descends. This is the presence of greater updraft and vertical speed shear being tilted. But in this case it is now being wrapped in low level moisture making it more visible to the naked eye. This is a condensing funnel and it can give the appearance of dropping to the ground. Upon touchdown it is only then classed as a tornado or twister.
The Enhanced Fujita scale (the EF scale) measures the strength of destructive winds from a tornado If this rope-like feature reaches the surface, winds are around 55 to 65mph very locally or an EF-0. An EF-1 is rare here but damage which would come under this level has occurred here. Winds can be as high as 100mph in a very localised area. If this type of tornado is witnessed, it could have a more conical feature extending from the base of the cloud to the ground with a wider appearance instead of a tight rope-like feature.
Elongated Funnel at Killucan, Co Westmeath:
Sea Spout, Bray, Co Wicklow:
(Aoifeno1/Youtube.com)
Karl Mehlhorn is a meteorologist who runs the Irish Weather Network. You can check them out on Facebook, follow them on Twitter and sign up for regular forecasts. The site has a live weather map of Ireland which is available here.
If you’re interested in owning a weather station yourself, they’ve written this handy guide.
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