Relativistic

Also worth mentioning the adjustments made to account for urban warming. This from the HadCET home page: "Since 1974 the data have been adjusted to allow for urban warming: currently a correction of -0.2 °C is applied to mean temperatures." Met Office Hadley Centre observations datasets WWW.METOFFICE.GOV.UK

10.4C and 55mm.

November 2016 was 5.6C which is 1.0C below the 1961-90 average. Another frosty one that.

Yes, it really was very extreme in this respect. Only one November has been warmer (1994).

Same can be said for December 2015: similar halves have happened before it, but never one after another. I think the first halves of the Decembers of 1898 and 2000 were above 9.0C. In terms of standard deviations from the mean it's not actually the most extreme month on the CET record (it is however notable because the distribution of Decembers is skewed towards cold). II looked into this a while back but can't remember which month was the winner by that measure; will try to dig up the post if anyone's interested. Edit: This post and the one below it are the ones I was referring to. June 1846 was furthest from the mean in terms of standard deviations.

My limited understanding is that stratospheric ozone concentrations do affect the likelihood of SSWs. When ultraviolet radiation is incident upon an ozone molecule an oxygen free radical breaks away, leaving behind a regular oxygen molecule. That oxygen free radical will scatter off other molecules, dissipating heat in the process, before recombining with another oxygen molecule to reform a molecule of ozone. Thus, the more ozone present, the greater the degree of stratospheric heating, ergo a weaker polar vortex.

Ten days later and the provisional figure is 1.6C, so a mean of 4.6C for the remaining four days would take us to 2.0C. Current forecasts suggest that this is unlikely to happen now, and that April 2021 could join one of only four other Aprils to record a sub-2C minimum CET -- the first to do so in 99 years. Precisely where we end up in the rankings will depend on the magnitude of the end-of-month correction.

The last time a month outside of the November-March period finished 1C below the 1961-90 mean was in October 2012 (September 2015 and August 2014 came very close). We could be looking to end that run.

With the provisional figure sitting at 5.6C then a modest downward correction of 0.2C at month's end would see us tie 1978 as the third-coldest first half since 1970. A larger downward correction would give us outright third, with zero chance of beating 1970 and 1986. The mean minimum CET is worth keeping an eye on. To the 16th the provisional figure is 1.2C, which becomes 1.0C with our modest correction. If the remaining 14 days averaged a little over 3.0C we'd still end up fifth-coldest on record; 4.0C lands us at around 10th and 5.0C around 20th. For context, the coldest is 1.4C from 1917. There's still a way to go yet, but it's nice to be able to talk about what might be a notably cold month.

I'm careful with my words for occasions such as this Still a way to go yet though.

Another supremely sunny day here in Edinburgh. Really enjoying this current spell.

Recent first halves (1st-15th) of April to beat are: 2013: 5.8C 2008: 6.7C 2000: 5.6C 1998: 6.6C 1996: 6.5C 1994: 5.8C 1990: 6.7C 1989: 6.5C 1986: 4.4C 1984: 5.6C 1983: 5.6C 1978: 5.4C 1977: 6.2C 1975: 5.6C 1973: 6.3C 1970: 4.7C We stand a chance of beating all those since 1986, although that's far from nailed on. A slim possibility we end up third coldest since 1970.

As per above, Greenland is a plateau and so the pressure at sea level is extrapolated. So when people talk about 1080mb Greenland highs (sometimes in the model thread) they're talking nonsense.

I remember falling snow and hard frosts during the first week of April 2013 (I was in Norfolk at the time). I think some forget just how chilly it was because the week that preceded it was firmly in the exceptional category. CET values for the 1st-7th April: 1st: 1.9°C 2nd: 2.7°C 3rd: 2.7°C 4th: 2.8°C 5th: 4.0°C 6th: 3.8°C 7th: 3.4°C That's a mean of 3.0°C for the opening week. The cold from the previous month really did linger.

I agree; I'm a weather enthusiast because I like interesting weather. Spring days can be lovely at this time of year, but a potent, late-season Arctic blast will pique my interest far more, just as the early-season warmth this week did. This topsy-turvy stuff is great. Won't happen, but if we had snow showers (whether or not they settle) from brisk northerlies for the first fortnight of April, I'd be very happy.

The min was corrected down to 8.3°C while the max came in at 20.2°C. The 15°C mark really is very difficult to achieve.

What were 850s like in '08? Can't view the Meteociel charts. Would be interesting to compare current model output to past April synoptics.

7.9C and 70mm.

We have a provisional minimum of 9.1C, so would need a maximum of 20.9C to give a provisional 15.0C mean. Will be close.

Indeed, there are a few 21C readings in East Anglia at present.

Oh dear, currently cloudy over much of the south-east. That may well have destroyed our chances.

I think the March temperature record is going to fall.

And it's mad how so many people assume they know -- or are at least very confident of -- the outcome of a month when there are 14+ days left. Not singling anyone out here, as such comments have been made on these threads for years.

Scotland set a new record of 23.6C (in Aboyne). I think that was the highest.

April 2012 was very memorable for its record-breaking rainfall. I remember the rivers in Chelmsford bursting their banks. I also remember the extremely changeable weather, with sunshine, rain and hail rapidly alternating under some of the most breathtaking convective cloudscapes I've witnessed in the UK. Also the occasional bout of thunder and lightning. It was also a cool month, with many places recording lying snow. April 2016 I remember less about, which suggests it was largely uneventful. The one thing I do remember, though, was the wintry final week, where I witnessed (in my then location of Selly Oak) falling snow on a number of days up to and including the final day of the month. One of those days saw falling snow for a number of hours, but it left slush only; the nearby Lickey hills and the surrounding area managed a covering.