An erroneous forecast

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Len W

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Nov 22, 2020, 11:23:11 AM11/22/20
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Postcode forecast this morning early and later for here was for overcast all day.
It has drizzled pretty well all day.

Model no good for this situation and radar not especially good for drizzle.
Solution: Needs a human observer on the ground.
That likely?
Dream on.

Len
Wembury


Len W

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Nov 22, 2020, 11:25:54 AM11/22/20
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I suppose it was correct for overcast.
The trouble is it missed the drizzle.

Len

Julian Mayes

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Nov 22, 2020, 12:37:09 PM11/22/20
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We know that human observers bring a number of advantages, not least with the 'days with' data such as snow and thunder records. But that's another issue.  I agree, dream on.  But the lowest pptn category on netweather radar DID show drizzle over you for much of the day and for much of southern coastal counties for a time. 

Which brings me me back to your subject line - there was a TV forecaster this morning who made no mention of the weak front over southern parts - just implied a fine day for those areas not affected by the showers in the north-west. But, go back to yesterday evening and bring on a superior forecaster, Nick Miller, and he DID give due attention to the cloud and drizzle in the south - and even mentioned the likelihood of the front waving back NE towards South Wales later - as often happens when a weak front gets stuck in a slack airstream.  I assume that was shown in model output.  

Well, that seems to be what happened as here on the south-western fringes of London, the frontal cloud was slow to clear south this morning. Then nice sunshine for a time. But by 3.30pm the cloud was encroaching again from the south-west - which is where the sun was, obviously.  These may seem like small details to some but a national forecast should tell us the weather different places are likely to get.  

Julian 
Molesey, Surrey.    






Len W

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Nov 22, 2020, 1:48:15 PM11/22/20
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Julian,
I was mostly referring to the hourly forecast  on the web from UKMO and Meteogroup which did not give drizzle, only a 10-20% chance of precpi.
I checked this through the day and they still did not want to give drizzle for my coastal location.
As regards the radar. I looked occasionally at netweather and the light blue was very patchy and not often over PL9 despite what you say.
I can say as an observer on the ground 😊 , that the drizzle was almost continuous throughout the day and delivered 2.7 mm to 1800 UTC in my 5 inch gauge.

Len

Julian Mayes

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Nov 22, 2020, 2:07:33 PM11/22/20
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Hi Len,    yes, I accept what you say about the radar in south Devon - the blue was only patchy and if you had that much pptn, then it clearly underdid it.  I don't know why I did not mention in my first post but Plymouth was reporting drizzle at the AWS at Mount Batten at times so anyone who wished to know about the drizzle could have discovered it.  

Julian  

Len W

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Nov 22, 2020, 2:19:00 PM11/22/20
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Discover it maybe, but did they know how long it was going to go on for?
They might have looked on their smartphones at the hourly forecast.
🥺 🥺

Len

Graham Easterling

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Nov 22, 2020, 3:11:57 PM11/22/20
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On the MetO forecast for Penzance at 10:00 a 10% chance of rain here forecast all day, with white clouds,. This despite the radar and the fact it was distinctly wet as it had been for hours. Ah, I thought, perhaps it's just about to clear, an quick glance at the radar & the satellite imagery soon put that idea to bed..

Not just drizzle, but soaking moderate to heavy drizzle much of the time today, with the water streaming off everything. It was heavy enough to show up very well on the radar, which fine coastal drizzle rarely does. Eventually started petering out mid afternoon. (Yesterday's forecast was pretty poor as well.)

It seems such a shame that whilst the model forecasts showed the position of the front so accurately several days ahead, that the actual forecast weather ON THE DAY was so bad despite all the evidence at their fingertips, including a manned station at drizzle soaked Camborne. 

The BBC forecast at least showed a high chance of rain.

On the plus side it was mild again, and almost totally calm. Several swimming in Porthleven harbour this morning at high tide, and a very nice wave on the south coast, north coast still messy.

Graham
Penzance
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