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Old April 21st 19, 08:31 AM posted to uk.sci.weather
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Default Penzance - Rubbish Maximum Temperature Forecast

Current MetO maximum temperature forecast for Penzance is 17C
https://www.metoffice.gov.uk/weather...ate=2019-04-21

Given that it was 17C at Camborne, Newquay & Penzance by 09:00, and Cornwall is the only bit currently coloured orange (18C) on the XCWeather temperature chart, I think they've undercooked it. Now 18C at Lands End (warmer than yesterday when it eventually reached 22.3C) and at nearby Bosullow. People are going to think it feels very warm for 17C.

Yesterday, they finally upped the forecast max to 22C late afternoon, just as it was cooling down. The thing is shouldn't a forecast precede the event?

Graham
Penzance


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Old April 21st 19, 09:45 AM posted to uk.sci.weather
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Default Penzance - Rubbish Maximum Temperature Forecast

On Sunday, April 21, 2019 at 9:31:27 AM UTC+1, Graham Easterling wrote:
Current MetO maximum temperature forecast for Penzance is 17C
https://www.metoffice.gov.uk/weather...ate=2019-04-21

Given that it was 17C at Camborne, Newquay & Penzance by 09:00, and Cornwall is the only bit currently coloured orange (18C) on the XCWeather temperature chart, I think they've undercooked it. Now 18C at Lands End (warmer than yesterday when it eventually reached 22.3C) and at nearby Bosullow. People are going to think it feels very warm for 17C.

Yesterday, they finally upped the forecast max to 22C late afternoon, just as it was cooling down. The thing is shouldn't a forecast precede the event?

Graham
Penzance


Around 19C across west Cornwall @ 10:00 from Newquay & Camborne down to Lands End, where it's now (10:30) 19.6C despite a 10-14mph easterly breeze!

Much like yesterday, whether the wind is on or offshore, it's making little difference to the temperature. It's all different if a sea breeze circulation gets established, that always makes a significant difference.

Graham
Penzance
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Old April 21st 19, 10:29 AM posted to uk.sci.weather
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Default Penzance - Rubbish Maximum Temperature Forecast

On Sunday, 21 April 2019 09:31:27 UTC+1, Graham Easterling wrote:
Current MetO maximum temperature forecast for Penzance is 17C
https://www.metoffice.gov.uk/weather...ate=2019-04-21

Given that it was 17C at Camborne, Newquay & Penzance by 09:00, and Cornwall is the only bit currently coloured orange (18C) on the XCWeather temperature chart, I think they've undercooked it. Now 18C at Lands End (warmer than yesterday when it eventually reached 22.3C) and at nearby Bosullow. People are going to think it feels very warm for 17C.

Model has the boundary layer depth incorrect by the looks, so you are still benefitting from the very low inversion - which will give a steep morning rise of temperature and will suppress the sea breeze formation. Boundary layer is forecast to deepen, but not really until this evening and overnight, so you should end up with a similar day to yesterday. Tomorrow likely different altogether with a developing south to southeast flow which should deepen the boundary layer further, plus bring along some patchy medium cloud and possibly a spot or two of rain from the thicker bits. It will be patchy development though, so perhaps the forecast emphasis should be on continued warmth and sunshine - but not as warm as today


Yesterday, they finally upped the forecast max to 22C late afternoon, just as it was cooling down. The thing is shouldn't a forecast precede the event?

Definitely!

Looks like armageddon here in Shropshire come Wednesday afternoon - but I will miss it as will be in Devon for the day!

--
Freddie
Dorrington
Shropshire
115m AMSL
http://www.hosiene.co.uk/weather/
Stats for the month so far: https://www.hosiene.co.uk/weather/st...201904APR.xlsx

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Old April 21st 19, 03:10 PM posted to uk.sci.weather
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Default Penzance - Rubbish Maximum Temperature Forecast

On Sunday, April 21, 2019 at 11:29:59 AM UTC+1, Freddie wrote:
On Sunday, 21 April 2019 09:31:27 UTC+1, Graham Easterling wrote:
Current MetO maximum temperature forecast for Penzance is 17C
https://www.metoffice.gov.uk/weather...ate=2019-04-21

Given that it was 17C at Camborne, Newquay & Penzance by 09:00, and Cornwall is the only bit currently coloured orange (18C) on the XCWeather temperature chart, I think they've undercooked it. Now 18C at Lands End (warmer than yesterday when it eventually reached 22.3C) and at nearby Bosullow. People are going to think it feels very warm for 17C.


Model has the boundary layer depth incorrect by the looks, so you are still benefitting from the very low inversion - which will give a steep morning rise of temperature and will suppress the sea breeze formation. Boundary layer is forecast to deepen, but not really until this evening and overnight, so you should end up with a similar day to yesterday.


Rise in temperature tended to stall a bit, not really down to sea breezes (though over in England Plymouth has a sea breeze blowing up the Tamar.) Most places in Cornwall seem to have peaked in the 20-22C range, as opposed to 21-23C yesterday. Penzance forecast max now up to 20C - not far off the mark.

Tomorrow likely different altogether with a developing south to southeast flow which should deepen the boundary layer further, plus bring along some patchy medium cloud and possibly a spot or two of rain from the thicker bits.. It will be patchy development though, so perhaps the forecast emphasis should be on continued warmth and sunshine - but not as warm as today

Yes, big change on the way.

Graham
Penzance
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Old April 21st 19, 08:24 PM posted to uk.sci.weather
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Default Penzance - Rubbish Maximum Temperature Forecast

On Sunday, 21 April 2019 16:10:18 UTC+1, Graham Easterling wrote:
On Sunday, April 21, 2019 at 11:29:59 AM UTC+1, Freddie wrote:
On Sunday, 21 April 2019 09:31:27 UTC+1, Graham Easterling wrote:
Current MetO maximum temperature forecast for Penzance is 17C
https://www.metoffice.gov.uk/weather...ate=2019-04-21

Given that it was 17C at Camborne, Newquay & Penzance by 09:00, and Cornwall is the only bit currently coloured orange (18C) on the XCWeather temperature chart, I think they've undercooked it. Now 18C at Lands End (warmer than yesterday when it eventually reached 22.3C) and at nearby Bosullow.. People are going to think it feels very warm for 17C.


Model has the boundary layer depth incorrect by the looks, so you are still benefitting from the very low inversion - which will give a steep morning rise of temperature and will suppress the sea breeze formation. Boundary layer is forecast to deepen, but not really until this evening and overnight, so you should end up with a similar day to yesterday.


Rise in temperature tended to stall a bit, not really down to sea breezes (though over in England Plymouth has a sea breeze blowing up the Tamar.) Most places in Cornwall seem to have peaked in the 20-22C range, as opposed to 21-23C yesterday. Penzance forecast max now up to 20C - not far off the mark.

That was likely due to the air above the inversion being slightly cooler than on Saturday. I think your warm temperatures on both days were pretty much completely down to downward mixing of the air from above the inversion rather than from heating of the underlying surfaces. This is illustrated by the lack of variation of temperature with wind direction. The inversion must've been very low to achieve this - certainly lower than about 500 feet. It does take a very low inversion to overcome the effects of SST - particularly at this time of the year.

--
Freddie
Dorrington
Shropshire
115m AMSL
http://www.hosiene.co.uk/weather/
Stats for the month so far: https://www.hosiene.co.uk/weather/st...201904APR.xlsx


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Old April 21st 19, 10:35 PM posted to uk.sci.weather
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Default Penzance - Rubbish Maximum Temperature Forecast

On Sunday, April 21, 2019 at 9:24:59 PM UTC+1, Freddie wrote:
On Sunday, 21 April 2019 16:10:18 UTC+1, Graham Easterling wrote:
On Sunday, April 21, 2019 at 11:29:59 AM UTC+1, Freddie wrote:
On Sunday, 21 April 2019 09:31:27 UTC+1, Graham Easterling wrote:
Current MetO maximum temperature forecast for Penzance is 17C
https://www.metoffice.gov.uk/weather...ate=2019-04-21

Given that it was 17C at Camborne, Newquay & Penzance by 09:00, and Cornwall is the only bit currently coloured orange (18C) on the XCWeather temperature chart, I think they've undercooked it. Now 18C at Lands End (warmer than yesterday when it eventually reached 22.3C) and at nearby Bosullow. People are going to think it feels very warm for 17C.


Model has the boundary layer depth incorrect by the looks, so you are still benefitting from the very low inversion - which will give a steep morning rise of temperature and will suppress the sea breeze formation. Boundary layer is forecast to deepen, but not really until this evening and overnight, so you should end up with a similar day to yesterday.


Rise in temperature tended to stall a bit, not really down to sea breezes (though over in England Plymouth has a sea breeze blowing up the Tamar.) Most places in Cornwall seem to have peaked in the 20-22C range, as opposed to 21-23C yesterday. Penzance forecast max now up to 20C - not far off the mark.

That was likely due to the air above the inversion being slightly cooler than on Saturday. I think your warm temperatures on both days were pretty much completely down to downward mixing of the air from above the inversion rather than from heating of the underlying surfaces. This is illustrated by the lack of variation of temperature with wind direction. The inversion must've been very low to achieve this - certainly lower than about 500 feet. It does take a very low inversion to overcome the effects of SST - particularly at this time of the year.

--
Freddie
Dorrington
Shropshire
115m AMSL
http://www.hosiene.co.uk/weather/
Stats for the month so far: https://www.hosiene.co.uk/weather/st...201904APR.xlsx


Sea breeze was stronger today here on SW Devon coast compared with yesterday.
The max was 22 instead of 24C. I think advection was a more dominant influence on these maxes than any entrainment from above the subsidence inversion you are talking about Freddie. Admittedly this would have aided the warming of the surface layer until the horizontal thermal gradient became dominant. The complexity of the coastline and the interaction of the scales make the numerical forecasting of sea breezes difficult.

Len
Wembury
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Old April 21st 19, 10:44 PM posted to uk.sci.weather
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Default Penzance - Rubbish Maximum Temperature Forecast

I agree with you for Devon, Len, but not for west Cornwall where there didn't appear to be any horizontal temperature gradients. There appeared to be something of a stronger gradient from Devon eastwards (10 knot northeasterly surface wind during the morning over east Devon, Dorset and west Hampshire coasts) which implies a slightly deeper boundary layer here. I saw no evidence of this over west Cornwall until the late afternoon.

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Freddie
Dorrington
Shropshire
115m AMSL
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Old April 22nd 19, 08:21 AM posted to uk.sci.weather
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Default Penzance - Rubbish Maximum Temperature Forecast

On Sunday, April 21, 2019 at 11:44:57 PM UTC+1, Freddie wrote:
I agree with you for Devon, Len, but not for west Cornwall where there didn't appear to be any horizontal temperature gradients. There appeared to be something of a stronger gradient from Devon eastwards (10 knot northeasterly surface wind during the morning over east Devon, Dorset and west Hampshire coasts) which implies a slightly deeper boundary layer here. I saw no evidence of this over west Cornwall until the late afternoon.

--
Freddie
Dorrington
Shropshire
115m AMSL


Thanks for your feedback.

The lack of any horizontal temperature gradient seemed to affect most south coast counties on Saturday, as demonstrated by locations such as Portland & St Catherines Point getting to around 22C, despite an easterly breeze. As you say, limited to west Cornwall by yesterday.

I don't recall a situation quite like it in April. The difference between the onshore & offshore coasts in Cornwall during warm spells in April / May, in a generally E or SE dift, can approach 10C under more 'normal' conditions. Rather annoying when it's 14C in Penzance & 22C at Newquay.

Graham
Penzance


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