One of Ireland’s best known long range weather forecasters says much of the coming winter will milder than normal with temperatures during the first half of the season up to 2c warmer than the average for the time of year.
However, Peter O’Donnell of Irish Weather Online (IWO) is forecasting temperatures to dip close to or slightly below the average for the time of year between January and March. According to the climatologist: “In general terms, the winter forecast for the UK and Ireland is for milder than average conditions about two-thirds of the time, and colder than average about one-third of the time, in the main winter months of December, January and February. I could add that both November and March show similar outcomes in the research model output so whatever your preference for a winter season, this should apply, mild spells will tend to outnumber cold spells.”
WINTER 2013-2014 WEATHER FORECAST
December looks particularly mild as well as early November, and mid to late February. January shows the greatest parity of mild and cold spells and may end up closer to long-term normal values. My IMT predictions with CET predictions in brackets for the various months at this early stage are NOV 7.5 (7.2) — about 1-2 above normal DEC 6.3 (6.1) — about 1-2 above normal JAN 4.5 (3.8) — close to normal or slightly below FEB 5.2 (4.5) — close to normal MAR 6.3 (6.0) — close to normal Although I have mentioned mild as the dominant theme, the fact that January sees more equal chances of mild and cold may rescue the winter from the category of very mild and snow-free “modern winter” that often dominated in the period 1988 to 2007, and perhaps this will be more of an “average” winter as a result, so my estimation of wintry disruption potential is something like moderate or about five to ten days in total for most regions (of the UK and eastern Ireland, probably three to seven on average in western Ireland). I’m expecting some rather lengthy intervals of very mild southwest flow and occasional heavy rainfalls and strong winds during parts of early November, much of December, late January and possibly into part of February although here I expect any mild spells to be more caused by southerly flow associated with European blocking. March by contrast may be dominated more by cold zonal flow patterns. When it might turn colder (notably parts of mid to late November, and then first half of January) there could be some briefly severe winter conditions and a large-scale reversal of the dominant circulation to high-latitude blocking and northeast winds so that as usual sea-effect snow could provide most of the snowfall potential with perhaps one or two cyclonic storm events in a southerly jet position. My research output is not very encouraging on severity and some of this colder weather may be of the 2006 variety, cold and dry. Given the overall set-up around the hemisphere, I am also going for a rather cold winter in eastern and central North America, and mild in far eastern Canada and on the west coast of North America inland to about the central plains and prairies.
The preferred escape route for arctic air this winter will likely be western Hudson Bay to Great Lakes towards the southeast U.S. states. Note that this pattern places ridges near 110 W and 55 W which if you do the math places the next downstream ridge close to the Greenwich (0W) meridian. That would suggest a Bartlett or Euro-high pattern but with such an active jet stream expected it’s more likely to become a fast stormy (SW) flow, so I have added the detail that at least one major windstorm is probable this winter. As readers of my forecasts know, I tend to favour northern maximum around full moon in Dec (16-17) and Jan (15-16) for wind storm potential with new moon a secondary peak. However, the new moon of 1 January is well timed to coincide with a circulation change and so that could turn out to be the stage for the strongest windstorm potential. The following new moon event on 30-31 Jan is also well timed from the trend in the model output.
Meanwhile the chances of a white Christmas seem rather low from this perspective, with a peak in temperatures right on the 25th in the research output, in fact Christmas Day is indicated as having the best chance of all dates this winter to set a record high temperature which would be 14 to 17 C in most regions. Not saying it will necessarily be that mild but above 12 would not surprise me at all given the strength of this mild signal (which then fades away rapidly by New Years). The coldest days of the winter are indicated to be around 10-14 January which in context of an otherwise rather mild winter brings up an analogue with Jan 1987. It may then turn out to be a case of a bland winter with one very notable cold spell which will some in from the ledge anyway. I should conclude by noting that the range of uncertainty in these seasonal forecasts is rather large and so these percentages indicate the assessed chances of the winter ending up in each of the 20% groupings based on all past cases: MILDEST 20% (very mild) … chance for 2013-14 is 26% NEXT MILDEST 20% (mild) … chance for 2013-14 is 33% NEAR AVERAGE 20% … chance for 2013-14 is 25% COLDER 20% (cool) … chance for 2013-14 is 13% COLDEST 20% (very cold) … chance for 2013-14 is 3%
The median probability places this winter around 34th mildest out of 100 cases. Autumn 2013 is expected to remain 0.5 to 1.0 C above normal in temperatures, with only a brief incursion of colder than average conditions foreseen around late September and early October. There may be long dry spells with some brief wetter intervals and brief spells of windy weather. Mid-October to mid-November is likely to be particularly warm compared with average, but by late November we foresee a highly variable pattern with introduction of some wintry cold at times.