You will recall from earlier briefings this week that the next wind/rain event was due in tonight and tomorrow. I can now give you a more detailed description on the associated timing and warnings.
· Rain will spread eastwards across all areas from around mid-evening and last for several hours
· However, forecast rainfall totals are rather lower now and across the south of the region the rain will be more intermittent in nature. This morning’s Flood Guidance Statement has kept the whole of the Northwest at Green (very low flood risk) for tomorrow and the Yellow alert for rain that previously covered the northern half of Lancashire and the whole of Cumbria has been removed. Good news, but in Cumbria certainly the susceptibility to surface water from short periods of heavy rain has been well highlighted over the last few rainfall events so we should retain a watchful eye on the radar this evening just in case.
· The main issues with this weather system will focus around the wind. This Atlantic low pressure centre is taking a more southerly track (across the northern half of Scotland) than its predecessors and hence we are more in line to experience the stronger winds. Although they’ll freshen along with the rain later this evening the period of strongest winds will occur during daylight hours tomorrow, well after the initial rain has gone through.
· The main risk period for disruption looks like being pretty much throughout the daytime period. The risk is focussed upon Cumbria and north Lancashire, and with the risk of 60-70mph gusts developing even inland we have issued an Amber warning (medium likelihood of significant impacts) for wind covering Cumbria and for Lancashire north of a line approximately Lytham St. Annes to Slaidburn. The warning text includes the possibility of gusts touching 80mph along the coast and over higher ground. Across Cumbria in particular, there will also be squally showers/spells of rain during the day, thus adding to the discomfort. The rest of the Northwest (with the exception of the extreme south of Cheshire) lies within the Yellow sector and here we should allow for gusts of 60-70mph along the coast and a range of 45-60mph inland, although the south end of Merseyside, together with Cheshire and Greater Manchester, may see only the occasional gust above 50mph with the majority closer to 40mph.
· What does this mean in terms of impacts ? Within the Amber sector expect disruption to travel with speed restrictions on motorways and high-sided vehicles at particular risk of being blown-over on elevated/exposed sections of motorway/road by sudden gusts. There will doubtless be trees blow over and some disruption to power transmission could well result. With town/city centres and out-of-town shopping centres likely to be especially busy in the sales extra care should be taken.
· We should start to see a gradual moderation in the winds from late afternoon through into the evening. Looking on the weekend it looks a kinder picture with appreciably lighter winds, some sunshine but also a few showers. Although the unsettled regime looks set to be maintained into 2014 there doesn’t appear at this stage to be any more severe wind events on the horizon once tomorrow is through.
An update briefing will be issued tomorrow,
Have a good rest of Boxing day,
Alan Goodman; Met Office Advisor (Civil Contingencies)