wdrag

FOUS 29kt at LGA and 28KT at PHL says to me 40 kt gusts possible in NJ beginning around 5PM. I dont want to overplay this but my experience with BL winds of 27kt or greater is a wind advisory. 34KT or greater HWW. So 5P could start 40 kt gusts. Also, once the pressure dips below 1000MB early Friday, the 1000MB wind is easily the guide for minimum gusts..possibly sustained. This should happen NYC north and northeastward. So if you have model 1000mb winds at 09z/25...check that too.

Haven't had time to study... Christmas doings here. Just check HRRR and others on here will have time to assist.

Hi! I'm not well educated on the subject. I ask that you google Richardson #, also BRN. From FSU this morning... LGA 12z/24 3K NAM winds and R#. You can see R# allows up to 950MB... but 50KT is modeled just above the sfc. Hope this helps and works pretty good as predictor. Here's a snippet. I look at SOLID red 0.25 surface to whatever layer and grab the max wind in that layer and trim 5 to 10 KT. In the limit of layer thickness becoming small, the Bulk Richardson number approaches the Gradient Richardson number, for which a critical Richardson number is roughly Ric= 0.25. Numbers less than this critical value are dynamically unstable and likely to become or remain turbulent.[1] The critical value of 0.25 applies only for local gradients, not for finite differences across thick layers. The thicker the layer is the more likely we are to average out large gradients that occur within small sub-regions of the layer of interest. This results in uncertainty of our prediction of the occurrence of turbulence, and now one must use an artificially large value of the critical Richardson number to give reasonable results using our smoothed gradients. This means that the thinner the layer, the closer the value to the theory.[2]

At 10PM, our NJ forum should be starting to get reports of 46-55MPH (wind advisory) gusts and isolated power outages-same e PA and w NJ. I trimmed these winds from Knots down to MPH.

Also, looked at 06z sounding... I see that as isothermal to 900MB at 06z (first line of convection LGA), and then the second line its' more unstable. Also, if the HRRR and HPC SREF are overdone, then I see it as a short term loss on modeling but a long term process to resolve. As it stands... I think those models are spot on as a minimum.

Hi!. Did anyone see the NAM (12K) 700mb VV (34 to 54 MB/sec later tonight). We know high res models are more extreme... point is, I think r# will win out on any isothermal sounding later tonight... IF the sounding caps gusts at less than 55 MPH in our forum... everyone is blessed w no power interruption and I'll have to drop the use of the R#. As it is, I use R# conservatively..I think max temp in CP will be 63-64Faround 1-3AM Friday. I could be high but BL temp now up to 15C at PHL and I think LGA 13C is conservative, probably SST modified low. Let's see how this goes. 326 FOUS61 KWNO 241200 OUTPUT FROM NAM 12Z DEC 24 20 TTPTTR1R2R3 VVVLI PSDDFF HHT1T3T5 TTPTTR1R2R3 VVVLI PSDDFF HHT1T3T5 ALB//896136 05807 211817 47040500 BTV//755539 05308 191717 46020203 06000898560 01208 161621 49090600 06000828161 03410 151618 48070500 12003969067 01604 101626 54110902 12004929261 -1004 111521 51090801 18014979266 -8901 021530 58121105 18009888666 -6605 041524 56110903 24023958847 07501 961628 59141105 24017927663 -9902 971525 59131005 30045958961 -9912 991622 51090400 30029969066 -9908 991721 54110601 36006933936 -1913 012311 40040094 36007874859 -2711 981617 46090297 42006864105 -4422 042810 26999386 42014954220 06918 002707 34009592 48000694502 00117 072312 16979185 48003663604 01921 042013 19979185 54000628603 -0712 092310 17979084 54000698804 03412 052015 17979084 60000645403 01516 112311 18979085 60000807704 -0410 072110 15979183 BOS//794741 00809 261817 47060501 LGA//784948 00010 221722 49100800 06000813759 00109 231719 50110602 06000826563 03706 181626 52130901 12002976266 -0706 191624 54110902 12003956571 05303 131629 55131003 18003985470 02305 131630 57121005 18046989770 34702 031539 62131207 24015978771 -1401 061637 61131207 24062989566 54701 981737 60131207 30011988354 10603 031826 59141106 30051987664 -9912 011723 50090400 36048989465 07812 031717 53090404 36002892610 -4422 052417 36019595 42011716255 -6924 042223 43029599 42000783704 -1321 092419 22979186 48000824006 -2322 072317 28999487 48000734702 -1517 112518 16969285 54000725302 -0814 082315 18009386 54000636505 -1618 122616 19978987 60000735203 00215 102516 19979486 60000653615 00221 142614 25979090 PHL//705159 00009 201718 50110901 IPT//907353 04604 171714 48040600 06000797668 01104 141625 54141003 06095989362 35302 111614 50060701 12000927669 -0903 081628 57141106 12177989566 49303 031706 55090803 18081967171 -2698 991635 61151307 18132999469 08300 921628 59131004 24087949165 -0408 992012 55110505 24080926660 04311 982412 46000098 30007832836 -1517 032511 40029996 30001843706 02215 032508 32989391 36000793605 -0621 082517 26989185 36001834901 03214 072513 18959185 42000704302 -1019 122516 15969084 42001765401 01816 102513 13948883 48000647907 -1017 142515 17968983 48000697903 00014 122514 16928584 54000545205 -3720 142614 22978988 54001654704 -0917 132410 20938787 60000603325 00024 152612 30979192 60000763917 01921 152610 25938788

Suggestion: if you have time. Monitor HRRR hourly gust performance vs reality. Already BUF 40KT as HRRR modeled.

This thread is modeled as a loser per modeling through 00z/24. The 29th is probably coming through as a cold front with a few showers on the 28th with possibly a little useless slight wet snow highest I84 terrain before wash away by a shower. The first of January is still on the boards, though it looks too warm, at least initially. That one is looking more robust qpf wise and surprisingly WPC has a halfway decent chance of freezing rain or snow down toward Allentown late NY eve. I won't add the D7 graphic here - time constraints, but will revisit Christmas morning. We just need separation of northern-southern streams on both dates and a more southern latitude track of the southern stream short wave, which for now, does not look promising. 536A/24

OBS and NOWCAST as this storm unfolds. Power outages may limit some of our participants from adding data. Be prepared for losing the internet, even if you own a generator.

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.. Have not looked at soundings but everything else discussed in yesterdays 518AM topic edit 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.

Hi! Good to see warnings up for Wind and Flooding in the various locations and watches elsewhere. In the morning, I'll add an OBS-NOWCAST thread for 6P Thursday-~6A or 10A Friday depending on what the 00z-06z/24 modeling consensus looks to be. Not much more I can add tonight. I know some of us will be wrapped up in Christmas eve activities and while I anticipate the ability to post at 5AM Christmas Day, lack of Internet may force me to forego??? All the best on somehow enjoying yet another big wind event. As with all topics, summary data will be added to the primary thread sometime late Christmas Day, or day after Christmas. Reminder while flooding will occur, note that larger slower rising rivers may not exceed flood stage til a day or two after the rain ends. 744P/23

If the 1000-500 thickness gets to 561dm it will get to around 61F or a bit higher in rainy BL wind in excess of 22 kt. In this case the NAM BL wind is 43KT... about as high as Ive seen it in a non-hurricane. I'll temper the NAM a bit for exuberance but it won't be more than 7 MPH too high, imo. The inversion looks more isothermal to me, and that 08z sfc temp is 57(probably SST nudged down). Warm the sfc temp to 60 or 61 and it becomes more unstable. Finally, a 12z map of HRRR max gusts (not HRRRX) for our area... a very good low starting point I think. Also, the HRRR is picking up on short narrow lines of convection after 06z in the Hud Valley LI eastward portion. This is very similar to the tamer ECMWF.

Don't have an easy answer... I trust models to 5 or 6 days except marginal or minor situations where there is a lot of variability. I trust patterns to as much as 11 days, especially if high amplitude stability. My hope for 12/29 is 20% or 30% at this time based on the modeling through 06z/23. Pattern favorable but not the 50/50 LOW lock! Other factors probably come into play--- some for which i'm not well skilled. Without a firm confluence zone in the St Lawrence Valley to northern NYS, or a 50/50 low, cutters are always possible. If the waa into the Great Lakes weakens and heads more east in future runs, then I84 comes back on the board. For now, letting it rest This is 5-6 days off and short wave interactions might force a somewhat different scenario.

read the doubts about wind. Here's my suggestion; Review all the High Wind topics and note the performance (we verify all these) of the topic that takes into consideration a slight high bias in guidance in advance, of the EC and HRRR wind gust algorithm. It's not by more than 5 knots (if we did a study) I'll add two graphics from the 06z/23 HRRRX for 06z/25 only... use the legend and lets see what happens. Take at most 5 knots off the HRRRX GUST wind guidance or just use the knots as MPH. Should be very close. It's an extensive problem that is coming. I also added the 80m wind... if you don't like the option from the gust algorithm, then use the lower speed 80m wind guidance as your gust. Maybe that will verify better. We never know for sure in advance, but it's better to prepare. If the models are right, and in advance we dismiss as way too high, sooner or later we automate these model guidances and outperform humans. The models are slowly improving. Gotta run. Back this afternoon, Walt

December 29 probably won't happen as snow I84, even though the EC EPS is coming around to the GEFS digging trough. Probably a little too late to prevent rain, instead of snow for I84-though I haven't given up hope for slower and further south on the digging short wave but for now, this first date option of the 29th has less chance of working out as snow. Also, for now, the less digging scenario now generally advertised means the event is faster, more likely occurring mainly on Monday the 28th. 1/1/21 An event is coming late NY Eve or NY Day. It too may be rain but for now has a little greater chance of snow, especially interior. No time to assess as 12/24-25 is my primary consideration.

Good Wednesday morning: There isn't much more to say except prepare for power outages, wind damage (outdoor decorations etc) and follow NWS Flood statements warnings. 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. I added the 5AM Watch for the USA highlighting the interior flood watches and the coastal High Wind. Also the 00z/GEFS chance of 60+MPH gusts for the period of ~ 6z-12z/25...impressive! and HRRR and NAM max gust potential ~ 1AM Christmas morning. 525A.

12Z/22 EPS and GEFS for you to decide. Just so you know the NAEFS continues colder and suggests a light to moderate snowfall for I84. I don't have time for all the graphics but here's the difference between the 12z/22 EPS and GEFS. Your call and you are welcome to professionally critique here any possible flaw-bias in my thinking. Right now, all options are on the board. I am doubtful of a big windup low in the Great Lakes on the 28th. Instead a weaker low, near L Erie with redevelopment s of LI, then a merger into a deepening low near the New England Coast on the afternoon of the 29th. If I am wrong, it will have been over reliance on the NAEFS 52 member ensemble vs the generally more highly regarded EPS , vs the sometimes maligned GEFS. I'd like another 00z/23 cycle to show me that I've incorrectly relied upon a GGEM-GFS ensemble blend. Blocking i realize is good but not ideal. Again, you decide what is best in your own mind.

What do you think about this digging? I see wet snow... but maybe I'm biased to the NAEFS and naturally biased to snow. This is starting to show confluence...a bit too far north...but I like how the GEFS is trying to carve out a hole in New England. Might be too little too late but this is still 7 days out... plenty of time to change. 06z GEFS 500MB members and mean.

Always good to be cautious. I like the overall opportunities but how much is realized in snow... the 50-50 block (LOW!) is most important. I don't see that yet but overall the anomalously strong and long duration (still next 14 daYS+) + 500 MB anomaly near the Davis Dtarit is a positive for snow options. I've added some minor WPC support with a D7 graphic for >1/4" frozen W.E. The darker green 30-49% chance. I like these graphics, but in clear cut event, they are very conservative. This one is not yet clear cut, so I can ride with it, EXCEPT as you can see from the issue time of 0455z/22... it is BEFORE the 00z/22 ensembles are seen (at least publicly). My guess this has to do with the shift hours. So, you're seeing later ensemble guidance from whatever resources and judge accordingly.

Nothing happened over night in our I84 forum. Wrong read on my part for minuscule event. All the QPF was just s of I78 in NJ to southern LI.

My once/day update to allow the models to be variable eventually coming to a consensus on both coming events. I've seen a few posts and agree. 29th: I don't think LI/NYC I80 south can get much if any snow out of the event late 28th and 29th. I think snowfall, whatever it is, is restricted to the I84 corridor with the se edge maybe 20 miles south of I84. How much, yet to be determined but a WET sticky snowfall seems more probable than a crystalline cold. I've added the 00z/22 NAEFS which shows a low in the eastern Great Lakes with a receded High over Nova Scotia, which eventually has a secondary s of LI merge and potentially rapidly deepen near Cape Cod on the 29th (00z/22 GEFS is interesting on the negative tilt eased deepening of the 500MB trough toward CC). The 0C sfc temp is near I84 to late on the 28th (last image) while the 1000-500MB thickness at 00z/29 (first image) is surprisingly cool. So that is my reasoning to keep faithful to an I84 3+" event with much less chance of snow this storm for NYC. Thinking could change in the future but for now, since models are all over the place, it is probably smart to choose a wetter scenario for NYC and not overpromise there. NY Day may be another story... I think snow is in the mix and to me it looks to be a better chance of some sort of lead WAA snow thump, before a possible change to rain for our forum. Just tooo far in advance for me to offer anything else, confidently. 558A/22

Saw some of the previous posts and agree... Topic edit at 522AM 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 HSLC heavy showers.The R#/wind profile combo on the NAM and even GFS tells me 45kt+ gusts all the major airports in and near 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 Richardson (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. I added the 00z/22 GEFS chance of 60+MPH gusts for 06z/25. I think pretty impressive for the the coasts-LI. I also added the LGA 06z/22 NAM time section. Note how close to the surface the 50kt winds at LGA Christmas evening-overnight. In my mind, to avoid damage, we'll need a stronger inversion or a weaker system and less wind aloft in future model cycles. (corrected many typos at 822A-my apology-was too much of a hurry)

Follow NWS on flooding. No one on here has said massive flooding. Flooding is possible, a few streams maybe but major?? My guess is very little if any because of shorter duration of R+/big warmth and fast cool down to near freezing Friday. I think clearing drainage basins, especially where more than 8 inches on the ground right now is a good idea, just to reduce any possible coding of water in those areas. Must be done SAFELY, if at all. Thanks.

I think, not much weather in se NYS after 9AM Fri.... the action is mainly 6PM Thu-6AM Fri, so far. I don't see much snow for you or I, less than 1" for sure, maybe just wet flurries. I think Fri afternoon is cold but decent and if it were me, I'd plan a go. We do the same for the part of our family in the Pocs... after 9A Fri, they should be able to travel safe.

A couple of maps showing yesterdays CoCoRAHS snowfall reports.