A little on the high side

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Jul 19, 2019, 5:11:43 AM7/19/19
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The Met Office warning for heavy rain was a little on the high side for south Wales - I would have thought 10 to 15 mm would have covered it.
There have been much wetter days up here that never got a yellow warning.
I wonder if they'll issue one for the rain that's forecast by the models for tonight in the SE?
At least the weather radar output seems to have returned to normal.





Jul 19, 2019, 5:28:28 AM7/19/19
to Weather and Climate
It'll be that impacts thing again, Bruce.  There's been a dry spell over the past month in the south, so people become unused to driving in rain.  That and the timing (rush hour) and the fact that the rain came in short heavy bursts meant that there could be rapid changes in conditions in short distances and time.  The South Wales rush hour is something to behold (I had to experience it for a year) with many roads (especially the M4) over capacity.  Therefore I think it was a well-targeted warning.  I agree the amounts were OTT but the potential was there for release of mid-level instability, so it needed to be factored in.

115m AMSL
Stats for the month so far: https://www.hosiene.co.uk/weather/statistics/201907JUL.xlsx

Julian Mayes

Jul 19, 2019, 6:19:42 AM7/19/19
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Never mind the impacts, the totals are not insignificant - maybe your post was a little early Bruce?  St Athan has had about 25mm since 06h (after a glance at the hourly totals), in heavy bursts. In frontal rainfall you could multiply that by 2.5 to get the inland rainfall over the hills but I concede that totals may have been more randomly distributed this morning. 



Jul 19, 2019, 8:20:25 AM7/19/19
to Weather and Climate
The threshold for yellow heavy rain warnings - and yes thanks for reminding me Freddie - warnings are issued for impacts and not thresholds these days - has now been reduced to such a level, that the Met Office may as well issue a blanket yellow warning for the whole of the UK if there's any kind of active weather system crossing the country. 

I'm sure that the people of South Wales know what to do when driving in heavy rain - let's face it they have had years of practice at it. 

I realise that the Met Office are just playing the 'health and safety - fear of litigation' game, but the whole country seems to me to be at serious risk of being mollycoddled to death. 

Yes there should be warnings issued for heavy rain events that would result in flooding, but rainy days are just part of the fabric of everyday life on this sceptred isle, and this event wasn't one of them.

Talking of flooding, over 64 mm of rain fell on the 11th close to Dingwall, most of that during the late afternoon (see my report). There was a yellow thunderstorm warning out for the north of Scotland for that day - but there were no thunderstorms - just torrential rain and flooding. The Met Office never updated their warning to amber or red, even though the 'wet desk' (if they still call it that) must have had full visibility of the SEPA (and EA) automatic rainfall network, as well as their own (the one that Julian is privy to but not members of the public). 

I don't know if SEPA issue flood alerts for Scotland, but they must have sophisticated GIS systems that they feed the latest NWP mesoscale forecast and and observational data into that are able to predict when trouble is brewing for low lying places such as Dingwall. I wonder if and how SEPA and Highland Council would have reacted to the issuing of a red warning for heavy rain from the Met Office that afternoon?


Jul 19, 2019, 8:49:57 AM7/19/19
to Weather and Climate

I've attached the 06-12 totals and as you say St Athan did report 27 mm.

It's always difficult when you don't have access to all the information like you both do.

In my defence - admittedly pretty weak:-

  1. That warning ran from 04 to 09 UTC and so without access to hourly values like you do I can only guess at how much fell in those 5 hours.
  2. Although St Athan does lie some way west of Cardiff it's borderline for that warning area.
Enjoy the rain!



George in Edinburgh

Jul 19, 2019, 9:17:01 AM7/19/19
to Weather and Climate
SEPA do issue flood warnings for Scotland. You have to sign up for them. Had a warning text a couple of hours ago.

George in Swanston, Edinburgh


Jul 19, 2019, 9:47:06 AM7/19/19
to Weather and Climate
For verification, totals for 0401-0900z:
Milford Haven: 4.2
Pembrey: 5.2
St Athan: 15.4
Mumbles: 18.2

FWIW I wasn't trying to imply that the drivers in Wales didn't know how to drive in rain - just that they may not be as used to it after a dry month :-)
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