Microbursts.

[iancar29]

Great explanations here Karl.
Gettin a clearer picture everytime i read anything on this FAQ page.

Heres one for ya tough.

Microbursts.... I can pretty much understand how  Dry Ones occur but not  Wet Microbursts , any help on it?

[Snowbie]

Both are rare to these shores but have occured but not on the scale as the US. We use the term Wind Shear and is more of a hazard for planes when planes approach for landing.

Wet MB are drove down in the precip under the Cumulonimbus cloud in warm moist air. It can be distinguished by a wall of water being propelled towards the earth at high speeds and diverging(wind shear) out in all directions upon impact. Unlike Dry MB as there so called, the precip evaporates as Virga before reaching the earth in dry air so we can't see the precip but the debris blown up from the earth as they impact the surface. These occur from high based storms over the plains of the US.

A microburst is a severe downdraft from severe Thunderstorms but can be felt over a wide area 1-2km. If caught under these microbursts, you could be swept off your feet, cars could be over turned but the greatest risk is to Aircraft on landing. One such case is from a plane landing in Dallas (I think) many years ago encountered one of these and crashed.

Most of the time you can't see a wet MB as it's contained in the precip but one distinctive shape of a microburst is the rolled cloud they form after hitting the ground. The diverging air in the outflow rolls back up and forms a sort of roll cloud structure under the CB as it rises and cools in the warm moist air.

[StratoQ]

The Kilkenny People newspaper in Jan 2008 documented what they referred to as a possible tornado at Kilkenny Golf Club. Various trees were flattened but crucially there was no rotational scattering evident.

The area was investigated by our well known tornado investigator John Tyrrell. Here is a snippet from his investigation of the event. (Conclusion : A microburst)

"Just back from spending most of the day in Kilkenny tracking this down. Most of the damage was on the golf course. Excellent assistance from groundsman and manager. But there were no eyewitnesses because it was in the early hours of the morning (unspecified). The damage was evident, strewn all over the place, when the staff arrived to open up the course in the morning. There had been at least one thunderstorm locally during the night. I mapped all the damage and debris zones. Most of the trees partially down or significantly damaged were pines - 34 of the total of 37 damaged trees. These trees were not strong. They were planted about 30 years ago, so are not fully mature by a long way. But they were bought as reject saplings from the Forestry, which meant their rooting systems were partially damaged from the word go. This may have contributed to the rather brittle trunks, quite a few of them being snapped off from heights of 12 feet upwards. Some were both snapped and pushed over. However, they have survived many a gale without being dislodged (as have most trees in Ireland!). The mapping exercise shows conclusively that this was not a tornado, but another microburst. It fans out from about 20 metres wide at the initial point of contact to about 0.5 km. Most of the most severe damage is along the fan edge at the furthest distance from the start of the damage 'track'. Most of this waqs on slightly higher ground in the area as a whole. I have not done all of the detailed measurements yet. But since we seem to be having a number of the microbursts being reported as tornadoes, I will be including some of these details in the appropriate annual report so they are documented and distinguished fromt he 'real thing'. "

 

[iancar29]

Thanks Karl, very well explained.
They must be very rare too catch and identify as they happen.


Very interesting story aswell StratoQ , i wouldnt of thought that we wouldnt get a cell strong enough over hear to create them.
But then again .... anything can happen as we all know!

[Danno]

What date in January 2008 was this SQ? If I am not mistaken, Kilkenny College is right beside the Golf Course on the NE of the city, I know people at the College and I might ask them to jog their memories if it was during school term.

[StratoQ]

As reported in the newspaper it was the early hours of the 16/01/2008, Dan. That night was a quiet one here from what I could establish.

The 06 fax chart for early Wed morn shows a small LP of about 980hPa almost centred on Kilkenny with a small occlusion fanning out to the South. It was, from what I remember a quiet night wind wise with low temps (near zero) and no squally winds of any sort. I think there was some sferic activity earlier (round midnight) out to the west Co. Clare/Tipperary).

A peculiar one alright. There were no eyewitness accounts either. The golf club people checking out the grounds first saw the scene of destruction at first light.

Now I do wonder did the paper get the exact date right - as the next night (into the 17th) was far more active from a convective point of view.

[Snowbie]

Here are some radar archives of the nights in question. The early hours of the 16th Jan 2008 where quiet with some light to moderate showers pushing up from the south.

16th

No acivity to be conducive to MB


On the 17th, the early hours looks more lively. Front crossing the country with squally winds ahead of it. MB activity be minimal


Lots of squalls beginning to cross the country overnight. This would have been convective alright.


This one moved into Kilkenny but seems weak at the south


This radar image would have been more intense from the echo and very squally with possible MB activity with strong or severe downdrafts.

[Danno]

Thanks Snowbie. Looks like the 17th was the morning in question then. Perhaps it was lazy reporting on behalf of the KK people newspaper where the night of the 16th/17th became a 16th timestamp.