03jtrickey

The roads don't look very well gritted! Still coming down now and it looks like an intense area is heading towards us...

Moderately heavy wet snow in Oxford...the heaviest that I've seen so far this year.

Moderate/heavy snow in Oxford now - the most intense I've seen so far this year.

Snow component increasing...but there's still light rain mixed in. Not especially heavy yet.

It's currently sleeting in Oxford.

I remember this event well...I was a chorister at Gloucester Cathedral, and we had just begun our evening rehearsal when the choirmaster told us that the heavy rain that had initially been falling had started to turn to sleet, and soon afterwards there were blizzard-like conditions outside. Frustratingly, I missed seeing most of the snow falling due to being indoors singing the service, which was a shame. Later, outside the cathedral, paved surfaces were completely glazed with sheet ice where the rain had frozen, beneath 1-2 inches of fresh snow. The snow was slightly deeper at home in Cheltenham. It was probably one of the best snow events from my somewhat snow-starved childhood.

Good point - I will add that to my list of things to test out. Thanks As I went to test that suggestion out I noticed a mistake in my AO/NAO/CET correlations (I'll blame it on copying formulas in Excel late at night). The updated values are as follows and affect the correlations between the CET and AO 60 days after displacement: Using these corrected values, the correlation between CET and AO increases for both displacements and split vortex events after SSW onset, and in both cases the AO is more strongly correlated with CET than the NAO after onset. Sorry about that.

Just to add a caveat to the above mean CET anomaly values and emphasise the variability in the data...here are graphs for displacements and splits with the upper and lower quartiles of the CET anomalies plotted for each day. The interquartile range has a tendency to increase every time there is is a strongly negative CET anomaly. This might indicate that the mean is being forced down at these points by just a few of the events, so while there could be strongly negative values at these points, it is by no means a certainty.

I have been doing some analysis today of the relationships between Central England Temperature (CET), NAO and AO in the 60 days before and after vortex displacements and splits. Here are some results: Some initial comments: Mean CET anomalies are relatively lower in days 60-30 prior to splits compared to displacements. There is a large peak in the CET anomaly prior to both displacement and split vortex events, but for displacement events this occurs 10 days earlier and is followed ~10 days later by a negative anomaly just before SSW onset (10hPa wind reversal). Both displacements and splits are, in the mean, followed by swings between positive and negative CET anomalies. The displacement event mean CET anomalies are almost the inverse of those for the split vortex events from ~days -5 to day 25 (i.e. the alternating pattern is shifted slightly earlier for displacements), but both splits and displacements have their strongest negative CET anomaly around day 40. I'm not sure what the exact onset of the previous SSW was (anyone?) but first few days of Jan +40 days would take us up to ~10th+ of February which would tie in well with the expectations of others on this forum. With regard to the AO and NAO, people have been commenting recently that the NAO in particular hasn't correlated well with the cold we have been getting. I did some simple r^2 correlation calculations for mean values of NAO against AO, CET against NAO and CET against AO in the periods before and after both types of SSW. In the case of vortex displacements, the daily AO values appear to become much less correlated with the NAO after displacement, and neither index is strongly correlated with CET temperature. In the case of vortex splits, AO also becomes less correlated with NAO after displacement, but the AO correlates quite a lot more highly with CET than the NAO does. Could this suggest that the AO is more important for post-split-SSW cold? (NB the correlations might increase if they were taken over longer than daily time periods...) Investigating the cause of these patterns would be interesting & I have yet to think about how they may relate to the precursors identified by Martius/Cohen and Jones. I will also probably do some more detailed analysis at some stage, to look at individual years, test correlations for different time periods, and look at the relative frequency of different anomaly values etc. However I would be interested to hear your thoughts (and please let me know if you see anything that is obviously erroneous) Methods: Dates of SSWs analysed are from Cohen and Jones (2012) and only events with no overlap between the onset +/-60 day periods have been included. The dates used are therefore as follows: Displacements: 30/11/1958, 16/01/1960, 08/12/1965, 02/01/1970, 29/02/1980, 04/12/1981, 24/02/1984, 23/01/1987, 16/12/2000, 02/01/2002, 07/01/2004, 24/02/2007, 22/02/2008 Splits: 30/01/1958, 23/03/1965, 24/02/1966, 08/01/1968, 02/02/1973, 22/02/1979, 02/01/1985, 22/02/1989, 18/01/2003, 21/01/2006, 24/01/2009, 09/02/2010 The Daily CET anomalies were calculated relative to the 11-point binomially smoothed climate normals for 1961-1990 from Parker (2009) "Anomalies of Central England Temperature Classified by Air Source". NAO/AO data is from the NOAA website (ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii and ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.nao.index.b500101.current.ascii).

Are these accessible online? If so, where can I find these charts? Thank you.

I can't find reference to it using a forum search, although it may well have been mentioned.

I've got to write three extended essays for my Geography degree...and I can write about pretty much anything. One of my modules was on seasonal prediction so I'm going to attempt something along the lines of "Will improved knowledge of stratosphere-troposphere interactions increase the skill of seasonal forecasts for UK winters?". I've really enjoyed following the stratosphere thread this winter (many thanks to chionomaniac & GP) so I thought I'd do something that's topical and that I'm interested in! I've just come across a very recent paper published online on 13 January 2013 which may be of interest. http://www.nature.co...l/ngeo1698.html "Enhanced seasonal forecast skill following stratospheric sudden warmings Advances in seasonal forecasting have brought widespread socio-economic benefits. However, seasonal forecast skill in the extratropics is relatively modest1, prompting the seasonal forecasting community to search for additional sources of predictability2, 3. For over a decade it has been suggested that knowledge of the state of the stratosphere can act as a source of enhanced seasonal predictability; long-lived circulation anomalies in the lower stratosphere that follow stratospheric sudden warmings are associated with circulation anomalies in the troposphere that can last up to two months4, 5. Here, we show by performing retrospective ensemble model forecasts that such enhanced predictability can be realized in a dynamical seasonal forecast system with a good representation of the stratosphere. When initialized at the onset date of stratospheric sudden warmings, the model forecasts faithfully reproduce the observed mean tropospheric conditions in the months following the stratospheric sudden warmings. Compared with an equivalent set of forecasts that are not initialized during stratospheric sudden warmings, we document enhanced forecast skill for atmospheric circulation patterns, surface temperatures over northern Russia and eastern Canada and North Atlantic precipitation. We suggest that seasonal forecast systems initialized during stratospheric sudden warmings are likely to yield significantly greater forecast skill in some regions."

Do the Met Office think the snow might extend as far east as Oxford? (I'd be very grateful for a reply but understand if you are not able to. I have really enjoyed following your posts so far this winter.)

That's total precipitation in millimetres predicted to fall between now and 6pm on Tuesday. Roughly, 1mm = 1cm of snow.

Latest NAE is very interesting: 48hr accumulations: If it plays out like that I'll be wishing I was home in Cheltenham rather than in Oxford!

Latest NAE output for Thursday looks interesting and a big change from the 06Z:

I cycled out to Wales on Thursday and stayed in the hills just west of Knighton. Yesterday morning there were some heavy snow showers and I was caught in one up on Beacon Hill (547m). Here are some pictures:

Thank you Was glad to witness a thunderstorm on the trip, especially when I had such a good view!

Last night I was lucky enough to witness a spectacular light show from my hotel room in Shenzhen, China: http://www.flickr.co...ckey/7718132034

Impressive video of a tornado near Sleaford. Apologies if this has already been posted: http://www.sleafordstandard.co.uk/news/local/breaking-news-tornado-hits-sleaford-area-video-1-4001325

Where was that?

Absolutely torrential rain and frequent thunder in Oxford for about 10 mins. Some lightning, but no forks visible. Quietening down now - a welcome break from essay-writing! Oh sorry, I'm currently in Oxford

Thunder rumbling away to SW

Wow!

Looks like Kidlington got quite a bit of action - only a few miles north of here. https://www.facebook.com/Kidlington