TECHNICAL DISCUSSION - Storm Eunice 18th February

I noticed that yesterday's UKMO 12z run was the most bullish in terms of wind impact on the southern half of the country, but as @Meteorite58 points out the GFS and WRF modelled this particulary well. I find the superforecast on windfinder.com (derived from GFS) is usually pretty accurate for my location. Just for fun, I made a note yesterday evenings TAFs from Dublin, Cork and Shannon airports and compared the forecasts to today's actual peak gusts:

Dublin airport: 100Km/h @ 11am (forecast gust 50 knots = 92.6 Km/h, but gave 40% prob of 60 knots)

Shannon airport: 106Km/h @ 10am (forecast gusts 50 knots, 40% probability of 65 knots)

Cork airport: 122Km/h @ 10am (forecast 60 knots = 111 Km/h)

So all underestimated slightly ignoring the 40% prob., but always interesting to cross-check the TAFs against the various models.

Hourly animation of gusts since 21Z yesterday. Ireland got off very lightly in comparison to southern GB and now the Netherlands. The snow in Ireland really didn't materialise away from Donegal. Certainly not the "drifting snow" that the Minister Patrick O'Donovan spoke of when referring to the orange snow warning counties on Drivetime yesterday.

Let's be honest, none of the data really supported widespread lying snow at low elevations and that's how it played out, despite interpretations to the contrary here and in other places. 150m seems to have been the snowline for a time and that's not bad going for an Atlantic storm delivery.

As for Minister O'Donovan, you could hardly expect him to be giving an accurate forecast briefing, just from those few keywords he picked up at the meetings he attended. Met Éireann were right to warn about the risk of snowfall causing disruption on the roads, albeit in short lived bursts, but perhaps a yellow rather than orange warning would have been correct in retrospect.

Looking back at the model performances, when the ICON was showing a track well to the south, it wasn't as far off as the consensus method suggested, although at the 48 to 60 hour time range, the main model error was not so much with track but that dual structure which only began to emerge on more recent model runs. So that makes the discussion of the track performance somewhat blurred by the fact that the northern set of track predictions verified for the northern centre that emerged, but the southern set were fairly good for the southern energy centre.

The fact that the storm took on that dual structure probably explains a lot of the eventual differences between forecast and actual weather, it was clear that the northern energy centre robbed the snowfall zone of full potential except perhaps in one or two places in Mayo and Donegal. It also tended to dilute the strength of northwest winds that would eventually join forces with the southern energy centre, and that probably explains perceived errors (as widely discussed in the other thread) in the orange level wind alerts in Leinster.

I guess I won't use the term landfall again after reading some comments about it, but it was a rather innocuous attempt to avoid a longer string of words relating to track analysis, for me "landfall" just means where the low centre reaches land and does not carry along any implications of "there shall many die" or "here will everyone pledge allegiance to the stars and stripes." Neither of those implications was my intent in using the term, it simply meant what I outlined above, the model depiction of where the low would reach land. In fact, while strongest winds often are found 50-150 miles south of a landfall point (and even for hurricanes, 20 to 50 miles is standard), in this case as with Darwin there was a tendency for strong winds to follow behind the track of the low centre, so I wouldn't say there is always the same relation between storm track and strong winds. Even so, no doubt the strongest winds of the storm were held off to the south and eventually went on to do considerable damage across southern England which was not a surprise to anyone I would think.

Anyway, +1 to Kermit for thinking this would be an event worthy of a thread, and +1 to Sleet and Snow for realizing that a technical thread would be a good idea. The larger general interest thread had a lot of good posts that I found useful, but also it tends to be a collection of comments that I could predict better than the weather itself, and usually from the same people at roughly the same times relative to the unfolding storm. While it's amusing at one level, it is also a pointless waste of time to read the back and forth about their opinions.

"Anyway, +1 to Kermit for thinking this would be an event worthy of a thread, and +1 to Sleet and Snow for realizing that a technical thread would be a good idea. The larger general interest thread had a lot of good posts that I found useful, but also it tends to be a collection of comments that I could predict better than the weather itself, and usually from the same people at roughly the same times relative to the unfolding storm. While it's amusing at one level, it is also a pointless waste of time to read the back and forth about their opinions."

^^^^ spot on, 100% M.T - thanks for all your time, experience and expertise you bring to these threads for ALL our benefit.

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I see cherries are ripe for picking right now.

One 30-metre-high exposed lighthouse out on a rock in the sea that always reads higher than anywhere on the mainland exceeds the previous record from 1979 and you use it in an AGW quest, ignoring previous data that showed storm windspeeds trending in the opposite direction. Not going to hijack this thread with that, but will just leave this.

That ship sailing northeastwards to the south of Ireland over the past couple of days is a container ship called Atlantic Star, and is en route from Halifax to Liverpool. They were releasing a couple of weather balloons every day over the past week, so the name is pretty apt. Without their vital upper data the models would no-doubt have done a worse job.

There's a difference between climate and weather.

It's like saying there's no such thing as global warming if we mange to get a bad cold snap.

The data actually does show wind speeds are getting slightly weaker. Dublin had its least windy year since 1959 according to ME.

That doesn't mean big storms and gales can't still be expected. But it's the overall trend over a decade or more that counts.

Thats fascinating that Roches Point was so high. I'm on Cobh only a few kilometers away line-of-sight and although ther ewas a fair rake of shielding from the land going on, speeds were quite low for me overall. Max gust of 88kmh, and mean winds of 40 - 50kmh only.