Summer 2021 General Discussion

I think the Atlantic Multidecadal Oscillation is the prime driver of this "rainy season" of Augusts in recent years. Like it greatly affects European temperatures, it also seems to increase the occurrence of so-called Atmospheric Rivers, which align over Ireland around August as the jet starts its annual southerly retreat.

The polar vortex starts to shut down in April, not fire up.

37.5mm in Sligo now for the rainwave

Re bad August's....August 2020 was good in Sligo for 10 days.

10.5mm in Finner on latest report

yep, they'll be towns badly affected after this

Definitely drew the short straw up north west. One or two showers during the night in west cork and blue skies this morning (with grey clouds to the west of me!). Wind calmed down and a lovely morning all round

I see weather models were hinting at an improvement in weather towards the end of next week have all backtracked. More of the same in store for the next 10 days.

The good weather is always 10 days away according to the weather modelling.

Kids will be back at school before we know it. I think this is pretty much the pattern now into September.

Moderate rain for the past two hours in North Kildare with some intervals of heavy rain too. Looks like this main area will be clearing me soon but there may well be further showers later in the afternoon.

The summer ‘monsoon’ or Atlantic onslaught which typically happens in July and August is due to the contrast between the continent and the oceans, nothing to do with the polar vortex. The stratospheric polar vortex does not reverse back to westerly until late August every year - some years it’s earlier or takes longer on the exact date but the range of deviations is very small so it doesn’t matter. It does not even come into play until late autumn for significant effects to be felt on the surface.

Most Augusts of modern times - as well as summer months - have been characterised by high latitude blocking with the summer NAO index consistently on the negative side. The summer season is more prone to negativity of the NAO naturally as compared to winter due to a weaker jet stream with no stratospheric polar vortex to drive intense westerlies across the hemisphere. However, I have spoken about numerous times before that this prolonged period of negative summer NAO that suddenly became apparent in 2007 is very unusual.

Equally, the run of ‘good’ or warm Augusts or seemingly backloaded summers through the 1990s and into the 2000s was also unusual. Traditionally, August is our wettest summer month for 2 reasons - it was/is often a humid and volatile month prone to heavy downpours - and due to the more active jet stream. It was the wettest month of the year on average at Phoenix Park for a certain period which I can’t remember off the top of my head as I’m currently out. It is still at the top end of wettest months for parts of the east but October to December have beaten it in modern averages.

Late spring is also characterised by high latitude blocking a lot of the time but with a weaker jet stream as the contrast between the oceans and the continent is smaller, so we don’t seemingly get as much of an Atlantic onslaught. The February to July period of the year is the driest portion of the year for this and other reasons.

Very breezy in East Cork this afternoon

Not far from you near Rathdrum and it's been raining all day. Nothing major mind but it has been overcast and raining softly here all afternoon.

I think the main reason that August often turns wet is because it is, on average, the wettest of all of the summer months. Just looking at the LTA's for Athenry for example, August is wetter, on average, than Feb, Mar, Apr, May, Jun, Jul, Sep, and ties almost, save a few mm, with January!

Rain in August or any summer month doesn't bother me in the least though. You can enjoy the outdoors every bit as much in warm summer rain as you can in the sunshine, and as this old saying goes..

Then there is the wind to dry the ground.