Linear Cloud Feeds (Streamers)

[misfitdog]

I've been watching the various weather radars as they have become more available over the last few years. Has anyone else noticed an increase in linear clouds feeds (streamers) where shower formations seem to be increasingly feeding in on thin persistant lines along the prevalent wind direction as compared to the past where they tended to scatter more.

I was wonderng if this could account for an increase in localised flooding problems. Very recently I was in Pirbright (Surrey) on a Sunday when they had over 5 inches of rain in 4 hours from a very persistant stream of thuderstorms feeding down in a 10 mile wide corridor from North West London. The event was extreme and down to the pattern as described.

The patterns obviously stand out on radar pictures and they really have become very common over the last two or three years.

Feedback from others is most welcome!

[johnholmes]

I doubt they have become more common. More probably that more and more people are able to view radar pictures of these events.

[misfitdog]

Maybe, but I suspect there may be something else happening. I will continue to watch and gather evidence on the area. It's been an area of interest for a while now.

[Stratos Ferric]

I doubt they have become more common. More probably that more and more people are able to view radar pictures of these events.

I tend to agree with you. There was an excellent example early this week, must have been yesterday I guess. There are two separate factors that can lead to the appearnace of shower lines. One is a localised hot spot setting up downstream shower activity, or some topological funneling. The other is convergence; we had a spectacular example with the unexpected snowfall over Lancashire and Yorkshire in (I think) late Feb this year where a sudden and sharp convergence developed.

What I have noticed is an increased ability to spot these latter features, and and increased tendency to mark them on the "Bracknell" charts.

[Dawlish]

I tend to agree with you. There was an excellent example early this week, must have been yesterday I guess. There are two separate factors that can lead to the appearnace of shower lines. One is a localised hot spot setting up downstream shower activity, or some topological funneling. The other is convergence; we had a spectacular example with the unexpected snowfall over Lancashire and Yorkshire in (I think) late Feb this year where a sudden and sharp convergence developed.

What I have noticed is an increased ability to spot these latter features, and and increased tendency to mark them on the "Bracknell" charts.

You can also get an input of moisture, especially downwind of lakes, in Canada and North America, which, combined with warming from the unfrozen lakes' surface, give rise to snow streamers, which are well documented.

[shuggee]

Also known as 'Lake Effect Snow' - which can of course occur from a wind in the easterly quadrant over the North Sea.

A topographical feature, probably known to you Paul - is one of the areas on Dartmoor/Exmoor (I really can't remember the name of the Tor) which with suitable conditions, including the wind from a sw'ly direction, creates showers in a line up into the West Midlands.

[BrickFielder]

Cloud streams tend to form from two distinct sources. The first is topographical (hills ,sea etc) and the second is due to wind convergence.

We may have seen a few unusual streams due to an increase in winds from the east over the last few years, and blocked high pressure patterns which have been on the increase would tend towards more convergence zones developing. It is not beyond the realms of possibility that we have had more streamers over the last few years , although I think I would tend to agree that it is just that we are noting them more often due to radar improvements.

[Thundersquall]

Remember the snow that just appeared to affect Beds, Herts and Bucks?

Or the snow that apparently affected High Wycombe and nowhere else?

:blink:

Maybe these were due to snow-streamers?

[Dawlish]

Cloud streams tend to form from two distinct sources. The first is topographical (hills ,sea etc) and the second is due to wind convergence.

We may have seen a few unusual streams due to an increase in winds from the east over the last few years, and blocked high pressure patterns which have been on the increase would tend towards more convergence zones developing. It is not beyond the realms of possibility that we have had more streamers over the last few years , although I think I would tend to agree that it is just that we are noting them more often due to radar improvements.

There was a streamer sat in the Irish Sea, from a Northerly, for at least a full day last winter. For the life of me, I can't remember when, but I remember writing about it. It fed snow showers towards NW/West Wales constantly. No snow was reported either side of about a 50 mile corridor.

Paul

Edited October 5, 2006 by Dawlish

[SP1986]

A good case study to use would be the incorrectly but adequately described 'Cheshire Gap streamer', this is in an area where there are numerous 'sub streamers'. The main Irish sea streamer would usually pass through the Wirral peninsula, affecting the extreme coastal areas of Liverpool and Northeast Wales. The 'sub-streamers' are down to wind change though and like said above are highly dependent on topography. Even a shallow valley can to an extent funnel air into a linear path and this is found to a certain extent from Crosby to Childwall. The more spectacular streamers are carried on a NNW wind through the Berwyn and Clwydian valleys. I dont think there has been an increase in flooding, but certainly streamers can ultimately influence higher rainfall rates in concentrated areas (for an example of a similar effect of concentrated rainfalls, there is Boscastle). There is also the argument that climate change will make this events more frequent, but the problem with this theory is that seeing as air/wind flow movement is often playing a large part in the directions of such occurences, one predominant windflow in the future may only affect the area that is susceptible to this air direction.