Archives for September 2011

All eyes on new october temperature records

Paul Hudson | 13:20 UK time, Friday, 30 September 2011

UPDATE:

New records were set on saturday.

Bramham now holds the Yorkshire October record, with 28.7C. Finningley recorded 30C, but the Met Office do not regard the airport as an official climate site anymore.

A new record was set in Lincolnshire on sunday, with 29.3C recorded at Coningsby.

ENDS

The exceptional early autumn weather looks set to last into the weekend, with UK temperature records on the line.

According to the Met Office the current UK October record was set on the 1st of October 1985 in March, Cambridgeshire, where 29.4C (85F) was observed.

Closer to home, 1st October 1985 also saw a new record in Lincolnshire, with 28.4C (83F) at Cranwell.

In Yorkshire, the highest October temperature on record was set in Whitby on the 2nd October, 1908, with 28.3C (82F).

Tomorrow both Lincolnshire and Yorkshire could see new October records, with 29C (84F) possible in one or two spots.

Already at 2pm today, the mercury at Finningley in South Yorkshire has hit 29C, with very similar meteorological conditions expected tomorrow.

The Met Office estimate a 30% chance of 30C (86F) being recorded at one of their stations across Eastern or Southeastern England.

A fall in temperatures is expected across all areas early next week.

By the second half of next week, night-time temperatures could fall low enough for a touch of ground frost in some sheltered locations, as weather conditions return to normal for the time of the year.

'Indian summer' on its way by middle of next week

Paul Hudson | 13:59 UK time, Friday, 23 September 2011

Following another disappointing summer, and an unsettled September, at long last a spell of warm weather will be on its way by the middle of next week.

A plume of warm air from the continent looks set to move northwards across the UK reaching many areas by Wednesday; with a good degree of agreement between all the main forecasting centres.

The meteorological chart shown below for friday of next week is called a 'thickness chart', and allows us to calculate temperatures. The lime green line, labelled 564dm, indicates the thickness of the atmosphere between 1000millibars and 500millibars. To have this line, and warmth, so far north is very unusual for this time of the year.



If this chart is correct, then temperatures in London, for example, could reach 27C (81F) by the end of next week.

High Autumn temperatures in late September/early October last occurred in 2006, and before that in 1995. Locally 1st October 1985 was exceptional, with 27.5C recorded at Leeds weather centre.

Such autumnal warmth is often described as an Indian summer, but technically speaking an Indian summer is a term to describe a warm spell of weather much later in the season, usually late October into early November.

The maximum temperature chart shown below, based on the American model for Wednesday gives an idea of the extent of the warm weather by that time, with many areas enjoying temperatures in the low 70's Fahrenheit.



This compares very favourably to the average temperature for the end of September in Leeds, for example, which is around 16C (61F).

Although in some areas mist and fog could be slow to clear during the mornings, this 'Indian summer' could last in some areas into the following weekend, if computer predictions are correct.

La Nina returns - what impact on global climate?

Paul Hudson | 12:27 UK time, Friday, 16 September 2011

After a lull over the last few months, weak La Nina conditions are re-establishing themselves in the Pacific.

La Nina is a term used to describe an area of water that is colder than average in the tropical Pacific.

It follows on from the major La Nina event which lasted from June 2010 to May 2011 which was one of the strongest on record, and which depressed global temperatures.

The last back to back La Nina event was recorded from 1998-2000.

In some areas of the world La Nina is a very important forecasting tool, as the colder than average ocean directly impacts pressure patterns, which in turn can lead to extreme weather.

In America, La Nina was blamed for this spring's flooding and drought.

It is also thought that La Nina last year was to blame for Australia's second wettest year since 1900, and forecasters believe another cool and wet summer in that part of the world is on the cards, although flooding on the scale that was witnessed last summer is thought unlikely.

Closer to home, there is little evidence to indicate how, if at all, La Nina impacts weather here in the UK.

As for global temperatures La Nina will have a cooling influence, depending on its strength and longevity.

Climate experts at NOAA believe that La Nina conditions will slowly strengthen and continue through winter.

And the Japanese climate centre expects weak La Nina conditions to continue into next year, and then strengthen by Spring 2012, as can be seen from the two projections below.

Ex-Hurricane Katia on its way

Paul Hudson | 16:30 UK time, Saturday, 10 September 2011

There's been much in the media in the last few days about Hurricane Katia which is expected to travel across the Atlantic and batter parts of the UK on Monday.

By that time it will have lost its hurricane status, and have been downgraded to a 'post tropical storm'.

This is because hurricanes can only develop when sea temperatures are greater than 27C, and once this source of energy is removed, as it travels across the Atlantic, it's strength will subside - although it will remain a powerful weather system.

Ex-hurricanes affecting the UK are nothing new. We only have to go back to 2009 when an even earlier Ex Hurricane (or post tropical storm) Bill brought severe gales to the UK on August 25th.

There has been growing concensus through the day that Katia is likely to be positioned on Monday off the far Northwest coast of Scotland.

Further south, across our region, if this forecast track is correct, estimates are for gusts to reach 50-60mph in many areas, but locally in more exposed places around 70mph is possible.

Wind speeds like this are nothing new, and occur several times a year, particularly in Autumn and Winter.

Should the storm system be further north, wind speeds would be lower. Further south, and wind speeds could be higher.

With trees in full leaf, this could lead to the potential at least of some trees being uprooted, especially where the ground is now soft, for example in Pennine areas where it's been quite wet of late, and high sided vehicles would be vulnerable.

I'll be monitoring this and will update if necessary on sunday and monday.

August global temperature update

Paul Hudson | 16:05 UK time, Monday, 5 September 2011

The latest global temperature anomaly for August has been released and according to the UAH measure is +0.325C above the running 30 year mean, similar to July's anomaly, shown on the graph below.

Adjusted to the more standard time period, the anomaly is approximately +0.578C above the 1961-1990 time period used by the Met Office and WMO.

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