An unsettled weekend ahead with developments associated with Storm ‘Alex’ (named by Meteo-France and set to bring some damaging winds to NW France tomorrow but thankfully not to most of the UK). ‘Alex’ will become the dominant low pressure centre, starting the weekend over the Biscay/W France region but gradually migrating northwards into the UK. Active weather fronts wrapped around it will swing westwards across much of the UK (including the Northwest) during Saturday, bringing an extended spell of moderate to heavy rain with brisk NE winds adding to the discomfort. Normally in such a regime with a prevailing NE’ly flow our region is relatively well-sheltered by the Pennine chain. Whilst this will still hold to some extent, there remains the potential for the rainfall totals to result in some impacts, both from river overspill and from surface water excess. The worst of the rain looks like it will be through by Saturday evening with a drier interlude ensuing overnight before further showers or longer spells of rain develop again during Sunday, by which time the low centre will be slap bang over the middle of the UK.
Rainfall totals during Sunday should be generally well down on those of Saturday but should any river-based impacts result then they could obviously run on into Sunday. Even beyond Sunday low pressure looks set to dominate the UK’s weather well into next week so it’s likely to be a case of further showers at times, possibly heavy, although the likelihood of any disruption currently looks fairly low.
Severe weather warnings/Flood Risk Guidance:
The initial warning for Saturday’s rainfall has now been issued and is attached above. The warning covers a wide area of the UK including Cheshire, Merseyside, Greater Manchester and the S half of Lancashire. The risk assessment depicts a very low likelihood of medium impacts. We are in the medium impacts column given that the very high forecast rainfall totals in parts of the warning area (not the Northwest) could necessitate escalation tomorrow or on Saturday itself. The remainder of Lancashire, along with Cumbria, have been left out of the Met Office warning for now, the thinking being that the Pennines should afford these areas sufficient shelter to keep rainfall totals below disruption levels, though it is worth noting that on this morning’s Flood Guidance Statement (FGS, also attached above) N Lancashire and Cumbria are included in the green area of concern, suggesting there is still a low likelihood of some minor impacts here. The yellow polygon on the FGS for Saturday and Sunday essentially mirrors the Met Office warning.
Potential Impacts:
The main threat across the Northwest during Saturday looks like being surface water excess impacting the transport networks with potential for localised flooding along the more prone sections of road/rail. There is also a small chance that one or two business/domestic premises could also be affected by flooding with the larger rainfall totals perhaps causing narrow urban watercourses to rise quickly.