Colder look to our weather late next week

Our weather could potentially turn much colder later next week with severe overnight frosts and wintry showers likely across northern parts of Ireland and in coastal districts.

According to the ECMWF, the European weather forecasting models, the change will come about next Thursday and Friday as a result of high pressure over Ireland being replaced by cold north to northwesterly winds feeding much colder polar air across Ireland and much of western and northern Europe.

At this point it looks like high pressure will attempt to build and push eastwards over Ireland shifting the threat of any wintry showers to Britain.

Subtle changes will occur in model output over the coming days.  Ireland could see a dramatic drop in temperatures with snowfall for some or end up being on the periphery of an Arctic plunge of cold air that hits Britain and other parts of northwest Europe. As it stands, we must look at the evidence that is presented to us at this point (Thursday AM, 28 Nov).

The below ECMWF chart is an atmospheric pressure reading for 1am on Saturday 7th December at 7am. The chart shows northerly winds over Ireland with high pressure to Ireland's west edging slowly eastwards. 

This sea level pressure chart from for Sunday, 8th December shows strong northerly winds which would bring heavy wintry showers across much of the country with perhaps the exception of southern parts.

The next ECMWF chart shows upper air temperatures or 850 hpas, which roughly correspond with the air temperature at 1500ms. Usually, 850hpas of -6c or more are required for snowfall to be a possibility at sea level.

The below GEFS Model ensembles graph for the Midlands region of Ireland indicates a drop in temperatures during the same period.

This graph indicates that the Arctic Oscillation (AO) is trending negative for the same period. The AO index signifies the degree to which Arctic air penetrates into middle latitudes.

The below charts for Sunday 8th December shows the potential snow cover for Ulster, North Connacht and Leinster.

According to long range forecaster Peter O'Donnell, it will turn a bit colder each day from midweek onwards, as highs slide down closer to normal values of 6-9 C.

He continued: "This colder turn still looks somewhat more dramatic (by Friday 6th and the following weekend) on the leading European model guidance, than it does on other model runs, and if correct, the northerly surge of arctic air could produce a few wintry showers in the north or even some accumulating snows; however, the milder signal is probably not being totally overcome and could then return within three or four days.

"There is also some chance that the colder turn will be less dramatic altogether, although only the Canadian GEM model currently takes that approach. On balance, we're currently saying that some snow is likely in higher parts of the north with mixed wintry showers for other regions, and a moderate degree of cold allowing for highs to fall to about 2-5 C, lows into the -5 to -2 C range. Some treatment of roads seems very likely, a more widespread problem for road travel is a less likely but possible outcome in Ireland, although more likely in some parts of Britain and the near continent.

"The eventual destination of the core of this cold appears to be over the Alps and northern Italy which can be associated with a slow warming trend long term in Ireland as winds (in about two to three weeks) return to a southerly direction," added Mr. O'Donnell.