As there is a big interest in the weather over the summer months Donegal Weather Channel will look at the seasonal long range forecast from the ECMWF SEAS5 model which looks 4 months ahead and is updated once a month. Forecasting so far ahead is unpredictable but sometimes certain oceanic and atmospheric conditions and weather events around the world can give us a idea of what may be ahead. Weather events like La Nina & El Niño can effect our weather here in Ireland and the UK.

What is El Niño

The name 'El Niño' is widely used to describe the warming of sea surface temperature that occurs every few years, typically concentrated in the central-east equatorial Pacific.

An El Niño is declared when sea temperatures in the tropical eastern Pacific rise 0.5 °C above the long-term average. El Niño is felt strongly in the tropical eastern Pacific with warmer than average weather.

The effects of El Niño often peak during December; it's name "the boy" is thought to have originated as "El Niño de Navidad" centuries ago when Peruvian fishermen named the weather phenomenon after the newborn Christ.

El Niño years are one factor that can increase the risk of colder winters in Ireland and the UK.

What is La Niña

'La Niña' or "the girl" is the term adopted for the opposite side of the fluctuation, which sees episodes of cooler than average sea surface temperature in the equatorial Pacific. The conditions for declaring 'La Niña' differ between different agencies, but during an event sea temperatures can often fall 3-5 °C below average. Cooler, drier than average weather is experienced in the tropical eastern Pacific.

There are also neutral phases of the cycle when conditions are closer to the long-term average (within +/- 0.5 °C). These may be within a period of warming or cooling in the cycle. Approximately half of all years are described as neutral.

La Niña can even influence the Atlantic jet stream and our weather here in Ireland & the UK.

Long range forecasts provide information about expected future atmospheric and oceanic conditions, averaged over periods of one to three months. Like the medium and extended ranges, the long range forecasts are produced by the IFS coupled ocean-atmosphere model. Long term predictions rely on aspects of Earth system variability which have long time scales (months to years) and are, to a certain extent, predictable. The most important of these is the ENSO (El Nino Southern Oscillation) cycle. Although ENSO is a coupled ocean-atmosphere phenomenon centered over the tropical Pacific the influence of its fluctuations extends around the world. Many other sources of predictability are also represented by the forecast system.

SEAS5

The fifth generation of the ECMWF seasonal forecasting system, SEAS5, was introduced in November 2017, replacing System 4. SEAS5 includes updated versions of the atmospheric (IFS) and ocean (NEMO) models and adds the interactive sea ice model LIM2.

SEAS5 data is contributed to the Copernicus Climate Change Service's multi-system seasonal forecast.

JUNE 2021 SEASONAL OUTLOOK

MEAN SEA LEVEL PRESSURE

The SEAS5 ECMWF seasonal forecasting system currently shows a 40% to 60% chance of higher pressure across Ireland and the UK over the month of June much the same as we discussed in our monthly long range forecast on Monday and last week. Higher pressure looks highest next week and the 3rd week of the month before it turns more unsettled over the last week of June

TEMPERATURES

Over the 2nd & 3rd week and of June higher pressure looks set to build bringing a much more settled pattern across Ireland and the UK. There are indications we will see temperatures in places above normal in the mid to high 20s across Ireland and possibly the low 30s in England . The below chart shows temperatures over the month of June been near normal for the month or slightly above in some southern places.

RAINFALL

Rainfall is forecast to be below normal with a 40% to 50% chance over much of Ireland but 50% to 60% chance across the western half of Ireland for the month of June.

Rainfall is forecast to be below normal with a 40% to 50% chance over much of England and Wales but normal across a bulk of Scotland for the month of June.

JULY 2021 SEASONAL OUTLOOK

MEAN SEA LEVEL PRESSURE

The SEAS5 ECMWF seasonal forecasting system currently shows a 50% to 60% chance of higher pressure across Ireland and the UK over the month of July which could indicate a very settled month overall with plenty of dry weather.

TEMPERATURES

Over the Month of June the ECMWF seasonal model indicates a 40% to 50% chance of above normal temperatures for the time of year across the southern half of Ireland, Wales and much of England with near normal temperatures across the northern half of Ireland, Northern England and Scotland. Temperatures during this month could rise into the high 20s across parts of Ireland and the UK with a higher chance of the low 30s across parts of England and Wales.

RAINFALL

Rainfall amounts from the seasonal weather model are indicated to be 40% to 50% below normal for much of Ireland and the UK with the western coastal areas of Ireland and central England at a slightly higher chance of below average rainfall amounts 50% to 60%.

AUGUST 2021 SEASONAL OUTLOOK

MEAN SEA LEVEL PRESSURE

The SEAS5 ECMWF seasonal forecasting system currently shows a 50% to 60% chance of higher pressure across Ireland and the UK over the month of August which could indicate a very settled month overall with plenty of dry weather.

TEMPERATURES

Over the Month of August the ECMWF seasonal model indicates a 40% to 50% chance of above normal temperatures for the time of year across the southern half of Ireland, Wales and western England with near normal temperatures across the northern half of Ireland, Northern/eastern England and Scotland. Temperatures during this month could rise into the mid to high 20s across parts of Ireland and the UK with a higher chance of the low 30s across parts of England.

RAINFALL

Rainfall amounts from the seasonal weather model are indicated to be 40% to 50% below normal for much of Ireland and western Scotland with near normal ranfall amounts across the rest of England, Wales and the rest of Scotland.