forecaster

I would expect Pembrokeshire to push into low double figures for a time next week In a light s to sw flow if models hold.

There is now little doubt that part of next week starts to see warming through much of the atmosphere but at this time of year and with light surface winds it may not be realised at the surface. At this stage hard to tell where is the boundary between cold continental drift and more maritime milder flow with possible downslope warming in the northeast. These fine details won't be resolved yet but likely the further se you go the lesser the impact of the warming airmass.

Me being no expert on equatorial waves, but I think what actually happens is that the CCKW's do not mimic an OLR signal, they create it. OLR anomalies (outgoing longwave radiation - not sure if that's appearing on the new mouse-over?) is a good proxy for convection in the tropics. CCKW's are a fastish, eastwards moving wave which come with a convective signature that shows up in the OLR anomalies. So the OLR signature is true, and real. I think the issue is that models find it hard to distinguish this from the MJO wave. (Broadscale) Convection in the tropics can be due to CCKW's, mixed Rossby-Gravity Waves, tropical cyclones, cold fronts, convergence zones, equatorial Rossby Waves, favoured zones of convection due to ENSO state.....and probably a lot more. The above operate on different time-scales and can interfere with each other. To isolate the contributions of different waves, they run their signals analysis (which I think is a fourier analysis) and try to identify which waves are contributing to the current convection. This can be difficult. It may be especially so when you're dealing with CCKW's and the MJO, because the two behave quite similarly. The structure of the MJO is often similar to a CCKW, but it moves more slowly. The models might perk up a bit when the CCKW and MJO are no longer in phase with each other and causing confusion of the signal.

I know. Sorry. It doesn't help that this years' upcoming easterly on the ECMWF det is progged for close to the same date!

Maybe a time to sit back and absorb this thread: http://forum.netweather.tv/topic/75166-model-output-discussion-12z-04122012/page-47 (not picking any page in particular, just the latter stages). (Glad I was not in the UK for that event!) Here is the EC det +192hr prog for that easterly: And this is what actually happened: A few days of chilly weather follow by a breakdown to westerlies. Is this going to happen all over again? Just noticed the 15th is a better example:

I would expect that for anywhere away from coastal west Wales, Cornwall, Ireland and N Scotland it will be a light continental drift for Sunday and Monday at least, with temperatures remaining low. "Concern" though because the 850hPa temperature rises from approximately -10C on Friday to +5C early the next week. This sort of rapid warming at the top of the boundary layer makes me think there'll be a very strong inversion. If stratocumulus forms there, it could persist. We could still get a few days of cold sunny weather though.

Not easy to fix these apparent biases. Models: take equations and integrate forwards in time. They don't see things the same way we do. Not the same thing as fixing subjective biases. Bias correction is the most bog standard statistical technique around, it has little impact on what people here complain about.

Just looking at EC ens clusters for 14th December.22/51 members going for Scandinavian High + Mid-Atlantic Trough (looks similar to the GFS 18z chart shown above). 29/51 for Scandinavian Low + Mid-Atlantic High!

Looking at an EC ensemble 850hPa temperature plume, both the control and deterministic are serious cold outliers within the ensemble. The control (32km) and det (16km) track near together. I'm no modeller, but that would suggest to me that the differences between the EC ens mean and det are perhaps more down to sensitivity to initial conditions and less to do with modelling resolution of the individual members.

Yes, but then you have to be aware of human biases. Regarding the EC Ensemble Mean this morning, notice that it was too flat with the northerly for this upcoming weekend at the 216hr range: In the end, for this upcoming weekend, at the 216hr range the EC det looks like it caught on better than the EC Ens mean. It doesn't look like bluearmy actually said that?

There's no shortwave troughs evident in that picture.

That's PV on an isentropic surface. I never have an easy time interpreting isentropic output. It's useful for some applications, but primarily academics love it because it's mathematically quite elegant. In the operational context, we view fields on isobaric surfaces most of the time and it's really hard to picture (at least for me, and I'm sure others also) how the 340 Kelvin* isentropic surface behaves (how does it slope, where does it slope?), and hence what relevance potential vorticity (which is a combined field of both a thermodynamic quantity and a dynamic quantity - and hence on it's own pretty hard to interpret!) has when displayed on that surface. What I'm saying is that I'm not totally convinced the chart shows what you say it's showing. * I mean, the 340K surface - is it purely stratospheric air, or does the sloping surface pass through the tropopause at some latitudes - if so, which latitudes? This muddies the waters even more.

With that chart I would expect a solid, thick deck of stratocumulus, coupled with relatively mild nights and maxima perhaps about 3C higher than the overnight low. Most places would still struggle to hit double figures.

I'm very sceptical of statements like these. Humans are fine tuned to find patterns. Sometimes this works well for us, sometimes our signals analysis is simply terrible and we spot a pattern which is not real. This is why we need things like statistics. We have internal biases and we need something to stop us getting carried away with them. See here (http://psiexp.ss.uci.edu/research/teaching/Tversky_Kahneman_1974.pdf) for an example study of all the sorts of illusions we internally (not necessarily on purpose) cook up. For me, the ultimate annoying sentence in this context is the one that starts with "scientists have found what __________ have known all along........". (Often, the ________ is "traditional people" or something like that).Well, there is plenty of stuff that we've "known all along" which has turned out to be a laughably inept representation of reality. So, when people say "something has changed in our recent winters", I want more proof than some vague observations without broader context. Now I don't have any strong personal opinions on this. Maybe something has changed (sea ice, snow cover, maybe, PDO...????), maybe it hasn't. I wait to be convinced. But if I am to be convinced, it will be with science and statistics, not solely by the claims of people. Observations have a major part to play (essentially, the major part!), but only in an objective and broad methodology. After all, even if something has changed in recent winters, we still experienced November 2011.

This doesn't look too far off (yr.no forecast):

Yes, they will take it into account. They try to get the initial conditions as good as possible; a lot of effort goes into that. Not sure if the stratospheric response occurs on a timescale small enough to become apparent to most models though.

Just popped one image in here because the winter thread is more high paced. Interesting to note that it seems to be going for northern blocking in Dec and Jan, then the anomaly shifted south in Feb.

New UKMO seasonal model run.

Yes, well said. There's a real radiation imbalance at this time of year, that chart would be dry but "wintry" in a particular kind of way.

Interesting to note, the EC operational appears to be a massive outlier in terms of 850hPa temperatures across southern England at the end of the period. The spread in the ensemble is huge....pretty much from -8C up to +8C, with the operational at the bottom of that range.

I disagree with this. I think you're wrong, and this is why. We could add "warm sector" to the model dictionary if it's not there yet. "Warm sector" is a recognised term that has been in use for.....I'm not sure.....possibly since the early 20th century. It's a key term in the conceptual description of cyclones. A warm sector noted on a chart tells you more than the 850hPa temperatures. Why? Because to draw fronts they will have been considering both moisture and temperature. Hence it's not "more scientific" to talk about T 850hPa rather than the warm sector, in fact it's more limited. It's relative, not absolute, the same way that all frontal notation is. So just because the warm sector isn't "warm" that doesn't mean you have to call it a "milder sector". If you want to go down that direction, start calling summertime cold fronts "cool fronts" or "not quite so very hot fronts".

No, it's not "blatantly obvious". The term is very ambiguous, that's the problem really. It can make it hard to follow explanations, or at least it's hard for me, and I don't think I'm entirely on my own. I don't think met training has anything to do with it since plenty of terminology is thrown around nicely already. Clear, unambiguous terminology just makes it way easier for the reader to suss what is being talking through.

Talking about "energy" seems to be a way of avoiding detail. I am not sure what people really mean when they're talking about "energy", and I doubt it's consistent from person to person. I've never heard a meteorologist use it when explaining a situation, but have seen the WPC discussions have it pop up from time to time. Does anyone have a definition they want to put forward?

What is that field? 850hPa Theta-e?

http://www.amazon.com/Introduction-Dynamic-Meteorology-Fifth-Edition/dp/0123848660 As a serious suggestion, I like all the articles here, they are a really excellent resource: http://www.theweatherprediction.com/habyhints/ He runs through things very nicely in a relatively easy to understand way, and he draws some pretty nice diagrams in some of them. I'm a meteorologist but I read heaps of his stuff. I can never remember which way is a negatively tilted trough......... http://www.theweatherprediction.com/habyhints/127/