Atlantic Storm #4 Desmond

[Summer Sun]

The only weather warnings in operation now are wind warnings for; Highlands & Eilean Siar, Orkney & Shetland, Strathclyde

[Harve]

19 hours ago, keithlucky said:

Plenty of studies over the years Extract from watkins study This study has demonstrated the value of historical sources in supplementing data derived from scientific techniques such as lichenometry and radiocarbon dating. For Cumbria it was possible to identify 34 extreme floods which affected upland catchments since AD1600. The evidence supports the information derived from geomorphological approaches indicating that there have been marked changes in the frequency of such floods in the last 400 years, but that the frequency of such floods in the last three decades is not unusual and has fallen markedly from the mid-twentieth century. The occurrence of extreme flood events in upland areas appears to be linked closely with negative NAO values. http://www.mangeogsoc.org.uk/pdfs/watkins_whyte.pdf

You seemed initially to be contesting John Curtice's claim that 352mm at Honister is a 24 hour record? This has nothing to do with rain guage measurements at an individual location?

[Interitus]

On 12/9/2015 at 4:00 PM, keithlucky said:

Plenty of studies over the years Extract from watkins study This study has demonstrated the value of historical sources in supplementing data derived from scientific techniques such as lichenometry and radiocarbon dating. For Cumbria it was possible to identify 34 extreme floods which affected upland catchments since AD1600. The evidence supports the information derived from geomorphological approaches indicating that there have been marked changes in the frequency of such floods in the last 400 years, but that the frequency of such floods in the last three decades is not unusual and has fallen markedly from the mid-twentieth century. The occurrence of extreme flood events in upland areas appears to be linked closely with negative NAO values. http://www.mangeogsoc.org.uk/pdfs/watkins_whyte.pdf

 

Interesting, though something of light read than a scientific piece which leads to it being flawed. Conclusions regarding trends must be taken with care with so few events and the obvious error of including the 2000s when published in 2008 misses the devastating floods of 2009.

Also the suggested link with negative NAO immediately leaps out as suspect and what it doesn't take into account is the difference between heavy summer thunderstorms and the autumn and winter stalled frontal systems. A quick look at the daily NAO data for the events since 1950 confirms this with the 3 summer storms having negative NAO as expected occurring in a slack flow regime. Of the 7 frontal system events, 5 occurred during positive NAO, to which the 2009 and 2015 events can be added.

The thunderstorm / frontal system distinction can also be extended to a devastating though localised flash flood from a thunderstorm within a single river catchment area, compared to a region wide event such as this month.

 

[Interitus]

An additional interesting thought is what the maximum rainfall total from Desmond might actually have been. From a study of the November 2009 rain - http://onlinelibrary.wiley.com/doi/10.1002/wea.568/pdf - Eden and Burt calculated that the UK record monthly total was set at Styhead Tarn with around 1430mm. This had to be estimated as the gauge is only read monthly and for whatever reason was read a couple of days late at the start of the month, and their calculation involves long term comparison with Honister and Seathwaite Farm for which Styhead is between 1.265 and 1.426 times wetter.

The monthly reading obviously means at this time Styhead 24hr totals are unknown, but by applying the previous ratio to the Honister 352mm gives a possible 24hr value of between 445mm and 502mm - or up to a smidgen under 20 inches!

 

[knocker]

John Curtin ‏@johncurtinEA 10m10 minutes ago

Provisional figures from EA Honister rain gauge #Cumbria -nearly meter of rain this month, following a meter in Nov!