Peter O'Donnell Answers Your Questions - 21 Dec 2010

iWeather Online Forecaster Peter O'Donnell participated this evening (21 Dec) in an hour long discussion on the IWO chatboard

All questions were submitted by members of the IWO community. Future questions and answers discussions will be publicised in advance on Twitter, Facebook and the chatboard.

[ian] POD : What are the main things that would keep these showers coming in off the Sea, Cape Values?, Temps?, winds?... or all 3..? Thanks
Peter O'Donnell: All three, but wind field is key. The temperature field on the larger scale is pretty much steady state, local variations are from wind speeds and mixing of marine boundary layer but not likely to be too much of a factor

[stickeysocks] why was there a sudden increase in temp in dublin in the last hour ?
Peter O'Donnell: The temp increase in Dublin is from the advection of marine boundary layer (the Irish Sea is still 8-10 deg as you know) due to somewhat stronger E-NE winds around this weak low off the coast. It pushed away the land breeze from the super-cold central counties. But this is also working to create what we call a pseudo-warm front inland that will mean heavier snow inland

[SandraD77] Can you ask Peter, what got him interested in the Irish and British Climate, instead of keeping his focus on Canadian weather?
Peter O'Donnell: I got interested in UK and Irish weather as part of my research into global climate and long-range forecasting. and this is because I have found that the research expands faster if I do real-time weather forecasting, it focuses my attention on details and not the large-scale pattern stuff that most researchers look at 90% of their time ... results have been good, I think, for the long-range forecasting, and I'm learning a lot about your weather too. But I never stopped working on North American weather, my day is pretty full

adagio): Hi, can you ask Peter if he believes this winter episode in an isolated incident or are we potentially locked into a cycle that may last for several years?
Peter O'Donnell: This seems to be part of a long-term pattern shift as you say, back to global patterns that remind us older weather watchers of the period that ended around 1987 (going back as far as you want to about 1940, not that I do) ... and yes, we'll see a few more severe winters yet, perhaps not every time, before there's another warmer interval.

[davesing] [/u]Peter Hi! are very confident that the this mild spell will hit over the weekend what’s your opinion on this??
Peter O'Donnell: I have been very hesitant to buy into this warmup as you may have noticed in my forecasts. Some of the model maps have looked dodgy to me, surface features don't quite match up with the uppers, especially if I think about how the surface is now (a) snow-covered and (b) surrounded by quite cold seas in particular the North Sea has chilled to 4-7 C. These are building blocks for sustained cold and the low coming along looks to be a bit challenged to do all the heavy lifting. So I think it may lose a lot of energy trying to move that cold block. Meanwhile, on snow for the breakdown, looking quite possible, we need to be concerned about freezing rain too. Hope not, nobody likes that stuff.

[SandraD77] Are you happy that you've managed to beat our National meteorological service with your more accurate forecasting? and that this site is generating some great press?
Peter O'Donnell: I don't think too much about the competitive aspects, I got into a daily forecast routine and it expanded from there, so I'm just following where fate leads ... this way of doing forecasting through internet sites has capabilities that were unknown 10-20 years ago (even) and so you have advantages like a steady flow of observations from a very widespread grid, you have flexibility where you can address what your readers want to know, and you have feedback (not all of it positive, which is good, because you need to know what to improve).

Will there be a return to our normal Atlantic type weather or just a brief respite before more cold for Jan/Feb/Mar?
Peter O'Donnell: Brief respite more likely ... foresee some more rather lengthy cold spells, and climatology says if cold continues, it could get even worse (or better depending on your frame of mind). I am saying about a 70% chance of below normal for both Jan and Feb at this point.

[audi-tek from cobH] Evening Peter, Could you explain why does Cork weather in general so differ,compared to the rest of Ireland in general.Is it anything to with the Gulf Stream effect.
Peter O'Donnell: Sure, the nearby warmer waters have a lot to do with it, the other day we saw how one of those weak frontal boundaries set up along the south coast, it was 5 deg at some outer stations and 2 deg at Cork, I think it was -4 at Shannon. We have exactly the same effects around here. Palm trees can survive the climate down by the waterfront in Vancouver and White Rock to my south here, but wouldn't survive here about 10 kms inland and 120m above sea level.

[Johnny the Fox] what effect if any does % humidity have on snow creation, I assume it affects the type of wintry precipitation?
It's not so much relative humidity as dew point. Snow is likely to fall at high relative humidities above 90 per cent. But as a general rule, the higher the dew point, the more water content there will be in snow. The lower the dew point, the more powdery and "fluffy" the snow. As the folks in Donegal and Mayo got last week, very cold air saturated can produce snow that has only half the water content of today's east coast snow.

[almae] Peter, do you think there will be a thaw xmas day/stephens day?
Peter O'Donnell: This would be quite an early call in such an uncertain situation, but the basic answer for most of Ireland is no for Christmas Day and only in southwest for the 26th. Might be delayed (if it arrives at all) to the 27th for some other regions and might never make it at all in some eastern or northeastern counties. But it's an uncertain situation as I say, it's the immovable object vs the resistable force.

[DanoHanley] Our last 3 summers have been poor and last winter also wet and cold. It seems we are getting more weather coming from the north, north west. With Greenland having an influence, are we seeing a trend here ?
Peter O'Donnell -> Peter O'Donnell: The summers have been poor because the jet stream has not lifted far enough north to allow the Azores high to dominate or to allow home-grown highs over France or the southern U.K. as in 2003-06. This seems to be a cyclical thing related to hemispheric large-scale processes that involve the Pacific circulation more than the arctic which is really only a big player from say October to about May. Summers in Ireland are almost always going to have a strong westerly influence of some kind, but when it's southwest with low pressure nearby, hard to prevent a lot of cloud and rain.

[mcriot29] hi peter whats your view on a mini ice age now and sunspots do you think the low sunspot numbers could be the reason for the colder wintersand maybe we are about to enter a dalton minimum type event thanks
Peter O'Donnell: Jury is out on that -- solar variation forecasting is not really in my toolbox so I rely on what I read in the literature from those who study it. From what I gather, we are either already in a Dalton-like downturn in solar activity (Dalton lasted about 1795 to 1828) or at least a smaller downturn like the one in late 19th century. But sometimes there's a longer quiet spell between active years. I tend to think we're in a Dalton type period and there is fairly convincing correlation with lower temperature. But variability does not go away, you can get mild winters and warm summers in a Dalton or even a Maunder type downturn. The great fire of London was in 1666 well into the Maunder.

[Fergal] Peter, you have for a long time signaled an energy peak that could lead to a major winter storm around now. Would that energy peak be focused on a small scale, like the low off Wales, or a large scale, like prolonging the polar vortex over us now?
Peter O'Donnell: I think when I made that forecast, I had this sort of pattern in mind but perhaps a stronger large-scale low that so far has failed to make an appearance, instead we've had this little chain of lows circling around the polar vortex and various small but (today at least) potent meso-scale lows within the vortex. So the energy peak has not quite made all the use it could have made of these synoptics, and that's probably a good thing looking at the travel disruptions already in place. I have to say, there's an outside chance that the breakdown warm front could decide to create a major storm, we're keeping a very close eye on this, as it wouldn't take a huge change in models to bring that about. I'm thinking of the end of 78 New Years 79 type of battleground low there.

[Johnny the Fox] Peter, do you rate the US UGRIB forcast charts? I've been using these for a while and find them very good for Ireland, they got today bang on.
Peter O'Donnell: I'm aware of them, yes, I tend to make daily meso-scale maps for my own use from raw model data, and I rely on that guidance once I've decided which large-scale input I trust the most (or what blend of it).

[johnk] hi peter,during the last few summers we have come to a certain point where we are getting huge amounts of rain in short space for time, and then sun again,what causes this and is it hard to predict
Peter O'Donnell: This goes back to the earlier question about poor summers. When you have low pressure around in the summer, and a generally southwest steering flow, if the fronts get a bit more active you can have very heavy rainfalls and this seems to have been a feature of each summer since 2007 (I almost typed 1007) -- as to prediction, usually there's a pretty good indication of this, I find that easier than regional snowfall prediction for Ireland. The inland southeast and central counties tend to have a convergence of regional sea breezes sometimes that makes them the place to look for the heaviest rainfalls, I mean about Carlow northwest to around Offaly

[Angelicboyne] Mark can you ask Peter if he expects disruption for people planning on going away for new years eve or will a thaw have set in by then
Peter O'Donnell: I am not picking up early signals from any source that point to major disruptions New Years eve or day. The period 2-5 January is indicated more for stormy conditions and this may be a difficult travel period.

flan_da_man125--->cork (ballincollig)] What are the chances in percentage of there being another cold spell in January and when do you think it might occur?
Peter O'Donnell: 70 per cent chance of at least one, my general outlook for Jan is very cold to start, stormy around 4th and 5th perhaps, more cold spells to mid-month, a very stormy period mid-month to 20th, some chance of a major thaw in there too, then perhaps a strong cold spell after that too, I think Russia has a lot of exporting it wants to do and not just natural gas.

[SandraD77] In your years of research have you noticed any evidence of global warming/cooling or trends that would suggest that weather patterns in general are becoming more severe globally?
Peter O'Donnell: The IPCC will have my head, but no, I think that severity of global weather, while somewhat cyclical in various regions, is rather flat-line. What makes it seem more severe? Well, I think there are several reasons for that. We think the weather is more severe because the media covers it more, there are more people in the way of it in some cases, and frankly, it feeds the global warming now climate change lobby's interests, whereas an unbiased scientific look might say otherwise. I would point to a few anecdotal but perhaps telling stats -- worst tornado outbreaks in US history 1925, 1974 ... worst hurricane damage in US history 1900 ... hottest summers in US history 1934-37 ... the great wind of 1839 in Ireland, the 1703 storm in England, the disappearance of whole islands off the Dutch coast in the 12th century. See where I'm going with that? Sure the weather has some fierce storms recently, but ... always has

[davesing] What do you think of Ken Rings weather predictions and forecasting and do you use the same methods as ken to predict the weather?
Peter O'Donnell: Ken Ring, some similar techniques, really haven't done a verification study on any of his forecasting. I have my hands full trying to improve my methods. His stated methodology only covers a small part of my research theory, but he may do other things I haven't read about.

[mpatton] Peter when you say stormy in January do you mean High winds or snow storms?
Peter O'Donnell: In the period 4-5 Jan, I mean probably snow more than strong winds, mid-month, there could be the more traditional Atlantic storm period.

[Johnny the Fox] IS the jet stream being further south the cause of this and last year's cold snaps. What may have caused this?
Peter O'Donnell: Jet stream shifts as "cause" of weather patterns -- this is a tough question because the jet stream has to be generally well out of position either south or perhaps west and far north to get a cold winter. But is that the "cause" or is it a related effect of some other outside cause? That's what my research is about.