wdrag

Please see bluewave posts little earlier on temps 61 or higher with big wind and then less wind where temps basically peaked in the upper 50s. Temperature profile makes a big difference,

Merry Christmas 2020! I will revisit this topic either late this afternoon or Saturday morning for a change in title featuring Jan 1--- but only if the EC is consistent at 55 + MPH gusts. Anything less, becomes our routine event. Something is coming Dec 31-Jan 2 and it may be more complex than what we see right now ranging from some sort of wind-flood event to a system with a very low prob of some wet snow. I kind of want to be careful about a topic adjustment, if any. For now consider the significant snow threat non existent though the GEFS,maybe by climo or whatever, has something for at least I84 on the first.

Saw the upper 50s temp cap on wind below 40 kt at ISP/GON so far, Also the 50-55KT at JFK/LGA/BDR. Not sure what CP max temp was--probably only 61ish. Also bluewave pointed out the MOS warm temps vs GFS raw were wayyyy too high for e LI (good catch). Am wondering if that contributed to the GEFS high bias probabilities for 60+ MPH gusts eastern LI? Merry Christmas! Walt

Isothermal layer probably prevented much more impact on LI..s Coastal CT... still fairly impressive in the area at 510A. Here are some platforms for cursory verification in a quick check.

47kt Tappen Zee light, 49kt Ocean City Maryland and 46 kt at Lewes DE. Coming up. should be blowing good midnight-6A LI. Might not be so bad nw of I287. Even Vernon NJ high terrain 53 MPH recently. Probably off line now thru 5A.

Suggestion: Do NOT use the NAM 10M gusts as what will occur. They look 10-15 MPH too high already. I think the HRRR is best.

Widespread pure drainage flooding can be expected along the edge of the snowpack in our forum overnight, anything 6" to a T.

thanks for the post. Vernon NJ (elevated ski area I think) hit 47 MPH this morning.

Let's temper that 10-15 MPH, and use that 80 for an extreme gust possible but not something I'd want to forecast. I'm staying with 5s5-65 MPH gusts with a few 70-75 MPH somewhere NYC eastward and northeastward. NAM can get a little ballistic. Still...it's potent, especially if lines cross the area 5z-12z.

I'll look for your report. Unusual flooding or debris, let the forum know and NWS as well. Good work/call etc.

Agreed with your concerns in heavier snowpack on northwest fringe of NYC subforum. Already well in advance flood "warnings" posted for PA/NYS Rivers in and near our subforum, showing confidence on the coming event.

For the record as a starting point: 11AM today. No significant outages eastern USA.

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.