Summer 2018 forecast: average

The thundery end to spring has probably built everyone’s hopes up that we’re about to experience a summer with plenty of fireworks in the atmosphere. But the current pattern that brought four consecutive days of thunder (the whole year average is 3.5!) – a continental influence on our weather – could just as easily flip to a mobile south-westerly.

Screen Shot 2018-05-28 at 10.34.52
Thunderstorms will probably continue to be a feature of the summer

The mean temperature for summer 2018 is looking average overall with average precipitation.

Like the most recent winter forecast I’ve looked in depth at ENSO, QBO and local meteorological data.

ENSO

The El Niño–Southern Oscillation (ENSO) is a periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean. Current neutral conditions are forecast to continue through to September so any impact is likely to be very small. I had a look at similar years were ENSO was 0.2 in May and came up with the following.

Temperature
Average: 40%
Rather cool: 40%
Cool: 20%

Rainfall
Average to slightly dry: 60%
Average to slightly wet: 40%

Sunshine
Average to slightly sunnier than average: 60%
Average to slightly dull: 40%

QBO

I also had a look the quasi-biennial oscillation (QBO), the quasiperiodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere. This produced only two similar years: 1963 and 2010.

Temperature
Average: 50%
Cool: 50%

Rainfall
Average to slightly dry: 50%
Average to slightly wet: 50%

Sunshine
Average to slightly sunnier than average: 50%
Singularities / patterns

sunset

Spring was consistently on the wet side this year with all months at least 127 per cent wetter than average, the total of 182mm made it the wettest for 10 years.

 

The mean temperature for the spring season, despite the very cold start, ended 0.8C warmer than average, just under a degree colder than last spring which was the second warmest on record.

If you take into account all years back to 1797 that were within +/- 10 per cent of these figures, some 10 ‘best fit’ years emerge.
The list of 10 summers, ranging from 1801 through to 2007, predominantly saw summers that were just on the cooler side of average – no real corkers stand out except for 2001 which saw a hot spell at the end of July that made it into my list of best heatwaves.

As an average this summer could be expressed as: Mean: 17.1C (just below average) Rainfall: 150mm (about average). Sunshine 535 hours (just below average)

Or, expressed in probabilities, I concluded the following:

Temperature
Average to slightly below: 50%
Average to slightly above: 20%
Rather cool: 20%
Cool: 10%

Rainfall
Average: 50%
Wet: 30%
Dry: 20%

Sunshine
Average: 10%
Average to slightly sunny: 30%
Average to slightly dull: 40%

 

From the above you could deduce that the next three months will be slightly below average for temperature, with average rainfall. And slightly duller than average.

To try to give some idea of what month will have the best weather I’ve broken down the summer into June, July and August probabilities.

Looking at June, after the weekend, the outlook is looking unsettled and gradually turning cooler after the first week. July looks average as does August which, apart from two years, has been a very disappointing summer month.

Perhaps the best weather this summer will be at the end of June and the second week of July – just as most schools break up?

 

* Taking into account the fact that temperatures in London are up to 0.66C warmer than they were 100 years ago I have added 0.66C to mean temperatures before 1915.

** Obviously, in the event of a series of direct hits from thunderstorms, my rainfall estimate could be hopelessly short – a symptom of abundant solar energy at this time of year which creates a ‘noisy’ atmosphere compared with winter.

*** The 1981-2010 average mean for summer in this region is 17.6C, with 144.9mm of rain and 564 hours of sunshine

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