RU848789

It is pretty out there - just got in from a Jebwalk - lots of reports of accidents as local roads are treacherous right now with sleet underneath snow.

It is pretty out there - just got in from a Jebwalk - lots of reports of accidents as local roads are treacherous right now with sleet underneath snow.

As of 7 am, down to 32F and 1.75" OTG and snowing close to heavily now, with 1"/hour rates the past 30 minutes. It's gorgeous out there with everything covered - first plow just went by our house. TWC was just discussing how the low pressure off DelMarVa is strengthening and noting that short term forecasts are for 1-2" per hour for the next 3-4 hours for much of CNJ/NYC/NENJ.

As of 7 am, down to 32F and 1.75" OTG and snowing close to heavily now, with 1"/hour rates the past 30 minutes. It's gorgeous out there with everything covered - first plow just went by our house. TWC was just discussing how the low pressure off DelMarVa is strengthening and noting that short term forecasts are for 1-2" per hour for the next 3-4 hours for much of CNJ/NYC/NENJ.

As of 6:30 am, still 33F and 1.25" of snow on the ground and snowing moderately - that's only 1/2" per hour rates - going to need more than that to even get to 5-6", let alone 7-8".

As of 6:30 am, still 33F and 1.25" of snow on the ground and snowing moderately - that's only 1/2" per hour rates - going to need more than that to even get to 5-6", let alone 7-8".

Given the overperforming snow to the NW, the NWS reraised snowfall forecasts for that area to 8-12", as per the map below.

Given the overperforming snow to the NW, the NWS reraised snowfall forecasts for that area to 8-12", as per the map below.

As of 5 am, we were at 33F with 1/2" of mixed snow/sleet on the ground and as of 6 am it's still 33F and we have almost 1" of snow/sleet on the ground with it being all snow since about 5:30 pm with moderate snow falling now (nice dendrites). Going to need more intensity (more than 1" per hour and we've been less than that), though, to get more than 7" by noon, when things wind down.. I woke up at 5 am so I didn't see the changeover, but the radar indicates we likely changed from rain to snow around 4 am. Every surface is covered including the streets in front of our house and it's likely having some sleet helped with overcoming melting as sleet pellets have a much lower surface area per unit volume than snowflakes and melting only occurs at the surface, so melting is much slower for sleet.

As of 6 am, it's still 33F and we have almost 1" of snow/sleet on the ground with it being all snow sinsce about 5:30 pm with moderate snow falling now (nice dendrites). Going to need more intensity (more than 1" per hour and we've been less than that), though, to get more than 7" by noon, when things wind down.

As of 5 am, we're at 33F with 1/2" of mixed snow/sleet on the ground. Just woke up at 5 am so I didn't see the changeover, but the radar indicates we likely changed from rain to snow around 4 am. Every surface is covered including the streets in front of our house and it's likely having some sleet helped with overcoming melting as sleet pellets have a much lower surface area per unit volume than snowflakes and melting only occurs at the surface, so melting is much slower for sleet. For all of those saying snow/sleet wouldn't accumulate after the rain with above 32F temperatures, you should've paid attention to my days of posts on this, lol.

Well folks, I just looked at all the major recent models at 0Z and 18Z (that haven't run 0Z yet) and apart from the GFS (not counting the CMC or UK which are too "old" now), the consensus is growing pretty strong for a colder storm with less intense snow (and less rain to start) putting down maybe 6-9" of 10:1 snow (of which maybe 5-7" actually accumulates at maybe 8:1 ratio) with 32-33F temps during the 4 am to 10 am timeframe where 90% falls (still a respectable 1" per hour of falling snow) and this seems to be the case for the whole 95 corridor from Trenton (and maybe even SW to Philly) to SE CT and 30-40 miles NW of that line and 30-40 miles SE of that line. Sure some folks who thought they were going to get smoked are likely not and some who thought they were out of it (SE of 95 especially) will do well and at least NYC metro looks to do decently (on grass at least), which is nice given how long it's been for them. And who knows, maybe some of us will get a few inches more than expected with some better rates than are being forecast right now. That's all a preface to say that if you had told me a week ago or even 2 days ago that this event might deliver 5-7" of snow, I'd have been ecstatic. Sure getting a monster storm over a foot would be awesome, but this is way better for snow lovers than an inch of sloppy slush on only grass many of us were looking at. I'm going to go out and walk around in this at least every 30 minutes and measure and hope I can get to my prediction of 7.2" for my house made last night, but considering my first guess was 2" two days ago, I'm pretty sure I'll be smiling on my JebWalks around the neighborhood. Pretty sure I'll even make a snowman with this stuff and a snow angel or two. Enjoy it folks and then let's hope a few of these other threats over the next 10 days deliver at least a few inches and maybe one blows up. It's been a pleasure tracking with everyone and I hope at least most of you get the snow you hoped for (or some of it).

This is wrong. Intensity is the key. At >1" per hour, snow will accumulate in April at midday at 35F, so 33-34F in the morning in February won't be an issue - if we get that intensity, which is more than enough to overcome the melting rate. Ratios more likely to be in the 7-9:1 range unless you're talking about areas where mixing is occurring in the column.

Those scores are always nice to know for accuracy from a big picture perspective, but what's important right now and in every storm is which model is most accurate for snowstorms and are there different types of snowstorms one vs. another model is better for? And nobody has ever really given more than anecdotal opinions on that that I can recall.

Did this for 0Z, so figured I'd do it for 12Z with the same preface, i.e., posting the relevant snow maps at 10:1, as that provides direct data on snowfall QPF, plus the algorithms for snow ratios aren't always accurate in cases of high intensity snow. I'm sure we've all discussed ad nauseum how for this storm, especially for areas S of 78 and east of maybe the NJ TPK, surface temps are likely to be in the 33-35F range, leading to melting/compaction which would make the snow ratio produced up high in the sky (which should be >10:1 given great dynamics in the DGZ) something somewhat less on the ground as accumulated snow, but with >1"/hr snowfall it's likely that Kuchera and snow depth algorithms are too low. They're 6-7:1 for areas with any temp above 32F, but with the expected intensity, I think we'll see more like 8-9:1 for 95/south of 78 (although Kuchera are probably good where there are column temp issues near where there are changeovers, i.e., at the coast. So take these maps as starting points for how much snow might actually accumulate.

Likely Dr. Greg Postell, who's a little pompous (many PhDs are and I should know, lol), but knows his stuff. Dr. Knabb former NHC Director is also awesome, as are many of the regular shift folks and as schmaltzy as he can be Cantore is fun and does know his stuff.

Nov 18 might be my favorite example. It was also an example where the NWS completely overestimated marginal temp impacts on a high intensity snowfall, both with regard to mixing in the column and melting on the ground - and I was posting all the same things for that storm as I have been for this one - intensity is everything (or at least a lot of it).

Come on in, the water's fine!!

You may be right, but several models have you over 6" at 10:1 or over 4" at 6-7:1.

Think TWC forecast is the best I've seen and they've really gotten much better the past several years (remember, they were the only ones who nailed Jan-2015) with some very good mets and model discussions these days. I think the NWS adustments at 4 am were in the right direction, but not enough, especially towards 276/195 and the coast, where I think TWC is likely to be better. We'll see of course.

If we get the 1-2" per hour rates advertised by most of the models, the snow will accumulate even on paved surfaces at 33-34F - will take a little while to start, but remember, once there's a layer of snow, the "surface" is now 32F slush, which will make subsequent accumulation much easier than on 33-34F wet ground and the heat transfer coefficient of air is 1/20th that of liquid/solid (wet ground), so melting will be greatly reduced once we're only relying on vapor phase driven melting. Trust me on this. We've seen it countless times in March/April, but the key is having >1" per hour intensity sustained for awhile. And I'm not talking about accumulation on treated, paved high traffic streets that are likely 38F or more. Also, even if accumulations on city streets and treated highways is minimal in some cases, visibility is going to be terrible with heavy snow falling, which will make driving difficult by itself.

So, NWS-Philly issued warnings for Poconos/Sussex for 9-12" of snow, for the Lehigh Valley, Morris, Warren for 7-10" of snow and for Berks, NW Bucks, Hunterdon and Somerset for 4-7" of snow. However, they inexplicably left Middlesex out of the warning (or at least the northern half, which will likely do as well as southern Somerset/Hunterdon), putting Middlesex, Mercer, Lower Bucks and Montco (but no Monmouth) under advisories for 2-4" of snow. These are all fairly close to what I was thinking above. Also, the NWS-NYC issued watches for Union/Essex/Hudson and NYC/LI for 5-8" and warnings for everywhere north of there for 7-10" of snow, which makes sense to me, even if those amounts are a little bit higher than I expected (I don't like to guess too high and felt I was already out on a limb predicting much more snow than they were) - they are in line with what models are showing. NWS-Philly just updated their map below as did NWS-NYC... Also, revising my initial guess of 2" for my house from Saturday night to 7.2" as my final prediction for my house (usually make these ~24 hrs before the snow starts).

NAMed! The 6Z NAM looks a lot like the 0Z Euro and is still the coldest model at the surface with temps around 32F along 95 during the snowfall (so Kuchera ratios are in the 8:1 range for 95 and 10:1 or more N of 78). Nice start to the 6Z suite.

Thought it would be helpful to have all of the relevant model snowfall maps from 0Z in one place, as I'm constantly trying to remember where they might be in a thread especially when looking back at a storm which I sometimes do. I'm only including the 10:1 ratio maps for brevity and because those at least give one the total precip as snow, too, which is important. Pretty impressive all together. I think we've all discussed ad nauseum how for this storm, especially for areas S of 78 and east of maybe the NJ TPK, surface temps are likely to be in the 33-35F range, leading to melting/compaction and there could be a warm nose aloft for some period leading to some sleet, both of which would make the snow ratio produced up high in the sky (which should be >10:1 given great dynamics in the DGZ) something perhaps considerably less on the ground as accumulated snow (maybe 7-8:1 and could be even lower at the coast), so take these maps as starting points for how much snow might actually accumulate.

Just for giggles, here's my guess as to what we'll see from the NWS at 4 am: I'd guess that the NWS-Philly will upgrade snowfall amounts at 4 am and go with advisories for 2-5" for most of CNJ (Hunterdon/Somerset/Middlesex/Mercer/Monmouth) and for Bucks, Montco, Berks and maybe W. Chester and warnings for 6-10" or more for all of the counties north of 78 in PA/NJ (Poconos/Lehigh Valley and Sussex/Morris/Warren) and that the NWS-NYC will also go with advisories for 2-5" for Union/Essex/Hudson, NYC/LI and warnings for 6-10" for Passaic/Bergen and SE NY north of the Bronx and all of CT. This is probably the hardest I've disagreed with the NWS ever or at least since Nov-18, which was somewhat similar with 1-2" of sloppy snow/mix predicted until the event was underway, but then everyone in CNJ/NNJ/NYC etc. got 4-8" and a nightmare on the roads as the snow hit around noon, like a wall.