RU848789

the WB maps show very little difference between 10:1 and Kuchera which is surprising with temps 34-36F during the snow; the Pivotal maps show a ~50% difference, at least along 95, where the ratios are likely to be the worst (vs 78 and north).

Major improvement for 95/coast in particular...although this is 10:1 and with surface temps around 34-36F while it's snowing, these numbers would likely be about half what is shown for 95/coast.

Cool. Yep that was me and still is, lol. I used to have a website at Merck where I'd post snowfall info and forecasts from the NWS and other pros (I linked to this site and pro sites all the time; I also did/do tropical weather), as well as trying to explain what was going on (and the various outcome probabilities) to mostly non-scientists and people could sign up for email notifications when I had an update - had about 750 people on that list when I retired and of those I now have about 200 people from work (many I never knew) on my weather emails (also have a family/friends list of about 200). Started doing this about 25 years ago when I was on the site crisis management team (which included snowstorm impacts). And there's FB and a couple of RU sports boards where I post similar info. Keeps me busy, lol. I don't post these long weather posts here because 90% of posters already know what's going on. Can you share the name or IM it? Just curious who it is.

Loving the Mesos, which are now in their range, showing a 3" line from roughly Trenton to Sandy Hook and a 5-6" line along 78 (at 10:1, which is unlikely for the RGEM with surface temps on the mid-30s, but possible for the colder NAM with surface temps in the 32-33F range). Maybe we can get lucky with the globals and beyond... And it's looking very likely that for 95, even if there's little accumulation on the roads, heavy snowfall rates and poor visibility will be hitting right during the morning rush hour, so the storm will still be impactful. And for areas along/N of 78 this will likely be a very impactful storm unless we see last minute track shift north. Also, for coastal areas, moderate flooding is looking likely with the storm as per the NWS AFD and could also see 40-45 mph gusts at the coast at the height of the storm Tuesday morning (more like 30-35 mph inland). https://forecast.weather.gov/product.php?site=NWS&issuedby=PHI&product=AFD&format=CI&version=1&glossary=1&highlight=off

Maybe if I stay awake and keep posting good things will keep happening, lol. the 6Z GFS just came out snowier than 0Z, especially for areas between 195 and 78, including NYC. Maybe the "trend" north has stopped.

Although the 6Z RGEM just came out snowier for 95/coast (this is why forecasting can be so tough) with the 3" line from Trenton to Sandy Hook and the 6" line roughly along 78 (at 10:1 which is not realistic for 95 and SE of 95 with surface temps 34-35F). Still an improvement vs. 0Z.

Well, the last holdout for significant snow for areas south of 78 and along 95 from Philly to NYC, the NAM, has caved to the rest of the guidance, with much less snow south of 78 at 6Z vs. 0Z. The 6" line is now along 78 insted of from Philly to Pt. Pleasant. Oh well. The 0Z CMC still had 6" along and N of 276/195, but it was much warmer than the NAM at the surface, so ratios would be far worse. Would be nice to not have this keep moving warmer and wetter so that those of us along 95 might still get the 1-3" shown by the NBM. I'll be bold and go with 2" for my house in Metuchen vs. 2.5" on the NBM and 1.5" from the NWS.

Thanks!! Not trying to be argumentative over the whole accumulation-intensity-surface temp topic - just trying to point out that there are situations where that can apply and this was looking like it could be one - as modeled with very high rates. I completely get that there are many things that can torpedo that and that the reality is we're likely to get a fair amount less than many of the models are showing at 10:1 given warm surface temps on most models. Another question for you since you've been very helpful on the NBM. Any idea why the NBM snowfall along 95 and SE of there would have co me down from the end of the 19Z NBM map, below, to what should be the beginning of the 01Z map below, when the only 0Z model that should be in that NBM would be the NAM and the NAM is quite snowy for 95 and towards the coast at 0Z (the NAM always comes out first as far as I know). I would think the NBM for the 0Z suite would start off kind of high or at least higher than the end of the 18Z suite when only adding in a snowy NAM. Any insights would be appreciated, again.

Well at least we have the NAM on our side. Also nice that it goes down to 31-32F for 95 from Trenton to NYC between 4 and 7 am and stays there, so we shouldn't have much trouble accumulating with good intensity snowfall (6+" in <6 hrs) and cold surface temps. Soundings also look good along 95 with sleet at 4 am then snow the rest of the way with a column well below 32F. Ratios are also pretty good even for 95 (0.8-0.9 if one believes the Kuchera), but a lot lower at the NJ coast. As modeled of course. How do we make this happen?

The Euro gets down to 32F along 95 by 7 am and most of the snow then falls with temps 31-32F along 95 and colder inland, which is why ratios are near 10:1 along 95 and higher than that inland. The other models do look to bottom out at the 33-34F range around 7 am and are likely there for 3-4 hours on either side of that with the heavy snow, but hard to know that with models only showing temp data every 6 hours and temps being in the mid 30s at 1 am and 1 pm. Need more granular data...

Schwing!! Coldest model with temps getting down to 31-32F by 7 am and staying there for the rest of the storm, which is why the Kuchera isn't much lower than 10:1 for 95 and is 12:1 or more well inland.

Don - all valid thermal/column/accumulation concerns, but if the modeling is correct and along 95 we get 1-1.5" per hour snowfall rates with almost the entire column below 32F, but just the surface maybe at 33-35F, I would think we'd actually do at least Kuchera ratios or higher, i.e., 0.7-0.8, as the falling crystals would likely be decent dendrites from the DGZ to near the surface and only melt a little near the surface, hopefully not enough to lead to significant compaction and low ratios. I liken this to some of the late March/April storms we've had with high intensity, but decent ratios (not 0.5 at least)/accumulations although that's relying on memory and with your treasure trove of data you have access to, perhaps those storms did have poor ratios (although decent accumulations were seen). If the models verify and we do get at least ok ratios, then we could be looking at 6" or more for 95 - and with heavy paste, we could then have substantial power outages. Will be interesting to see.

Hey @wdrag- I recall you explaining what the NBM snowfall "model ratio" meant but can't recall it or find it. Any chance you (or anyone who knows) could refresh our memory? Thanks!

Well, to be fair, for the last 2+ years most winter storms have underperformed vs. what forecasts predicted, some terribly so, so people get gunshy and would rather predict 2-4" and then have to bump that up to 4-8" early in a storm than to have to have a 4-8" storm fizzle down to 1-2". I get it.

NYC has truly been screwed. I live just 25 miles SW of midtown and we have 7.3" this winter, which is weak, but not atrocious.

here it is...not too different from the NBM (slightly less snowy).

As per the last several GFS runs, for the 18Z GFS, verbatim, we're looking at 90% of the 7-8" (what falls at 10:1) of 95 corridor snow falling from 4 am to 10 am for >1"/hour rates at slightly above 32F, but at those intensities, I would expect easy accumulation and we might even be pleasantly surprised with better than Kuchera ratios (which look to be in the 0.7-0.8 range), once accumulation gets going (have seen this before with high intensity systems with marginal surface temps, but cold columns with good crystal growth in the DGZ). Soundings do look like a brief (hopefully) period of sleet after the changeover. If intensity is lower or we get an extended warm nose or any number of other things, accumulation will be much harder, but as modeled, I think we'd get decent accumulations.

Well, the GFS has moved the southern extent of 6"+ snow (at 10:1 ratios - maybe not a good assumption) north about 75 miles since 0Z, such that the 95 corridor from Trenton to NYC is now much closer to the "it gonna rain" line vs. 6Z and 0Z last night. However, If folks want to know what a trend looks like, I give you the CMC, lol, as it's come hundreds of miles south over the last 36 hours. But at the end of the day both the 12Z GFS and CMC are at least much closer to each other than they've been, so there's that.

If the 6Z GFS is correct for Trenton to NYC along 95, for example (and we have no clue), it's showing 7-8" of 10:1 snow falling from the sky from 10 am to 4 pm with good looking DGZ snow crystal formation/growth, column temps well below 32F until very close to the surface and surface temps around 33F. Verbatim, that snow is ;likely going to accumulate easily at over 1" per hour rates and will likely do better than the Kuchera algorithm, which treats a 1500 foot deep 33F layer aloft the same as it does a shallow 300 foot 33F layer right at the surface (it only takes max column temp into consideration, not depth=time at that max temp) and those aren't the same, as less partial melting will occur in the latter case, meaning less compaction and loss of good ratios. If the GFS is correct. Interestingly, the GEFS shows warmer surface temps of 35-37F during the event, but since it's showing a smoothed mean of many members, the ~6" of snow it shows falls over 9-12 hours, so at maybe 0.5" per hour, which is not nearly as dynamic and that could be why there is less cooling at the surface; at those temps during the day and at lower intensity, though, one would expect a fair amount less snow to accumulate. One would think the Op is more likely to show dynamics better than the ensemble mean, though. Intensity is going to be so important for this storm if the GFS is close to right, especially during the day...

Interesting that the GEFS mean max snow moved south with the 95 corridor being along that max for the most part (and is now fairly similar to the EPS mean), while the GFS Op max snowfall axis moved considerably north (losing a lot of snow for SNJ/SEPA). NYC looking to be set up nicely. Don't love that the GEFS surface temps never go below 35-36F from Trenton to NYC though (the GFS does get down to 32-33F as does the EPS), which will certainly cut down on accumulations some, verbatim (although with most of the snow falling at ~1"/hr rates, the snow will accumulate).

Euro looking similar to the GFS in many ways, although it's a little earlier and not as snowy - but a big improvement over 12Z, especially for those along 78 and even 95. The early part would help with accumulations as ~90% of the snow falls before 7 am (after a good 3/4" of rain, at least for 95). Euro and GFS vs. CMC and UK, I guess.

What is wrong with you people? Just kidding, but normally, when I'm away from the internet (poker night) for many hours during the run-up to an event, I judge whether things went well in the model suite by how many new pages there are in the thread and there was only one new page, so I assumed the GFS and CMC were both terrible, but then I check and the GFS looks great while the CMC was just way south with most of the precip, much earlier. So at least it's not all bad - neither model really budged much I guess from previous runs.

The fall line is the 95 corridor for the purposes of weather along the eastern seaboard and especially from DC to Boston. More formally it's where the coastal plain meets the Piedmont and just NW of the fall line is where elevations start to increase and the fall line is often along rivers, like the Delaware in SNJ/SEPA. https://en.wikipedia.org/wiki/Atlantic_Seaboard_Fall_Line

And Mt. Holly is much more optimistic than this morning, when they were only calling for a chance of snow well NW of 95; here's their latest...I like the part in bold... LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Unsettled weather on tap for the start of the new work week as a developing storm system impacts the Northeast and Mid- Atlantic. However, there are numerous inconsistencies among the models that leads to a low confidence forecast. A deep upper trough over the West Coast ejects into the southern Plains, and the base of the trough pinches off into a closed upper low over the Southern Plains and Gulf Coast states Sunday night. Surface low pressure develops out ahead of it and moves towards the Mid-Atlantic on Monday. This is where the models go awry. The 12Z/08 ECMWF has the low passing through southern New Jersey and Delmarva Monday night, and then the low intensifies off the New Jersey coast as the H5 trough follows behind it Tuesday morning. This system then departs Tuesday afternoon. In terms of sensible weather, the predominant ptype will be rain on Monday, changing to snow over the southern Poconos and northern New Jersey Monday night and Tuesday as colder air filters into the region behind the departing low. A plowable snow is possible for those areas, and possibly even down to the Fall Line. The surface low is faster in the 12Z/08 CMC, with rain moving into the region earlier on Monday, and has the low over eastern Long Island by Tuesday morning. The storm is then gone Tuesday afternoon before the cold air filters into the region. This results in minimal snow accumulation. The outlier, though it has been a consistent outlier, is the 12Z/08 GFS. The storm is much slower, with the low still over North Carolina and Virginia Tuesday morning, and then passes through Delmarva during the day Tuesday before departing Tuesday night. With high pressure building in from the north, cold air advection will be underway, and temperatures drop to below freezing across much of the region. This results in at least a plowable snow across much of southern New Jersey and into Delmarva. The NBM snow probabilities have a less than 10 percent chance for 4 inches of snow or more in 24 hours ending at 00Z Wednesday for most areas south of the Fall Line, and up to 25 percent chance for 4 inches of snow or more in the 24 hours ending at 00Z Wednesday for the southern Poconos and northern New Jersey. Due to the low confidence in the forecast, opted to follow the NBM guidance closely. This results in likely PoPs for Monday afternoon and Monday night, and chance PoPs for Tuesday morning. Opted to keep slight chance PoPs continuing into Tuesday afternoon, mainly due to the GFS being slower.

Walt - the NBM, which I know you and the NWS favor, is finally showing at least a minor snowfall for NYC Metro (1-3"); granted it's hard to know how much of this would truly accumulate, but if we see anything like the rates the GFS is showing, it won't matter much, whereas if we only get light to moderate rates during the day, it's white rain. Too early to know those details.