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Central PA - February 2017


MAG5035

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19 minutes ago, MAG5035 said:

Also could strike the Scranton/WB area pretty squarely and that has been a region that has had fringe problems for several seasons going it seems. NortheastPAwx looks pretty good either there or NYC where he is now. 

You thinking a slight northwest trend?

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The 0z NAM trio all in agreement with a warning type event for a large swath of PA. This storm could very well be an I-70 on north special. The areas of greatest potential for high accumulations look to be elevation areas to the west of Chambersburg and anyone in persistent banding on the NW side of the low. I haven't looked in depth at each NAM run, but given the H5 and H7 look on the NAM 12km, the state is in a good spot. I could see double digits in some spots in eastern half of PA if the surface feature intensifies as modeled. 

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5 minutes ago, MillvilleWx said:

The 0z NAM trio all in agreement with a warning type event for a large swath of PA. This storm could very well be an I-70 on north special. The areas of greatest potential for high accumulations look to be elevation areas to the west of Chambersburg and anyone in persistent banding on the NW side of the low. I haven't looked in depth at each NAM run, but given the H5 and H7 look on the NAM 12km, the state is in a good spot. I could see double digits in some spots in eastern half of PA if the surface feature intensifies as modeled. 

as normal w/ NAM's overzealous precip outputs, i was wondering what the upside really was as their surely is good lift with this and the dynamics are in our favor.  Lets hope the big guns show the same.

Nut

 

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1 minute ago, pasnownut said:

as normal w/ NAM's overzealous precip outputs, i was wondering what the upside really was as their surely is good lift with this and the dynamics are in our favor.  Lets hope the big guns show the same.

Nut

 

Yeah. I'm not seeing wide spread double digits, but there's potential. I'm sure there will be a few reports. I like eastern PA from Berks county to north and east as the sweet spot. 

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1 minute ago, MillvilleWx said:

Yeah. I'm not seeing wide spread double digits, but there's potential. I'm sure there will be a few reports. I like eastern PA from Berks county to north and east as the sweet spot. 

best of show come end of storm....Monroe county IMO.

they are in the perverbial bullseye.  I'm just glad to see tonights early trends continue to get more of us into the goods.

 

Nut

 

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Well we can start with rule #1 -- NAM QPF is almost always overdone at this stage... especially if its a wetter outlier. Knock ~30% off those snow maps for a more reasonable expectation.

Rule #2 would be that these rapidly deepening storms tend to trend NW in the last 48 hours but the track and setup for this one is pretty unique so I'm not sure that rule really applies. I'll let the red taggers chime in on that thought though.

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21 minutes ago, Atomixwx said:

I wonder if the warm water off the coast could totally wreck this thing like what happened a few years ago during the botch heard 'round the world...

Probably not, this won't develop a really strong low level jet right off the ocean like that debacle had, and by the time the low starts winding up as it hits the coast the flow will be more northeasterly. This is going to be more of a boundary thing, with cold pushing down from the north throughout the event. The southern tier might have some initial issues but with the precip rates and lift that models are generating the column should allow for snow in fairly short order in PA. And temps should continue falling throughout the event. 

Now when it comes to the low pressure itself interacting with those warm waters, well I wonder if most models are underdoing the deepening of the coastal low. Might not be to the extreme that the RGEM was at 18z (972ish), but it could end up being a pretty deep low. Cold air coming in will eventually make a pretty decent gradient. 

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1 minute ago, skiier04 said:

Well we can start with rule #1 -- NAM QPF is almost always overdone at this stage... especially if its a wetter outlier. Knock ~30% off those snow maps for a more reasonable expectation.

Rule #2 would be that these rapidly deepening storms tend to trend NW in the last 48 hours but the track and setup for this one is pretty unique so I'm not sure that rule really applies. I'll let the red taggers chime in on that thought though.

I agree and while im no tagger, your rules are very valid, but as we are now basically at 24 hrs till go time, I think a tick either way is all we have left, to which most are safely in (except me....lol).

Nut

 

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How is this possible, I thought winter was over already?

All kidding aside, all of the models are putting most of us in a good spot for a warning level snow storm.

The best part is that the long range pattern looks fantastic for the next few weeks, which should give us a few more good winter storm chances. The PNA & NAO, along with the MJO heading strongly into phase 8 & then into phase 1, could work together to give us a great last month of winter!

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1 minute ago, MAG5035 said:

Probably not, this won't develop a really strong low level jet right off the ocean like that debacle had, and by the time the low starts winding up as it hits the coast the flow will be more northeasterly. This is going to be more of a boundary thing, with cold pushing down from the north throughout the event. The southern tier might have some initial issues but with the precip rates and lift that models are generating the column should allow for snow in fairly short order in PA. And temps should continue falling throughout the event. 

Now when it comes to the low pressure itself interacting with those warm waters, well I wonder if most models are underdoing the deepening of the coastal low. Might not be to the extreme that the RGEM was at 18z (972ish), but it could end up being a pretty deep low. Cold air coming in will eventually make a pretty decent gradient. 

I'd add that the trough axis is also not negatively tilted which as Mag states gives a NE wind, and not an E wind, saving most once it hits the coast and goes....

 

BOOM!

How'my doing Mag?

 

Nut

 

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1 minute ago, Blizzard of 93 said:

How is this possible, I thought winter was over already?

All kidding aside, all of the models are putting most of us in a good spot for a warning level snow storm.

The best part is that the long range pattern looks fantastic for the next few weeks, which should give us a few more good winter storm chances. The PNA & NAO, along with the MJO heading strongly into phase 8 & then into phase 1, could work together to give us a great last month of winter!

I know.  I've been seeing the MJO headed strongly into 8 and AO/NAO finally coming around.  Exciting times for the back half.

Sure hope so.

 

Nut

 

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1 minute ago, MAG5035 said:

Probably not, this won't develop a really strong low level jet right off the ocean like that debacle had, and by the time the low starts winding up as it hits the coast the flow will be more northeasterly. This is going to be more of a boundary thing, with cold pushing down from the north throughout the event. The southern tier might have some initial issues but with the precip rates and lift that models are generating the column should allow for snow in fairly short order in PA. And temps should continue falling throughout the event. 

Now when it comes to the low pressure itself interacting with those warm waters, well I wonder if most models are underdoing the deepening of the coastal low. Might not be to the extreme that the RGEM was at 18z (972ish), but it could end up being a pretty deep low. Cold air coming in will eventually make a pretty decent gradient. 

Yeah, the low-level u-wind anomalies are not that impressive early on during this event. Later, when the low intensifies, eastern PA, NJ, and New England get into the stronger maritime flow and see intense precipitation.

The weird thing about this event is that we start out with a frontal type wave out west, combined with a lee trough/lee cyclone that develops on the warm side of the temperature gradient in northern VA. I think this favors an initially broader swath of precipitation, where despite the limited easterly flow, we get a tightening frontal gradient between the westerly flow associated with the weakening frontal wave and the southeasterly flow associated with the strengthening low/trough (850-700 mb).

As the storm interacts with the mid-level trough and intensifies, the most intense banded precipitation will likely be over the eastern part of the subforum, though any further shifts in the storm track NW would prolong the period of enhanced precipitation.

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6 minutes ago, MillvilleWx said:

Yeah. I'm not seeing wide spread double digits, but there's potential. I'm sure there will be a few reports. I like eastern PA from Berks county to north and east as the sweet spot. 

Now that we're pretty close in I've been starting to look at some of the finer details. I think snow could really pile up fast if we get heavy rates and once we start accumulating. This seems like one of those events where snow ratios will be improving as the event wears on with the low and mid levels cooling throughout the event. First off, look at the NAM 700mb VV at 30 and 33 (!!!)

nam-vvelprs-700-usne-30-B-000.png

nam-vvelprs-700-usne-33-B-000.png

 

That coincides with temps at the 700mb layer at h30 and 33 being:

 

nam---usne-30-B-700rh_tmp_hgt_wdb2.png

nam---usne-33-B-700rh_tmp_hgt_wdb2.png

One can see the 700mb temp will be falling as the low gets to the coast. While not directly in the ideal DGZ, temps of -5 to -8ºC should allow for some relatively decent ratios from a dynamic standpoint (perhaps 12-15:1ish). Even 850 temps in PA aren't all that bad once the event is in full swing, with a very tight gradient ending up between DC and the mason dixon. At hour 33 the -4ºC 850 line is pretty much running the mason-dixon line in the eastern half of PA. I'd be curious to see some of the full BUFKIT data, I guess if there's some good lift a bit higher than 700mb you might have even better snow growth. I'm sure heavy_wx could really elaborate on this subject. 

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Not surprisingly, chilly temps continue to hold on here with my temp holding at 42 degrees.

Finally getting a tad excited about the incoming snowstorm.  With the snow, now I wish some good cold would hang on to help preserve it, but it's looking like a good portion may melt over the weekend from warm temps and/or rain.

Nevertheless, it will be nice to have more than 0.7" of snow (my deepest depth season-to-date) on the ground come Thursday morning!  :)

 

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3 minutes ago, MAG5035 said:

Now that we're pretty close in I've been starting to look at some of the finer details. I think snow could really pile up fast if we get heavy rates and once we start accumulating. This seems like one of those events where snow ratios will be improving as the event wears on with the low and mid levels cooling throughout the event. First off, look at the NAM 700mb VV at 30 and 33 (!!!)

nam-vvelprs-700-usne-30-B-000.png

nam-vvelprs-700-usne-33-B-000.png

 

That coincides with temps at the 700mb layer at h30 and 33 being:

 

nam---usne-30-B-700rh_tmp_hgt_wdb2.png

nam---usne-33-B-700rh_tmp_hgt_wdb2.png

One can see the 700mb temp will be falling as the low gets to the coast. While not directly in the ideal DGZ, temps of -5 to -8ºC should allow for some relatively decent ratios from a dynamic standpoint (perhaps 12-15:1ish). Even 850 temps in PA aren't all that bad once the event is in full swing, with a very tight gradient ending up between DC and the mason dixon. At hour 33 the -4ºC 850 line is pretty much running the mason-dixon line in the eastern half of PA. I'd be curious to see some of the full BUFKIT data, I guess if there's some good lift a bit higher than 700mb you might have even better snow growth. I'm sure heavy_wx could really elaborate on this subject. 

Those 700 VV's are impressive and certainly would generate intense lift over the eastern half of the state. The rapid cyclogenesis is obviously the main show, but I'm wondering if a separate QPF Max further to the NW into CPA can't form as well. Given the crash of temps in the thermal layer, a tight gradient should form and add a secondary enhancement away from the main deformation axis. image.png

Take a look at the thermal gradient within the 700mb level in PA. Strong mid level CAA on the NW side crossing within a steep layer of ascent will almost always cause a secondary banding structure that can provide really nice ratios due to high omega within the DGZ. This is where we could see the impressive totals on the eastern half of the state, with other higher totals showing up across true Central as well. 

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