On Thursday, January 10, 2019 at 9:46:08 AM UTC, Graham Easterling wrote:
On Thursday, January 10, 2019 at 9:09:22 AM UTC, John Hall wrote:
In message
writes
On 29/12/2018 17:28, Keith Harris wrote:
My daughter texted me after reading something in the paper and I
could give a balanced answer as to what effect this may or may not
have on our weather and why, but what I couldn't answer was what
causes this warming to occur.. Doing a quick search and I couldn't
find the answer?

Is there a simple answer to this question?

Keith (Southend)


A BBC met bod vague wittering about SSW yesterday evening. GFS has no
trace of any NH SSW out to 15 days. So is the significance a week or 2
after a SSW, , so a "consequence" of the 06 Jan 2019 one?


I've read that it takes typically 2-3 weeks for the effects of a SSW to
make themselves felt down in the troposphere. So yes.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

Being a bit cynical, I cant' help noticing that every cold spell we get seems to be down to SSW. If it occurs at the same time or just after, then it's the cause. If it occurs 3 weeks after, it's still the cause due to the reason you describe.

I appreciate it takes time to work down to the troposphere, but it is rapidly become the explanation for all our cold spells (makes a change from SST anomalies or El Nino I suppose) without (seemingly) anyone doing a decent job of explaining a the formation SSW event. What explanations there are being at a very general level, as this thread demonstrates. Similar to geography 'O' level (ox-bow lakes are caused by a river meandering) without any explanation of why rivers meander.

Wait for the next fashionable explanation.

Graham
Penzance

Glorious sunny moring after the 1st air frost (-0.1C) of the winter.

You can't expect one weather type at the surface to follow exactly n days/weeks after another event at a different level in the atmosphere Graham. You know there are many other variables and feedbacks in the mix.
Once the polar vortex weakens and splits, as it did over Christmas/New Year, a chain of events will follow which may lead to colder than average winter weather somewhere at the surface. The lag is thought to be about 2 to 3 weeks, a bit vague I agree, and only 60% of Sudden Stratospheric Warmings lead to unusually cold conditions at the surface.
No one variable leads colder than average winter weather.

Having said that take a look at this and get your longjohns ready.
:-()
http://www.wetterzentrale.de/show_di...05&lid=ENS&bw=

Len
Wembury