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Status:
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Finalised Material from: Tim, Mohamed, Linus
Discussed in the following Daily reports:
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http://intra.ecmwf.int/daily/d/dreport/2015/12/21/sc/ http://intra.ecmwf.int/daily/d/dreport/2015/12/22/sc/ |
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1. Impact
During the Christmas week the northern parts of the British Isles were hit by floods. The worst affected areas were in N England, from Lancashire across to Yorkshire, with the cities of Manchester, Leeds and York all featuring in reports, as well as southern Scotland.
http://www.bbc.co.uk/news/uk-35193682
2. Description of the event
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The deepening of low B must have been associated with broadscale dynamical uplift, and that broadscale ascent, together with the close proximity of the frontal zone, the slow moving nature to the front due to multiple lows/wave moving along it, the warm airmass source region near Morocco, and some orographic enhancement seem to have all contrived, together, to deliver the high rainfall totals observed.
3. Predictability
3.1 Data assimilation
The animation below shows the observation rejection (low weight) charts for subsequent assimilation cycles. Wind observations with low weight is marked with symbols and the 250 hPa wind speed in the analysis is plotted with shades. The position of low A is marked with a black dot. On 23-24 December a cluster of observations were given low weight over U.S, probably connected to severe convection.
3.2 HRES
The plots below show the accumulated precipitation between 25 Dec 06z and 26 Dec 06z and MSLP valid 12z on 25 Dec. The forecasts from 24 December 12z and earlier the position of low A is too far too the west and the band of precipitation is shifted somewhat to the north.
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