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December 10th/11th winter storm threat


jamesnichols1989

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Make that a tenth up through central Mass. A quarter from LI to the elbow.

 

It's not too far off from other guidance down along the S Coast/SE MA with that number.  Was 0.36" on the NAM and 0.45" on the GFS.  09z SREF was right around 0.25" as well.  GGEM/RGEM probably closer to Euro/SREFs.

 

Thanks.

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Funny that the weather weenies aren't posting the RPM - shows 0" of snow north of C NJ. 

 

 

Never a fan of that model. 

 

1-3 or 2-4 to the SE seems reasonable right now.  If the 18z models don't back off then higher totals may be warranted despite the Euro which is playing catch up.   If we assume the NCEP guidance has overshot again those ranges should be fine and are borderline supported by all guidance including the Euro.

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Never a fan of that model. 

 

1-3 or 2-4 to the SE seems reasonable right now.  If the 18z models don't back off then higher totals may be warranted despite the Euro which is playing catch up.   If we assume the NCEP guidance has overshot again those ranges should be fine and are borderline supported by all guidance including the Euro.

 

Yup.

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I'd probably go something like 1-2" for the interior in a BED-ORH-BDL-BOS quadrangle and then a little more for SE areas where 2 to 3 tenths could give 3"+ if ratios are good (which right now, soundings support)

 

But I'd also be leery of dry air to the north which may chew up some of the modeled QPF on the northern periphery, so I could see a coating instead for interior areas. But given the slight NW trend right now, I don't think an inch is unreasonable...or even 2.

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Maybe when the Euro caves, it's got an algorithm that shows only minute creeping in the direction of the consensus so as to not emphasize the magnitude of the cave :/

 

I've always believed there is a component of continuity in it's algorithm that normally benefits it significantly.  The GFS/NAM are prone to wild swings usually too far west/wet only to come back towards the center.  Euro trudges in one direction only very slowly usually and therefore is less prone to seeing dramatic run to run swings.  We saw this type of deal many times last winter on systems the Euro had 1000 miles to the south that the GFS would show as a 5" event...that ended up being about an inch or two in the end.  Euro slumped that way gradually each run, GFS wildly overshoots and then moves back to the center.   Honestly don't think that's happening this time, but it still may be a little wet.  I think that's what is happening here and I like Will's numbers above.

 

There could be a wicked band in this too, but that is impossible and unwise to attempt to forecast yet.  1/3 or 2/4 is very reasonable.  Can be fine tuned tonight/today as the other models update.

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Maybe but since it keeps coming NW and increasing Qpf, that tells me it's struggling

 

lol we'll see

 

Seems like it's some subtle differences with the phasing that leads to the issue here. The GFS phases 2 streams a bit faster than the Euro and the whole system is 75 mile farther northwest. 

 

A close call - I'm not sure which to believe. 

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Maybe when the Euro caves, it's got an algorithm that shows only minute creeping in the direction of the consensus so as to not emphasize the magnitude of the cave :/

 

 

The Euro rarely does make huge jumps or run to run swings...one of the reasons it is so good. It isn't prone to massive errors in short lead time. That said, it's not totally immune to its issues. But inside of 60-72 hours, its very hard to beat. It did have a big bust last winter on 2/26 with showing big snows for the interior about 18-24 hours out, but it ended up way too cold.

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could see how precip distribution might be more variable than usual, relative to what models are showing. going into it, soundings are very dry (like -30C td at 800 mb) and we don't advect in moisture in the low levels in the traditional sense per se as the flow is WSW throughout the column...the gfs and nam both have some really strong 7h fronto forcing skirting along the S coast - so could be a pretty good band thereabouts - but north and west of it, things could have a hard time being much more than a little bit of -sn. 

 

just a thought. 

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I'd raise a flag more on the Euro than this system.  If one has the proper expectations 1/3 or 2/4 for now...

 

24 hours ago the Euro barely had a trace to ACK with the bulk staying WAY SE.  It's clawed it's way back from embarrassment slowly on this one.

 

You may be missing the point. This has the look of an all or nothing band. I don't see this as your basic situation where the amounts of snow tail off slowly north of the heaviest echoes. This has the look of an abrupt drop off in snow if you get north of any strong banding. So it's quite important to see where this ends up. That is the premise of my earlier posts. I'm just not sure how far north that band gets. It's not that areas can't get 1-2" of snow...they can..but where is that band setting up?

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I'd probably go something like 1-2" for the interior in a BED-ORH-BDL-BOS quadrangle and then a little more for SE areas where 2 to 3 tenths could give 3"+ if ratios are good (which right now, soundings support)

 

But I'd also be leery of dry air to the north which may chew up some of the modeled QPF on the northern periphery, so I could see a coating instead for interior areas. But given the slight NW trend right now, I don't think an inch is unreasonable...or even 2.

 

 

could see how precip distribution might be more variable than usual, relative to what models are showing. going into it, soundings are very dry (like -30C td at 800 mb) and we don't advect in moisture in the low levels in the traditional sense per se as the flow is WSW throughout the column...the gfs and nam both have some really strong 7h fronto forcing skirting along the S coast - so could be a pretty good band thereabouts - but north and west of it, things could have a hard time being much more than a little bit of -sn. 

 

just a thought. 

 

Like we all thought the same..lol.

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You may be missing the point. This has the look of an all or nothing band. I don't see this as your basic situation where the amounts of snow tail off slowly north of the heaviest echoes. This has the look of an abrupt drop off in snow if you get north of any strong banding. So it's quite important to see where this ends up. That is the premise of my earlier posts. I'm just not sure how far north that band gets. It's not that areas can't get 1-2" of snow...they can..but where is that band setting up?

 

You referenced the Euro and then flags...so I assumed that was where your anxiousness was coming from as your Met degree is on the line with Gulf Stream.

 

My point to you is there's no way we're going to know where that may setup for another run or two.  But the Euro is like 600 miles north from it's run of just 24 hours ago for 12z tomorrow.....  with every major model wetter this run vs previous runs I think that's the important thing to note vs the Euro still being on the lean side.

Again if your expectation and mine is 1-3 or 2-4....not the 6 or 10" amounts being tossed around which will be entirely band dependent.

 

The high res NAM highlights the pitfalls of potential banding well...but like I said way too far away for details look at what happened yesterday.

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You may be missing the point. This has the look of an all or nothing band. I don't see this as your basic situation where the amounts of snow tail off slowly north of the heaviest echoes. This has the look of an abrupt drop off in snow if you get north of any strong banding. So it's quite important to see where this ends up. That is the premise of my earlier posts. I'm just not sure how far north that band gets. It's not that areas can't get 1-2" of snow...they can..but where is that band setting up?

yeah that's how i see it as well. 

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lol we'll see

 

Seems like it's some subtle differences with the phasing that leads to the issue here. The GFS phases 2 streams a bit faster than the Euro and the whole system is 75 mile farther northwest. 

 

A close call - I'm not sure which to believe. 

Either way we get some accumulating snows regionwide..no getting around that.

 

i guess safe way to go for now is 1-3..but mention that could certainly increase in time

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You referenced the Euro and then flags...so I assumed that was where your anxiousness was coming from as your Met degree is on the line with Gulf Stream.

 

My point to you is there's no way we're going to know where that may setup for another run or two.  But the Euro is like 600 miles north from it's run of just 24 hours ago for 12z tomorrow.....  with every major model wetter this run vs previous runs I think that's the important thing to note vs the Euro still being on the lean side.

Again if your expectation and mine is 1-3 or 2-4....not the 6 or 10" amounts being tossed around which will be entirely band dependent.

 

The high res NAM highlights the pitfalls of potential banding well...but like I said way too far away for details look at what happened yesterday.

 

Well then my advice to you and others is not to take QPF verbatim. It may be more within the band and less outside the band. So to speak. It's not an easy forecast and one where taking the QPF over your house may not work out. Models are horrible at resolving mesoscale features. If somebody north of the band axis has 0.15" of QPF on model output but ends up smoing cirrus..you know why. Subsidence FTL.

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You may be missing the point. This has the look of an all or nothing band. I don't see this as your basic situation where the amounts of snow tail off slowly north of the heaviest echoes. This has the look of an abrupt drop off in snow if you get north of any strong banding. So it's quite important to see where this ends up. That is the premise of my earlier posts. I'm just not sure how far north that band gets. It's not that areas can't get 1-2" of snow...they can..but where is that band setting up?

 

Yeah - prior to the forcing both the GFS and NAM have a bone dry later around 800mb. Red flag for a sharp cutoff. 

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Well then my advice to you and others is not to take QPF verbatim. It may be more within the band and less outside the band. So to speak. It's not an easy forecast and one where taking the QPF over your house may not work out. Models are horrible at resolving mesoscale features. If somebody north of the band axis has 0.15" of QPF on model output but ends up smoing cirrus..you know why. Subsidence FTL.

it's analogous to what we saw with the last anafrontal set-up and what transpired over the OV into PA. you had to be in the perfect spot to really get in on the goods. and that one was more robust anyway.

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Yeah - prior to the forcing both the GFS and NAM have a bone dry later around 800mb. Red flag for a sharp cutoff. 

 

 

it's analogous to what we saw with the last anafrontal set-up and what transpired over the OV into PA. you had to be in the perfect spot to really get in on the goods. and that one was more robust anyway.

 

Of course it may setup right over our heads..lol. In that case, James is weenie of the day, but just something that we may beed to look out for. FWIW, the lift over SNE is near 500mb it seems. 700mb lift more near the south coast. We can be just fine with 700-500mb.

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Well then my advice to you and others is not to take QPF verbatim. It may be more within the band and less outside the band. So to speak. It's not an easy forecast and one where taking the QPF over your house may not work out. Models are horrible at resolving mesoscale features. If somebody north of the band axis has 0.15" of QPF on model output but ends up smoing cirrus..you know why. Subsidence FTL.

 

This is true but I haven't really talked about QPF at all.  My only real question is does the best band set up towards you Bob and Ginxy or further south towards me.  As long as we don't see a bust to the SE of the main shield I don't think anyone in that area is going to have trouble getting to 1-3".

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