Sea breeze in Plymouth

[Len W]

Quite early in the year for a sea breeze but we have had sunshine all day with a weak gradient wind.

[Graham Easterling]

Just enough of a NNW gradient wind to stop the sea breeze in Penzance, though the effect meant it fell near calm early/mid afternoon. With prolonged sunshine from around 11:30 the temperature to rose to 13.2C, and with the sunshine it felt pleasant enough. 

Very hazy still, despite the wind now being NW. The Mount was only just visible from Penzance. 

At 16:00 looking ENE from the Jubilee Pool Cafe the sky looks blue.

But look SW

The headland, Penlee point, is only just >2 miles in a straight line. The people are all in the geothermally heated section for some reason. Air temperature at the time 12 - 12.5C in an offshore F2-3 breeze.

Graham

Penzance 

[jack.h...@gmail.com]

I studied sea breezes quite a lot in my gliding days especially when giving forecasts as weatherjack.

Conditions required for a sea breeze are quite specific (I've forgotten most of them now).   Factors such as depth of convection between 5 and 10,00 feet, offshore wind < 10 knots plus others that I really have forgotten.  But it is the land/sea temperature contrast  - and it need be only 1 degree - that is significant, not the actual warmth. 

To draw a parallel, yesterday with snow on the nearby fields, at one point I saw a "heat haze" over the brow of a hill.  "Heat" at a mere +2C was a misnomer but the road surface was presumably at a higher temperature than the very cold air.

So 'relative', not absolute.

Jack

[Graham Easterling]

It's important to remember it's the temperature of the land surface, not that read in a Stevenson screen, which is important. Hence you can get a sea breeze in spring when the air temperature is no higher than the SST. The sun is strong enough to raise the temperature of bare fields significantly. Especially true of the light sandy SSE facing fields behind Penzance.

The physical geography is very important in the sea breeze strength. Marazion is prone to very strong sea breezes due to being backed by a marsh. F4 sea breezes are that unusual at Marazion, which is why it's a windsurfing centre. 

The sea breezes here in west Cornwall are very interesting, as the NW facing 'north' coast has the strongest heating later in the day than the south coast. So, assuming near calm conditions, a decent sea breeze at Marazion will set in early. Later, as the sun goes around, the north coast sea breeze kicks in. This typically proceeds right through Hayle Saltings & Marazion marsh (It's only 4 miles coast to coast) to replace the sea breeze at Marazion. Bemused holidaymakers suddenly find them on the wrong side of their wind breaks!

The north coast sea breeze, often reaches Penzance around 16:00, with a sudden, sharp fall in temperature. The sudden onset of the north coast sea breeze can result in effects like this

An extreme example I've posted before! 

I love the fact that in sea fog patches you can go from visibility of <50 metres to >30 miles in a minute or so.

Graham

Penzance

[Graham Easterling]

"F4 sea breezes are that unusual at Marazion"

should read

"F4 sea breezes are NOT that unusual at Marazion"

Graham

[Len W]

You may of noticed from the chart that Plymouth was not the only place with a sea breeze on the south coast.

There was one on the Isle of Portland and at Shoreham.

As Graham mentions it is the land temperature which is important. Usually places with sun facing slopes are the most likely to have a sea breeze.

The south facing slopes of Dartmoor are effective in Plymouth's case.

Plymouth's air temperature was 14C and SST was 10C.

For Shoreham the South Downs would have helped. Not sure about Isle of Portland though, perhaps the hills and soil type of Dorset played a role.

Len

Wembury