Winter 07/08 A half time round up

[snowblizzard]

I still think the cold will come back. If we can get a cold summer then we must surely be able to manage a cold winter.

It'll probably take a big natural disaster like a volcano eruption to trigger it though. What did the Mount St Helen's eruption cause in the early 80's??

Yes, cold spells will occur in the future but much less frequently than in the past and for the southern half of the British Isles that has always (in my lifetime) been an infrequent occurence! Despite our latitude, being an island the majority of our winters are likely to be relatively mild & probably damp. I think during the past few years it's the lack of severe cold over central & western Europe that has prevented any severe wintry spells of weather in the UK. Even when we have had the required easterlies, the air mass has not been cold enough and by the time it reaches our shores it's always above freezing at ground level. How many times has snow been forecast but we end up with drizzle or sleet, it's a heart breaking situation for those of us that enjoy extreme cold & snowy conditions.

[david16]

Even more frustrating is that the synoptics of early this month of that eastlery lasted less than 36 hours, as long as a brief northerly and lacked punch other than for the elevated parts. At one time such synoptics would have brought prolonged heavy powder snow for a while even to unelevated levels and then it would have been below freezing for at least a couple of weeks with the chance of more moderate or heavy powder snow, then there was eventually battlegorund between the east and the atlantic with the low pressure systems trying hard to move in, before the atlantic finally win, even then it snowed for a time before it finally turned mild again but we didn't have to wait that long before that next spell of bitterly cold weather from the east. Now in Jan 2008, after the 36 brief hour (in the main toothless) easterly, the atlantic suddenly charged back in, with a true spell of easterly weather (if any eastery spell at all) looking very remote.

Early Jan 2008, it was more like a kitten pawing rather than the undisputed world heavyweight champion showing his class.

That's the depresssing state of affairs it is now. Even the polar maritime we've had here in Scotland the past couple of weeks hasn't delivered to unelevated levels of Scotland the way it did in 1984 e.g..

Edited January 20, 2008 by david16

[Thundery wintry showers]

I think the main differences between the last two weeks, and the 1984 spell, are:

1. SSTs are higher in the Atlantic.

2. The airmass track over the Atlantic has been much longer, reducing the potency of the cold air.

The thing with higher SSTs is that it doesn't just force more modification of the airmass, it also makes point 2) more likely, by having an increased chance of spawning shortwaves in the flow. Of course, we can't blame this individual event on 'global warming', but taking the last 10 years or so, it does seem that zonality tends to be more of the mild form, and that colder zonal setups, while always relatively rare, have become even more rare in recent years. (I'm not just thinking about

I reckon the last time a large majority of Britain was blanketed in a significant cover for upwards of a few days will have been the notorious "wrong type of snow" February 1991 spell, with near approaches occurring in Feb 1994, Jan & Feb 1996 and Dec 2000 (in those cases there was near countrywide snow cover but many areas had just one or two inches).

I think there were definitely numerous such occasions in the 1980s. Although the period 1977-87 was anomalously snowy relative to the early 70s and the 1990s, I don't think it was actually all that unusual- the 1940s and 1950s, for instance, were at least as snowy as that period. Even in terms of temperature, while the Februarys were certainly anomalous, the Decembers and Januarys weren't that cold overall, in the context of the last 100 years.

[Stratos Ferric]

Yes, cold spells will occur in the future but much less frequently than in the past and for the southern half of the British Isles that has always (in my lifetime) been an infrequent occurence! Despite our latitude, being an island the majority of our winters are likely to be relatively mild & probably damp. I think during the past few years it's the lack of severe cold over central & western Europe that has prevented any severe wintry spells of weather in the UK. Even when we have had the required easterlies, the air mass has not been cold enough and by the time it reaches our shores it's always above freezing at ground level. How many times has snow been forecast but we end up with drizzle or sleet, it's a heart breaking situation for those of us that enjoy extreme cold & snowy conditions.

A minor augmentation. Japan is also an island, and significantly further south than the UK, yet is far more snowy. Being an island is important, but more important is our west coast location. We are downwind of a warm ocean; Japan is downwind of a cold continental interior.

Hey SF--

Do you think the recent Colder weather at the start of March cold be down to a slightly later thermal lag in the oceans & net effect on the jet because of the high Summer SST's ?

S

It's a good question Steve, and I have pondered it previously. I think the answer is that it MIGHT be the case, though I struggle to see logically why it should be so, with one caveat. The polar ice in recent yers has reached its nadir slightly later than norm, and has then been slower reforming. This means there's more feedback at high latitudes in early autumn and I guess it's just about possible that this somehow resonates through winter.

The hemispheric minimum is a trade off between increasing incoming radiation, and outgoing radiation. The former isn't changing at source, but I suspect it could be possible, particularly if snowc over is arriving later, that reflection peaks a bit later, and that the net effect is that the minimum balance is higher than it used to be (consistent with warmer temperatures), but also, related to this 2-3 weeks later. That would pull us well into early-mid Feb, and given that there's some inertia in the atmosphere, the low energy season for the jet would be expected to be sometime after this.

So, I think a case can be made, but I think we'd need to do a lot more reseaarch and testing. The bottom line for the passing reader is that for all January is disappointing at present, February and early March are different considerations. It doesn't follow that they will be cooler, but nor does another mild January mean that they can't be.

[Peter Henderson]

Here's an interesting longish range forcast from the Metoffice (14 day outlook)

http://www.metoffice.gov.uk/weather/uk/ni/...st_alltext.html

UK Outlook for Sunday 27 Jan 2008 to Tuesday 5 Feb 2008:

Many parts should be fine at first with some sunny spells, as high pressure is expected to be centered to the south of the UK. Northern and some western parts will be more unsettled though with cloud and outbreaks of rain as well as some strong winds, perhaps gales over northwest Scotland. It will be mild generally. However, some colder air is expected to spread across the UK from next Tuesday onwards, and this will bring showers or spells of rain, with wintry falls over hills, and perhaps to low levels in the north. It is likely to be windy at times too. The driest and sunniest conditions are most likely in the south and east. Temperatures will be near normal to rather cold after the mild start.

Updated: 1158 on Tue 22 Jan 2008

That looks very promising, especially for Northern Ireland, Scotland, and Northern England. It'll be interesting to see if it's a prolonged cold spell (rather than one day) and what transpires over the next few days.