eduggs

I'm mildly intrigued by the 3rd - 4th on the GFS, but minimal ensemble support and lots of disagreement between the other models. No clarity in weenie range when day 7 still isn't close to being resolved.

Brooklyn posts a lot in several subforums and has a red tag. Few people provide a counterpoint to his posts despite their sometimes repetitive and simplistic nature. Non-red-taggers get constant push back so I don't feel it would be constructive to police all their posts.

Really nice plot. The correlation between PNA+ and NYC snowfall jumps out. But one thing that a stickler would say is missing from the analysis to make it statistically robust is an accounting of the relative frequency of time spent in each quadrant. For example, hypothetically if 95% of winter days occurred with an AO- PNA+ combo, observing a majority of significant snow events with these parameters would not be telling. What you're getting at is the relative likelihood of significant snow on any given day with each combination. And for that, some kind of normalization of the data is required.

Gotta marvel at the 12z CMS with 3 rain events and another just past the end of the run as we approach peak winter climo. Fortunately other mid-range guidance starts to differ early in the run.

Yes please occasionally post something other than toggled 500mb anomaly charts that you think show a favorable "pattern" for cold and snow. Better yet, spend some time on analyzing why so many of your highlighted patterns fail to portend cold and snow. Once you have a better handle on that, you will be a much better mid- and long-range forecaster. I'm not sure if this applies to you, but I really think younger forecasters are at a disservice having grown up in the era of tropicaltidbits, pivotweather, and various plotters to view historical data and "patterns." Without a deep understanding of statistics and a more intuitive feel for forecast uncertainty that comes with age and experience, the ease of data access gives youngsters the impression that they understand things that they really don't understand.

Well Brooklyn primarily posts about "favorable" signs - usually mid or long range ensemble mean anomaly charts... over and over again. It's been like that for a few years now if my memory servers me correctly. That seems kind of weenyish to me. Sometimes I appreciate it... but other times a bit more objectivity is warranted. Presumably he will acquire more balance with more experience.

Yeah exactly. In hindsight it's easy to identify what went wrong. But model ensembles 10-15+ days in advance miss key details.

That's slightly more optimistic than I would mentally lock in. But statistically it's not unreasonable.

Nothing on the 12z ECM out past 10 days either. Well other than rain.

Agreed that operational runs are nearly useless past 7 days. Ensembles are decent for airmass forecasting, okay for general storm prediction, and poor for snow forecasting at that time range.

I think you have a short memory. There have been several very favorable looking periods over the past 3 winters that all failed to precede significant snow in our area. I want big snow as much as anyone. But we're ultimately going to need to see it on operation runs inside 7 and particularly 5 days before excitement is warranted.

2 problems with that: 1. The correlation between "favorable periods" and local snowfall is relatively low. 2. Ensemble means out past 10 days have a degree of uncertainty that is large relative to the regional synoptic scale. In other words, model error at that time range significantly exceeds the average synoptic different between rain vs. snow or storm vs no storm. And regional snowfall is driven more by shortwaves in the flow than the longwave "pattern." Since ensembles are heavily diluted by averaging out past 10 days, they cannot "see" the shortwaves that make or break snowstorms for us. That's why modeled favorable patterns fail to portend significant snowfall far more often than they successfully predict it (esp outside mountainous regions). The uncommonness of significant snow as a Bayesian backround state also has to be considered, regardless of what the ensembles look like.

Ensemble charts are averages of dozens of individual runs. That's why a great ensemble "look" often does not lead to a snowy outcome locally. The details are everything with snowstorms and ensembles don't resolve the details.

I am serious. Trof axis and shortwave spacing and timing look poor for local snow on the GFS and CMC out past 10 days. Snow threats may or may not pop up regardless of what ensemble averaged anomaly charts look like.

12z GFS and CMC don't look great out through fantasyland. Enemble spread and run-to-run changes as usual offer some hope. The 0z ECM was different and a little more encouraging IMO so 12z will be interesting. A recurring problem I see with Twitter forecasters is they equate modeled negative (blue) 500mb height anomalies with snow. Unfortunately for us coastal plainers, we need more than blue height anomalies at day 10, +PNA, -NAO, favorable MJO etc. We also need very lucky shortwave timing and interaction. Outside the mountainous regions, no snow is always more likely than snow, regardless of the so-called "pattern." That's why the Twitter hype fails far more often than it succeeds. Unfortunately most Twitter Mets overrate their own prognostic abilities and have a poor instinctive sense of bayesian statistics.

A lot of those SLP positions at hr204 look pretty sweet, but based on the snow depth change through that time period, temperatures outside the mountains are a problem. We watch.

How long will the snow last under full sun? Already melting fast despite the relatively low dews.

This recent string of posts is the best and most objective I've ever seen from him. It counters the overconfidence and unsupported optimism quite well. Snow is uncommon in the low elevation coastal plain. A lot has to go right to get it. Failure is the default outcome. Many people still haven't learned that there is more uncertainty in long range ensembles than they think.

The RGEM has a distinct swirl of vorticity slide through on Thursday evening. A few other models also have this minor feature. Wdrag mentioned it yesterday in the N&W thread. It looks dry for now but might bear watching for another refresher.

I gotta admit this upcoming New Year's period looks disgusting: cold and wet. It kind of spoils the festive feel from this recent bit of wintry weather. What an ugly synoptic setup.

Ensembles and weeklies only get good after Jan. 6 or so. And the favorable period may not last more than a week. Plus ensembles have only modest reliability at that range. Ultimately snow vs no snow will come down to nuanced shortwave interactions as always. So applying some realistic skepticism of a "wildly amazing pattern" is warranted IMO. We go through this almost every year and seem to end up disappointed more often than not. That said, I think optimism is warranted too. It's better to see ensembles looking favorable than the other way around. It's just helpful to remember that statistics are generally against us when it comes to snowfall.

Yeah GEFS mean is pretty wet for eastern areas. Finally coming around.

Consensus is two QPF maxes: one in EPA and one in EMA. Ratios might be better in PA but it's impossible to know where best banding will set up.

A serious step back towards the wild 6z run. Not quite as expansive on the NW, but still great for eastern SNE. We probably won't know until nowcast time.

I see it now, thanks!