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Met Éireann operates the national synoptic, climate and rainfall observing systems. All climate science is based on high quality observational data. Met Éireann operates the national observational network to World Meteorological Standards, the data is quality controlled and securely stored in the national climate archive.

The data, once quality controlled is available for analysis. This analysis defines the climate of Ireland, for example, Long Term Average values are produced against which current observational observations can be compared. A range of products are generated from the analysed data. Statements are published for each monthly, season and year, gridded data sets are generated for rainfall and temperature. Specific products are generated, for example, for users in the agricultural and engineering sectors.

Met Éireann is involved in global climate modelling through its participation in the EC-Earth consortium, and downscaling of global models to a regional level through partnerships and collaboration with the EPA, universities and the Irish Centre for High End Computing (ICHEC). A high resolution reanalysis of Ireland’s climate since 1961, MÉRA, has also been completed.

Met Éireann is committed to an Open Data policy, a wide range of data is available to download under an open license, from observations to grids to reanalysis. The range of data available is continuously expanding and tools are being developed to enable improved future access. Data not available online may be obtained by contacting us directly.

Click here for Latest Farming Commentary.

Soil Moisture Deficits, Evaporation, Potential Evapotranspiration, Actual Evapotranspiration and Runoff:

• Soil Moisture Deficit (SMD) is the amount of rain needed to bring the soil moisture content back to field capacity.
• Field capacity (SMD=0) is the amount of water the soil can hold against gravity i.e. the maximum water a pot plant can be watered and not leak water. Negative SMD indicates a water surplus, which will be drained over time through either infiltration or overland flow or both.
• Saturation is reached when SMD= -10mm, i.e a water surplus of 10mm. Positive SMD is below field capacity and rain can infiltrate to the capacity of the SMD amount. In a saturated soil all of the available soil pores are full of water, but water will drain out of large pores under the force of gravity.
• Evaporation is the rate of water loss from a free water surface such as a reservoir, lake, pool, or saturated soil. A Class A Pan is used for measuring evaporation. This is a circular tank 1.21 m in diameter and 0.25m deep, partly filled with water and mounted on a frame to allow free circulation of air underneath. Additional water is required to maintain a set level.
• Evapotranspiration is the total water flux into the atmosphere, i.e. the sum of evaporation and transpiration (water flux through plant stomata).
• Potential (or Reference) Evapotranspiration (PE) is the water flux under non-limiting soil water conditions. A lysimeter is used to measure the rate of potential evapotranspiration from grass. It consists of four sunken tanks, each some 0.25m sq. in area and 0.75m in depth. The soil surface in each tank is at the same level as the surroundings. Grass cover is maintained on the tanks. Measured Potential Evapotranspiration is recorded at Johnstown Castle, Co. Wexford and Valentia Observatory, Co.Kerry. In Met Éireann the FAO Penman-Monteith formula is used to calculate the daily Potential (Reference) Evapotranspiration, using meteorological data recorded at our Synoptic Stations.
• Actual Evapotranspiration (AE) is the water flux which actually occurs. This is limited by the amount of moisture available in the soil. Estimates of Actual Evapotranspiration are derived from calculated values of Potential Evapotranspiration and current SMDs.

Soil Moisture Deficit Model

A hybrid SMD Model* has been developed which accounts for differences in drainage regimes between different soil types in Ireland. Three soil drainage classes, well drained, moderately drained and poorly drained, are defined as follows:

• Drainage is the amount of water lost from the topsoil through either percolation or overland flow and is dependent on the soil drainage capacity.
• Well Drained: Soil never saturates, remains at field capacity even on very wet days in winter. Minimum SMD=zero. When SMD > 0mm AE is less than PE, decreasing linearly to zero when SMD is at a theoretical Maximum of 110mm.
• Moderately Drained: May saturate on wet winter days, but return to Field Capacity on first dry day. Minimum SMD= minus10mm. When SMD >0 AE is less than PE, decreasing linearly to zero when SMD is at a theoretical Maximum of 110mm.
• Poorly Drained: Saturates on wet winter days, water surplus is drained at very slow rates, in the order of 0.5mm per day. Minimum SMD= minus 10mm. When SMD >10mm AE is less than PE, decreasing linearly to zero when SMD is at a theoretical Maximum of 110mm

Daily Soil Moisture Deficits and calculated PE and AE are available for the three different soil drainage classes for our Synoptic Stations. Soil moisture deficits and surpluses are computed from the differences between rainfall and actual evapotranspiration. Soil moisture surpluses are assumed to be removed by drainage and surface run-off over time.

Potential (Reference) Evapotranspiration Calculation

The potential evapotranspiration, ET0 is calculated according to the FAO Penman-Monteith Equation (Allen et al., 1998) for a reference grass crop at an assumed height of 0.12m :

where ET₀ is the potential evapotranspiration (mm d-1),
R_n is the net radiation at the crop surface (MJ m-2 d-1),
G is the ground heat flux density (MJ m-2 d-1),
T is the air temperature at 2 m height (°C),
u₂ is the wind speed at 2 m height (m s-1),
e_s and e_a are the saturation vapour pressure and the actual vapour pressure, respectively (kPa),
Δ is the slope of the vapour pressure curve (kPa °C-1),
and γ is the psychrometric constant (kPa °C-1).

Soil Moisture Deficit Calculation

The Soil Moisture Deficit (SMD)is calculated as follows:

where SMD_t and SMD_t-1 are the SMDs on day t and day t-1 respectively (mm),
Rain is the daily precipitation (mm d-1),
ET_a the daily actual evapotranspiration (mm d-1),
Drain the amount of water drained daily by percolation and/or overland flow (mm d-1)

Actual Evapotranspiration

For each soil drainage class a critical Soil Moisture Deficit, SMD_c, is defined. When the current SMD is less than this critical value then moisture is not limiting respiration and Actual Evapotranspiration equals to Potential Evapotranspiration:

When SMD <= SMD_c

When the current SMD is greater than this critical value, moisture available is no longer unlimiting; as a result, Actual Evapotranspiration is less than Potential Evapotranspiration. In this case it is assumed that AE deceases linearly to zero as the SMD approaches a theoretical maximum value, SMDmax.

 When SMD > SMD_c

The value of SMD_c for well and moderately drained soils is zero, and 10mm for poorly drained soils. The value of SMD_max is 110mm for all three soil types.

Drainage

It is assumed that drainage by means of percolation or overland flow only occurs when soil moisture exceeds field capacity (SMD < zero).

• Well Drained soils: These remain at field capacity even on very wet days and are never saturated, all water in excess of field capacity is drained immediately.
• Moderately Drained Soils: These carry water surpluses on wet days but return to field capacity on the first subsequent dry day. This corresponds to a maximum drainage rate in excess of 10mm/day.
• Poorly Drained Soil: These can carry surplus water for a number of days, water drains at the maximum rate of 0.5mm/day when SMD is -10, decreasing linearly to zero when SMD > zero

Effective Drainage is the total drainage amount, i.e. through percolation and overland flow.

The Agricultural Meteorology Unit page is here.

*References

• Allen, R.G., Pereira, L.S., Raes, D. and Smith, M. 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. FAO irrigation and drainage paper 56, 227 pages.
• R.P.O.Schulte, J.Diamond, K.Finkele, N.M.Holden and A.J.Brereton 2005. Predicting the Soil Moisture Conditions of Irish Grasslands. Irish Journal of Agricultural Research 44: 95-110.

Click here to Request a Legal Weather Report

Met Éireann provides meteorological reports for the legal, insurance and engineering professions or from private enquirers. Our Meteorologist carefully analyses and interprets detailed weather information extracted from archived data.

Sample archived data:

• Hourly Synoptic charts
• 6-hourly North Atlantic charts
• Upper level winds
• Radar Images
• Satellite pictures
• Lightning strike maps
• Climate data

Met Éireann Services to the Legal Sector

Weather Reports

Met Éireann provides weather reports for the legal, insurance and engineering professions or from private enquirers. A report is produced by a professional Meteorologist who examines all relevant information and gives an opinion on the actual weather. Only online applications are accepted.

Response Times:
We endeavour to provide reports within 2 to 4 weeks of receiving an online application. However as resources and demand varies, sometimes it can takes longer.

Urgent Requests:
Urgent reports are usually provided within 2 to 3 working days on payment of a 50% surcharge.

Charges:
Meteorologist reports are provided under the terms of the Met Éireann “Statement of Public-Service Functions” and attract a charge* which represents the cost of provision of the service. The charge is based on the number of hours taken to produce the report with a minimum of 1 hour. For a report covering a single location for a single day, the minimum charge is applied. Current charges are available here.

Liability for charges:
The person/company requesting a report or court attendance is liable for cost and this cost must be paid promptly on receipt of the invoice. The use to which the report is put and whether/when/how much the requesting individual/company is eventually paid for their services does not affect this liability.

Confidentiality:
Met Éireann treats requests for reports in confidence. It occasionally happens that a report may be requested by both parties involved in a case arising from the same incident. In this case, the requested reports will be provided without reference to each other. Any person/company requesting that a Met Éireann Meteorologist attend court or be on standby to attend is directly liable for the charges involved. This is an arrangement made directly with Met Éireann and payment is due without reference to the outcome or timescale of the case.

Court Attendance

Met Éireann typically provides hundreds of Meteorologist reports each year. Where court proceedings are initiated, the question of court attendance by a Meteorologist may arise. Court appearances are immensely time-consuming and have the potential, even in moderate numbers, to overwhelm our Meteorologist availability and cripple our ability to perform other important work. Therefore, we would ask our customers to consider the following when considering the need for a Meteorologist in court.

Is the weather contentious?
It is our experience over many years that the weather report is often not a source of contention. Weather reports are normally agreed among parties but this sometimes happens after our Meteorologist has travelled to court or put in some preparatory work. Even when our Meteorologist is called to give evidence, this often amounts to merely repeating and confirming the contents of the report, sometimes involves providing a little elaboration or supplementary opinion and rarely involves any questioning of the report contents. We would urge all parties to attempt to agree the weather report if possible before requesting a Meteorologist to do preparatory work or actually travel to court.

Logistics of Meteorologist court attendance:
In order to make potential court attendance as efficient as possible and to minimise charges, we provide the following options:

• Forward alerting. This gives us an indication that court attendance may be needed at a specified date in the future. It allows us to plan. There is no preparatory work and no charge.
• Standby. Placing a Meteorologist on standby for a specific date or range of dates means that the Meteorologist will review the weather report and familiarise with the weather over the relevant period. S/he is then available to travel to court at 1-hour’s notice. The charge for standby is half the rate for attendance. The minimum charge* is a half-day and charging is in half-day blocks. If standby is not cancelled before 1 p.m., the afternoon will also be charged. If standby is cancelled before the day arrives, the minimum half-day charge will apply to cover preparation work and disruption to other work.
• Actual attendance. This is where a Meteorologist is requested to travel to court. Charges* apply in half-day blocks including travel time. If attendance is cancelled 5 working days in advance ( i.e. attendance on Friday cancelled the previous Friday ), no charge will be made. Cancellation at shorter notice will attract a half-day standby charge.

Who will attend?
In some instances, we are requested to provide the same named Meteorologist who produced a report. This may be possible but sometimes is difficult or impossible. Given the length of time it takes for a case to come to court, it is often the case that the author of a report has been relocated or has retired. When the date is known, we can provide the name of the Meteorologist who will attend. We would greatly prefer to provide services by arrangement with our customers in the most mutually beneficial way.

The following charges for the supply of climatological data and reports apply from Jan 2017 until further notice:

1. Basic Data

Historical climate data sets are now freely available on our website. Applications for free access to climate data not available on our website may be made under the Information on the Environment Regulations (AIE), turnaround time is usually two to four weeks.

An overall minimum charge of €45 + vat applies for urgent requests i.e. supplied within three working days.

2. Analysed Data

Analysed data/reports are prepared and issued by different meteorological grades and charged for at the appropriate hourly/daily rates (detailed below).

An overall minimum charge of €45 + vat applies.

3. Weather Reports

Weather reports are prepared and issued by different meteorological grades and charged for at the appropriate hourly rate. Legal reports are produced by a Meteorologist. Customers requesting priority treatment are charged 50% extra. The minimum charge for a weather report is the hourly rate for the relevant grade.

The following charges apply:

Hourly rates:

Daily rates:

In cases where daily rates are appropriate, such as court attendance or site survey, travel and subsistence charges also apply. The minimum charge is for half a day. A standby charge of 50% of the daily rate applies where staff may be required to be available to be called to attend court.

Note: Finance Act 2010 and Value Added Tax

In accordance with Section 117 of the Finance Act 2010, from 1st July 2010 public bodies engaged in VAT-able activities will be obliged to register and account for VAT. Accordingly from 1st July 2010, invoices issued by Met Éireann for climatological data and services delivered after that date will include VAT at the higher rate.

Weather Events in Public Works Contracts

An objective and measurable approach was adopted in relation to what is considered to be a weather event which could trigger a delay event, i.e. the contractor gets additional time. A delay event is triggered when a weather event exceeds a defined threshold (90th percentile) value in any given month.

Weather events are:

• Number of days per month with a rainfall amount > 10mm.
• Number of days per month with a maximum 10-min. mean wind speed >=15m/s.
• Number of days per month with a minimum temperature < 0 deg. C.

Monthly Weather Data

Monthly weather events for our Synoptic stations are available online, simply select a station from the map via the link below. To view the Weather Events for Public Works Contracts data, select a station first, then click the link just below the map.

View Monthly Weather Data

The Department of Finance document describes how weather events are calculated and the historical data used to determine entitlement to an extension of time. Threshold values (90th percentiles) are detailed in this document.

The 90th percentile is the lowest value which has 90% of the sample data less than or equal to it. All available data for each station was used in its calculation. A station was not used unless there were at least 10 years of data available in the last 12 years for each calendar month.

View Rainfall Return Sample (PDF document 10kb)

• Information on the frequency of heavy rainfalls is often required by engineers, architects and others, usually in connection with design criteria for water management or drainage schemes. In most cases it would be uneconomic to construct a system capable of coping with the most extreme rainfall possible, even if the magnitude of this is known. Instead, it is usual to design the system so that it will be capable of accommodating a rainfall likely to be exceeded only once in a specified number of years (return period).
• A depth duration frequency model allows for the estimation of point rainfall frequencies for a range of durations for any location in Ireland. The model consists of an index (median) rainfall and a log-logistic growth curve which provides a multiplier of the index rainfall.  Rainfall station data were analysed and an index rainfall calculated for each station. Computer algorithms were written to fit the model to station data, calculate model parameters across the map and produce outputs of the return period rainfalls at any location in Ireland.
• The set of parameter values summarising the rainfall Depth-Duration-Frequency (DDF) relationship enables the production of consistent estimates of point rainfall frequencies over durations ranging from 5 minutes to 25 days and return periods of 6 months to 120 years. These estimates supersede those provided in Fitzgerald (2007).
• These Rainfall Return Period tables are now freely available by submitting the form below.

Method used in the Estimation of Point Rainfall Frequencies

Mateus, C., and Coonan, B. 2023. Estimation of point rainfall frequencies in Ireland. Technical Note No. 68. Met Éireann. http://hdl.handle.net/2262/102417

Request a Rainfall Return Period Table

Note:

A Rainfall Return Period table will be sent to your email address within the next hour. There is no check to ascertain whether the File Name matches the co-ordinates supplied. * Please ensure that you use Irish Grid co-ordinates, not ITM.
Irish Grid Reference Finder is available here

Download 1981-2010 Annual Average Rainfall Grid

Please contact us at enq@met.ie if you experience any problems.

The previous version of the Rainfall Return Period from is available here

Monthly Rainfall and Temperature Grids are available here