The Irish Sea Vs The North Sea

[Backtrack]

Was just having a discussion with Ian Brown about these two 'snow machines'

thought it would be a good idea to open a thread to stop the model thread being clumped up. Here's my post:

Actually the Irish Sea is very much on par with the North Sea in terms of convection. Similar to the Easterly too last year. Extreme coastal areas such as Scarborough saw rain, whilst just 5-10 miles inland saw tonnes of snow.

Discuss!

[Isolated Frost]

Scarborough saw rain on a rather marginal event IIRC. The North Sea is generally colder than the Irish Sea and so does not moderate as much, but under similar uppers, the irish sea sees more convection... but then again as we are closer to the coldest airmass (polar continental) in winter we usually can get equal or more convection due to colder uppers, while the Irish Sea delivers convection to western parts using NW or W winds, which tend to be milder than most true easterlies or north-easterlies.

[Geordiesnow]

Got to remember also Backtrack, I'm around 9-10 miles away from the North Sea and even under an Easterly, there was periods where the snow started to turn very wet snow and sleet or icy pellets with uppers of -7 or so. It means whilst western areas could potentially see alot of showers this weekend, the snowrisk is slim but I do fancy the Pennines to get a bit of snow though. I think if the model output stays the same then I wouldnt be surprised to see snow reports coming from Inverness(although thats quite high up in fairness), Glasgow or even Edinburgh or anywhere low ground away from the Atlantic but I think settling snow at lower levels do look slim at this stage.

[Nick L]

In what respect are you discussing Backtrack? Do you mean the intensity of the showers as a result of convection?

[Snow free zone]

Although we have our moments (last 2 Decembers and a Christmas day 2004 I think) it has to be very cold to get lying snow in my location from Irish Sea showers. I think this cold NW will be just a bit too soon for lying snow here, but I expect the Lakeland hills and Western Pennines do do well. There will probably be a sleety mix here, with wet snow further inland but I think you'd need altitude for any accumulation.

We have a problem over here, we need a more WNW for the showers, but that in turn increases the risk of higher temps coming in off the sea. We have been lucky in the past 2 years, in that the temps have been cold enough for heavy snow with a more Westerly element to the wind blowing the showers in off the sea.

I expect there will be plenty of showers around but it just looks a bit too warm yet down here for lowland snow.

[Thundery wintry showers]

Going by previous experiences in Lancaster, I would expect a mix of rain, hail and sleet there from the progged synoptic setup, with the "snow line" getting down to about 250m on the western flank of the Pennines. Anywhere to the west of the M6 will probably struggle to get any advance on sleety rain, to the east of the M6 some wet snow at low levels is possible.

On general grounds Isolated Frost is right- the main reason why eastern coastal areas traditionally see more lying snow than western coastal areas is because they get most of their heavy wintry showers from northerlies and easterlies, both of which generally bring colder air than westerlies and north-westerlies. Another factor is that during northerly blasts, convergence near the east coast peps up the shower activity (as the surface wind direction is typically backed from the isobars as you head inland- hence a NW'ly 5 miles inland clashes with a straight N'ly along the coast) and with winds blowing close to parallel to the coast, the warming effects of the sea are lessened. I don't think western coastal areas have an equivalent with the Irish Sea, hence their reliance on westerlies and north-westerlies.

[I remember Atlantic 252]

might be same convection wise, but for southern areas, Irish sea too mild for snow, wind from SW-NW, where as north sea a much colder airstream like 30 nov last year

as much as i dont want to, agree with Ian (negative) Brown on this, no snow for low levels

[Backtrack]

In what respect are you discussing Backtrack? Do you mean the intensity of the showers as a result of convection?

Just the basics really Nick. Different factors effecting different areas in a NW'erly and an Easterly.

Both seas are very good for creating convective showers, and it's Polar low's in the Irish sea that give the West our largest snow falls.

[Cheese Rice]

Well if your relying on polar lows then the NW is pants for snow as they don't come around too often (unfortunately)

Anyway while yes both seas can provide rigorous convection the North Sea has to win on this one. For starters the 850 values will always be colder due to less modification from the Atlantic. We rarely see -10 850s from a North Westerly but its typical in a proper easterly blast to see 850s at or below -10. The Irish seas ST values are significantly warmer which while this in theory should promote stronger convection the higher 850s even this out and as a result provides rain or hail a good 20 miles inland.

[conor123]

There hasn't been a good Cheshire Gap streamer here since the beginning of March 2006, last winter failed to produce the goods with that initial North Westerly here in Mid December whilst just down the road had 4 inches.

[damianslaw]

Having lived in both Windermere and Newcastle upon Tyne - I have experienced on many an occasion the full force of convection off both the Irish Sea and North Sea.

The North Sea tends to generate deep convection when there is a very unstable northerly/northeasterly outbreak - a true northerly tends to keep convection away out to sea with the coast only benefitting from showers. A northerly/northeasterly airstream does bring colder uppers than a northwesterly airstream therefore snow has a much greater chance of lying at the coast than in coastal areas near the Irish Sea. Later in the winter as the N Sea cools down sufficiently there is less moderation and convection decreases markedly - the NE becomes more reliant on trough features.

As for the Irish Sea - yes it can produce very powerful convection. The Lake District can be pounded by heavy snow showers in a unstable NW/W flow. If winds are more NW/NNW the Lakes are more sheltered. Even SW flow off the Irish Sea under cold uppers and arctic airmass as we saw in Dec 09 can produce the snow goods - we saw a foot of snow from thundersnow convection - very rare but it did occur.

The lakeland fells aid further convection and evaporative cooling - central and eastern parts of lake district can do very well for heavy snow showers, could place to head too is Dunmail Raise at 800m it is generally kept open through the winter months unlike Kirkstone Pass and you are often guaranteed lying snow under NW polar blasts.

[Verglas]

you won't get many reports on Irish Sea weather because my attempt to have a separate thread for Isle of Man last year, rather being clumped in with england, Ireland or Scotland was dismissed out of hand by the mods.

It wasn't a nationalistic thing, just that our weather bears little comparison to the surrounding areas, never as hot, never as cold, more windy etc., I gave up bothering to post reports after that !

[Cheese Rice]

Isn't there like one member that lives on Isle of Man on this forum, goes under the name of 'Verglas'?

lol

[Harps]

The Irish sea works similarly to the North Sea during an E or NE this side of the water. The east coast got over 30cm of during both November and December last year with thundersnow on several occasions. Obviously it's not going to be as good for Britain with NW air rarely as cold

A good example with convective streamers here

Edited November 30, 2011 by Harps

[Chris D]

I don't think I'll be seeing 25cm again unless another batch of the cold that came in Dec 2010 comes around again. Most of the time, for a coastal location such as Southport we miss out a vast majority of the snowfall from the Irish Sea (from NWerlies). It's simply due to the low elevation, proximity to the sea and the fact we are in the NW (lol).

So since I now live at the opposite side of the country, I'd say the North Sea because it can't be any worse.

But in terms of convective potential, I'd say the Irish Sea since its generally warmer.

Edited December 1, 2011 by chris93

[Verglas]

Isn't there like one member that lives on Isle of Man on this forum, goes under the name of 'Verglas'?

lol

I assume you didn't search the members list with a location filter of 'Isle of Man' then :lol:

[Weather-history]

I don't know how often it happens with easterlies, at specific locations but what I notice is when we get a NWly flow of Arctic origin, we get snow showers but they also tend to clump together either through troughs etc. For instance just before Christmas 2009, there were a couple occasions, we got clumping of snow showers especially that Tuesday morning that produced heavy snow. It happened during Christmas 2004 evening, the showers massed and then pushed through producing a short period of snow. The showers seem to clump together when they get to the Liverpool Bay area, the Liverpool Bay clumper. It seems to happen generally with NWlies when its active showery. I don't know if you get this clumping effect with easterlies, I know you get streamers such as the Thames one.

[Aaron]

The North Sea is better for snow in my opinion, and delivers far deeper snowfalls to lowlying areas in eastern Britain (including the South East) then western England with the Irish Sea.

Edited December 1, 2011 by Aaron

[J10]

NW winds can be very productive in terms of producing convective snowfall. The best wind direction is NNW, which allows a Arctic blast but also allows convection to occur from the Irish Sea to form heavy showers for South Wales and SW England. The particular advantage for South Wales is that the initial warming effect of the sea is mitigated due to the distance from the west coast. Such events have brought 4-6 inches of snow regularly over the past 10 years. Pembrokeshire can see more snow when a streamer sets up, however, it can be more marginal.

However most events occur overnight and before 9am in the morning, perhaps showing that marginality is a factor

It seems to me that many people underestimate the snowy potential from a good NW/NNW snow streamer

As for Eastern areas, I have no knowledge, but just by looking at the heavy snowfalls last November, this does show that massive snowfalls are possible. .

[Thundery wintry showers]

The North Sea tends to generate deep convection when there is a very unstable northerly/northeasterly outbreak - a true northerly tends to keep convection away out to sea with the coast only benefitting from showers. A northerly/northeasterly airstream does bring colder uppers than a northwesterly airstream therefore snow has a much greater chance of lying at the coast than in coastal areas near the Irish Sea. Later in the winter as the N Sea cools down sufficiently there is less moderation and convection decreases markedly - the NE becomes more reliant on trough features.

A good summary overall, but I don't think the bit in bold strictly holds true. The main issue is that as the season progresses, we increasingly need a pronounced cold pool at the 850hPa level or else the air-sea contrast ends up too small to generate much instability and we end up with dry cloudy weather- this is particularly true when we pull in continental air. Once we get into March we have the added issue that the continent warms up, and so we become increasingly reliant on Arctic-sourced northerlies and north-easterlies for convection off the North Sea.

But an Arctic-sourced north-easterly will still bring many heavy snow showers off the North Sea, even well into March, as happened around the 1st/2nd and 17th/18th March 2001.

I don't know how often it happens with easterlies, at specific locations but what I notice is when we get a NWly flow of Arctic origin, we get snow showers but they also tend to clump together either through troughs etc. For instance just before Christmas 2009, there were a couple occasions, we got clumping of snow showers especially that Tuesday morning that produced heavy snow. It happened during Christmas 2004 evening, the showers massed and then pushed through producing a short period of snow. The showers seem to clump together when they get to the Liverpool Bay area, the Liverpool Bay clumper. It seems to happen generally with NWlies when its active showery. I don't know if you get this clumping effect with easterlies, I know you get streamers such as the Thames one.

The Tyne and Wear/Northumberland/Durham area certainly gets this clumping effect- quite often in an easterly or north-easterly regime we will be hit by a succession of snow showers that merge into a longer spell of snow, and then a drier slot afterwards. Last November (26th/27th in particular) provided two very stark examples in association with troughs, when snow showers out in the North Sea banded together into organised "arcs" of snow as they headed onshore. Due to the lack of really pronounced river banks the region isn't prone to "streamers" like the Wash and Thames ones.

It seems to me that many people underestimate the snowy potential from a good NW/NNW snow streamer

The main issue with NNW'lys concerns people in western Scotland and north-west England, where the Irish Sea coastline runs NNW-SSE so most of the showers stay out at sea, but you are absolutely right in suggesting that the potential for snow showers in Wales and SW England is often seriously underestimated, as Wales "sticks out" somewhat into the Irish Sea.

[Verglas]

here in the middle of the Irish Sea if it's from the NW we get the usual soggy wet snow flakes, if it's easterly we tend to get nice powder snow, like last winter

[Bobby]

Had 10 inches in a few hours from an Irish Sea streamer last December, one of the heaviest snowfalls I can remember. Normally further N and W in Wales is better though.

[Alex95]

I don't know how often it happens with easterlies, at specific locations but what I notice is when we get a NWly flow of Arctic origin, we get snow showers but they also tend to clump together either through troughs etc. For instance just before Christmas 2009, there were a couple occasions, we got clumping of snow showers especially that Tuesday morning that produced heavy snow. It happened during Christmas 2004 evening, the showers massed and then pushed through producing a short period of snow. The showers seem to clump together when they get to the Liverpool Bay area, the Liverpool Bay clumper. It seems to happen generally with NWlies when its active showery. I don't know if you get this clumping effect with easterlies, I know you get streamers such as the Thames one.

New Years Day 2010 was a fantastic example of 'clumping' - we had about 3 hours of continuous snow at one point. It also occurred on the 27th and 29th of November last year, but the latter instance was the thundersnow event which was tied in with a cold front, if I remember correctly. Usually we get 3-5 inches from the North Sea in one day, whereas the Irish Sea rarely delivers more than 2-3 inches. Obviously there are some exceptions to that though, such as December last year!

P.S. April 2008 is a great example of what the North Sea can deliver late in the season, there was about 2 inches within a mile of the coast the day after London got the snow.

Edited December 1, 2011 by alza

[Andy_]

It's a love-hate relationship living so close to the North Sea, although i think the Pro's outweigh the Con's...

Pros

• Heavy Intensity Snow Showers (And Torrential Rain in the Summer)
  
• Connectivity is Excellent in Easterly Airstreams.
  
• Marginality can be removed under heavy showers with evaporative cooling.
  
• Lots of Snow Showers can build up from a large surface area as air crosses a large Sea (significantly wider than the Irish Sea).
  
• Under ideal conditions more snow showers fall nearer to the coast where intensity is highest. (Con for those further west)
  
• Large depths of snow under ideal conditions (1 Foot measured last year in my back garden (not in a drift)).
  
• Air source is often from the European continent and Scandinavia, which when it arrives is often Colder, as it has travelled less distance, than say from Greenland to the Irish Sea, which has to travel thousands of miles from Greenland (moderation is high).
  
• Easterlies tend to be more sustained (Northern Blocking) than the NW-erly topplers that affect the west of Britian, often due to Low Pressure system which will move on within 24-36 Hours.
  

Cons

• Marginal situations are common, in which a closer distance to the sea may see the onshore wind warming temperatures to the wrong side of the marginal. (Rain and Sleet nearer Coasts)
  
• There may be higher falls of snow nearer to coasts under ideal conditions, but being close to the coast means you are more inclined to marginality.
  
• Height is often needed in such marginal conditions, much of Tyneside is fairly high compared to other North Sea coastal areas however.
  
• My area tends not to do so well in North Westerly air streams as we miss most (or all) of the showers.
  
• South easterly airstreams can also be quite tedious as showers are eaten by the NY Moors, and we still get the warming effect from the Sea. (Although this is not always the case when connectivity is high and there are plenty of showers about.
  

Edited December 1, 2011 by Andy163

[Aaron]

Being inland but not too far from the North Sea is best. Places like Durham seem to do well out of snowfall, being so close to the North Sea but far enough inland to not have an ocean breeze.