wdrag

This will have to suffice til CoCoRaHS post Tuesday. NOHRSC snowfall analysis. Think this pretty much captures it...maybe has measurable 10 miles too far north?

No model consensus and lots of possibilities that this could be less because of the track and stage of development. It's out there... we know it is of interest but when you see the NOHRSC snowfall analysis on the OBS page, you can feel the disappointment. Might happen again.

I'll add the CoCoRAHS snowfall on here as a wrap late Tuesday. Clearly this thread was biased too far north and inaccurate for our area. 1/2/22 EC OP, SREF were not helpful. 12z/2 EC OP was my greater disappointment...SREF we know it can have issues at the edges and then the GFS not drying out north fringe qpf. The gradient from 1" to 12" in coastal s NJ will be very large when all is evaluated. I think it went from a Trace of melted w.e. to 1.26" at Atlantic City over a 60 mile distance. The gradient may have been even tighter. The good news is the mid Atlantic did get hit hard as others were pointing out and now a pseudo warm frontal boundary may be set up to our south (snow depth s NJ through VA).

I agree. I'm not in direct conversation with NWS colleagues. So they may be more aware than I of this problem... no question it was a serious issue with GFS on this event. Sometimes you fix one thing and something else goes bad.

Cyclic modeling of the EC/GGEM and ensemble portion of the GFS since this weekend has been developing a fast moving late developing coastal low, resulting in a period of precipitation occurring mainly between midnight and 6PM Friday. Tracking and therefore precipitation type are uncertain but recent ensembles were offering at least 2" of snow to portions of our area, the EPS furthest west and the GEFS/GEPS a bit further east. The GFS op model has been generally offshore. If the low develops further north or further east, very little snow will occur here. Right now 850MB Low development looks too far north for a moderate event but probably worthy of monitoring and trying to figure it out. Based on the model performance for the 1/3/21 grazer snow, we may not know much til we see the NAM consistently give us 1/4" qpf in frozen form with more than 2" of event Total Positive Snow Depth as shown on the Tropical Tidbits web site. 12z/3 500MB ensemble plots below serve as a baseline to witness future modeling departures, GEFS top and EPS next. IF this approaching short wave ends up weaker or further north, it will be difficult to receive meaningful snow here. At 321PM added the 16z/3 WPC D4-5 probs of 1/4" frozen W.E. (lower 2 graphics) which bridges Friday morning 12z/7. The darker green is greater than 30% chance.

So, what do the EPS and GEFS ensembles look like 12 hours into a forecast. The 12z/3 cycle attached ending 00z this evening. This is only 1 vendor. So the EPS looks more throughly available... but notice how much light snow it put into the dry air nw of I95. Ditto the less spatially complete GEFS, but there as well, too much snow into the dry air and these are only 12 hours into the forecast. So there were still a variety of solutions with the 12z init. This tries to demonstrate some limitations in the ensemble utility... the core axis should usually should be reasonable in big systems, presuming it's consistent, not wind shield wiper = back and forth.

9.5" in ACY as of 1P...makes it top 14 snowiest January on record and I think Bluewave indicated we might get top 10 snowiest day. Right now #16 snowiest 24 hour snowfall in a climate calendar day. All this means (for me): it was a big one for that area.

NW edge obviously dried out and SREF in particular was too far nw while the multiple model ensemble axis S+ did well (GEFS/EPS/SREF)...many reports 8-12" just south of DCA to near or just south of ACY. GFS obviously has a problem drying out snow, despite its decent soundings. Even the drier NAM was too robust on the NW side. Am thinking similar drying out problem with the EC. Which leaves the SPC HREF best of the short range groups with its 00z/2, 12z/2 and 00z/3 cycles attached. It was a grazer as initially threaded by Forky. As a planner-preparer for minimizing impacts, even though essentially nada occurred NYC, I would prepare similarly again. The downside is far larger problem than the successful zero accumulation forecast. It's a matter of all of us realizing that the gradient edges of ensembled, or operational cycles can be wrong and keeping that in mind as we anticipate. I'm sure we're in a far better place with the modeling than 10 or 20 years ago, let alone 50 years ago.

Definitely a concern that dry air ingest cuts back snow accums I95w itself...NYC could escape with NIL and PHL less than currently modeled-forecast?? Just need to wait til 1030AM to be sure (for me). The storm is still near Hatteras so we should see a northward push by Noon... I added the HRRRX which looks reasonable to me. At 830A widespread 1/4S+ to 1/2S DCA-BWI-ACY. Now awaiting some northward advance in NJ around 10A. You can see the scalloped edges of northern snow boundary as dry air evaporates the falling snow LI-PHL.

Seaside in Ocean County is the southern fringe of our area. Thanks for your report.

No thread on Friday but GEFS-EPS ensembles have decent interior snowfall for 96+ hours away. Euro and GGEM continue steady for the event and 06z GFS working its way west. Waiting on results for today before looking ahead.

Out of area but to illustrate the potency..Asheville NC just had a nw wind gust to 51 knot at 506A and of course snowing there... maybe more than here in NYC.

NYC-LI on the edge. The SPC SREF came down NYC to around 2-3" and that may be too high. Think best chance NYC to transfer from virga storm to a brief period of steady snow is Noon-3P. Follow the models and the we'll check the results around 7PM. Graphics below are the SPC HREF--- looks good to me and NWS ensemble probs for 1" and a foot. NAM banding page suggests 1-2"/hr snowfall rate potential s NJ 10A-3P. We'll see if that encroaches into Monmouth-Ocean counties midday?

All good... as of 520A... the forecast posted by the NWS looks good. Dry air eats us up along the northwest edge with T-2" NYC. When it does descend through the dry layers below 700MB, it could come down at 1/2MI vsby for a short time JFK eastward sometime Noon-3P. As of 5AM I like TDWR EWR as the northern edge edging north now and snowing extreme southern Monmouth back through PHL/DCA areas. From this point forward am on the nowcast thread.

My final post on this thread and for this evening. The amounts you see where 4+...its going to be 2-3"/hour. May have some TS+ 1/8 Mi. This is the one in 10 chance from Mt Holly, the overall Winter Storm Severity Index - both collaborated at 3P this afternoon, the 00z/3 3K NAM snowfall as a start, and the 00z/3 HRRRX. You want big snow, you go south and get there by 5AM. Should be a 6 hour window of some embedded white out down in s NJ somewhere. I checked 18z/3 NAM soundings. It all looks quite good for all snow after 8AM.

I'm not sure who is saying 2" max there? As a planner, you can know the deterministic and be alert that the forecast may go awry on the heavy side. The SREF and all ensembles on this system have not been wild, only trending northward.

New NAM at least 1" NYC now..starts NYC around 10A-Noon.

Hi... before the 00z/3 NAM says I'm wrong... the SREF has value, especially the SPC SREF. While it can be wrong, especially gradients, better not ignore it when it has these amounts. I'm pretty sure we'll see a stripe of a foot or so in the DelMarva, far s NJ. Sharp lift and strong UVM. So whether it has too much snow on LI/NYC, (and there has to be doubts), I cannot cast aside the SREF (not within 24 hours). Added the 21z SREF for LGA which is now up to 7". This in part driven by several members up near 20". Even so, of the 22 members, only 1 is ZERO. All other members more than 1" there. In my opinion, It's going to snow in NYC---maybe not much but I think we need to be prepared for 4 in NYC and count on one inch, especially if the 00z NAM follows the 00z/3 HRRR north. I could be wrong and I don't like eating humble pie, but tomorrow morning should be fast changing on radar.

Checked 18z GGEM, EC, 15z SREF... not much recession if any... this suggests some modeling is going to be major error in the northern side gradient change between NYC-LI and Toms River. HRRR/HRRRX look a little more like the NAM...s of NYC. Going to be some large errors, especially 12z/18z EC if this ends up like the much further south NAM. May post once more before going to rest, then up early to recheck.

Not threading Jan 7 til i get a handle, either 9P tonight or 6A or 6P Monday.

I'll be offline 3P-830P - someone is welcome to add the WATCHES and WARNINGS map when it finally completes at 5PM. I'll add the winter storm severity index at 9P and we all can update all the modeling-data-observations from that time forward. I suspect our first mPing wintry precip will show up in southern edge around 3A-4A.

A moderate to major 6-12 hour snowstorm will occur Monday, mainly from somewhere within the I95 corridor southward. Snow, sleet, rain or freezing rain should begin between 3 and 6AM in NJ and NYC-LI-s CT around 6A-8A. Any mixed precip will change to all snow soon after beginning. Temperatures may be still be just above freezing at the start, but drop into the mid 20s by 10AM with wind chill down into teens and north-northeast winds gusting 20 to possibly 30 MPH. Drifting snow should develop wherever amounts exceed 4". 12z/2 NAM 900-500MB and 800-600MB banding suggests 1-2"/hour snowfall for a couple of hours during the height of the storm across central NJ and southern-eastern LI. Details of how much and where the sharp cutoff on the northern fringe (NYC), NNJ/s CT/se NYS still to be determined but too many models have slowly shifted northward the past day of cycles to prompt concerns for a significant impact storm. 03z and 09z/2 SPC SREF modeling has broad range of solutions but suggest close to 5" LGA with the blizzard conditions remaining just offshore. Let's keep the modeling-storm discussion in the January thread til after the 9PM (00z/3 NAM cycle has posted through Monday). MPing may be helpful. The 12z/2 ECMWF Kuchera snowfall map has been added per our thanks and appreciation to the ECMWF-Weather.US. This is a single operational member of all the modeling but represents potential... This could shift a bit either direction with time and amounts might end up significantly less in some areas but overall, it seems to have the axis of high impact travel concern fairly well outlined.

Courtesy the EC and Weather.US... I appreciate their data. I have to think the GFS/SREF has been better than most other modeling, in advance...all catching up to the GFS. Northern fringe of the GFS can be argued drier but there is no doubt (in my mind) about a high impact storm very close to NYC. I'll fire up the OBS-nowcast thread... lets leave it alone til about 10PM then have at it...keep all the discussion of the storm here til we get to within 6 hours of starting. Thanks... Good job on getting this thread started and enjoy. Here is one EC op model Kuchera solution from the 12z/2 cycle. It's not what the final solution will be, but I'll believe a big 6-12" snowstorm is coming to s NJ and very close to NYC. If its mixed with sleet, amounts less, but removal still difficult.

I hope our forum members read. I'll rereview and attempt to clarify.

That increase by the way was added between 0830-10z... but 08Z is what helped bias the conservative ensemble approach. It's quite a process with few staff at 330AM to make big changes to the products...