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As there is a big interest in the weather over the months ahead 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.

Note that the ECMWF SEAS5 model is also used by Met services across Europe and sometime can tell us if there is changes ahead looking at the upper atmosphere.

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.

JULY 2021 SEASONAL OUTLOOK

MEAN SEA LEVEL PRESSURE

The SEAS5 ECMWF seasonal forecasting system currently shows a 40% to 50% chance of higher pressure across Ireland and the UK over the month of July which could indicate some settled periods over the months of July with the risk of some unsettled periods at times.

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 eastern half of Ireland and much of Scotland, with near normal temperatures across the rest of Ireland, Across England and Wales it shows above normal temperatures with a probability of 50% to 60% 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 near normal across Ireland and the UK for July apart form the northwest of Scotland where it may be just above normal and below normal in the far east of England. Some Thunderstorm activity during the month may cause some flooding.

AUGUST 2021 SEASONAL OUTLOOK

MEAN SEA LEVEL PRESSURE

The SEAS5 ECMWF seasonal forecasting system currently shows a 40% to 50% chance of higher pressure across Ireland and bulk of the UK and 50% to 60% across the south of England over the month of August. Based on this the month would be rather mixed with some unsettled weather still feeding on of the Atlantic at times in August.

TEMPERATURES

Over the Month of September the ECMWF seasonal model indicates a 40% to 50% chance of above normal temperatures for the time of year across the eastern half of Ireland, England and Wales, Elsewhere temperatures to be near normal. Temperatures during this month could rise into the mid to high 20s across parts of Ireland and the UK.

RAINFALL

Rainfall amounts from the seasonal weather models are indicated to be 40% to 50% below normal across the southern half of Ireland and Wales no data is indicated for other areas so average rainfall amounts may be possible there.

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SEPTEMEBR 2021 SEASONAL OUTLOOK

MEAN SEA LEVEL PRESSURE

The SEAS5 ECMWF seasonal forecasting system currently shows higher pressure than normal across Ireland and the UK for September a 40% to 50% chance of higher pressure for many areas but 50% to 60% chance of higher pressure across western & northwestern Ireland as well as northwest Scotland.

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TEMPERATURES

Over the Month of September the ECMWF seasonal model does not show any clear indications of the possibility’s of below average or above average temperatures. Temperatures over the month are likely to average on the latest forecast.

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RAINFALL

Rainfall amounts from the seasonal weather models are indicated to be 40% to 50% below normal across the bulk of Ireland and southwest of England but no data is indicated for other areas so average rainfall amounts may be possible there.

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OCTOBER 2021 SEASONAL OUTLOOK

MEAN SEA LEVEL PRESSURE

The SEAS5 ECMWF seasonal forecasting system currently shows higher pressure than normal across Ireland and the UK for September a 50% to 60% chance of higher pressure for Ireland, England & Wales and 40% to 50%. This could indcate a settled October.

TEMPERATURES

Over the Month of October the ECMWF seasonal model shows temperatures possibly just above average across the northern half of Ireland and average elsewhere.

RAINFALL

Rainfall amounts from the seasonal weather models are indicated to be 40% to 50% below normal across the bulk of Ireland and Scotland and 50% to 60% across Ireland.