summer blizzard

30th October 2000 produced proper frontal snow on the back edge which settled in Yorkshire. 2012 saw a light overnight shower. Others have claimed snow in 2008 and 2010 though nothing here i think.

Pacific wave now forecast to be a little stronger than previously forecast meaning that the wave progresses further east through October. This may promote blocking to the north/east as we head towards the final third (hopefully we have a Polar Block to keep some retrogression). Also note that the Indian Ocean is now dead.

27SEP2023: Nino3: 2.0 , Nino3.4: 1.5 , Nino4: 1.1 ONI for September increased to +1.6. JAS should come in around +1.3.

Rolling CET for October-September rose to 10.98C. Has wiped out all progress since the May update.

Models should take the eruption into account since they will record the water vapour level even if they don't know where it came from.

The interesting question after the horrific heatwave to come is what happens next, it looks like a high in the Atlantic will have influence from around day 8.. Disagreement on the pacing leads to quite different outcomes.

Regarding May, i think your overestimating what is possible. The old record at 32C does certainly suggest that 33C is possible however you have to remember that during most April and May's, the European continent is fairly cool still and as such it is not as simple as replicating a summer pattern because that same pattern is not likely to produce the scale of uppers required. It's why most of our heatwaves with SE winds are not overly humid until July normally. We could potentially plume with more of a SW element of course but then you move over cooler seas and generate more cloud.

Just playing around to look forward and the signal i see is for a milder than average Oct-Nov, Average Dec and Feb, Cold January and March (need 3.0 and 4.9 for the coldest since 2010 and 2013 respectively). SSW likely between Jan 2nd and Feb 9th. My pre-winter excitement level has risen a notch.

20SEP2023: Nino3: 2.1 , Nino3.4: 1.7 , Nino4: 1.2

The mid-May to mid-June spell produced no rainfall here in 29 days, that is something not seen since at least summer 1995 here. So it was exceptional, it was just too early to take advantage of hot uppers. But yeah, mid-June to August was just cyclonic, damp and often humid.

Yes, it's notable that while the Nino has not been strong enough to cull the season, the US trough is basically chucking every system out to sea (apparently nothing further east than 80W), hence the disruption to our pattern.

Still quite a split between dynamic and statistical models. Since the forecast is for a peak in NDJ most likely it's worth saying that we probably only have 2 or 3 waves to cross the Pacific at whatever strength they can get. So far the big ones were in March, May and August. Cold pool is present though not especially strong with a somewhat more traditional colder west-warmer east split for a Nino. No significant convection around currently though in the forecast, hence the somewhat stall in ENSO development.

GFS and GEM try build pressure to a greater degree than the morning Euro but largely fail in the end. UKMO backs the morning Euro. Autumn has arrived.

We were solid from the 29th Nov-18th Dec so that's a solid two thirds.

Euro has backed the other models from yesterday morning this morning in not allowing the ridge to last more than 2 days before imposing zonality. GFS agrees and has kept faith. Both the UKMO and GEM despite UKMO highlighting the pattern first have cowed to pressure and back a more ridgy solution. So while this would have been a great victory for the UKMO had it held true (and it wins in spirit), i think it could be a GFS victory upcoming (of course, it does tend to handle zonal patterns and secondary lows better than other weather typres).

11.1C, 137mm

August MEI rose to +0.4, the highest August value since 2015 but a record departure between ONI and MEI values. August QBO fell to -0.2, the lowest August value since 2021. August PDO rose to -2.4, the lowest August value since 2012 as we continue to plod along at near record seasonal/annual pace. August AO fell to -0.6, the lowest August value since 2019.

JJA ONI came in at +1.1. To update our list and ranking. Our updated list for AMJ. 1957: +1.3 1972: +1.1 1976: +0.2 1986: +0.2 2002: +0.8 2009: +0.5 2014: 0.0 2018: 0.1 2023: +1.1 We've moved to joint second (this is where 2014 went off the boil for a bit as well). To update on our ENSO trades index, August finally coupled and came in at -0.6 (though September looks like it might struggle to maintain this).. https://www.cpc.ncep.noaa.gov/data/indices/cpac850 To compare to our primary analogue list since 1979 (standardised): 1986: -0.8 2002: -0.2 2009: -0.5 2014: -0.8 2018: -0.6 2023: -0.6 Remember that our analysis last month showed a corellation between how early the event coupled and eventual strength so this may be another sign that the models are OTT (i still lean in the +1.3 to +1.7 range).

30AUG2023: Nino3: 2.3 , Nino3.4: 1.6 , Nino4: 1.1 06SEP2023: Nino3: 2.2 , Nino3.4: 1.6 , Nino4: 1.1 13SEP2023: Nino3: 2.2 , Nino3.4: 1.6 , Nino4: 1.1 August ONI was +1.3. JJA ONI was +1.1.

The Euro highlights potential retrogression. GEM keeps us on the warm train. GFS6z actually agrees more with the UKMO regarding Ex-Nigel but does pump the ridge with another low behind. GFS0z was more like the GEM0z. So the Euro is currently the outlier with some form of mild zonality favoured and a SW/SE split.

I don't get too excited during October with regards to blocking (though it may feel seasonal) however if we look at -1 AO October values then we get.. 1960 1966 1968 1974 1979 1981 2002 2006 2009 2012 2014 2016 (Note that they are basically all grouped into two which may imply a multi-decadal cycle) Regarding the following winters though (Jan-March) 1960 - Followed by -NN 1966 - Followed by N++ 1968 - Followed by --- 1974 - Followed by +NN 1979 - Followed by -N- 1981 - Followed by NN+ 2002 - Followed by NNN 2006 - Followed by +-+ 2009 - Followed by --N 2012 - Followed by N-- 2014 - Followed by +++ 2016 - Followed by NN+ N - Neutral January - 33% were negative AO, 41% were neutral AO, 25% were positive AO February - 33% were negative AO, 50% were neutral AO, 16% were positive AO March - 25% were negative AO, 33% were neutral AO, 41% chance positive AO So a neutral AO is still favoured during Jan-Feb but more chance of negative than positive. A positive AO is favoured during March.

Summers 2010, 2014, 2015, 2019, 2020 and 2022 were all -AO albeit only 2011, 2015 and 2019 produced a more negative AO month since 2009 than August 2023.

Euro looks very unsettled and probably not too warm.

There is. Basically it’s atmospheric wavelengths. When forcing is in the ordinary Nino zones and coupled it produces areas of subsidence or enhanced convection, normally producing a stronger convective response in the West Indian Ocean. What S is alluding to is that when forcing is biased to the west like 09 then it can in turn push those areas of convection and subsidence further west. In that case the Indian Ocean received minimal forcing because it got pushed to Africa. 2019 was different in that the IOD was the driver and not the follower.

Quite often they'll back the Euro ensemble mean so if the primary cluster is still not backing the solution they'll restrain.