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Thames Snow Streamer Event 1/2nd Feb 2009


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Posted
  • Location: Leigh On Sea - Essex & Tornado Alley
  • Location: Leigh On Sea - Essex & Tornado Alley

Okay so the Burning question on everyones Lips, How and why did it happen for many and why was it such a Damp Squib for many Coastal Locations. On the Night on Sunday 1st February I was as bemused as Most People Living on or near the Coasts of Norfolk, Suffolk, Essex and Kent as to why a Set-Up with -12 Uppers and a Cold Pool from the East could fail so Miserably when 95% of other Events I have Researched have Scored Direct Hits, Esp 2003, 1991, 1987 etc etc.

The 1st Thing to Look at and what Baffled me was the Radar was Showing the Precip as Moderate for most of the Night but in reality all that was falling was Tiny Polystyrene Balls of Snow which did not amount to anything. The radar returns were as heavy as places further west yet they got heavy snow and places on or near the coast got this type of Snow. WHY ??

post-24-1234217994_thumb.jpg - During the afternoon a Keen North Easterly was bringing frequent Snow Showers to the North Kent Coast, and SE Essex, SE Suffolk these Penetrated a little way into land but these were not the main show that was to come, although this 1st Part of the Story was to become the 1st part that went against Coastal Parts. SST's in the Thames Estaury were at 9c in the Shallower Waters and with the onshore breeze (1st NE) And then (2nd ENE) this created a layer of Moist Air at between 750-800mb or about 4,000-6,000 Feet, this would have a major effect on Shower Clouds that would form later on in the Day when the Cold Pool was at it's greatest and Instability Primest between 21z and 09z (2nd Feb)

post-24-1234218589_thumb.png - This next Chart shows Near Surface Flow, Notice the Flow is Backed from the NE Further In land this is caused by Frictional Drag from the Flow. This resulted in a Number of Convergence Zones near the Thames Estuary and Channel Coast. The Red dashed Line is effectively a Coastal Convergence Zone that is Pushed Inland due to the Strong Synoptic Flow from the East.

post-24-1234218928_thumb.png - The next Chart shows how much Surface Based Cape was Available as the Instability reached its maximum (120jkg) this was enough to Tower the Convective Clouds to a Height of around 8,000-9,000ft just Offshore in the Thames Estuary and Up to East Coast as far as Lowestoft.

post-24-1234219082_thumb.png - A Forecast Sounding for Near to Leigh On Sea (Computer Generated) shows 24jkg of Cape and LI Of -1 (00z) But the major problem for Coastal areas was just about to become apparant from the next Chart.

post-24-1234219286_thumb.png - This Chart shows a Cross Section from W-E of the Thames Estuary (The Dashed Line is Greenwich Meridian) The major part of this Chart is showing the Shower Training effect, Notice how the Cloud Tops get deeper the further West along the Estuary as they gain Height (Up to 16,000ft) And also how the Clouds are Capped by an Inversion at the Eastern End of the Estuary and Up the East Coast, This was to become the 2nd Major Problem for Eastern Areas as Cloud Tops could not get any Higher due to the Cap (Hence the Lack of Thundersnow Reports in the Eastern Thames Estuary)

So What effectively Happened to places within 10 Miles of the Coast ??

Shower Clouds Initiated unfortunately too Close to the Land Mass and adequate Mixing could not occur (In 2003,1991 Shower Clouds Formed 100-150 Miles further East so no such problem) When the Showers moved onto the East Coast they were Capped to a Certain Height, The radar was showing Moderate Precip which was falling into a Warm/Moist Layer of Air in the Atmosphere (Turning It to Rain) this then continued down and as It hit the Extremely Dry Dewpoints near the Surface we were left with little more than Polystyrene Balls For 2003 Set-Up See Pike 2004 Radar Study Online

post-24-1234219683_thumb.png - This next Chart is pretty much the Same as Above but Tilted more from the NE-SW Too Show just How London and SE/S & SW London got their Most Snow since 1991. You will notice the Dashed Line is again the Greenwich Meridian, One thing that is glaringly apparant is where the City of London is situated on this Chart, as the Showers train over the City a Certain amount of Urban/Heat Effect Could have been the reason why the Showers gained Intensity and with the backed NE - SW Flow further Inland this then only had 1 place to go and deposit large amounts of Snow from Strong Convective Clouds and that was SE/S & SW London. Although not proven 100% I really feel this might be the reason for the exceptional Amounts of Snow (52cm) Seen in this Region.

post-24-1234219992_thumb.png - This last Chart pretty much backs up the above and shows how the Showers trained in Lines and hit places Hard whereas over places nearly missed them altogether.

So I hope this goes some way to Help people know how they got record levels of Snow and How some on the Coasts got a Mere Dusting of Dry Powder Balls.

It has certainly enlightened me and made me think twice about Easterly Set-Ups in the Future and has also Facinated me at the Same Time just how diverse Weather Can be.

Special Thanks to Waghorn (David) For running the Model Simulations for Me.

Regards

Paul S

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Posted
  • Location: 14m als, Clacton-on Sea,NE Essex
  • Location: 14m als, Clacton-on Sea,NE Essex

Amazing,,that was a real interesting read and certainly explains why i saw them stupid polystyrene balls instead of flakes, alot of work has obviously gone into this work,, and i thank you

do you think it will be a re-occuring feature in easterlies or just very bad luck for us this year ??

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Posted
  • Location: Leigh On Sea - Essex & Tornado Alley
  • Location: Leigh On Sea - Essex & Tornado Alley
Amazing,,that was a real interesting read and certainly explains why i saw them stupid polystyrene balls instead of flakes, alot of work has obviously gone into this work,, and i thank you

do you think it will be a re-occuring feature in easterlies or just very bad luck for us this year ??

Just very bad luck Donna, Too have an Inversion, Moist Layer of Air and Showers Forming and not allowing Mixing to go on are pretty rare in these types of Set-Ups, In fact I am still trying to find more than 1 other occurance at the moment.

Paul S

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Posted
  • Location: Ratby, Leicester.
  • Weather Preferences: Snow, storms
  • Location: Ratby, Leicester.

Great post Paul, I couldn't believe the amount of precip that was hanging around London on Sunday afternoon/night when it happened. The radar had moderate/heavy precip hanging around that area all night and I knew it wasn't anaprop because of the reports of several inches of snow coming in. I knew it was going to be a special event for London, I was pretty envious though! I got my 4-5 inches of snow though by Monday evening so I was happy then.

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Posted
  • Location: West/Central London (W11) 27m (88ft) ASL
  • Weather Preferences: Snow and thunderstorms!! (With the odd gale thrown in)
  • Location: West/Central London (W11) 27m (88ft) ASL

That was stunning Paul...How informative.

Was stunning to see, even though I didn't get as much as some people just a couple of miles away, but what fun.

Thankyou for the time and effort!

Edited by Sno' problem
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Posted
  • Location: Liphook
  • Location: Liphook

Interesting report, certainly an odd event.

Ialso noticed a small streamer form right near the south coast during this ENE type airflow, steming from just SW of Dover, perhaps the slight change in geography down there in terms of the map is to blame for sparking a certain amount of instablity.

Edited by kold weather
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Posted
  • Location: Near Matlock, Derbyshire
  • Location: Near Matlock, Derbyshire

Thanks Paul for that. Those are very similar conclusions that I came to when looking at this set-up. I also concluded that if the winds had been slightly more north of east than they were, then the slightly longer sea track would have helped those of us along the coastal strip as these showers would have formed a little earlier. We were unbelievably unlucky on this occasion, but it all helps us to learn more about our weather and how it works - it also shows how difficult it is to get the perfect set up!

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Posted
  • Location: Ipswich, Suffolk
  • Location: Ipswich, Suffolk

Fantastic analylsis Paul! :) Thanks! IMO this is what meteorology is all about. As you promised, the whole event was a blinding unlucky affair for so many down the east coast of EA and Kent. Will be interesting to see if this sequenece of events has ever been replicated in previous winters? From past experiences, everything seemed to be set up so nicely!

Thanks again for trawling through the wreckage and helping a rather disillusioned Suffolk dweller to understand that we were, really really really unlucky! :) Until next time! :)

Edited by MattS
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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

only just seen this Paul, super piece of work and in my view well worth being put into the Guides somewhere

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Posted
  • Location: The Wash - Norfolk side
  • Weather Preferences: Storms storms and more storms
  • Location: The Wash - Norfolk side

Brilliant Paul - a fascinating read - this should be put in the guides for posterity.

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Posted
  • Location: Home near Sellindge, 80m/250feet, 5miles from Coast
  • Weather Preferences: Severe Storms and Snow
  • Location: Home near Sellindge, 80m/250feet, 5miles from Coast

Brilliant write up and it showed me it wasn't just the winds which ruined our heavy snow which it was you said :)

Damn :)

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Posted
  • Location: Bexleyheath (south), Kent
  • Location: Bexleyheath (south), Kent

An excellent analysis Paul. Many thanks for taking the time to research and then explain in a user friendly format. Shows how lucky my area was with the excellent snowfall. I also think that the UHI aided by the cold uppers had some sort of positive effect on the level of snowfall. A very interesting perspective which in a more marginal setup may not have come to fruition!

Best regards.

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Posted
  • Location: SE,London (Catford)
  • Location: SE,London (Catford)

Yes at last someone has explained it... Cheers paul.. Mind you that does happen roughly every other year for me.. But not to that rare event.

I suppose you should go and explain why huge t/storms brew up over london now ;)

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Posted
  • Location: Basingstoke - 134m asl
  • Location: Basingstoke - 134m asl

A very intersting read, thank you!

In our area it was really apparent just how localised the depth was in places when compared with others. It seems that the showers tracked in a line through London, and then west through Surrey. 10 miles South of us there were a few inches at best, whereas here we had 28cm of the stuff! Truly unbelievable for us, and I wish you guys along the East coast much better luck next time we get a similar set up!

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Posted
  • Location: W Kent/E Sussex border (T Wells) 139m ASL
  • Location: W Kent/E Sussex border (T Wells) 139m ASL

Paul,

That is fascinating stuff and helps to explain some of the extreme variations we have seen in terms of snowfall in the region. Thanks also for your efforts in putting this together.

It does shows just how precise things need to be for all the ducks to be in a row - and even something considered unlikely can come along and ruin the piece. It also shows just how difficult snow forecasting actually is. When it rains no-one really notices the variations (it rained) - but with snow the effect can be dramatic.

In this part of the world, although we got a total of about 4" in total (which I am not going to complain about) the direction of the wind was too near an easterly for us to get any effect of the Thames snowstreamer on the Sunday night. We really needed an ENEasterly to get the full effect (as in 1987 and 1991).

MM

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Posted
  • Location: Heybridge, Essex!
  • Location: Heybridge, Essex!

Just to echo the thoughts of others, a very interesting read Paul and i appreciate the time taken to provide such a detailed explanation! :) At least now i know why that evening was so frustrating! :lol:

The radar was truely puzzling for all concerned and those polystyrene balls were a pain in the you know what! :)

Matt.

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Posted
  • Location: Leigh On Sea - Essex & Tornado Alley
  • Location: Leigh On Sea - Essex & Tornado Alley

Many Thanks for the Kind Comments

Just for future Reference I have been speaking with Paul M and If in the later part of Winter or when a Big Synoptic event occurs in the Summer (Eg Another Boscastle) We are going to aim to run the Netweather Models to try and show why these things have happened or what made them happen. I feel these will be great threads to let members get a better understanding of what caused such events.

Paul S

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Guest North Sea Snow Convection

Superb analysis Paul - very interesting :(

Was it a cathartic release for you unlocking the reasons why you missed out on the snow!? Sometimes knowing why something happens (or doesn't) can help. Very hollow consolation I know though.

I fortunately got a few cms of snow from the initial snow shower train on the sunday afternoon and evening, plus the persistent snowfall of course during the Monday on top of that.

Edited by North Sea Snow Convection
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Posted
  • Location: Melbourne, Victoria
  • Location: Melbourne, Victoria

absolutely fascinating post Paul. we were certainly very lucky indeed. particular atmospheric conditions, seen rarely, conspired to see large amounts of snow over a small area. a classic london snow event. just a pity more couldnt join in on that ocassion.

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