eduggs

Model soundings actually showed a bit of an inversion early this morning. Elevation hasn't mattered much so far. Soundings show the inversion reversing during the day so elevation may matter towards the end. But so far this has been banding and rate dependent.

Some areas going way over forecast. Other areas in subsidence leading to light intensity or rain. I posted 2 days ago (guessing) that I thought there would be winners and losers... that these types of overrunning events lead to narrow bands and funky distributions... and that's how it played out. These are the most wonderful events for those in the jackpot zones!

That is so awesome, enjoy it! I'm in Putnam County right now and we have less than an inch and main roads are wet. I'm still loving it.

It can snow and stick even in NYC in this airmass. NYC is a big place. It helps to be away from the immediate shoreline, outside of the heavily paved areas, and preferably a little north or west of Manhattan. If intensity is moderate or heavy, it can accumulate anywhere at 33.5F. If you are in a less favorable location within NYC and intensity is not particularly heavy and the temperature is 35F, then it is difficult to accumulate. But there are no hard and fast rules about predicting this. This kind of event happened many times in the past, including in the distant past.

Looking at radar, could be some 6-8" totals in NEPA and maybe stretching into extreme NNJ and W Orange County. Parts of Rockland and Westchester could get 3-4" if banding holds together. Pretty well advertised actually. NAM was too dry.

Two nights ago WPC snow probs for 2" accumulation had Nyack at 2% chance and Middletown at 20%. I said at the time they were low. I have no idea what they were looking at/using. Those are not mountainous regions. This was not a last minute shift or some kind of big surprise.

Subsidence in eastern Orange and Putnam Counties from the heavy band to the south and some downsloping off the escarpment. Meso models also showed this effect.

This is nonsense. Models don't forecast snow. Their output is liquid precipitation. 3rd party vendors convert that to snowfall using, for example, a 10:1 ratio. So if a model correctly predicts falling snow but it doesn't accumulate due to intensity or temperature, that's not a model fail. That's a user fail for not understanding 3rd party vendor maps and not looking at model forecast soundings. A lot of people in Orange, Rockland, and Westchester Counties were not expecting heavy accumulating snow this morning due to downplaying of the event by the NWS and local media (and certain posters on this board). That's a fail on their part since models have advertised the localized banding with this very well. The WPC snowfall probability maps are trash. Use them with extreme caution.

I don't wanna get carried away. But radar looks like it could be 4-6" for you. Mesos have been hinting at narrow heavy bands for days. Has been very consistent. Maybe it breaks up... we'll see. But IMO, poor job by NWS recognizing this. 24 hours ago the forecast was for <1" of snow. WPC odds of 2" were <10%. That is simply unacceptable considering the very consistent model guidance. Not enough warning for very bad morning commute driving conditions.

WPC map fail! You're going way over 2" lol

The 0z GFS still looks pretty solid. General mean of 0.1 - 0.3" liquid across all guidance. The radar is a little ragged but slowly building and snow isn't expected until just before dawn. Do we get cranking or does it fizzle? Nowcast in the early morning... 0.25 liquid over 8 hours is a fairly respectable average intensity if it happens.

Not much margin for error since the cold side precipitation is unlikely to be extremely widespread. But run to run changes are decreasing in magnitude and most mid-range guidance appears to be converging on at least some wintry precip. locally. Obviously a fringing or ZR to rain are still possible but the envelope appears to be shrinking.

Wintry 5 days on the GFS! Might even squeeze in some flakes or ZR on Xmas day in the weak wave in between the Tue and Fri night events.

Both GFS and GFS-AI ticked slightly further north vs. 18z. Still snowy (some ice SW) for most areas. Kind of the sweet spot right now.

HRRR (01z), RRFS, and ICON are a little juicier than the NAM: 0.2 - 0.3 liquid for NYC. Heaviest band could be fairly narrow. Snow accumulations along coastal plain likely intensity dependent. So far no obvious change at 0z.

Some flakes reported on mPING in northern MD near Hagerstown with the initial finger of overrunning. Latest HRRR and current radar look decent. Hoping for a good burst of snow in the 5am - 11am timeframe. If moderate or better rates materialize, it should accumulate for most.

I'd feel more comfortable too with colder temperatures but this airmass should support accumulating snow in most areas away from the coastline. Yeah should drop a few degrees when the lower levels fully saturate. Before then the temps are likely to rise as clouds move in and then stabilize or fluctuate slightly. Should be approx. 30-36 until precip. starts and then 30-34 (elevation and location dependent) with mostly snow late tonight.

Maybe this misses south. But I say, let's get to the modeled cold side first to avoid rain and then hope it nudges north in the short range when model changes tend to be smaller.

This could be either a great local NWS forecast or a terrible one. With multiple days of 0.1 - 0.3" liquid model forecasts with a snow-supporting model profile across the interior... forecasting <1" of snow accumulation is ballsy. I respect the conservative approach. And there are reasons to be cautions with an unfavorable angle of precip. approach, non-uniform precip. shield, and possibly above freezing surface temperatures. But if it turns into a messy morning commute, many will be unprepared.

0z and especially 06z EPS mean and members show some serious CAD on Friday. Love the thermal gradient even on the means, with mid teens in ENY and 50s in SWPA. If this stays south or shifts further south we're likely to lose some of the QPF too, which is a fair tradeoff I think. We could also see a snap back north today after a major shift south. Fun times when there are multiple threats inside 5 days to track!

Don't even look at the GFS "clown" maps for Friday. You will not be able to unsee them.

That's a big shift from the GFS. It represents the southern edge of its ensemble spread from 12z and 18z as well as several of the ECM ens members. We pray! If it's real we would expect to see movement from other models over the next day or two. I'm doubtful for now but the ECM has been hinting at this possibility...

0z GFS has a significant snowstorm for Friday.

I don't put too much stock in the GFS-AI, but it's showing snow and ice for Friday 12/26: >0.5 liquid with surface temps at or below freezing NYC north throughout the event. It has hinted at this wintry outcome for several cycles. There is a little support amongst the ensembles, particularly the ECM suite, but the majority of mid-range guidance takes the boundary well north of us, favoring NNE for wintry precip.

The WPC maps have <10% probability for 2" of snow in the far northern reaches of the OKX forecast area, including elevations above 1000ft. That should have nothing to do with "white rain." Those areas might not get 2" of snow. But I would like to know what the basis is for assigning a probability of less than 1 in 10 chance.