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wdrag

HIGH IMPACT Stormy Christmas (EVE and morning) 12/24-25/20 6P-10A

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2 minutes ago, qg_omega said:

Rain stabilizes the lower atmosphere, convection mixed winds down not heavy rain

That’s what I meant sorry didn’t specify they think 50-60knots mix down

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8 minutes ago, bluewave said:

We will have to monitor the actual temperatures. The MOS numbers are running much higher than the raw guidance on Long Island. If Long Island gets into the 60s, then it will be easier to mix down the stronger winds especially with the multiple squall lines forecast.

KFOK   NAM MOS GUIDANCE   12/24/2020  0000 UTC                      
 DT /DEC  24            /DEC  25                /DEC  26          /  
 HR   06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 18 00 
 X/N                    62          55          56          27    35 
 TMP  41 43 44 59 60 57 59 61 66 69 63 55 52 50 45 38 34 31 30 33 27 

 

Raw

  24 12/25 06Z   55     53     153      30    0.01  0.01    559    566   10.7 -13.8 1008 100       013OVC362    0.0   14.2
  27 12/25 09Z   54     54     157      35    0.11  0.02    561    564   11.3 -13.6 1004 100 -TSRA 006OVC343    0.0   11.1
  30 12/25 12Z   54     53     156      36    0.06  0.02    562    564   11.7 -12.7 1002 100 -

Most of the area is already in the 50s and south shore or nyc out east and jersey shore already gusting to around 30

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.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
The main weather hazards with the strong cold front will be
strong winds with gusts up to near 65 mph, possible flooding,
both from heavy rain and coastal flooding. Winds will continue
to increase in the low levels of the atmosphere Thursday night
along with the rain. The rain will become more widespread and
will become heavy. Vertical forcing is shown with Q Vector
convergence in the 850 to 500 mb layer. PWATS with all the
increasing southerly flow will rise near 1.5 to 1.6 inches by
early Friday morning, which is above the maximum moving average
climatology for OKX according to SPC sounding climatology. Model
soundings show warm cloud depth 10-11 kft. Despite the lack on
instability, still a lot of dynamic forcing and anomalous
moisture so flooding will be a possibility including flash
flooding. With the strong SE flow, that should enhance rainfall
amounts for the higher terrain north and west of NYC with
orographic lift. Those locations could end up being on the
higher side of total rainfall amounts. See hydrology section
for more details and for the coastal flooding see the
tides/coastal flooding section for more details.

For the winds, there will be a low level jet strengthening
through the night, with around 90-95 kt winds in the 850 to
900mb layer as a max near 7-11Z for NYC and locations north and
west, SW CT, Central Long Island in the 8-12Z time period and
9-13Z to the east using the 3km NAM Bufkit. The NAM shows a
stronger inversion so only a fraction of this jet will be mixed
down, but with the downward momentum from the heavy rain, winds
at 1500 ft could easily mix down and those are in the 50-60 kt
range. The models have a consensus of a main cold frontal squall
line that moves into the forecast region and then strengthens
as it moves across Long Island and Southern Connecticut. With
GFS Bufkit shows this as well but overall timing with the whole
cold front and highest winds and rain is a few hours earlier
compared to the NAM.
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1 minute ago, wdrag said:

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

Latest HRR actually got a little stronger with the winds for nyc east 

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Strong winds lasting  during  4pm today to 9am tomorrow.     Breezy outside this range.

Dangerous winds are during 2am tonight to 7am. tomorrow morning------that is Santa huffing and puffing because the old boy has gained so much weight over the year.

Good luck and tie down or take in loose objects now!        Check roof antennas too.   

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3 minutes ago, nycsnow said:

12z nam pretty much consistent winds 40-50 around 3pm peak gust 70s over night. Not sure what soundings look like 

Strong inversion.

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Just now, NJwx85 said:

Strong inversion.

this will be the wild card-if the inversion holds this will be largely a non event.   40mph winds in winter aren't all that big of a deal.   60 or 70 different story

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1 minute ago, Brian5671 said:

this will be the wild card-if the inversion holds this will be largely a non event.   40mph winds in winter aren't all that big of a deal.   60 or 70 different story

Wonder if the warmer temps are gonna make a difference some places are already upper 50s

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Just now, nycsnow said:

Are you able to tell what actually mixes down?

Nobody knows that but the soundings are strongly inverted NYC and SE. NW of the city the inversion isn’t as pronounced. 

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1 minute ago, NJwx85 said:

Nobody knows that but the soundings are strongly inverted NYC and SE. NW of the city the inversion isn’t as pronounced. 

Guess time will tell thanks

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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

 

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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.   

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Just now, wdrag said:

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.   

How are the soundings comparing so far to the nam?

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29 minutes ago, wdrag said:

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.

Is there a resource you (or someone else who'd know!) could point to for reading about the R# and how it relates to mixing winds to the surface? How are you determining the R#, and what values are you looking at as a threshold for more wind mixing than.. For example, the BUFKIT momentum transfer product, would suggest?

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9 minutes ago, wdrag said:

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. 

Screen Shot 2020-12-24 at 10.07.31 AM.png

Some models are showing costal locations gusting 40-50 by 4/5pm what are your thoughts 

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42 minutes ago, Treckasec said:

Is there a resource you (or someone else who'd know!) could point to for reading about the R# and how it relates to mixing winds to the surface? How are you determining the R#, and what values are you looking at as a threshold for more wind mixing than.. For example, the BUFKIT momentum transfer product, would suggest?

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]

Screen Shot 2020-12-24 at 10.46.29 AM.png

Screen Shot 2020-12-24 at 10.47.03 AM.png

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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. 

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6 minutes ago, wdrag said:

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. 

Walt, would the same be true for the south shore of Long Island near JFK?

 

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