Mostly cold, dry and sunny except for the SW

The northerlies expected in the second week have come to less than expected, and mild south-westerlies are now upon us.

The 19th March will be dry with sunny intervals over most of the country but showers will affect the northern half of Scotland, while it will be cloudy and drizzly near the south coast. It will be very windy in the north. It will be dull and wet on the 20th across all parts, with top temperatures mostly between 11 and 13C on both days. The 21st will see brighter weather in eastern, central and southern England where it will turn very warm again- highs of 14 to 16C are expected- while other areas will be cloudy with some rain and temperatures of 10C. This rain will spread across all remaining parts on the 22nd followed by brighter showery conditions.

The 23rd-25th will have a generally south-westerly flow bringing cloudy weather and some showery rain to Scotland, Ireland, north Wales and north-west England, while eastern, central and southern England and south Wales will be mostly dry with some sunshine, and temperatures will reach 12-14C in these areas. It will be quite windy across all parts. Low pressure is expected to remain in charge until the end of the month, but with indications for a build of pressure from the west, giving colder north-westerly winds for a time, and some wintry showers are possible around the 27th-29th especially in northern areas. Temperatures are expected to fall back below the seasonal average during the last few days, reaching highs of between 6 and 9C.

Into April, we can expect a warm settled start to the month in the south with high pressure building from the south-west bringing some warm sunshine to southern areas, though Scotland and Northern Ireland will be affected by changeable westerlies on the northern flank of the high with some bands of rain at times. There is a continued signal for pressure to remain relatively high to the north-west, which suggests a significant chance of northerlies affecting the British Isles as we head into the second week of April, which may bring some wintry showers. My March CET prediction of 5.6C is still looking plausible at this stage, indicating mean temperatures 0.5 to 1.0C below the long-term mean over much of the country.

Due to a wet second half of the month, rainfall totals are likely to rise to near normal levels in Northern Ireland and western and northern Scotland, with excesses of up to 20% in places. Elsewhere it will end up as a dry month, with less than 40% of the normal over much of eastern England.

Sunshine is expected to come out well above average in eastern, central and southern parts of England with excesses of 40-60%, despite more unsettled weather in the second half of the month. Northern and western Scotland can expect sunshine within 10% of the normal, while intervening areas will have excesses of 10-30%.

Forecast update issued by Ian Simpson (aka Thundery wintry showers) on 18 March 2010.