Forecast Verification For March 2012

[Thundery wintry showers]

My forecast ran as follows:

nother warm dry March for most

With high pressure remaining dominant to the south of Britain it looks set to be another mild dry March except for western and northern Scotland.

However before the mild dry weather returns there will be a cloudy wet blip over the weekend of the 3rd/4th March. An Atlantic weather system will bring rain eastwards on the 3rd followed by brighter showery weather, the brighter weather not reaching East Anglia and the southeast until evening. A southerly tracking depression will then bring a cold, wet and windy day across England and Wales and southern Scotland on the 4th, with temperatures suppressed at 4 to 7C for most and gales in some coastal areas. There will also be snow on high ground across southern Scotland and Wales, with some sleet possible to low levels. As cold air digs in behind from the north, wet snow may occur more widely to low levels across southern England overnight 4th/5th.

After the cold wet episode high pressure will again establish to the south of Britain bringing mild westerlies, but eastern parts of England (especially East Anglia) are likely to have another cold wet day on the 5th, while other areas become dry and sunny, with a slight frost early in the day. During the 6th the dry sunny weather will transfer to southern areas while western and northern Scotland will become cloudy and wet, and it will turn milder. The 7th will see the rain belt spread south-eastwards across the country (though with only small rainfall amounts in the south) and brighter weather with wintry showers across the northern half of Scotland.

High pressure will be persistent to the south during the second week of March, bringing dry and generally sunny weather to most of England and south Wales, but in north Wales, north-west England and most of Scotland and Northern Ireland it is likely to be cloudy with rain at times. Eastern Scotland will most likely be dry but often cloudy. Temperatures will be consistently above the seasonal average, but never exceptionally so, reaching 10 to 13C by day across most regions. Frosts will be rare, though some central and southern parts of England may see slight frosts under clear skies.

The signals for mid to late March suggest high pressure extending further north. An interlude of chilly northerly and north-westerly winds is likely in the third week as part of the transition, with some short-lived snowfalls possible across Scotland and northern parts of England plus northern Ireland and north Wales, but in the south temperatures probably won't fall far below normal. The last third of March will probably be dry and settled with warm days and near-average temperatures by night as high pressure settles close to the British Isles.

Overview

March 2012 will be quite a mild March, I am predicting a Central England Temperature of 7.3C. Mean temperatures will be 0.5-1.0C above the 1981-2010 average in most regions, though note that they will be more like 1.5C above most earlier reference periods.

Despite a wet interlude on the 3rd-5th, March is unlikely to alleviate the water shortages in southern and eastern England. Rainfall will be close to average in western and northern Scotland but elsewhere shortages of 30 to 60% are expected, with the largest shortages occurring in south-east Scotland and south-west England.

Sunshine totals will be above normal in most regions for the sixth consecutive March. Slight shortages are expected across Northern Ireland and western Scotland (about 10 to 20% below average) but excesses of 10 to 30% will occur in most central and eastern parts of England and also in south-east Scotland.

Forecast issued by Ian Simpson (aka TWS) on the 3rd March 2012.

Overall I think this forecast went pretty well during the first two-thirds of March, with the main weather episodes correctly pinpointed although the "interlude of chilly northerly and north-westerly winds" in reality ended up as a slack area of low pressure which gave a fair number of showers in places but not much in the way of widespread snowfall.

In the last third of March I identified the right synoptic pattern but vastly underestimated the amount of warmth and sunshine associated with it- I had envisaged a "cold origin" high whereas the high we got was a "warm origin" one that tracked north. Hence while rainfall during March was much as I expected, temperatures were about a degree higher and sunshine totals, after running at levels close to what I predicted until 21st, then proceeded to skyrocket well above the values that I had been expecting.

It goes to show that at long range it is easier to pinpoint general patterns than specifics, but I nonetheless feel that this month's forecast was quite successful.