Wednesday, 9 January, 2019
Forecasts for Ireland
TODAY ... Cloudy with a few brighter intervals, isolated showers or patchy drizzle, in light northerly breezes (backing to westerly near west coast later). Rather cold especially in Ulster and Leinster. Highs will range from 6 C near east coast and in most of Ulster, to 10 C in Kerry and some other coastal areas of south and west.
TONIGHT ... Variable cloud, isolated showers or drizzle, cool. Lows 2 to 6 C.
THURSDAY ... Mostly cloudy, moderate southwest winds returning (40-60 km/hr in coastal north and west). Highs 8 to 11 C.
FRIDAY ... Overcast, isolated showers, moderate southwest winds, mild. Lows near 7 C and highs near 12 C.
WEEKEND OUTLOOK ... Rather windy at times, outbreaks of rain (5 mm could fall), and temperatures steady 9 to 11 C.
NEXT WEEK ... Possibly quite unsettled and windy, with a growing risk of colder weather developing from the north or northeast at some point between Thursday 17th and Monday 21st. Temperatures will hang on near 8 C until this change occurs and could then fall sharply. As guidance is still very uneven on this transition, it's a question of probability of when the transition will begin. It could take longer than ten days but I believe it will happen before we reach the end of the following week. When the colder spell begins, it could last quite a while so be prepared for that possibility. At some point in the next two weeks to a month, a disruptive cold and snow event seems fairly likely. We can't really begin to guess how disruptive until the details show up on charts, every cold spell has its own quirks and singularities. Some are rather dry and produce only marginal amounts of snow (like March 2013 for example). Others rapidly produce large quantities of snow (like December 2010 and last February into early March). I would say the period from 24 January to 10 February is the highest risk period at the pace of change currently. Change is already beginning to show up in North America with eastern regions facing a sharp colder trend. The first signs of colder weather on any guidance show up around Friday 18th so that is probably the earliest that any wintry weather could strike, perhaps we could say the probability starts around 10% there and increases by about 5% a day until it levels off around 70% by 1st of February.
My local weather on Tuesday was overcast, quite cold and a very light snow turned heavier by late afternoon, so we now have 3 cms on the ground and more gradually accumulating, with freezing drizzle mixing in, and temperatures steady near -2 C. Once this moves through, we are moving back into milder weather as central and eastern regions turn sharply colder. A possible snowstorm for the Washington D.C. region looms for this weekend but this storm will be coming together out of just some dry cloud formations west of Mexico's Baja peninsula at the present time (a front spinning off the Pacific storm hitting further north). The flow is about to buckle allowing much colder air to sink south into the Great Lakes region, then it will be held in place there as storms rotate around from the remnants of Pacific storms until they reach Greenland. What we need to see for Ireland and Britain to turn colder will be for the Greenland region to develop higher pressures at all levels steering these storms back into the Canadian arctic, and allowing higher pressure near the north pole to slide south into the vacuum left by the rise in pressures near Iceland. This will force the persistent high near Ireland and northwest France to push west to avoid being battered by the southward moving arctic jet stream. This scenario keeps appearing on 10-15 day time scales on various models and will become a big deal for the weather when it finally begins to settle into shorter time frames that are more reliable (and then actually happens).