RU848789

After about 4 hours of light to moderate snow at 33-34F, with a few light dustings established and then melted quickly as intensity lessened, just now we're finally getting sustained moderate snow (maybe 3/8 of a mile visibility (maybe 600-700 yards) at 32F and we now officially have a "full dusting" or "light coating" (whatever that is, lol) on the colder surfaces (and a good 1/4" on trees, but that doesn't count, lol) which translates to about 0.1". My guess is now that we're 2.5 hours past the full height of the sun and a little cooler, the snow will accumulate at least a little now. Radar looks good for me for the next 30 min or so. If we can hold onto this intensity once we have a cold layer on the ground, maybe we can pull off a whole 1/4-1/2". My other guess is that we've probably had 1/4-3/8" per hour snow "falling" rates for ~4 hours (I always think of 1/4" per hour as light with 3/8"/hr as getting moderate), so that's about the melting rate - could've had 1-1.5" over those 4 hours, but it's midday at March and it's been 33-34F until right now. Anyway, that's probably TMI for most, lol, but I get excited about this stuff, lol.

Just woke up from a decent nap and it's been snowing light to almost moderate and just trying to accumulate a little and then I was rooting around on the interwebz and a few minutes later, without having looked back outside, I checked the radar and basically said, OMG that should be close to heavy snow and looked up and it was, lol - almost a dusting! Down to 34F.

Just posted this elsewhere as a reality check, but damn if this verifies or even close to it, it makes our winter, given what we've gotten so far. The modeling gods wouldn't take this away from us now, would they? :>) This is not a forecast - it's just one model run, but it's a doozy... We've officially been NAM-ed, as the 12Z NAM which just came out shows the potential of this highly complex, very powerful nor'easter. This snowfall map is crazy and the snow falls after almost everyone gets an inch of rain on Monday (the transition to snow is by about 1-3 am Tuesday for most and is over by late Tuesday night). This kind of possibility is why so many have been following this so closely. We could still mostly whiff and get mostly rain for CNJ/NENJ/NYC and even much of NNJ/EPA, but this model run shows what is possible in this kind of explosive setup. Also, we're not 5 days out, we're 24-30 hours from the start of the event late Monday morning. Reminds me of the NAM for Jan 2016's blizzard, where it was the first model to sniff out the huge potential (about 48 hrs before the event, iirc). Stay tuned folks.

They're wrong, at least for what the NAM is showing, with great growth, heavy rates and surface temps dropping to around freezing (Kuchera only looks at the max column temp)...

It'll be at least 10:1 with good growth in the DGZ with the incredible lift and supersaturation we're going to have up there and surface temps now down to 31-32F during the height of the storm - CCB FTW!

Holy...

Comparison of 6Z/0Z Euro snowfall through 15Z Tuesday (10 am EST/11 am EDT), showing significant improvements for CNJ, NENJ, NYC/LI, which is key since before 15Z has better rates and is before the sun is too high (especially before 12Z), so accumulations are less likely to be melted.

The NWS in Mt. Holly upped their snowfall totals at 4 am relative to 4 pm yesterday, which is a good sign, as they're usually slow to respond to increases in modeled snowfall, but you can see that the NWS-Upton did not, given the discontinuities at the county interfaces (from 1-2" in Morris/Somerset/Middlesex to <1" across the magical border into Essex/Union/SI. I think the Mt. Holly numbers are much more reasonable, even if still conservative at this point, which I get, since 0" of snow and all rain are still on the table for these locations.

Best CMC run in 2 days...

Kuchera is an awful algorithm, though and often quite wrong, especially in moderate to heavy snowfall rate scenarios, where the ratios are largely set by the crystal formation in the DGZ, which can be fantastic regardless of the warmest temp in the column, which is the only variable Kuchera looks at - and assumes ratios get lower when that temp is above 32F, regardless of where in the column. So one could have fantastic growth rates/high ratio snow falling and Kuchera might still calculate a low ratio if the surface is at 34F, which is nonsense, since the surface goes from 34F to 32F once rates exceed melting and a frozen layer is established on the ground. Wrote a far longer post on Kuchera's suckage a couple of years ago - might try to dig it up. Having said all that, with modest to low rates and surface temps above 32F, Kuchera is better than 10:1 for guesstimating accumulation, but I also like the 10:1 maps, since they indirectly also always provide the QPF, whereas Kuchera doesn't.

Huge difference for NYC Metro/NENJ/LI at 60 hrs on the NAM3K vs. the NAM12K with respect to snowfall...

Thanks so much for the clear, detailed explanation, although it took me a little more time to digest it and looking at the 12Z Euro maps at 500 mbar and 700 mbar and comparing them to the ones you showed really helped. At 78 hr one can see how much further east the CMC closed off 500 mbar low is vs. the Euro and at 78 hr. Now let's see if I remember this for more than 2-3 model cycles, lol. And at 78 hr one can easily see how much further NE the CMC 700 mbar low is vs. the Euro, such that NW of the CMC 700 mbar low is New England and for the Euro that's far NNJ/NYC/LHV.

Definitely true, as the 12Z has the 6" line roughly around 80 and 18Z has it roughly around 78, a difference of ~20 miles and 20 miles is ginormous to those of us on the fringes of good snowfall, i.e., anyone south of 78. Still doesn't explain the discrepancy between SV and Pivotal snowfall maps, though.

Have seen moderately large discrepancies several times in the past week between snowfall amounts on SV vs those on Pivotal, with SV amouts being much higher and we're seeing it again. Does anyone know the difference between their snowfall estimation algrithms to know if one or the other is more accurate?

Very odd run with the wrap-around snow for NYC Metro delayed 12-24 hours from previous runs and other snowy models...look when NJ gets its snow, when the low is near ME!

Can you illustrate that difference? Not an expert on upper air patterns, thanks...

UK way east with limited precip for NJ, except near the coast and into NYC, with most of the precip NE of NYC; also too warm for snow for the 95 corridor...

exactly - see my post with the SLP/precip graphics...

Odd, surface low is closer to us on the CMC, but has no precip at all over NJ during the time where the GFS is hammering us despite being further away (same SLP). I'm not a met, so can't explain that one, lol (maybe less NS interaction?)

CMC looking similar to the GFS through 0Z Tues...

no words needed...

GFS much improved!

White rain for the past 30-45 min - at least it's nice to see. Nothing will accumulate with 35F temps unless we get some heavy snow and it's light to moderate right now.

Of course they are, but the point remains that the NWS said all rain and we have 3 models saying quite a bit of snow to fall, even if it doesn't accumulate...

The NWS says the 2nd batch should be all rain near/SE of 95, as per below. Just for the record, though, the NWS would not have seen the 6Z NAM, GFS or the 8Z HRRR, which show 2-3" south of 80 and along and SE of 95 down to the coast and for NYC/LI from 4 am to 10 am) when they wrote the discussion above - could they be this wrong (the NWS or the models)? This is why forecasting is so hard, lol. Most of the rain and snow has tapered off. However, as that system over northeast Pennsylvania passes through New Jersey, precip will ramp up again later this morning over northern New Jersey and southeast Pennsylvania. For areas south and east of the I-95 corridor, temperatures should stay warm enough for precip to be all rain. For the southern Poconos and far northwest New Jersey, precip will mostly be snow, and an additional 2 to 3 inches will accumulate. Will cancel the Winter Storm Warning for Monroe county, and will carry a Winter Weather Advisory for Carbon, Monroe, and Sussex (NJ) counties through this morning. For the Lehigh Valley and portions of northern New Jersey south of I-80 and north of the I- 95 corridor, precip should be a mix of rain and snow with minimal snow accumulation. Will cancel the other Winter Weather Advisories.