Libby's weather analysis

Libby Greenhalgh looks back at how her forecast for last weekend compared with the real thing

See Libby's forecast for last weekend here

Weekend weather analysis 7-8th December 2002.

Saturday started damp with less than 3 knots of wind from an eastnortheastly direction with visibility slowly improving from the initial 2km. The wind strength fluctuated in the morning between calm and 5 knots, but not until early afternoon, 1400, did the wind strength freshen and the visibility improve. The wind increased towards 10 knots from 030deg.

The Tuesday (3rd December) outlook, forecast winds of roughly 10 knots from the east. The update forecast on Friday (6th December) was for a northeasterly wind of 12 to 15 knots. The discrepancy in wind strength can be contributed to the low pressure centre forecast off the west of the British Isles not developing until Saturday afternoon. This meant that the high pressure trough broadened and therefore the isobars were less tightly packed producing a lighter wind.

The trough of high pressure tightened over Saturday afternoon as the low pressure developed to the west of the British Isles. The effect of the trough tightening meant the wind direction on Sunday was around 045deg which was more northerly than the forecast of 080deg. The forecast wind strength for Sunday (15-18knots) was generally right with between 10-16 knots of gusty and shifty conditions as the wind bounced off the land.

The racing tactics were dominated by the shifting conditions due to the land effect as was expected on the Friday update with shifts reaching 20˚ or more and the wind strength changing between 2-5 knots of the mean.

The damp cloudy conditions of the weekend were caused by an occluded front that pushed across the channel from Europe on Saturday and continued to linger through the weekend into Monday. Forecast air temperatures of 3deg C and windchill of -5degC were not achieved on the Sunday as the slightly more northerly wind meant the bitter cold air temperatures of Siberia were not brought over until Monday.

Outlook.
Next weekend looks like the synoptic situation will be similar to the weekend just gone with a high pressure centered over Scandinavia dominating the weekend. The winds on Saturday will be light 0-5 knots as a filling low centre off the southwest of the UK produce cyclonic easterly winds and cold conditions. The low centre should disperse across Saturday and the trough of high pressure will produce stronger winds (10 knots) from a more northeasterly direction for Sunday. With fronts and shallow troughs likely conditions across the weekend will be wet and misty first thing, clearing slowly as the wind increases.