We were very lucky yesterday when a really nasty piece of weather passed very close to us without doing us any damage although others in the area were not so fortunate. I'll leave the technical explanations to several met experts on here if they want to comment but did want to show a few photos and give some details.

The photos were taken by a friend who decided to set up in the known path and to follow the storm after it passed.

A very tight, intense, and fast moving sort of storm called a Supercell passed through today. These are the storms that tend to produce tornados and always bring high winds, lots of rain, and usually some hail as the move along. The lower edge of this one containing the worst of it passed less than 1000 yards north of us as it moved east at about 40 mph.

It did contain a tornado although for most of the time, the bottom of the funnel was aerial and rarely touched down. You can clearly see it in this shot.



There was some serious hail and sizes (from storm spotter reports) ranged from half-inch diameter to baseball size. Since I never hear about hail in the UK, a quick explanation: hail is a warm weather thing caused when there is rain and the winds aloft move the raindrops in a circular pattern up & down. As the drops go up into freezing temps they turn into small ice particles and with every drop back into the rain, pick up additional moisture and up again, growing a little larger with each pass. When they get heavy enough, they drop out and fall to earth with the wind's speed deciding how large they get before they are too heavy to continue circulating.

These were fairly small but still heavy enough to cause some damage given their speed when they hit. Larger ones can hurt or kill if your head is unprotected. Some of the baseball size fell less than a half mile from our house with smaller 3" diameter hail stones being widely reported inside this beast.







Here are several photos of the clouds as the storm passed us and continued to the east. I have no idea what produces this sort of clouds with the flat tops but they usually signal some really nasty stuff below.





We barely got any wind and no rain from this supercell as it passed.

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Hi Newt,

These are cumulus-nimbus clouds, otherwise known as anvil-heads or thunder-heads.

When warm air rises and meets lower temperatures, moisture in the air condenses out forming a cumulus cloud.

This condensing occurs at the 'dew point' for the particulur day, which depends on the amount of moisture in the air (humidity) and the temperature.

Look at any cumulus cloud and although it has a fizzy top, the bottom will be flat and every cumulus will have a flat bottom at the same height.

(The height can be caculated if you know the ground temperature and the dewpoint for the day).

Usually cumulus clouds are capped by an inversion, a layer of higher temperature air, high up.

But on 'good' days, when the moisture in the cloud condenses it releases the 'latent heat of condensation' (the sun's energy used to evaporate the moisture in the first place).

This extra energy allows the cloud to punch up through the inversion layer and the cloud now begins suck in cooler air from below (wind direction will often change as the cloud approaches, a sign that the updraft is sucking in air).

When the process is really motoring, the moisture being released is too much to be supported and the rain begins (nimbus = rain), releasing even more energy.

As the rain begins to fall below, above a tower grows quickly (if you see a tower suddenly start to grow from a cumulus cloud, at the same time those deirctly below will experience a cold shower).

The tower is affected by windshear, which produces an anvil shap, and will climb to the thermoclime, where it can go no higher, producing a flat top.

Meanwhile, down below, all that moisture laden air being sucked into the bottom of the storm causes the air (and cloud) to start rotating, like water going down a plughole, and you now have a supercell (particularly if some clouds have all joined together).

It's fascinating to watch, more so particularly if you know the basic physics involved know what each part of the cloud is doing, and how that is going to affect you on the ground (knowing precisely when the rain is suddenly going to hit).

(Bloody scary if you are flying a glider with one of those heading towards the airfield where you are trying to land, but even with airbrakes full open, you start going up instead of coming down, and the windsock keeps changing direction).

We do get hail in the UK, but I've never seen anything more than pea-size, which can hurt.

I'd hate to be caught in the open and have those things battering me! :gulp:

This post has been edited by Leon Roskilly: May 12 2008, 08:38 AM

Here are more photos from among the 140 or so Carl took.

http://carltyson.com/33.html

Nothing that spectacular to the untrained eye but some supercell features that may be of interest to those with some Met background.

Glad to hear you and yours are OK Newt.
Those hailstones look as if they might make serious holes in someones bivvy.

your lucky wev'e had sun storms for days

This post has been edited by chesters1: May 12 2008, 06:37 PM

Know what you mean Chesters, i got caught in one last week and ended up looking like a pickled beetroot.

roll on autumn or better winter

I've always felt sorta sad to have so many friends and acquaintances who happen to live where there really isn't much weather. It must get boring for you.

And here I was missing the daily thunderstorms of southern Mississippi... You could count on a rain everyday at the same time to bring releaf to the heat.

Glad you missed out on the hail Newt. Just think what might have happened to that shiny new 5th wheel you've been eyeing!

Jeff, I kept moaning about what the weather could do to the fifth wheel and my sentimental other half's response? That's what they make insurance for