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Synoptic situation
Heavy, thundery downpours developed by midday across south-west
England on 16 August 2004. These showers formed bands which aligned
themselves with the wind helping to maintain the heavy rain across
certain areas of north Cornwall for several hours. The trigger
mechanisms for these storms appeared to be convergence of winds
along the coast and the high ground in the local area which also
helped to generate showers. It would appear that the serious nature
of these floods was exacerbated by the local topography around
Boscastle.
Synoptic situation below for 1800 GMT on Monday 16 August 2004.
South-west
England 1971-2000 rainfall averages for August
More
information on climate in south-west England
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Other similar serious flooding events
that have occurred in the past include:
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Rainfall information
The following data was obtained from the Environment Agency on
19 August 2004. No quality control
has yet been undertaken on the data.
Map of locations
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24-hour rainfall totals ending 0900
GMT 17 August 2004
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| |
NGR |
24 hour total (mm) |
Main event total (mm) |
| Otterham |
SX 169 916 |
200.4 |
- |
| Trevalec, Lesnewth
|
SX 134 900 |
184.9 |
181.0 (11:30 to 16:30 GMT) |
| Trevalec, Lesnewth TBR |
SX 134 900 |
155.8 |
152.8 (12:15 to 16:19 GMT) |
| Creddacott |
SX 231 956 |
123.0 |
- |
| Slaughterbridge TBR |
SX 109 857 |
76.5 |
- |
| Bude |
SS 208 063 |
46.7 |
- |
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TBR = Tipping Bucket Rain gauge
The 24-hour value from Otterham would give a return period in
excess of 200 years (using the Flood Estimation Handbook method).
Lesnewth rainfall graph
Graph below showing 15-minute rainfall totals for Lesnewth TBR
(Tipping Bucket Rain gauge).
Map showing radar rainfall accumulations
Radar imagery: Click
for full size
The animation below uses 15-minute data between 1030 GMT and
1930 GMT. The images are composites, based on a mixture of the
best resolutions available.
Please note: The empirical relationship between radar reflectivity
and rainfall rate is fixed whereas in reality this is highly dependent on precipitation type
and is very different for rain and hail.
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