eduggs

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!

The HRRR is a dangerous tool, highly susceptible to wishcasting. 500mb on the HRRR would be helpful to guard against model field hallucinations, but I don't think that parameter is available.

To me if looks like the lowest surface pressure is a couple of mbs lower on the western lobe and a couple higher on the eastern. Pressure field looks otherwise very similar to 18z when I toggle between them. The biggest difference I see is a bit more precipitation NW of the low. It's a good shift but still looks minor to me.

The pressure field doesn't look too different to me. Precip. field too. The placement of the L on the map can be misleading. The pressure field is like a topo map of terrain elevation with ridges and peaks. There isn't always one solitary summit. It looks like a minor shift to me... typical run to run variation. But I'm hoping for a positive surprise.

It's an unsexy dampening wave, but there's a good antecedent airmass. The high QPF signal on the GFS catches my eye. Recent runs were fairly wet as well.

There's a pretty decent QPF signal for the damping wave(s) Dec 24-26 on the GFS. Warm front pushing into entrenched cold air. The ECM and CMC have it too, but slightly drier. Kind of an under the radar threat, but it's something to watch.

The GFS has been throwing some pretty significant precipitation into the cold air Dec 24 - 26. ECM and CMC to a lesser extent, but with a similar idea. Wherever the warm front boundary sets up could get some sneaky good snows (and/or ice) around Christmas. Early guess would be CNY through CNE. Still way out there though.

12z GFS was pretty f'in close for EMA and esp EME. If that NS wave can dive south from ON and phase a little faster it could work out OK for parts of SNE. Not much time though. Can't have any set backs over the next few model cycles.

Nice little Xmas snowstorm on the 12z GFS just north of NYC. The GFS has been hinting at this kind of setup for several runs with limited support from other models. As shown it's an unlikely outcome, but something else to watch. As yesterday morning's short duration, moderate snowfall across parts of the LHV demonstrates, with cold air in place it doesn't take a perfect setup to get a beautiful wintry scene.

Drove through the Hudson Highlands this morning and there was an impressive snowcover around the West Point area. It must have really pounded early this morning. It wouldn't surprise me if there were a few spots up there that got 5 or 6 inches of snow.

Missed another one. No snow between Morristown and Montville. Well maybe a light dusting of snow/ice on the mulch. I think the CAD held the cold along and to the west of the terrain fall line. So snow was basically confined to west/north of I-287. Pretty well modeled actually except slightly more snow than ice compared to the progs... although observation yesterday from down in MD and PA suggested a slight overperformer with respect to ptype.

Weather model improve every year. Verification is significantly improved since 2004. Regional synoptics are well resolved out to 5 days, whereas 20 years ago that was fantasyland territory. Surprise storms are a rarity these days. Here are a couple of graphs of two verification parameters for the ECMWF. Other models may have improved more or less than these scored parameters indicate.

That area of vorticity in the southeast might play a role in antecedent downstream ridging, but to me the bigger factor is to the north. The key trof/shortwave diving SE from the Dakotas towards the Ohio valley has to be on the downstream side of the longwave trof and/or the polar jet trof up in Canada for it to deepen and take on a negative tilt. On the GFS, the main shortwave is on the upstream side of the polar jet trof until too late, delaying the phasing process and subsequent cyclogenesis until the wave is well east of our longitude. On the ICON, and especially on a few wrapped up runs over the past few days, the key shortwave was positioned upstream of the polar shortwave diving sse-ward through Ontario. This timing and positioning of waves is key to amplification.