A Review Of The Latest ECMWF Output

'Frozen Sea', New Quay, Co Clare. Pic Susan Byron

iWeather Online's synoptics forecaster Fergal Tierney analyses the latest output from Monday's 12Z ECMWF model run, courtesy of the Danish and Icelandic Met Services. 

The Danish surface pressure and wind loop for the next 24 hours shows the low forming off northeast coast of Greenland and moving northwards towards Svalbard, deepening to 983hPa by 18Z Tuesday. At the same time a high is taking up position over western Greenland, reaching a core pressure of 1043hPa.

The Icelandic charts show surface pressure and 850hPa temperature, with the dark blue contour signifying below -20°C. By 18Z Wednesday we can see an extremely tight pressure gradient has formed between the two pressure centres, with a pressure difference of some 88hPa over a distance of ~800kms, which leads to an extremely strong northerly flow catapulting the cold air southwards towards Ireland and the UK - the Greenland Express!
The following loop nicely shows the modification of the 850hPa temperatures as the airmass tracks over warmer sea surface temperatures, which range from around 4 - 10°C between Iceland and Ireland. 

The low, which had been tracking southwards towards the Orkneys, takes a dive westwards, which will serve to ensure the coldest air stays on track towards Ireland and the UK, and does not become pushed east by the large mid Atlantic High. 
By Friday, sub -5°C uppers are extending down into Biscay, with Ireland lying between -7 and -10°C. This is a few degrees warmer than the GFS forecasts, so it will be interesting to see exactly which model verifies. The GFS does have a bias towards overdoing northerly outbreaks, so it could be that the truth lies more in the ECMWF solution. This would still be an extremely cold situation for such a long sea track, and will be enough to ensure that the numerous showers and comma features will fall as snow, at least away from north and west coasts.

By the weekend, the low is hovering near or over the country, so depending on its exact position, some areas may see more snow than others at certain times. With a covering of snow over many parts bringing increasing nightime cooling, the slightly warmer uppers by then should still not be warm enough to overcome the cold boundary layer, so precipitation should still be snow for the majority.

For more see the IWO Daily forecast HERE