wdrag

Good Monday morning north and west suburbs! Just missed in nw NJ yesterday, and se NYS only flurries from what I can tell but Islip on LI measured tiny snow from the general light snow along I95. CT and MA did better with 1/2 to 1 inch amounts. So, I add one graphic for the period of 9PM tonight to 9AM tomorrow. No guarantees on slushy accumulations as depicted by this 06Z HRRRX but I do think some snow/sleet/rain showers will occur during the night with surface temps near 30 or 32F.

I am considering a new topic to post around 730AM this morning for a moderate or greater rain changing to snowstorm event for the I84 region, possibly down to the immediate NYC north and west suburbs for next Monday-Tuesday-Wednesday 28-29-30 (special emphasis Tue-29th). I need more time to think it through. DT from yesterday or before and BlueWave and others in the previous several days have highlighted the potential. I think it's on the more defined modeling board now for general awareness (EC first op, I think but please correct me if I'm wrong). Need to frame it reasonably, leaving options open because of thermal profiles/tracking.

Looks like nw 1/4 NJ and a part of interior se NYS, and most of ne PA will have missed this minor short duration negligible impact event except to brighten the spirits of the snow enjoying families/shoppers. I thought we'd at least get flurries up here but NOT so far. Not complaining. Just an observation. Nice day up here, despite no snow.

12z GFS is in a hurry... and weaker than previous few cycles and not accepting GFS parallel as the solution. Not buying 12z/20 GFS. Upper air features w ATLC and near 80W were 00z/06z ensembled strong. I'm waiting this out til tomorrow morning 00z-06z/21 cycles. I expect the GGEM EC and UK will be a bit slower and stronger than the 12z/20 GFS. I agree w general perception the GFS P is better than the current V15 version, but I know not always. I suspect on two or three cases, the Parallel V16 will do better than the current V15 version on separated trough s of 40N... handling amplification and slowing better. Just a gut feeling. This one is not that. Gotta run.

Snow concentration seems to be southeast of I84, close to I95. Howell NJ via mPing with snow now. Enjoy this NYC.

Via mPing: now a bit of snow in the air around Allentown, PA

Good Sunday morning everyone, Dec 20. The windshield wipering of the models continues back and forth but there is more consensus. There is no doubt that we have a pretty good storm coming, that may be lights out for some on Christmas, and where did the water come from along a few rivers and streams, even in still snow clogged street drainage basins of the interior. Topic: back to the more robust initial discussion this morning with minor adjustments. Timing varies from the faster locked in GFS to the EC op that has been wipering a bit, and slower. Duration of the occasionally heavy rain may extend now up to 18 hours. Therefore, WPC's 1.5" qpf now covers all of the NYC subforum and there is a modeled option maybe spot 4" in some of the interior higher terrain, if duration of the heavy rain swath is indeed closer to 18 hours. 00z-06z/20 op model consensus now has 75-85 KT 850 jet for Thursday night-Friday morning (EPS/GEFS clearly 55 kt or greater). So the 70 MPH gusts could affect a small part of LI with a more general 50-65MPH expected elsewhere along the I95 corridor and possibly a few ridges of the interior,though my confidence on this ridge gust occurrence is lower than NYC, NJ and CT coasts. MMEFS suggests a number of rivers may approach action stage or go into flood so I suspect this will eventually need a flood watch as we draw closer to the 24th, and of course dependent on the updated qpf. Follow NWS statements on this. Tail end snow on Christmas: still possible, especially hilly regions near I84. Have added the 00z/20 GEFS chance of 60 MPH gusts at 06z/25. 606A/20

Periods of light snow or flurries today in the I84 corridor will possibly maximize their accumulations near Interstate 95 between 10AM and 3PM with a narrow stripe of 1," possibly just sw through north of NYC and a chance of measurable in the city. Not all models agree but the NAM, RGEM, HRRR from 06z/20 are on board. Doubt if it will much impact on well traveled pavements, especially treated, but side streets etc may become slush covered with this pleasant refreshing of the snowpack, wherever more than 1/4" occurs. Central and eastern LI may not see snow or if any, it would be too warm for accumulation. Checking the 3K NAM profile, there is a small chance visibility will lower to 3/4 mi in S- for an hour or so during midday. For the I84 corridor, maximum snowfall appears destined for CT and occurring there mostly this afternoon. One experimental snow accumulation graphic is added from 06z/20 (HRRRX) Not for this thread, but a heads that increasingly unstable moist lapse rates may bring a surprise 1" to parts of our NYC suborum between 10PM Monday and 10 AM Tuesday with the passage of a fairly strong cold trough aloft. A separate thread will be started for that on Monday, if that speculation still looks reliable. 536A/20 Edited 105PM: Looks like nw 1/4 NJ and a part of interior se NYS, and most of ne PA will have missed this minor short duration negligible impact event except to brighten the spirits of the snow enjoying families/shoppers. I thought we'd at least get flurries up here but NOT so far. Not complaining. Just an observation. Nice day up here, despite no snow. No change on thinking for early Tue. 103PM.

Holding off til 530A Sunday, to be more certain it will be worthwhile. Looking halfway decent for bit of new snow NYCby Noon Tuesday.

Am on the cusp of a minor snow topic for 1-3" of snow NYC combined events Sunday and Tuesday. Will review at 3P. If RGEM/GGEM NOT on board then probably, no topic.

Agree w you Don et al!! This is your $8/pp tax payer dollar whatever, WELL spent. You're getting bang for the buck from a broadly talented -dedicated - high effort group, throughout the agency.

Understanding NWS processes: While there are attempts to update all the local storm reports and public information statements with 'final' values, there are time constraints on what might in my words only not the NWS, meaningful work. If it's only an additional inch or so and will not make much difference to the analysis (accurate #s needed for NWS verification of their Watch, Warning, Advisory program), then I can see it is not done. Remember, there are hundreds of reports that need to be constantly filtered. (CoCoRAHS is considered official- my own report may not be included because I'm not CoCoRAHS). The climate program is always point specific accurate.- NWS controls. All the other reports are updated as time allows. We need to remember: Pandemic reduced in office staffing, that the forecast process is complex adjustments of digital elements that automatically make the words and interoffice and national guidance collaborated. That there are focal point duties -everyone has an area of responsibility- to maintain currency in the program and outreach to the partners-training the partners and vice versa- mine was the rip current and marine program for MT Holly 2010-18. This takes time to be fluent and then there is TRAINING of staff in your area of expertise. This akin to Research to Operations (RTO) training for frequent improvements in NWS processes and understandings (simulator requirement training). There is also training directed down from a national level, including do's and don'ts with regarding to security. So, it's not all about the numbers. NWS folks are paid well for their time and do the best they can to accomplish everything with multi customer satisfaction. Walt (my own interpretation of what we tried to accomplish during my days as a NWS meteorologist)

06z Euro continues dusting Sunday, almost to NYC.

The period of light snow that affects the nw-ne suburbs during the daylight hours Sunday might Trace in NYC.

Topic: not quite as robust this morning but no changes. The good news: If this less robust solution prevails, power will continue. There are diverse model solutions and so am riding this out as proposed yesterday. The 00z-06z/19 cycle might indicate a slightly slower onset-end? The EC moved its 70 MPH gusts to CC, but still has 75-85 KT 850 jet for e LI Friday morning, increasing to 90-100 kt for Cape Cod. So the 70 MPH could eventually come back west, if modeling eventually reverts to yesterdays 12z/18 solution. The 06z/19 GFS op is right there with the EC for LI at 850 MB. So I won't dismiss the topic as invalid, at least not till there is consistent modeling that says... only an ordinary storm. MMEFS suggests one or 2 rivers in NJ may flood but for now, nothing widespread major, based on snowmelt and ensembled qpf. Tail end snow on Christmas: still possible. Wish all a good day. Walt

Good Saturday morning NYC nw-ne suburbs... a chilly one over the suburbs snow cover. Generally near zero to above at 6am. Minor stuff next couple of days, mainly for the I84 high terrain... Tomorrow-Sunday the 20th: a dusting to 1 inch parts of the I84 high terrain, mainly during the daylight hours. Tuesday the 22nd: since the storm on Monday the 21st is still not quite close enough... a dusting to 1 inch possible I84 corridor Tuesday morning-midday.

CoCoRAHS 2 day totals. Most, if not all of these, are just one ob/day.

This will get buried and forgotten, but the HRRR seems to have a pretty good algorithm going for snow ratio incorporation. Here's a graphic to help describe.

My final, I think, on this event. CoCoRAHS two day totals.

20th and 21st continue with light snow threats.

Topic Edit 508AM: Added HIGH IMPACT and the time back in to the topic and extended 4 hours. Strongest winds in NJ/ne PA/se NYS roughly 10PM-4A, NYC/se NYS 1A-6A, LI/CT 2A-to possibly as late as 9A/25 e tip of LI. Minimum wind gust on LI 55 MPH with max 75MPH, NYC-se NYS minimum wind 50 MPH isolated max 70 MPH. Please follow NWS on all warnings/statements. I'll leave it yourselves to add graphics etc as need be. I'll begin an OBS-NOWCAST thread by 6A. Have not looked at soundings but everything else discussed in yesterdays 518AM topic edit below including HSLC SVR's continues. We may reach within 2F of the record 66F-2015 max temp for Christmas Day at CP. Flooding of some of the larger rivers, if it is to occur, may be delayed 24 hours or more after after the rain quits Christmas morning, Max rainfall axis in our forum looks to me to be CT, isolated 4", not including snowmelt runoff. If anything is missed, please let me know. Thank you. Topic Edit 518AM Wednesday 12/23: No significant changes. The prime threat period might by 2 hours too fast but not enough evidence to change the primary initialization period of weather related issues. My assessment tells me to prepare, without science, for many many thousands without power starting 9PM to midnight Christmas Eve evening, and then across se NYS, LI, CT, MA beginning midnight to 6AM Christmas morning. Gusts NYC airports should be 45-55kt, with potential for isolated 65KT LI/CT/MA. I expect SVR's for the HSLC lines of heavy showers to help focus the primary short-fuse threats. Lower chance of any damage northeast PA but ridges there will be most vulnerable there to ~ 55 MPH gusts. There is limited science on power outage wind damage with leaved trees, without, softer unfrozen ground versus frozen but I don't have this information nor any private services predictive algorithms. I still think that wind damage will prevail as the most important aspect of this storm, but please follow NWS flood watches, warnings as issued, due to the combined snowmelt and new widespread NYC subforum rainfall of 1-2", with isolated 4" potential inland-most of this in a 9 hour period during Thursday night, Any snow on the backside is exceedingly minor on the I84 high terrain. There actually might be a little better chance for a slight coating of snow Christmas night with the weakening trough aloft passage. --- Topic edit at 526AM Tuesday the 22nd: Changed the title to WILL be accompanied by damaging wind LI, and restricted the period of accumulative snow to the interior. I think the wind damage potential is the largest threat from this rapidly deepening 980s surface low moving northward up the front into NYS predawn Christmas. SVR's possible (in my mind likely, even if no lightning) for High Shear Low Cape (HSLC) heavy showers.The Richardson (R)#/wind profile combo on the NAM and even GFS tells me 45kt+ gusts all the major airports in NYC sometime between 10P/24 and 5A/25 . This is further supported by multiple models 80KT+ 850MB winds over LI, in some cases around 90-95kt. From my looking at R# and wind grab, this has the most favorable potential in my past 3 months of examining to realize downward transfer 50-65KT from the lowest 25 to 50 MB of the boundary layer. Whether an isothermal sounding in the lowest part of the boundary layer, or even a slightly inverted sounding can diminish-mute the potential, I don't know. What I do think, is that a lot of folks could wake up with lights out Christmas morning across LI, and possibly NJ/CT. Flooding potential to me looks the same as it did yesterday-previous days, all a matter of qpf, snowmelt combo to prompt a few rivers into minor or eventually moderate flood stage, even as temps plummet from 60ish near midnight Christmas morning, to near freezing by ~ Noon Friday. Please follow NWS closely on flood potential-they have more tools than I. Snowfall, accumulation less than 1 inch probably restricted in our forum counties only I84 high terrain northwestward. I'll copy this to the last page of this topic and add a couple of wind profiles there. The future posts will look at FOUS BL winds, which I think will exceed 34kt at LGA and BOS around 06z and 12z/25 respectively. IF not, then I'm a little too severe on my wind expectations. Also, I'll be adding shorter term wind gust potential graphics, especially Wednesday onward. (corrected many typos 826A) --- Below from the origination date of Friday evening the 18th. This topic is started primarily because of the recent operational model cycles at one time or another offering a more than ordinary 12-18 hour period of weather here near Christmas, on top of melting snow. Always uncertainty. Uncertainties abound, including how far inland can a couple of hours of 60 degree temperatures penetrate to melt the snowpack, and will there be any hazardous snow accumulation closer than the hilly western and northern suburbs? Add to that, is there an inversion thats prevent excessive low level winds from reaching the ground.? Snowpack will be melting a bit the next few days,, til a sudden brief surge of 60 degree warmth Thursday evening or very early Friday morning, associated with a strong cold front. That front is embedded within a high amplitude trough. It's slowed by a strong 1030-35MB high anchored near the Maritimes, and there is potential for northward moving low pressure along the front, as it traverses across the NYC forum. Max rainfall should be concentrated just inland (se or sse surface wind) and combined with remaining snow, may? be enough to promote some small stream flooding? Flooding will be dependent on how much snow melts on the 24th/early 25th combining with around 1" to possibly 2" of rain, prior to the sharp cool down to near freezing by midday the 25th. Current 12/18 river response models to multiple ensembles are not alarmed at this point so I don't want to make this look worse than it will be. Of greater concern is the ECMWF cyclic offering of 60+ MPH gusts to LI (50 inland) which may cause some damage. Recent experience with the storm of the 16th-17th suggests to me, that we will need at least 60 MPH gusts to see significant damage along the coasts and ridges. It's possible - IF the 850MB southerly jet can exceed 75 knots, preferably 85 knots. The 18z/18 GFS has 80 knots for e LI and the 12z/18 EC has near 100 knots for all of LI. IF the ECMWF were to verify, it would be lights out for many and not a pleasant Christmas morning. Timing of the event probably sometime at night (6P/24-6A/25 EST) Snow: Backside snow doesn't often accumulate significantly with temperatures falling rapidly from the 60s to near freezing. Thinking best chance I84 corridor high terrain sometime Friday morning the 25th. Graphics: 1) 12z/18 EC 850 wind. EC surface gusts, GEFS chance of 60 MPH wind gusts early Christmas and finally, the WPC qpf forecast from ~18z/18. 608P/18

Excellent posts this page - haven't had a chance to check anything else. I will begin a topic for 12/24-25 at about 715PM which will go without much ensemble support - always a concern, but the EC, GFS and WPC offers a good start 6-7 days in the future. It will include damaging wind, potential for ''minor or at worst moderate stream flooding" and maybe an inch or 3 of snow on the back side, Christmas morning.

Overall impact maximized nw of our forum where you're seeing top 20 event historically. Thanks for all the insight on NYC records. We will do better along the coast, maybe this winter??? I dunno. Might depend if the Nina continues weakening. That I don't know either. I just hope that everyone appreciates how locked in some of these events in Nov - Dec have been 7-11 days in advance. That is all the worlds modelers improving physics via research-more observation platforms contributing (satellite, radar, aircraft etc) and computers. The oldsters among us know. This graphic from the WPC web site.

Near closure on this event. Added NOHRSC snowfall analysis (multi platform). I think this analysis missed the 10" near Union or is it that spec of yellow?

Posts on p38 (This one) are helpful for me and it is an interesting time. Not to go against anyone, but I'm thinking we are tending to expand the database with more extreme weather the past couple of decades here in our forum. I might be wrong on this and will listen to counter science. This could be related to the warming (cycle) planet. Have appended several graphics to ensure everyone has seen this and has an idea in advance what is ahead (flooding? but if we're lucky, some spring snowmelt for the reservoirs in April). Also, there is anecdotal evidence (unsure of the science research on this) that the southern edge of the snowpack tends to set up the warm fronts and future low pressure development (easier in warmer air with northward advance of warm fronts often slowed by the colder denser surface air associated with snow cover). Didn't add snow density because I don't understand the numbers and how they relate to impacts but I think it may have to do with difficulty passing through (walk, transportation)and/or removal. If there is a link--- please add on. Thank you.