Great post as ever SC.
One of the things I love about the weather in this country is just how unpredictable it is none of us saw how cool and wet this June would be neither did any of the Pros. A cet under 14c looks likely now maybe even under 13c. And also perhaps a record breakingly wet month as well.
Thanks - sadly I can't enjoy the unpredictability like I used to now that I've become one of those 'Pros'. One of the worst things about being involved in longer-range guidance is knowing so much about what could have been, when the reality is one of the least desirable outcomes.
During the final week of May, the following signals were at hand for June:
- Warm opening couple of days, then near-average remainder of week (for day + night combined)
- Slow-moving low near or over the UK for at least first half of 2nd week of month. Origin SE of the UK so movement through France more likely than across UK, with warm but showery conditions affecting much of England and Wales.
- Arctic blocking reducing for 2nd half of month, and NAO moving from negative to positive. Signs of slow-moving ridges across NW Europe; predominantly warm pattern for the UK. Some thundery interludes likely.
The way that low moved last week was truly exceptional. Historically, our poorest runs of June weather have come from the Atlantic, not mainland Europe. Even more extraordinary was how the low positioned such that it was able to draw cool maritime air off the Atlantic to mix into the very warm from Europe before any of it reached the UK - except briefly the far SE on the Tuesday. The more typical outcome would likely have left the CET somewhere in the 14s as of mid-month.
Now, looking forward, we're seeing the long-anticipated waning of Arctic blocking looking less and less convincing, and there's signs that the NAO will be equally 'disobedient'; the ensembles are now favouring a continued negative state overall.
A big factor behind the Arctic blocking and NAO issues is some tropical thunderstorm activity in the western Indian Ocean. This was expected to be outgunned by activity moving into the Pacific from the eastern Indian Ocean (i.e. the MJO) but instead it's of similar intensity, and a few days ago, it even gave rise to a rare June tropical cyclone that tracked close to the west of India.
Such Indian Ocean sourced interference has been witnessed a couple of other times in the past couple of years, derailing the August heat and December cold last year.
Unfortunately, long-range modelling is currently very unreliable for tropical thunderstorm patterns, with even short-range predictions for just 3-5 days ahead often significantly wide of the mark. So there's no way to reliably anticipate when there's going to be interference that begins nearly a fortnight into month, like it has in June 2019.
Last week's unusual low behaviour pretty much ruled out a CET in the high 15s or above.
The failed positive NAO switch for 2nd half of June now has now stacked the odds against a CET higher than the mid-14s.
Any bets on a scorching July?