Models completely fail to pick up this evening's thundery showers over Devon...

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xmetman

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Apr 21, 2018, 1:35:54 PM4/21/18
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Although the NWP used by the BBC and the Met Office identified the area of thunderstorms over Sussex and Hampshire, they completely failed to pick up the line of thundery showers that developed late this afternoon across Devon Even at 6.30 pm Darren Betts was trying to put a brave face on it and completely ignore reality into the bargain.



xmetman

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Apr 21, 2018, 4:59:36 PM4/21/18
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I notice the Met Office finally issued a belated warning at 2047 BST this evening for southern England for thunderstorm, that had in reality started at least 3 hours earlier.

The day shift obviously thought that they could get away with it, and then the night shift came on and thought differently, or maybe it was because the latest 18 UTC run had finally got a handle on the likely extent of the thunderstorms.

xmetman

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Apr 21, 2018, 5:14:07 PM4/21/18
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I notice that in this evenings video forecast from the Met Office for the overnight period, the NWP graphics are again completely out of skew with the reality of the situation.

The model seems to have lost its grip with the extent of these thunderstorms and there doesn't seem to be an easy way to adjust the graphics to reflect what's truly going on across southern and this evening.

xmetman

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Apr 21, 2018, 5:40:15 PM4/21/18
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I notice that the BBC, or should I say MeteoGroup, rather craftily started with a sequence of real time weather radar overlaid with SFERICs on the 1030 pm weather forecast.

It just shows you that you can always rely on observational data when the models gone to pot.

It looks like the main area of thunderstorm activity is across Bournmouth, Southampton and Portsmouth areas at the moment.

Martin Rowley [West Moors/East Dorset]

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Apr 22, 2018, 3:52:58 AM4/22/18
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" It looks like the main area of thunderstorm activity is across Bourn(e)mouth, Southampton and Portsmouth areas at the moment."

... classic 'electrical storm' evening here (just north of the Poole/Bournemouth/Christchurch conurbation): there were two periods of CB-based activity; between 1825 and 1915Z, a fairly 'standard' multi-cell TS/CB cluster passed to our SE - we got the glancing blow with not too much rain, but I see from Hurn SYNOPs/METARs that the highest wind gust was 31 kn in the hour to 19Z, with the VIS reduced to 1200M on the 1850Z observation, and small hail recorded - we missed out on that, though the wind was a bit frisky here around that time ...

EGHH 211850Z 13015KT 1200 +TSRAGS BKN040CB 15/12 Q1015

Then, phase 2, PPN re-started ~2020Z lasting off/on until the early hours of the morning (22nd) but never very heavy and only 2 mm total accumulation; however, from around that time,
very distant lightning seen well to the south, already reasonably frequent (the sort of thing Hollywood directors like to show when the alien spacecraft is about to descend and
scrumble the earthlings!), but by the time the activity reached us around 2300/2300Z (21st), the lightning (CC/IC, very ISOL CG) was near-continuous, and lasted that way
for at least half-hour, only slowly disappearing to the north of us after midnight.

I haven't heard of any damage reports but visually, a truly remarkable event and one we don't often get these days.

Martin.


Paul Garvey

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Apr 22, 2018, 4:17:29 AM4/22/18
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Been frustrating here over the last day. The MetO missed the showers yesterday morning, yesterday evening and they've missed the mist this morning. Usually good, but not over the last 24 hours. 

Martin Rowley [West Moors/East Dorset]

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Apr 22, 2018, 4:18:47 AM4/22/18
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" ..... but by the time the activity reached us around 2300/2300Z (21st), the .... "

CORRECTION: 2300/2330Z (21st) etc.

Also, I've since seen that we have a major fire, which the FB are saying /may/ be lightning related, in Bournemouth last night - would have been due to the first of the activity reported,
which is sensible as that generated more CG activity locally than the second/'sheet' episode.

Martin.

Trevor Harley

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Apr 22, 2018, 4:22:19 AM4/22/18
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PPN? Private property network?

xmetman

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Apr 22, 2018, 5:10:53 AM4/22/18
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Len W

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Apr 22, 2018, 5:12:46 AM4/22/18
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It just shows the models continue to struggle to forecast the detail of the mesoscale Bruce.
It is down to nowcasting with the the aid of radar data if you want detail.
How many times have we said this?
All depends on the forecast bench personnel who seem more and more weather unaware these days.

There ought to be a rule:

Model output appears crap
Go to obs..

Len

xmetman

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Apr 22, 2018, 5:38:10 AM4/22/18
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Len

I think a big part of the problem is that the forecast graphics are still too tightly bound to the NWP data, and the graphics don't seem to be editable in anyway, so when the model is wrong the graphics remain wrong.

They require some version of Photoshop with which the can add/delete/move areas of rain, as well as merging the latest observation weather radar image, so at least for the T+0 they've got it right!

This mismatch is the reason why you rarely get a forecast for the first 6 or 9 hours, more often or not the evening forecast doesn't starts till the next day.

Bruce.

Martin Rowley [West Moors/East Dorset]

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Apr 22, 2018, 5:46:55 AM4/22/18
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... I think I'll have to resurrect the FAQ/Glossary!

PPN = precipitation, in common use in meteorological circles since at least the 1950s (also PPTN which dates back to at least the 1940s/2WW)

Martin.

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