Geographical Association - Carlisle Case Study: What caused the heavy rainfall?

Carlisle Case Study: What caused the heavy rainfall?

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January 7-8 severe storm development

During the second part of the first week of 2005, a very mild and moist tropical air mass engulfed the UK, bringing gale-force south-westerly winds. A depression centre passed near to the north of the area on Thursday 6 January, with associated cold fronts, bringing strong frontal uplift and convection. The main cold front, marking the boundary with cold polar air, was more or less stationary over northern England on Friday 7 January.

For most of Friday this cold front lay close to the Cumbrian fells, which lay in the moist tropical airmass all day. Late on Friday a new low pressure system developed west of Ireland, deepened rapidly and moved over the borders. The cold front pushed east over Cumbria with severe gale-force westerly winds, followed quickly by an occluded front which wrapped its way round the depression bringing storm force winds and heavy rains back into Cumbria on the morning of Saturday 8 January.

The rainfall increased over the high ground of Cumbria as the airstream was forced upwards (the orographic effect). However, the storm was rare because of its length, rather than the intensity of the rainfall. Meteorologists suggest an overall return period of about 100 years (1%). Rainfall totals of more than 200mm were recorded at some gauges. Although significant amounts of rain fell throughout Cumbria, the heaviest was over the high ground of the Lake District, the Howgills and the Yorkshire Dales.

At some locations, the return period of the rainfall was 175 years (0.57%) and many gauges had totals with return periods over 50 years (0.5%). The rainfall was accompanied by hurricane force winds, which themselves caused significant damage and hampered the efforts of the emergency services. There is evidence of a sting jet forming on the morning of Saturday 8 January, bringing winds gusting to over 100 mph (85 knots) over parts of northern England, and 130 mph (110 knots) over the Pennine Peaks.

One hundred flood warnings were issued by the Environment Agency as the relentless rain brought widespread flooding to these areas, with Carlisle particularly badly affected.

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Daily Rain Gauge Data (50k)