Winter 2018/2019 - General Discussion

Dull and foggy... And obviously calm. But mild, of that's any consolation.

The 18Z GFS had a number of extremely unusual glitches and fragmented frames during tonight's rollout - it stalled for a long time around the 120h mark and then randomly threw in frames out of order (so for instance, 180h appeared some time after 120h, leaving the times in between still showing their 12Z charts) and as a result of this and its somewhat outlandish FI output, many over on Netweather have suggested that something screwed up the run, perhaps an unusual synoptic situation it was trying to get a handle on, but that either way the output is suspect / compromised and shouldn't be read into too closely unless tomorrow's runs follow suit. Just before anyone panics due to the horrendous +NAO being shown by the 18Z's FI charts, which essentially have Ireland and the UK under a cyclone with hurricane-esque central pressure by 216h

Even now it's still fragmented and missing quite a few frames. General consensus is to discard and wait for the morning's runs.

The stress seems to have gotten to the folks on Netweather, this is what they had to say about this evening's model runs

I just closed the winter forecast contest to further entries. This is a summary of what 22 of your fellow boards weather forum members have predicted for the winter of 2018-19 ... almost all of the participants are long-time monthly contest forecasters and have made winter forecasts several years previously, so as far as some experience goes, this is about as good as you're going to find outside the locked doors of the weather agencies. (or maybe better, who knows?)

The participants foresee a slightly colder winter than normal, with all of the negative departures likely to fall in January and February after a slightly milder than average December. The average for Jan-Feb is expected to be about 0.7 deg below normal, with some going as low as 3.5 degrees below. A minority of the forecasters believe the full winter season will stay mild, as most think December will be, generally 0.5 above normal.

The consensus calls for a near normal range of temperatures from -9 to 15 degrees, and on the maximum there is only a small spread of opinion. As it has already reached 14.2 in early December, few think it will get much warmer but when they do, they mention February as the more likely month (some mentioned January). On the coldest temperature, there is a wide spread of opinion. Some believe we will not see colder readings than we already had in November (minimum -5.2 is the highest value in the contest). About one-third think it could get down below -12 C. These are the same forecasters calling for heavier snowfall (at Casement, the contest validation site). Here, the range is quite large too, from 2 cms to 41 cms. The consensus value is 12.0 cms for Casement. Recent analogues would suggest that means 25-40 cms in snowier parts of Leinster ... the contest question avoids any insight into snow potential from northerlies in Ulster and Connacht. Personally I think that looks to be no different from long-term averages. The snowfall season for the contest includes March and early April so this would not all necessarily have to fall in the winter months. As far as strong winds are concerned, the spread of forecasts is fairly tight and the consensus is a maximum gust of 76 knots, while the range is from 65 to 84 knots. Nobody entered an extreme value in the 90-100 kt range but I was being conservative, the scoring in any case is by rank order of forecasts so it wouldn't impact much on your score if you were ten knots low, as long as everybody else was too.

Most of the forecasters believe December will be a little wetter than normal, while January and February are likely to be on the dry side of normal (which correlates well with their colder than average calls). The ranges are not extreme, with few individual forecasts outside the range of 80 to 120 per cent of normal for any month. The range for the season is from 89% to 124% of normal precipitation, and the consensus is very close to normal.

(it should be mentioned that consensus varies considerably from the milder and colder forecasts in the group, this is by no means a shared consensus)

Just playing devil's advocate (and snow hopeful!) here, but does anyone else notice how the GFS always seems to blow any type of blocking away as soon as you switch over to the 192+ low res part of the run? Is this something to bear in mind or is it wishful thinking? I've noticed on a few runs both now and also during the heatwave in the summer, that you'd have high pressure reasonably stable up to 192, then you'd click over to the low res section and the whole forecast would go to hell.

Confirmation bias or an actual thing?

Clonmel1000 wrote: »

Nice bright calm morning here this morning a little on the cool side but not bad at all.

Same up here, great to see the sun and blue sky again

Ferocious shower of graupel in West Clare, great to see some exciting weather. Temperature 4.6c and dropping.

KingdomRushed wrote: »

Looking like it’s going to be storm watch next week given the latest GFS output. Severe weather likely. A very violent depression showing for next Thursday.

From what i've notice over the last few months following these threads is that anything over 24hrs seem to be FI when it comes to any storm so i'd expect or wouldn't be suprised to see that downgraded.

Today, its bloody freezing now in Dublin, i'd expect some of that rain we are having to fall as snow in the Wicklow mountains.

John Hammond, a former UK Met Office forecaster, wrote the following on his blog:

"There are signs of more severe cold as we head into the New Year

You’ll have inferred, then, that I am not yet going to commit: Green or White Christmas? It’s simply too far off!

However, there are several reasons within the set-up of the atmosphere this winter that suggest the cold air will be back sooner rather than later. El Nino is one; the cycle of spots on the sun is another even more distant influencer.

Additionally, in the last few weeks I’ve spoken of signs that the usually strong stratospheric westerly winds that circle the Arctic (know as the Polar Vortex) may weaken markedly as December ends. This signal is becoming more ominous. It’s important because it introduces the possibility of a ‘Sudden Stratospheric Warming’ in which the Polar Vortex goes fully into reverse. Ultimately, it was this which led to the severely cold spell that struck the UK late last winter.

From start to finish, this process takes several days, if not weeks, before such a reversal works its way down to ground level. But on balance, there is an increasing chance that cold air will return from the north or the east as we go later through the Christmas period, and more particularly into the New Year.

Exciting times ahead – for the child and the weather enthusiast in all of us!"

Also, Ian Ferguson, a current Uk Met office employee, has said their main model(glosea5 ?) suggests a SSW will occur at the end of the month

SleetAndSnow wrote: »

bitterly cold in cork city with winds starting to pick up now and very heavy, squally showers out of nowhere. Goes from blue sky to darkness. Worst kind of weather. Come on the snow!

I think that was just daytime turning into night, given the time of around 17:00.