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January 22nd-23rd East Coast Winter Storm Model Discussion.

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Just my 2 cents but...

 

I don't see much if any sleet or mixed pcpn up to phl this run. With the upper low tracking ene rather than up the coast, it will be hard to get enough warm air this far north to get mix. Using the ECMWF, the zero line at h8 is S of State of Delaware. Even though some warmer air may be up to 800 or even 750 mb, I dont see it making it up here. I also looked at the GFS and it seems too cold for any mix based on track and soundings.

 

GFS soundings for Sat night imply embedded convection with some instability around 600 mb and above. Psbl thundersnow if it forms,

 

I do see a difference between the 72hr GFS and ECMWF and this has to do with the circulation around the closed upper low to the south. Visually the GFS seems a bit more expansive than the ECMWF. In my mind this means the GFS also means a more northern extent to the very heavy snow and if it forms, any thundersnow. 

 

Something to watch when we get closer is for an inverted trough to form off the east coast that will suggest the track of the sfc low and how far north the core of the system can get. I know this is old style fcstg, but if the trough does not get up to the Jersey coastal waters, then all pcpn should be snow since the warmer air will be staying to the south. 

This is a really good post. Thanks for sharing your thoughts.

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Here is what I grabbed from Amwx - so a more uniform qpf distribution across the mid-Atlantic

 

QPF:

2.1 IAD

1.9 BWI

2.0 DCA

2.3 Winchester

2.1 Frederick 

1.9 Richmond

 

 

Thanks Chubbs!

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In the better late than never department here is the 96-hour ukie - previous hours unavailable - looks reasonably close to euro fwiw.

 

post-18-0-80851700-1453316585.gif

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Those EC QPF of 2-3 inches are off. Less than 2 QPF here at VAY. 

 

Be careful assuming looking at the very high QPF's fcst by the models. This far away from the high precip moisture that is available on the e and se side of the low you will need very strong dynamics and/or instability to squeeze that amount out. M However, I still think snow amounts in excess of a foot should fall near PHL. Looking at the soundings, the snow formation zone looks to be 650 to 600 mb meaning good dendritic formation based on the fcst temps in this layer. This means better than 10:1 ratios.

 

Considering my expected higher ratios, these higher ratios should offset the lower qpfs that I expect. If convection gets this far north, then watch out, but based on current models runs, I think most of this convection should stay to the south.

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Be careful assuming looking at the very high QPF's fcst by the models. This far away from the high precip moisture that is available on the e and se side of the low you will need very strong dynamics and/or instability to squeeze that amount out. M However, I still think snow amounts in excess of a foot should fall near PHL. Looking at the soundings, the snow formation zone looks to be 650 to 600 mb meaning good dendritic formation based on the fcst temps in this layer. This means better than 10:1 ratios.

 

Considering my expected higher ratios, these higher ratios should offset the lower qpfs that I expect. If convection gets this far north, then watch out, but based on current models runs, I think most of this convection should stay to the south.

 

Have to watch out for Wxservice Delisi wind's fracturing the dendrites too.  But point taken, just texted Tom I thought qpf was too robust. 

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Be careful assuming looking at the very high QPF's fcst by the models. This far away from the high precip moisture that is available on the e and se side of the low you will need very strong dynamics and/or instability to squeeze that amount out. M However, I still think snow amounts in excess of a foot should fall near PHL. Looking at the soundings, the snow formation zone looks to be 650 to 600 mb meaning good dendritic formation based on the fcst temps in this layer. This means better than 10:1 ratios.

 

Considering my expected higher ratios, these higher ratios should offset the lower qpfs that I expect. If convection gets this far north, then watch out, but based on current models runs, I think most of this convection should stay to the south.

Yeah, wouldn't be surprised if the QPF goes another tick down. Models overdo it a lot. Could strong wind keep the ratios down? 

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Good luck to all operational forecasters. It is easy sitting here and looking at the weather pattern now that I am retired. However, when you actually have to forecast numbers and pinpoint the forecast by location, amount and time, that is not so easy.

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Yeah, wouldn't be surprised if the QPF goes another tick down. Models overdo it a lot. Could strong wind keep the ratios down? 

 

Of course they will, but still more than 10:1.

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From an I-95 view that map is the opposite of last January's big storm - high in SW low in NE.

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per euro, along i 95 and interior s jerz 40-50 mph gusts..coast is up to 60mph gusts..nw burbs and lv 30-40 mph gusts

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Of course they will, but still more than 10:1.

this shows it pretty well, solid omega in the DGZ

 

omeg.png

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I couldnt overlay the two, but here are the omega and winds for PHL. 20 knots usually is the fractionalizing speed.

 

 

post-27-0-81597000-1453318034.png

 

 

 

post-27-0-72335500-1453318041.png

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I couldnt overlay the two, but here are the omega and winds for PHL. 20 knots usually is the fractionalizing speed.

 

 

attachicon.gifbarb.pn

almost looks like a subsidence zone there on hilly. GFS kind of hinted at that 12z with banding to west

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I couldnt overlay the two, but here are the omega and winds for PHL. 20 knots usually is the fractionalizing speed.

 

 

attachicon.gifbarb.png

 

Based on your graphic, easily over 20 knots. 

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almost looks like a subsidence zone there on hilly. GFS kind of hinted at that 12z with banding to west

 

 

Based on your graphic, easily over 20 knots. 

 

Looks like there is a window late on Saturday, probably when the last deformation zone passes over that it (winds) could be less. Plus its the gfs, this is one spot I trust the nam more, but not at this forecast time period.

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Do you know what the snow ratios are based on?

 

No.  It spits them out for each 6-hour interval, but I don't know if it's EK or some other method.  And I'll admit, 20.5" off 1.70" (or some sources say 1.75"), which would be a storm-average average ratio of 12:1, seems suspect to me with little if any dendritic growth modeled, and what there is of it being very high up allowing for a lot of riming before those flakes hit the ground.  But alas, I just report the numbers!

 

 

Edit: Though as Tom pointed out, there is impressive omega in the DGZ, despite it being rather thin, so maybe it isn't as unrealistic as I first thought...

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Let's not get hyped up on a single snow forecast totals. 20" one run isn't going to be 20" the next. Just worry about the General qpf and its orientation. Totals will work themselves out.

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12z totals by location from Wxbell

Coatesville - 19"

ABE - 11"

DYL - 15

Harrisburg - 14

LNS - 17

PHL - 17

RDG - 14

PTW - 16

York - 20

AC - 18

OC - 11

EWR - 16

VAY - 18

Dover De - 20

ILM - 17

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12z totals by location from Wxbell

Coatesville - 19"

ABE - 11"

DYL - 15

Harrisburg - 14

LNS - 17

PHL - 17

RDG - 14

PTW - 16

York - 20

AC - 18

OC - 11

EWR - 16

VAY - 18

Dover De - 20

ILM - 17

How 'bout TTN?

Sent from my iPhone using Tapatalk

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