MAG5035

Here’s the 15z NBM,

CTP’s initial snowfall forecasts are following that fairly close so far. That covers the whole duration of the event through the rest of the NE and such. So the blend that makes up the NBM is quite pessimistic on that broad area of light to moderate accums getting on the other side of the Apps except for that stripe thru VA and the Delmarva associated with the coastal currently. We’ll see if it eventually improves a bit like some of the op’s did today for the area. Either way, definitely a shame this system can’t amplify at least some. That is a huge expanse of accumulating snowfall from Texas thru the Ohio Valley. 

1 hour ago, Voyager said:

So I'm not as weather savvy as some of you so I'm wondering, why are we getting these consistent, unrelenting high winds? Usually we have a windy day (or two) after a storm, but then they subside. The cold I can handle, even though it sucks when you haul water for a living, but the wind that's going along with it is just brutal. 

We’ve had a persistent NW cyclonic flow via the deep low in the 50/50 realm being locked in by blocking regime in place..recently reinforced by Monday’s storm. Look for another windy day today in C-PA…especially eastern and northeastern zones, where the neighboring Poconos counties actually are under wind advisories today. High pressure builds in tonight/tomorrow ahead of the likely light snowfall Friday Night, and winds should finally settle down. 

10 minutes ago, Bubbler86 said:

I think 2-4 here (most of this sub), if the NS Vort can get close enough, is not out of question. 

It would likely only take a swath of one to two tenths QPF to get there. Thermals are great for high ratio snows (potentially in the 20:1 realm) with most of PA residing at or near -8ºC at 850ºC and -10ºC and lower at 700mb. That’s what I’m eyeing out of this event, a potential swath of 2-4” snows where some marginally better forcing aloft coincides with the nice thermal column. Sus Valley is the question area right now for me, though tonight’s NAM looks better so far.  I def could see the shadowing effect occurring in a weaker interaction with the northern stream as the southern shortwave ejects out towards us and the SW flow downslopes off the mountains, especially as a secondary develops and tightens the remaining precip down to the south. 

The late afternoon back end delivered only about another half inch here, making the storm total 1.8”. Just missed it all today haha.. the best 850mb FGEN to the south (expected), the best 700mb FGEN to the north (not expected), and lastly the 500mb vort pass to the south which by the obs down there has gotten the Mid-Atlantic folks fairly close to their forecasted totals. 

1 hour ago, WmsptWx said:

Probably 2.5" if I had to say from eyeballing. It was enough to undo any clearing attempts that was made after Saturday morning's shock event. It was more than I expected.

You might have a chance at some more surprise bands the next couple days. High res models are showing a Huron connected band developing Wednesday with a favorable alignment through your general area and perhaps into State College again. 

My initial thoughts with the end of the week system is I think there will be at least a wave of lighter snows that moves through the commonwealth as the southern system over system ejects out and there’s a least some interaction with the northern stream. Euro hangs it back and northern stream diving in ahead shears the southern energy out. GFS has been trying to phase it, and through 102hr it looks like the 18z GFS is going to really be quite a solution. 

4 hours ago, WmsptWx said:

It would appear as if the snow has stopped.

How much did you end up with this morning? 

1 hour ago, Bubbler86 said:

Interesting and obvious thoughts in the MA forum.  I say obvious because they are but not sure I had thought of it yet.   We were so gung ho on using Kuch because of the antecedent cold air but if one looks at the 10-1 maps maybe the model outputs were a bit more realistic.  QPF in Lanco was 2-3" on a lot of outputs....10-1 that is 2-3" of snow.  It is almost 30 degrees here right now.  Kuch may have over done it this time (sometimes Kuch is lower of course but obviously much higher up this way for this storm.)

I think their lower ratios down there were more of a result of what was going on aloft, especially in the mid levels. Here’s some mesoanalysis maps at 11z this morning one at 700mb and the other at 850mb.  At 700mb, a lot of that subforum was between -2º to -4ºC and was so overnight during the bulk of their snowfall. Cold enough to maintain the snow column of course but those are very warm temps at that level, and would have promoted poor snow crystal growth. They had the better forcing at the 850mb level  and 850mb temps were roughly the same as the 700mb temps.

700mb at 11z

850mb at 11z

These 850mb and 700mb features were also fairly far to the north, especially the 700mb low.. which was why the best lift probably ended up where it did this morning. I’ve mentioned the secondary max a couple times since Friday, and noted the Euro had it about where it actually ended up on its 12z run yesterday. I didn’t anticipate the big separation between the two though. I expected the 700mb forcing to be in position to boost totals in the bottom two tiers of PA counties. I also expected the meso models to at least pick up on this stuff a little bit prior to the event arriving. They really didn’t.. the northern PA band ended up being more of a nowcasting deal. This was already a fairly progressive system given the setup and positive trough orientation, and I think it just ended up being more so in the end. 

On 1/5/2025 at 2:31 PM, MAG5035 said:

One thing at the mesoscale level I noticed on the 12z Euro is that despite it remaining on the lighter side with overall snowfall it managed to have a secondary band of enhanced QPF that extended from Pittsburgh to Clearfield to Williamsport, giving our northern folks in those spots approx 2-4”. Stuff like that will be need watched for on the meso models as we get close to start time. 

On 1/3/2025 at 1:49 PM, MAG5035 said:

I’m not budging from my original thinking quite yet of advisory snows I-80 south and warning snow potential in the bottom two tiers of counties across C-PA. I may eventually concede one or both of those tiers but I want to see the short range play out more, as we’re just barely into range of the NAM/RGEM and not even into the longer HRRR range. That stuff is going to see how the overall precip shield sets up better. I think we’ll still eventually see a more widespread snow shield into PA even if it’s lighter snows and we concede the whole swath of 6”+ to the DC folks. But if that happens the northern tier above 80 and especially NE PA might not see much.

Other thing to consider may be a secondary swath of higher snowfall due to better ratios. Lift would be further aloft (700mb level or a bit higher) in a further south solution and temps are plenty cold up there for good snow growth in that scenario with this storm and on down the column as well (less than -8ºC at 850mb on the Euro). 

Only 1.3” has fallen so far, woof. Starting to get some of this backend stuff but it’s gonna have to do some work. I was targeting about 4-5” here. I’ll be lucky to get 3” to verify the advisory. 

It’s pretty evident that some of the better mid-level forcing is currently residing further north. Best band of snowfall right now appears to be residing all the way up between I-80 and US 6 corridor. Looking at mesoanalysis, this coincides with the area of 700mb frontogenesis and thickest dendritic growth zone layer. This may be the result of the 700mb being further north and more robust + temp advection in that layer.

700mb heights/frontogenesis

DGZ depth

DGZ relative humidity and omega (lift) 

Moderate snow here with about an inch so far. 18°F

511PA cams showing it snowing at least as far as far NE as the US 219 corridor between Somerset and Meyersdale, so looks mostly on schedule with the onset so far. 

Obs here is cloudy and 19ºF/12ºF temp and dewpoint. Nice crisp airmass for a snow event. 

34 minutes ago, paweather said:

I haven’t been in the MA thread maybe once so far. I am happy for them. They deserve it every once in a while. I’ll take my 3-5” and be happy as well. 

It’s likely to be the biggest snowfall DC metro has seen in a number of years, they were 100% overdue for a moderate-heavy event like this. 

Whatever happens here I think we can all agree that it’s really nice to hash out the details for an all snow event that hasn’t really had any threat of mixing the last few days anywhere in this subforum. 

15 minutes ago, Bubbler86 said:

Not gospel of course but the HRRR would dictate a WSW for basically the entire LSV.  Basically a hold from 12Z.   Knocked 1-2" off far East and NE locales in the valley., 

This might be one of those situations that their zones would be better with splitting York/Lancaster in half (advisory north warning south). Either way I have a gut feeling those counties eventually get upgraded for a low end 4-6 warning. As was discussed in my post a couple pages back pertaining to the CTP disco, the shortwave over New England that is the possible detriment for more expansive heavier snow further into C-PA is not going to be in the HRRR’s realm until the 0z run later. So that might be most important model run of our lives coming up haha. 

One thing at the mesoscale level I noticed on the 12z Euro is that despite it remaining on the lighter side with overall snowfall it managed to have a secondary band of enhanced QPF that extended from Pittsburgh to Clearfield to Williamsport, giving our northern folks in those spots approx 2-4”. Stuff like that will be need watched for on the meso models as we get close to start time. 

1 hour ago, AccuChris said:

CTP had an interesting take and write-up this morning about the ongoing disagreement within the models. They point to the more suppressed models focusing on a mid-level vort in northern New England enhancing drier advection from Canada versus the HRRR which cant even see that in its domain. Time will tell as always

“Still quite a bit of uncertainty with 18 hours or less until
first flakes. The ECMWF and Regional Canadian models are on the
lower end of the snowfall total spectrum. Part of the reason
for this might be that they both develop a stronger midlevel low
pressure system over northern New England late Monday from a
shortwave trough originating east of Hudson Bay at 00z Sunday.
This could act as a kicker to bring in drier air more quickly
and shorten the window for moisture advection early Monday
before the Mid Atl coastal system gets nudged offshore. This
shortwave trough is outside the domain of the hires models (HRRR
and 3km NAM) and will remain so until the 00z Monday runs.
Given that the HRRR and 3km NAM together make up about 1/3 of
the NBM weighting in this time period, IF this Hudson Bay
feature is indeed responsible for the lower snow totals in the
ECMWF and Canadian models, it`s certainly possible that we see a
shift south in snowfall totals over the next 24 hours. That
said, the HRRR does represent the worst case scenario, with
warning criteria (6+ inches) across much of central PA from I-80
southward, which can not completely be ruled out at this point.”


.

Here’s what CTP is alluding to in their AFD on the 500mb prog with a GFS vs Euro comparison (using the 6z run). I x’ed the vort responsible for our storm and the one over northern New England. The arrows indicate the flow, and they converge (aka confluence).

I did notice this feature yesterday scrutinizing the 12z models. At that point track and precip expanse was similar on the Euro v GFS but the Euro wasn’t bringing the heavier precip up. That feature above New England was not nearly as prominent on the GFS as the Euro. And as you can see today, both models now have it (A Euro win). 

I can only go back to 18z yesterday on the comparison, but here’s the 6z GFS (new 12z run is similar) vs yesterday’s 18z run. X’s again denote the shortwaves and arrows illustrating the confluence on the left. Now look at the right one in the circled area (yesterday’s 18z). No closed off low with that shortwave above New England. 

The flow speeds up in a confluent pattern, and thus as CTP mentioned would limit the window for moisture advection. As I mentioned yesterday, the WAA precip phase was going to be the primary part of the event for most in here outside of the far southern tier (which could catch the back end of the shield with the upper feature passage). So it’s not really an issue of north or south with the actual storm, models have been similar with expanse of precip. It comes down to simply being a more progressive event here, which lessens QPF. Honestly, a good catch and call by CTP IMO by factoring that in their accum forecasts (since high res won’t account for it til 0z) . Now that doesn’t mean we can’t get some north trend back to a degree, but that’s their reasoning for their headline placement… which is solid at this juncture. I think there’s still room to expand advisories a bit, and maybe the LSV advisories to low end warnings. This affects the heavy swath to the south too, as I think we’re back to the ceiling of a general 6-10” event (maybe some 12s) in the axis of heaviest. 

1 minute ago, mahantango#1 said:

Relax, he will have 2 more maps(2nd call and final call)...and possibly more  8in.contours to confuse you more.

The start time spaghetti plot is where it’s at lol. 

14 minutes ago, MAG5035 said:

And speaking of CTP, since there was great consternation here (and esp on social media lol) with the rather generous ranges that map product of theirs cranks out. If you select point instead of range you’ll see a much more straight forward map. 

 

Actually to further on the NWS and one wanting to get into the reasoning of what they’re putting out product wise, when NWS Pittsburgh issued watches for their CWA last night and posted that to their social media (Facebook). I saw this in the comments.

Definitely a candid response, whether CTP subscribes to that method precisely like PBZ does (rarely using deterministic) I’m not sure. But their map products are heavily derived from that NBM nonetheless. 

From a northern expanse standpoint, GFS and Euro are pretty close. Where they differ is in the intensity of the WAA precip.

It’s an important aspect for us because that’ll be the majority of the event up here in our subforum. Once that low transfers to the coast, it’ll pull the precip shield south and away and we’ll probably miss the back end of the shield that hangs back with the 500mb vort except for possibly the southern tier below the turnpike. That will further add to the DC/Mid-Atlantic folks’ totals. The short term/high res guidance has been coming in hot in the early going with regards to that surge of more intense WAA snowfall. So unless that changes wholesale as we get more into the nearer term, I’m more inclined to go with a more bullish outcome in the southern tier. I think CTP’s watch placement is fine right now. 

And speaking of CTP, since there was great consternation here (and esp on social media lol) with the rather generous ranges that map product of theirs cranks out. If you select point instead of range you’ll see a much more straight forward map. 

2 minutes ago, mahantango#1 said:

So with this model JB might be on to something.

Perhaps, NAM is putting out 0.6”-1.0”, with the 1.0” or so being near the DC area… which is probably about the limit given this system not really having a chance to wind up to any kind of full fledge coastal.

If this is going to actually crank out a swath of 10-15” amounts it’ll be due to ratios.. which may actually benefit the southern tier. In the NAM’s positioning, best mid level forcing would likely be in the southern tier which could enhance ratios thru more efficient snow growth further aloft. It’s already a pretty cold column as is, with the Kuchera method (which doesn’t account for actual snow growth processes) calculating 15-16:1 ratios for AOO/JST/MDT/THV/LNS. Could be a band(s) somewhere in there that may even best those ratios. Obviously a further south solution takes those dynamics south of the M/D line.

The NAM is indeed a winner for most, but it also has one heck of a cutoff near I-80 in central and I-78 in eastern. 

5 minutes ago, WmsptWx said:

You're the only person I know of crazy enough to ski on that sheet of ice. They've gotta be having a banner start. Are they at 100%

4 trails open right now lol. Presuming they get a clean event Monday and a half decent amount of snow on top of the LES/upslope, it might actually be a good up there next week. 

It can keep doing this up in Blue Knob, they’re under a nice band right now.

I’m not home today but here’s the situation there. Some of the snow on the ground is from the inch of wind driven squalls we got New Year’s night.

I called in for an official close up measurement of the snowboard haha, about an inch today so far with the snow squall warned stuff still incoming. 

56 minutes ago, Itstrainingtime said:

Flurries and 33 in Maytown.

Most important thing I saw from the Euro is it didn't move further south. 

I’m not budging from my original thinking quite yet of advisory snows I-80 south and warning snow potential in the bottom two tiers of counties across C-PA. I may eventually concede one or both of those tiers but I want to see the short range play out more, as we’re just barely into range of the NAM/RGEM and not even into the longer HRRR range. That stuff is going to see how the overall precip shield sets up better. I think we’ll still eventually see a more widespread snow shield into PA even if it’s lighter snows and we concede the whole swath of 6”+ to the DC folks. But if that happens the northern tier above 80 and especially NE PA might not see much.

Other thing to consider may be a secondary swath of higher snowfall due to better ratios. Lift would be further aloft (700mb level or a bit higher) in a further south solution and temps are plenty cold up there for good snow growth in that scenario with this storm and on down the column as well (less than -8ºC at 850mb on the Euro).