All change ahead. Equinoctials on the way.

[Len W]

Could this be Storm Evert?

Arriving on Wed/Thurs

Len

[Julian Mayes]

Hi Len, is there actually any evidence for the frequency of gales or strong winds peaking around either equinox?    I can understand people noticing an increase at the autumn eq. as we are going into the season of autumnal and winter gales.  Spring is another matter - as we proceed to the annual minimum of the W type and pressure gradients in May. 

Just wondering.  

Julian  

[Len W]

Evening Julian,

Not sure there is much proof for an increase in gales per se. And we are not talking about at the equinox, more so as we approach the equinox , windiness increases across the baroclinic zone.

Len

[Graham Easterling]

In Penzance   (which is of course very sheltered for west Cornwall)  gale frequency is simply associated with the coldest part of the year, the equinox has no affect. Peak just after the winter solstice.  In fact in Penzance the average number of gales over the last 30 years

So 

January 1.8

February 1.3

March 0.7

April 0.4

May & June >0 to <0.1

July & August 0

September >0 to <0.1

October 0.7

November 1.1

December 1.5

March has seen some severe gales, but not the frequency of November-February, just part of the downward trend into Summer. 

It's a bit like the off used phrase, 'cloud breaking to the lee of high ground' which suggests these sheltered coasts are sunnier, not true in Devon & Cornwall. The sunniest spots in Devon & Cornwall being the west facing exposed coasts of the Lizard, the Lands End peninsula & the north coast, as the MetO sunshine records & maps show.

Graham

Penzance

[Graham Easterling]

Just checked days with gusts>60mph at my site, there have been 27 (around 1 per year). All in October to February, apart from 1 in March, and that was a real classic.

Gust of 73mph, but the worst sea conditions in living memory, according to many who are in a good position to know.

Worth a look, click images for larger version

http://www.sennen-cove.com/10march08.htm

There was no weather warning, I did query why, I won't bore you with the reply.

Graham

Penzance

[Julian Mayes]

Len,  I'm afraid I don't follow what you mean about as we approach the equinox , windiness increases across the baroclinic zone.  You are suggesting that specific date does have some effect.  

By the way, the main who set this place up, Xmetman, Bruce Messer, still lurks here and y'day he sent me this link to where he has discussed this topic....    

https://xmetman.com/equinoctial-gales-fact-or-fiction/

He confirms Graham's observation that we just have a strong seasonal cycle in strong winds and no equinoctial effect.   However, the graphs he shows (Lamb classification gale index) do show a dip in mean air pressure at the end of March which I'd been unaware of (unrelated to strong winds or equinoxes). 

Julian  

[Len]

The weather is highly variable around the vernal equinox for good dynamical reasons.

The break up of the stratospheric polar vortex in the spring is called the final warming.

Planetary wave activity is upset as the atmosphere in mid lats adjusts to more solar input.

There is a perception of windiness, when everyone is looking forward to the more settled weather and less windiness of summer.

You have to wait until May for the reality of that.

So in some ways the strong winds around the vernal equinox are the last hurrah of winter and stick in peoples minds because they are looking forward to  more pleasant weather.

Wind not up to gale force here yet but

an equinoctial gale is forecast to arrive on cue tonight.

😉 😉 😉

Len

Wembury

[Graham Easterling]

Yes, it's a shame Bruce no longer posts here.

If you read this Bruce, please come back!

Graham

Penzance

[Smartie]

A dataset of max recorded gusts from 10 Irish stations ( at least 10-year continuous for each station)   (European Climate Assessment & Dataset plotted with KNMI Data Explorer) going back to 1945. There appears to be an increase in 'storminess' during June and a tendency for an increase beginning in October and possibly as early as August

The most striking thing about the data is the multi-decadal trend with a decline in 'storminess' since the 1990s (remarked on previously and elsewhere)

A 26-year history of gusts at the K13 buoy in the North Sea suggests March is still a winter month in that area (in terms of 'storminess')

[Julian Mayes]

Thanks for this, David - yes, the time series is interesting as I thought there were some conflicting data-sets around.  Is the graph published or will it be?  

  The low values in 1960, 1987 and 2010 are each in years with a low 'westerly' score over the UK so fewer depressions deepening over the NE Atlantic and then passing over UK - 1960 being the very wet, cyclonic year with a southward deflected storm track. Maybe the latter factor discouraged really severe deepening.  I remember compiling mean annual wind speeds for London some years ago and finding that 1987 was the least windy year within what was probably the 1961-90 period. Of course, no-one believed me!  

Julian  

[Graham Easterling]

Thanks for all that

The most striking thing about the data is the multi-decadal trend with a decline in 'storminess' since the 1990s (remarked on previously and elsewhere)

I've probably mentioned the  fairly dramatic decrease in gale frequency in Cornwall since the 1990s too often already! Looking back through the records 1990s were not unique. Lambs 'The English climate shows a gale frequency over the tip of Cornwall of 20-30 hales per annum (1918/1937). Far less than this century so far, & much more typical of the '90s.

I rather suspect depressions have got stuck in mid Atlantic much more of late, as based on frequent checks on Sevenstones (off Lands End) I'm not sure there has been much change in the frequency of large swells (>20'). I haven't recorded details, in retrospect I would have, so if there is any data available from Sevenstones or any of the buoys in the SW approaches which may provide evidence of this, I'd appreciate it. From a surfing perspective there have been a number of occasions with huge surfable waves on the north Cornwall coast, under light southerly winds & a deep near stationary low mid/west Atlantic in recent years.

I think storminess continues later into Spring in the North Sea than on the Atlantic coast, after all the SST is very low and depression have a habit of diving down the North Sea (Spring northerlies.) SST currently 5-6C of East Anglia, 10C at Scilly.

Graham

Penzance

[Smartie]

The KNMI explorer doesn't have useful buoy data and/or all the needed reanalysis variables but here is significant swell height and swell+wave height  from the coupled ERA5 Reanalysis for a 5deg box centred at  50N,-7.5E for the years 1979-present ( 6hr/day data, 1-year max).

I've no idea how much relation this might bear to reality.

(Data:  Copernicus Climate Service processed with CDO & Panoply)