This is the third issue of the Donegal Weather Channel Monthly Long range forecast issued every week looking up to a month ahead using data from the ECMWF and GFS models.

Please note that the longer range forecasts are more uncertain and will not always be right.

Extended Range Output

The output is rather different from the shorter period output of HRES and ENS products.  It provides a more general overview of the forecast up to Day 46, focusing mainly on the week-to-week changes in the weather rather than attempting to give unsupportable detail on individual days.  Output is mostly in the form of anomalies relative to ER-M-climate and is mainly shown as 7-day means for calendar weeks Monday-Sunday.   Specialised products for the extended range also include information on potential tropical cyclone activity and the MJO during the coming month.

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If you have a business and would like to sponsor our weekly month long range forecast for a period of 1 week or 1 month please do contact Donegal Weather Channel at info@donegalweatherchannel.ie or message our Facebook page . Donegal Weather Channels service relies on sponsorship/advertising. Without sponsorship/advertising Donegal Weather Channel would not be able to give so many hours and a daily service.

The forecast will be issued by myself Kenneth and i will try to keep it simple making it easy for everyone to understand. If there is a term I use in the forecast which you may not know what it means I will explain what I am talking about .

Before I start with the long range forecast I will just explain what we will be looking at and how the forecast will work.

The forecast will be broken up into 4 section Example below :

• Week 1 - Monday 10th May 2021 -Monday 17th May 2021

• Week 2 - Monday 17th May 2021 -Monday 24th May 2021

• Week 3 - Monday 24th May 2021 -Monday 31st May 2021

• Week 4 - Monday 31st May 2021 -Monday 7th June 2021

Things we will look at in the forecast:

• Mean sea level pressure: Weekly mean anomalies

• 2m temperature: Weekly mean anomalies

• Wind

• Precipitation: Weekly mean anomalies (eg. rainfall and snowfall for a example.

• Dust forecast ( Only in Week 1)

• UV forecast outlook

• Potential Pollen Levels

Forecaster - Kenneth Mc Donagh

Week 1 - Monday 10th May 2021 -Monday 17th May 2021

Mean sea level pressure: Weekly mean anomalies

Lower pressure than average across Ireland this week ( Week1 ) this will bring the risk of heavy showers in places at times. Some parts of Ireland will also see good bright and sunny spells at time so overall not the worst.

Precipitation ( Rainfall): Weekly mean anomalies

Rainfall amounts over week 1 will be above average again across Ireland but this will very from place to places due to the showers coming in the form of thundery downpours, At the moment the lowest rainfall amounts look set to be across the west and midlands of Ireland with the highest amounts across the Ulster, Munster and south Leinster. Further showers some which will develop into thunderstorms will develop again on Wednesday, Thursday and Friday, This weekend also favors good conditions for the development of thunderstorms. Some heavy downpours will lead to spot or localised flooding with some of these showers also falling as hail. Thunderstorm warnings are likely to be issued on some days for parts of Ireland.

Wednesday risk

The main risk of thunderstorm activity on Wednesday will be across south Munster, south Leinster and Ulster.

Thursday risk

The main risk of thunderstorm activity on Thursday will be across the North/East Connacht, Ulster and Leinster.

Friday risk

The main risk of thunderstorm activity on Friday will be across North Connacht and Ulster

Rainfall amounts between Tuesday 11th May to Sunday 16th May 2021

Ulster - 15mm to 45mm ( Highest amounts in west & central Ulster)

Connacht - 10mm to 30mm ( Highest amounts in northeast Connacht)

Munster - 30 mm to 50mm (Highest amounts in south & southeast Munster)

Leinster - 15mm to 50mm (Highest amounts in south Leinster)

2m temperature: Weekly mean anomalies

Temperatures over this week (week 1) will be below normal across Ireland between 1C to 2C below. There will be no risk of frost this week . Overall day time temperatures will range between 10C to 14C/15C up until Sunday the 16th of May.

Wind forecast

Overall winds this week will be rather light across Ireland. No deep low pressure systems are forecast to track over Ireland bringing any major winds.

UV forecast

Even with a cooler week than average for this time of year expected UV levels will be Moderate in any sunshine with the risk of sun burn possible.

Pollen Forecast

Pollen levels will be moderate to high over the week with pollen levels lowest during cloudy and wet weather and highest during any sunny & dry periods. The main type of pollen will be tree this week.

Dust forecast

Dust levels will be low across Ireland during week 1.

Forecasters final note on week 1

Overall week 1 will see a mix of bright and sunny spells but heavy showers in places also with some of these forming into thunderstorms. The main hazards this week will be heavy rainfall leading to flooding and some heavy hail showers. Farmers and Gardeners will see no risk from frost this week. The risk of heavy thundery showers will continue into this weekend but there will be some good bright and sunny spells in places also.

Week 2 - Monday 17th May 2021 -Monday 24th May 2021

Mean sea level pressure: Weekly mean anomalies

The latest outlook heading into week 2 is for just below average pressure to sit close to Ireland at least for a part of the week. Over the Atlantic there are signs that the Atlantic will become that bit weaker and have less of a influence on our weather which may allow higher pressure to build again over the later stages of this week with a higher chance sunshine.

Precipitation ( Rainfall): Weekly mean anomalies

Week 2 at this stage shows rainfall amounts above normal especially across the west and north of Ireland. Early there looks set to be some heavy thundery showers but the current trend coming into the end of the week and over the weekend is for drier weather as there is signs higher pressure will sit close to Ireland

2m temperature: Weekly mean anomalies - Wind

Temperatures look set to be around 1C to 2C below normal over week 2 but with signs of high pressure near the end of week 2 this may bring back near Normal temperatures for this time of the year.

Wind Forecast

There are no signs of any strong winds over week 2.

UV forecast

Even with a cooler week than average for this time of year expected UV levels will be Moderate to high in any sunshine with the risk of sun burn possible.

Pollen Forecast

Pollen levels will be moderate to high over the week with pollen levels lowest during cloudy and wet weather and highest during any sunny dry periods. The main type of pollen will be tree this week.

Forecasters final note on week 2

Week 2 look set to start of cooler and unsettled with the risk of thunderstorms in places but there are signs of a more easterly airflow and higher pressure building later in the week into the weekend with a chance of warmer and drier weather.

Week 3 - Monday 24th May 2021 -Monday 31st May 2021

Mean sea level pressure: Weekly mean anomalies

The forecast for this period is a little more uncertain but the current signal is for near average to above average high pressure to sit close to Ireland on week 3. This will see mostly settled conditions. There airflow looks like it will be from the southeast/east which would bring warmer conditions.

Precipitation ( Rainfall): Weekly mean anomalies

The latest ECMWF and GFS models are showing below average rainfall across Ireland over week 3 as higher pressure sits across Ireland. With signs of a southeast to east airflow this would mean that the driest of the weather would be across the west and northwest with any rainfall mostly across the east and south east this coming in the form of showers with amounts also low.

2m temperature: Weekly mean anomalies

Temperatures over week 3 look set to be near normal and again with a southeast to east airflow this would bring warmer conditions across Ireland with temperatures in the low 20s for parts of the western half of Ireland but cooler along eastern areas in the mid to high teens due to a onshore easterly breeze.

Wind forecast

Week 3 at the moment does not show any signs of windy conditions.

UV forecast

UV levels will be Moderate, High to Very High in any sunshine with the risk of sun burn.

Pollen forecast

Pollen levels will be high to very high over the week with pollen levels lowest during cloudy and wet weather and highest during any sunny dry periods.. Grass pollen would then start to rise this week.

Forecasters final note on week 3

Overall week 3 will be rather settled with high pressure. Any rainfall will come in the way of showers and at this stage the eastern half of Ireland most at risk. There will be good sunny spells also over the week with near normal to above average sunshine amounts. At present no weather hazards look possible this week.

Week 4 - Monday 31st May 2021 -Monday 7th June 2021

Mean sea level pressure: Weekly mean anomalies

Confidence in this week is rather low and uncertain. The week may start of drier with high pressure still around.

Precipitation ( Rainfall): Weekly mean anomalies

Again Confidence is rather low for this week but the latest signal is for near normal to possibly just below normal rainfall amounts in parts of Ireland.

2m temperature: Weekly mean anomalies

Again Confidence is rather low for this week but the latest signal is for Temperatures over week 4 to be near normal across Ireland maybe just above with temperatures in the high teen to low 20s in places.

Wind forecast

Again Confidence is rather low for this week but if high pressure stay around over week 4 then this will bring less of a risk of windy weather

UV forecast

UV levels will be Moderate, High to Very High in any sunshine with the risk of sun burn.

Pollen forecast

Pollen levels will be high to very high over the week with pollen levels lowest during cloudy and wet weather and highest during any sunny dry periods.. Grass pollen would then start to rise this week.

Forecasters final note on week 3

With low confidence the latest signal for week 4 is for possible lower than average pressure with the higher risk of above normal rainfall amounts and windy conditions. Note that this is subject to change.

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