wdrag

More spread and some slight nw trend... track is good...

Just scanned the abstract and closing remarks, including the caveats. I myself am not sure how to account for this in a forecast, except to keep it in mind. I use the variable density snow forecast from the HRRRX, sometimes good, and other times not so. I'll presume surface wind above 18 knots shatters dendrites a bit, making the layer more densely packed. Here's my concern... minor as in the closing pgh. I cant even pinpoint snow ratio itself, or exactly where best banding (in advance)... then I need to use model winds... for the near surface, and the winds we see are generally 8-10 meters... need face level wind, not commonly available. Snow measuring every 6 hours will reduce this problem, especially in events where wind is primarily at the tail end. Later, Walt The surface wind speed plays a minor role by decreasing snow ratio with increasing wind speed. Although previous research has shown simple relationships to determine the snow ratio are difficult to obtain, this note helps to clarify some situations where such relationships are possible.

No changes yet to TOPIC headline (MAJOR Nor'easter snowstorm because I|'d like to try isolate some numbers but nothing is backing down thru the 12z cycle... at least not yet. I add the late morning NWS expected qpf and D5-6 chances of 3+" of snow. They're qpf looks up a little as do their chances. I may not add much more for a few hours. Have seen the 12z GEFS ensembles for 850 LOW, 24 hr qpf and snowfall. As mentioned by others earlier... it seems a KU storm is at hand... things can still shatter (or be less extensive), but I think when you combine both Monday and Wed-Thu, 2 feet ""possible"" in some places between I84 and I80...especially if banding occurs near the southern edge of the deep RH. i sure hope these ensembles don't let me down. Also, the southern edge of the snow which will be wetter and especially windy LI NJ coast, Power outage potential... more speculative details tomorrow or Monday. Only one thing stands out to me that differs from my own earlier days thought process, a little slower start- still an 18-24 hour snow blitz. I know several others always thought further s of I80. I'm still not convinced and await model guidance to confirm for me, one way or the other, which may be two days in the future. Awaiting model guidance that says this will not happen as intensely modeled now.1232P/12

I've heard that but Im not sure if there is science to that effect.

Not sure of the impact... but the 06z EPS members for 12z/17 .. not quite as intense a storm but many members in the NYC bight. We may know more in 24 hours. May mean slightly less qpf near the storm center, and also more option of ice/rain up to I80?? I don't know.

Saw the 06z/12 EC less than 2" snow depth change for Monday. Not worried about it being down a bit. At least its flagging snow just w and n of NYC. But the 12z/NAM has a nice 2" swath of positive snow depth change. I like it. AND have added the way I look at numbers... total snowfall 10 to 1... I look at real good for all snow and sub 540 thickness. Total positive is base for the +540 thickness and or daytime temps in the 30s. Ferrier is the heavier and often times more accurate version of Total Positive. Finally Kuchera...probably very good for powder and sub 540 thickness... but I don't think very good for over 540 1000-500 thickness.

Late Fri or Saturday from the northwest--- clipper? Long shot and we're too busy before that to think about it but something is coming southeast rom the Great Lakes and I'm pretty sure we'll see some flurries or a period of snow.

Measuring difficulties with powder blowing (multiple in the open area to get representative new depth every 6 hours), and in the wet plastered areas... might be a little easier. Tipping buckets might get junked up with wet snow NJ/LI??? . I won't detail now since uncertainty, but sometimes NWS heated comms antennae dishes get snow covered with heavy WET snowfall rates and we'd have to go out and broom sweep the snow off so comms wouldn't be impacted.

If you like the Euro... then folks LI and s of I80 need to be aware of probably less than 10 to 1 snow ratios, a water snow and sleet mix (rain coasts). The 850 and 700 temps are not that cold flaring with -2C.

I don't really know... BUFKIT allows access to that. It could be 15 to 1. Bottom line lots of powder. (EC is seemingly too strong but might be right...if so, all the better for the healthy snow lovers.. i just need to look for break downs. Seemed to me the 06z/GEFS slightest edge south but .. keeps our forum in big time axis, especially I84-I80 (exclusive of LI warming aloft).

Am 75% confident of a Monday morning-midday hazardous snow (wet clingy snow) advisory situation of 2-5" somewhere in the hills of ne PA, far nw NJ se NYS, with amounts trending down in CT. Model consensus growing. I do not think this will be snow for NYC... or if so, just a mix. Probably a good idea to clear the snowfall Monday afternoon, to prep for the much larger snow Wednesday into Thursday, This is also a good day to make sure the snow stakes are in and snow removal equipment is in good working order. The 00z/12 GGEM did not have any qpf for Monday, and if this continues into Sunday, then this snow expectation will be wrong. I did note the companion RGEM has quite a bit of QPF Monday so the reasoning for forging ahead with the snow expectation. I added the WPC early morning forecast qpf for Monday. Have also checked SPC snow plumes which support this snow accumulation concern.

Written with maybe too much faith in the consensus through the 06z/12 cycle?? Take this with a grain of salt .. i just am reading what i THINK the consensus is telling me. Now stakes in by Sunday night? Snow blowers the ready? Hope so, at least for the interior. Until something in the modeling breaks down, thinking of planning ahead is a good idea. So far so good for the nor'easter snowstorm through the 06z/12 cycle. I'll add some support graphics. Model trends, maybe minor south in some cases but overall the NAEFS says stay the course! I will not call this a blockbuster snow storm yet with near blizzard conditions for parts of NJ/s CT since rain could mix in, and timing 3 hrs of 1/4S+ and/or BS, plus gusts in excess of ~35 MPH is fraught with uncertainty 5 days in advance and could more easily not occur. However, modeling continues, so far, to allow for an easy over a foot in some parts of our area. BUTTTTT... thermal profiles on the EC are dangerously close to a mix or rain across NJ s of I80 including NYC LI.... AND...modeling can break down and weaken the cues. So, barring a greater flattening of the 00z/12 ensembled 500MB forecast upper air short wave which would mean less lift, less developed closed lows at 850-700MB, I am thinking the jackpot of big time powder 1 foot plus is the I84 corridor (ne PA-extreme nw NJ/se NYS interior CT) to near I90. A wetter snow down here near and s of I80 (my non scientific heart attack amounts if all snow for those with vulnerable conditions). This would be associated with not only DGZ, but snow ratios well above 10 to 1, maybe 13 to 1???? I don't have the snow ratio tool so I cannot be sure. The other factor, the southern edge of the 700MB RH in the northern semicircle of the probable weak 700MB low, usually slow movement, favorable for a 700MB front and associated banding. Again, BARRING a future weakening of the model 500MB short wave and associated fraying of 700 and 850MB lows. Coastal flooding: A moderate event seems probable Thursday morning, for LI/NJ coasts (minor Wednesday morning) and must absolutely follow NWS guidance on this--they have some tools I don't have. Just quickly referenced the Stevens output and knowing that we will see 45 MPH wind gusts on LI/NJ immediate coast (60 MPH gusts possible s of LI on the open water near 44025?), and the ensembled low pressure near 995MB and the high near 1034MB over Quebec and ~24 hours or more of Ekman transport suggests to me a significant coastal flood event. Timing of onshore winds and lowering of pressure is always critical but with an an astronomically high tide, it's easier to flood. Graphics: NWS ensembled consensus for 3+ inches of snow Wednesday. , their human interactive assessment of qpf amounts (the heavier 1.5" purple is usually associated with rain, the weather.us presented EPS ECMWF low pressure for Thursday morning (ever deeper consensus and nicely clustered--note the big high over Quebec., a snapshot GEFS probabilistic of 6+" of snow (10 to 1 ratios)-Yellows pushing 70-75%. I just cant post the ECMWF amounts yet... but suffice to say it's been spotting 18" here and there for the past 5 cycles in the northeast and is tending to settle on a SNE PA/nw NJ axis. I want to wait another day before I lock in on the EC. 557A/12

I always worry about these D5-6 forecasts. And now i see some servers can't handle loading new model data in a timely fashion. One downside i neglected to mention, in my haste to get this going... overall weakening trend of the 500 MB trof, flattening and speeding up as it exits east of LI. Progressive... Our numbers will in part be dependent on how much 850 low forms Ohio Valley. I think we're going to need that. Check of the 12z/11 NAEFS looks good. Also duration may only be 12-18 hours..??? and with cold air... comes dry air and I can see dry air eroding the northern part of the ensemble qpf (I90?). I always like deep closed lows to our south. In this case 850 to our s looks good. That's about all for me tonight. Oh, don't think highest amount... be satisfied if it's 3" NYC-LI-coastal NJ and 6-9" elsewhere. Always look for the downside on these storms. That can reduce surprise disappointment.

Topic's have been split for next week. All the best on this.

Edit topic: 525A Wednesday 12/16: No change in thinking including uncertainties along I95. I just cannot shake the basics: S+ axis is usually 90 miles left of the 850 low and the northern half of the 700MB low and the deformation zone near 500 MB with contribution from the nose of the 850MB 50-65 kt easterly jet (moisture transport). This favors I84 and banding casts northwest to a central PA - east central NY area (roughly IPT-ALB) where 20-25" seem probable within 60 miles of that axis - at least in the high terrain, but must consider mountain shadow lesser amounts in the leeward valleys. There a multiple models showing that axis. In our forum, I think most everyone will see a period of sleet near or after midnight and that the bulk of the snow occurs in a 6-10 hour period prior ~ midnight, but that there will be a tail of moderate to heavy snow toward dawn with still 1-4" after sunrise Thursday on top of whatever occurs before sunrise---the heavier 4" potential ne PA, extreme nw NJ, se NYS and CT {where 5" may occur in 2-3 hours after sunrise Thursday}. Drifts to 4 feet possible ne PA, se NYS and northern CT where 18" accumulates since winds will gust 30-40 Mph at times overnight. NYC CP still 6-10" in my mind but shakey and may be too high because of only 10-1 snow ratios at best, sleet and possibly rain compacting as well as temps near 33F at times during the night. The power outage concerns continue near I95 with 45-50 MPH gusts (9P-6A). Coastal flooding - please see NWS offices for minor or moderate near the time of high tide Thursday morning. Finally, even if it rains or is above freezing w LI and Monmouth/northern Ocean County NJ tonight--- there could be sudden icing near sunrise Thursday when the wind switches from northeast to north and drops temps 5-10F in an hour, and iceing the residue and make travel very hazardous again in leftover new snowfall. Otherwise temps in the I84 corridor ~20-25F throughout the event. Will add some graphics by 6AM on wherever the last page of the thread. NOT a top 20 for NYC...best chance is MPO-POU axis in our forum. This is my last topic update for this event. Edit Topic: 445 AM Tuesday 12/15: NO change in thinking. Except for the outlier south GFS/GEFS, all systems appear go for a major snowstorm as outlined below in the 6AM Monday topic update. Will detail in the latest page by 545AM. 00z/15 EC/NAM/RGEM/UKMET/GGEM/UKMET operationals on board! There will be multiple (~12 graphics of supporting model documentation-most probabilistic and 2 day top 20 snowfalls in the available period of record). --- Edit Topic headline at 6AM Monday 12/14/20. Please monitor NWS Watch-Warnings for this storm and associated statements and still uncertainty on where highest impact. There is/was some overall slight southward shift in the guidance in the past 24 hours and so my uncertainty for the forum is northern CT-Catskills, and LI/I95 southeastward. WPC still has 1.5"+ qpf just s of I80-LI and 3/4" into northern CT. If you have travel plans Wednesday into Thursday I95 northwestward from VA through WV, PA, NJ, NYS and southern New England it's probably a good idea to consider changes, based on your NWS or other favorite media outlet forecasts. I think this will be a top 20 snow storm for a few parts of our NYC subforum (basically ~ 1 foot will prompt that review) but unsure where. For now between I95 to I84. Anticipating (not guaranteed) widespread closures or delays for all transportation systems I95 corridor northwestward Wednesday evening into Thursday morning,. For those who have access and wish to do so, you can calculate an experimental storm index to get an idea of what is probably coming. I don't want to presume more than Major yet (crippling is the next step up). Here is some information. https://www.ncdc.noaa.gov/snow-and-ice/rsi/?nesis Still variability in northward extent of heavy 1 foot snow ranging from the NAM Adirondacks to the GFS-RGEM I80-LI. UKMET is still quite far north. Ensembled r/s line looks to remain mostly south of I80-LI but awfully close, close enough to think sleet, rain or freezing rain mixes in for a time after the initial Wednesday evening thump for LI and s of I80. EPS continues almost unyielding on the widespread 8-18" snowstorm (isolated 2 feet possible in the banding somewhere north of I80-LI). Major power outages possible wherever the 6" of 32-33F wet snow accumulates along with wind gusts of 40-50 MPH. If this were to occur, it would most likely develop between 9 PM and midnight Wednesday evening per consistent modeling of snow onslaught and wind gusts increasing past 30 MPH. Am targeting LI south coast and NJ coast but this will require 6" wet snow (32-33f). Isolated wind gusts above 50 MPH possible on those coasts. Snowfall rates of 1-3"/hr possible in northward transiting bands Wednesday-evening/ night. Where these tend to park on the northern extent of the storm, will probably be the 2 feet of snow, especially with ratios drier than 10 to 1 (maybe 13 to 1). NWS has the multi model ratio blend tool and BUFKIT can assist for those who have that tool. There could be closing bands of moderate snowfall Thursday morning after sunrise into early afternoon as the comma head tends to fold southeastward behind the eastnortheastward departing storm. Clearing the first few inches of snow around 8-10PM Wednesday will make it easier to remove the additional snow Thursday morning. Where it's wet-caution for those with heart conditions., This strong easterly surface gradient (northeast wind) between the cold 1035MB high over Quebec and and the probable 995-1000MB low near Cape May early Thursday will produce minor to moderate coastal flooding, for the Thursday morning high tide cycle. Follow NWS statements. No graphics update with this topic edit. --- Edit Topic time at 506AM Sunday... otherwise an 18-24 hour nor'easter coming with the uncertainties continuing as previously listed below. HIGH impact late Wednesday afternoon into Thursday morning with many cancellations probable of whatever activities in this Pandemic. It's 5-6 days away but taking my cue from our participants, have separated Wednesday-Thursday (16-17) from the prior 5 day (14-18) topic. Modeling is showing the potential for a 6"+ snowfall for a large part of the NYC forum area, somewhere between the I95 corridor and I90. There is model uncertainty regarding the intensity of the upper air and surface systems but enough information in the models to monitor this storm for possible high impact in parts of the NYC subforum. Some potential exists for nearly a foot of snow in a small portion of the forum area, IF everything comes together correctly... but it's too early to be sure and it's best not to focus on the higher amounts yet. Banding in the DGZ could make for as much snow along and north of I84 as may occur closer to the storm center in NNJ where the snow could be a lot wetter. Usually it takes -3 to -5C at 850MB this early in the season with wind off the 40's SST, for snow not to change to rain. So LI and the NJ coast are presently in the modeled greatest uncertainty region whether it's mostly rain or snow. Astronomically high tides Wednesday and Thursday mornings seem destined to allow some coastal flooding within 2 hours of high tide, but this is going to be driven by storm intensity and wind direction. Just too early have a good handle on flood potential but I would think minor at a minimum. Not posting a topic for late Friday-Saturday Dec 18-19 as that storm could easily pass to our south. Just good enough to know that appears to be a highly unusual week, potentially, for the NYC forum to have up 3 different snow events of varying magnitude in a 6 day period. Added this afternoons NWS ensemble driven D6 chance of more than 3" of snow, which has increased considerably over the past 24 hours. I also added the GEFS probability of half a foot of snow or more... use the legend color (greens-yellows edging past 65%) for your area of interest. The Dec snowfall's in NYC since 2010, 2nd column from the right. and The daily almanac for NYC CP-Wednesday Dec 16...the 5.3 " is the daily snowfall record. Small chance of daily record snowfall??

This may be the first of 3 storms this week (14-19) with northeast wind in the NYC forum and a strongly -NAO with blocking in progress, that could dump up to a foot of snow, (in total) on parts of the forum by midnight Saturday. Uncertainty exists, especially intensity of the storm and associated upper air pattern, as well as it's track. This one so far with uncertainty on the r/s line and qpf amounts but potential exists for several inches of wet snow on the northern fringe of this late developing but weak nor'easter as it passes to our south. It may finally bring NYC it's first minor measurable amount of wet snow (twas a close call on Dec 5th at CP). Tides are astronomically high so that there is a small chance of minor flooding in a few spots at the time of high tide both Monday and Tuesday morning's. Since most of the snowfall (or of any snowfall) should be during the daylight hours Monday in our area, pavements will tend to be wet where it snows except the hilly areas west through northeast of NYC, if it occurs there and comes downs hard enough. This is probably a day, to get snow stakes into the as yet unfrozen ground, and prep your snow blower-thrower for possible use Wednesday. By the time Monday afternoon rolls around we should pretty much know whether this will be a week of substantial snowfall for parts of the NYC forum.

Will get new topics up for both Monday and Wednesday-Thursday (14, 15-16) around 230PM. This per taken the cue from one of participants- a good idea. That may be a good time to shift discussions. I'll add some base graphics that will serve as a spring board for the future.

Have seen 12z GEFS... same as 06z..half a foot+ southern CT to nw NJ... also develops the 850 low a little sooner and a tad further south restricting the nrn extent of qpf to just n of I90. Long ways to go... wont have it studied up til 330P and then will definitely separate this thread to the weak low risk northern fringe snow on Monday and good sized snow event for a portion of our forum. Later... Walt

And so, for those who want an event Monday... I'm betting the 12z GGEM will be on aboard... 12z RGEM has qpf. Unfortunately that model shows generally rain.

Understood... I see your point. Plan to get this done around 5P. Thanks.

Also for those who like to hunt these comparisons down... the last time we've seen a modeled surface pattern similar to Wednesday's projected (early this mornings WPC guidance)???... I think its' been at least back to March 2018, if not before?

One model I've not heard much about... the IBM model that is supposed to be much better than the available models that we all look at. This model made some news a year or two ago about picking up on some storms sooner. Has it been implemented? Any public guidance available?

Tentatively, based on 12z/11 and 00z/12 model cycles,, I'll update-rewrite the topic for the 14th and 16th-17th events (saving the original at the end) and drop the 18th. This could be a nice pair of events around parts of our area. No changes for me though, prior to 5P or possibly not til 6A Saturday.

RMOP added for the GEFS. Lots of confidence on trough ne USA... and confluence to me appears across NNE. fwiw..the 06z GEFS and 00z EPS are about the same on snowfall..nice ~6" SNE nw NJ and ne PA. Plenty of time to move south, or north.

If it does, we're going to have to see the 850 LOW's on both GEFS/EPS trend south. Could happen. If the ensembles on this feature don't trend south in the future, then the winter action will be more n of I80 than s. I just don't know.