eduggs

I feel like you don't actually read what I write, which is a shame. Being an "old-school" poster, I put a lot of thought into what I write and it's often more than 280 characters. I thoroughly enjoyed the snow yesterday evening in Putnam County and then late last night in Morris County. I'm certainly not complaining. I'm trying to make a point about the NAM so that people are less likely to make the same mistake during the next event.

Don was ripping the NAM before and during yesterday's event. It should be obvious to anyone that the NAM (from ~60 hours out) performed better than the NWS and most other guidance for our area. Don was wrong. If he wants to do a verification of the NAM, he should do it with a more precise parameter than reported snow accumulation. At the very least he should use more than 4 stations. I think the NAM is getting hosed in Don's "verification." A few of the entries look wrong. There's also the issue of sleet: EWR and possibly Central Park experienced some sleet yesterday evening. If this was the dominant ptype during any time point, pivotal will record it as 0 snowfall for that period. But since sleet accumulates, using the pivotal algorithm will under-predict accumulated snowfall. I think the entire purpose of the verification when it was originally proposed was to bash the NAM, assuming it would fail. But it did not. The writing was on the wall early yesterday (HRRR, RAP, ECM, radar). Some noticed. Others doubled down .

But that's the question. How does Pivotal retrieve the raw data? It's suspicious that the NAM would output so much more "snow" for MMU than EWR considering their relative locations and the general snowfall distribution it was predicting. I'm wondering if it pulls the raw data from a location further southwest than the airport.

The numbers from the 18z 12/26 NAM run on Pivotal (which doesn't add anything to the totals for sleet) were: Bridgeport: 5.8 Islip Airport: 5.0 Central Park: 2.8 Newark Airport: 0.8 However, the annotated totals shown for NWS reporting stations don't match the colored boundaries drawn on the map. I've marked Newark Airport and MacArthur Airport with red dots as an example. Based on the graphical boundaries and the legend, the estimated NAM totals are: Bridgeport: 5.5 Islip Airport: 5.5 Central Park: 2.8 Newark Airport: 1.8 So now I'm wondering how the values shown on Pivotal get populated. Is the data drawn from the exact lat lon of the reporting station cross referenced to the raw NAM data, or is there some kind of apprimation going on...?

Where did you get your 18z NAM numbers?

Middletown is a funny case. For the Tue event the NWS hoisted a last minute WAA and the area ended up with warning snows. For this relatively long lead WSW event, I believe that area ended up in the upper tier of advisory snows. Snow is very difficult to accurately predict.

Couple minor comments: on the 18z NAM snowfall map I looked at on pivotal at 10:1, Islip was 5.0, NYC was 2.6, and Newark was 0.8. But the colored graphics look wonky - I'm not sure how accurate they are. Point and click shows about 2" for Newark. It shouldn't be much different than MMU considering their relative lat lon positions. Secondly, I don't believe those numbers count sleet. I believe the algorithm ignores accumulated sleet and only displays the snow equivalent. So some sleet accumulation (NYC and EWR) would lead to underestimation. Since snow accumulation is a very inexact metric to both forecast and measure, I don't believe a subset of reported snow totals is a good method to assess model verification.

It looks like officially NYC got more snow than BOS. But the greater Boston area received about the same amount of snow as the metro NYC area. It sure didn't look like that would happen 2 or 3 days ago.

Don't ignore the NAM inside 48 hours. Yes, it's prone to bigger run-to-run shifts than the globals, but its multi-run trends are meaningful. And it wins more often than any other model when it's a perceived outlier. And to counter potential false memories, the NAM 36 hours ago had some support from the ECM. When the short range models plus the UK and others started to follow suit, it should have gotten more attention. This really could have been better forecasted if people hadn't ignored the best short range model we have for this kind of forecast. In any case, most of us woke up to a beautiful morning today!

Nice f'in job by the NAM yesterday at go time. It nailed the jackpot zone, the 3-4" across NYC metro, 4-6 LHV, and less in NJ. It even showed the inv trof lingering into daylight hours today. Sure you can quibble about minor misses here and there (remember this is 3rd party estimated at 10:1)... like it had more sleet than snow overnight in NJ which slightly underestimated final totals there and SWCT might be a little low. But with snowfall forecasting, no forecast map is ever perfect. But the NAM was hands down the winner. GFS performed horribly.

4.3" In basketball parlance we'd call that a make-up-call.

Love how it's still snowing!

The low at 700mb passed north of Lake Ontario. The surface reflection was in NEPA or WNY. There definitely was a dry slot visible on radar/satellite yesterday evening associated with this shortwave in WNY that pushed through the southern tier of NY. As the "primary" weakened and began to redevelop further south, this dry slot began to fill as well. Clearly the best dynamics were north and east of the NJ-NY border. The NAM showed this very well yesterday morning. All other guidance missed how far north (into NY) the surface low would track and how long the mid-level lows would stay defined. That led to the meat of the precipitation arcing from Long ISland, through CT, to ENY. South of that, the combination of spotty precipitation and a warm tongue near 700mb significantly decreased snow totals. Great job by the NAM IMO.

Radar returns have moved east of Morris County, but it's still snowing steadily. Looks a bit like an inverted trof. I suspect it's low level stuff below the radar beam. Let's keep it going a few more hours!

Driving around near Morristown... I don't think there's 2" of snow/sleet on the ground.

The NAM and ECM were pretty spotty with 0.2 - 0.4" by 2z. They didn't have it completely right but they had the general idea of heaviest precip well north and east.

We tried to warn people. But people believe what they want to believe.

The event is not over. And bust is harsh because snow forecasts are always difficult. That said, I'm not sure what people were looking at. NAM and ECM signaled the northeast shift with the mid-level lows north of Lake Ontario and surface low into WNY. Then the HRRR continuing to trend right to go time made it clear. It should have been pretty obvious unless you were willfully deluding yourself.

Monster dry slot in WNY. It looks even more prominent than the NAM/HRRR were depicting at 18z. That will probably clip us later tonight and hopefully fill in somewhat.

Western Putnam: Sleet and snow grains. Vis 1 mi. 2.5" on the ground. Initial burst of snow lasted about 1.5 hours.

NAM has been showing solid snow accumulations in northern Westchester. South of the NJ-NY border it has a big cutoff.

Get out and enjoy it if you can. It's glorious outside.

Western Putnam: Heavy snow. Vis < 1/4 mile. 1/2" in 20 minutes and 1" in 30 minutes. Can't keep up with measurements.

It's a great looking radar for Albany. I would be pretty excited being up there right now (and they're not typically a snowy location). Should be heavy snow for several hours with great ratios. Major event incoming for them.

Doesn't seem funny to me. Neither does the matching radar.