December 16/17 Winter Event

[nj2va]

3 minutes ago, DCTeacherman said:

Seeing the 06z euro is “nam like” on phillywx.  I’m guessing that’s not good for us...

I took a quick peak and it looks very similar to the 00z run.  Really clocks western areas again.  Since the margins matter for the cities, it looks like its a touch warmer at 925 (haven’t checked surface but would imagine that is the same). 

[40westwx]

4 hours ago, MillvilleWx said:

Okay y'all. So, here are my thoughts with the 00z runs and why the trend towards a more tucked solution is becoming favored, but it's not going to be the end all for everyone when it comes to snow chances. 

So, looking at MSLP plots for each of the 3 major globals (ECMWF/GFS/CMC), the models are pretty much in lock step with each other until the storm begins to breach the latitude of Hatteras and that's where we see some separation from the CMC/Euro combo and the GFS. The GFS is the flattest solution as it's not as aggressive with the digging jet associated with the s/w trough located over the Mississippi valley. Height rises out ahead of the trough are more subdued, so the storm doesn't amplify to the degree of the CMC or Euro. Both the CMC/Euro combo are fairly similar in the depth of the trough and relevant height rises along the Atlantic seaboard. This allows for SLP genesis to gain latitude a bit more with a northerly movement before becoming caught up by the negatively tilted 5H trough progressing through the Tennessee Valley. The GFS is a more NNE trajectory with less amplification and slower strengthening due to the lower dynamic field played by the weaker 3H jet alignment. In turn, by Thursday at 00z, there is a sub 1000mb low on both the CMC and Euro tucked into the Delmarva coast where the GFS is a 1003 about 100 miles off ORF. I think we'll see a correction in the GFS with a more tucked solution, but perhaps not to the degree of the CMC/Euro tandem that have it basically onshore at Lewes in the same light. After 00z Thursday, the CMC is much more progressive with the 5H trough and actually motions to the NE prior to weakening with a due easterly motion. Euro becomes stacked right south of Cape May and then begins to pull eastward, leading the QPF shield to slowly wane from the sub and end by Thursday AM. CMC is a little more aggressive with ending the precip as it punches the dry conveyor overhead overnight due to it's NE movement away from the coast. A general compromise would be a slight backing from the Atlantic seaboard which would keep the 925/850mb easterlies from overtaking the boundary layer back towards the fall line. This would lead to less sleet/rain and more snow, albeit lower ratios due to the warm tongue that will still creep into the boundary layer.

Now the dynamics side of the precip field. The first round of precip will come in from SW flow aloft bringing in moisture off the gulf with qpf field expansion due to exit region of the 3H jet pivoting north into the area. There's a fairly robust area of diffluence ahead of the negatively tilted trough moving into the Tennessee valley on Wednesday, so regional lift is maximized, which is pretty standard for setups like this. We know this precip typically arrives a little sooner than modeled, and the current dew point depressions leading in are not insane and should be overcome fairly quickly with wet bulbs near and below freezing for most of the sub-forum. Areas along and SE of I-95 will likely be a touch on the warm side, but upper levels are still supportive of snow for a time west of the bay, so there will be flakes flying, at first. MSLP will develop along the SC coast and motion to the north, allowing for increasing low level dynamics to take shape with SFC and 850mb frontogen increasing in intensity as it gains latitude. Low level easterlies on the northern edge of the emerging surface low will begin throwing more Atlantic moisture into the mix as the WCB is fully established at + Theta-E advection noses along the Atlantic coast into the mouth of the Chesapeake. At this point, the 7H trough will be pivoting eastward with increased mid-level forcing focused over the Mid-Atlantic, allowing for increased banding potential over NoVA and Central-Western MD. Right now, current frontogen placement has the best mid-level ascent focused over the I-81 corridor over into central MD where areas of heavy precip will likely develop with embedded banding structures becoming more pronounced.

By 00z Thursday, a classic pivot of the precip field will become recognized as the 5H trough axis begins to close off overhead and the added torque in the upper jet will take the SLP and draw it closer to the coast. This is obviously subject to some fluctuations pending the total evolution of the 500mb trough, but it's looking more likely with ensemble guidance indicating a bit more "tucked" solution, which the NAM12km (Yeah, I hate it) has as well. I don't see it being that amplified however, so the bias of the NAM is likely being shown and should draw away from the inland runner solution. In any case, as the 7H trough moves overhead, models show the trough closing off over the Delmarva which would lead to enhancement of the 700mb frontogenesis field with a more defined deformation axis becoming established. There's some indications of a TROWAL developing on some guidance as the 7H Theta-E analysis begins to take the classic "S" shape on the NW focus of the surface reflection, and is in conjunction with the closed 7H reflection. Pending the extension of the S curve will be where there's potential for a region of enhanced precip within the heart, or just north along the strongest 700mb frontogenesis. This is something to never overlook when it comes to heavy precip potential, and is generally a good indication of where the heaviest rates will occur within the developed CCB. On the Euro, there's excellent lift in two regions; the first is along I-81 where the strongest mid-level fronto is positioned. There's also a secondary precip enhancement near I-95 where 850mb frontogenesis is at it's max. Looking at 850mb temps, you can see the crash between 21-00z on the run when areas of CMD see temps in the lower boundary layer fall from +1-2 to -3-5C in a few hrs. That the CAA pattern typically associated with maturing cyclones on the west side of the SLP due to CCB as air cools considerably due to the deformation element. This will lead to a secondary banding structure that can lay down a solid amount of snow in time, and that's what the Euro has for our northern tier east of Carroll on this current 00z run.

The CMC is a bit more drawn as the TROWAL is located a bit further north and intersects the incredibly strong 7H frontogenesis that is present over PA, extending into the northern portions of the sub-forum. The TROWAL is more pronounced than on the Euro, and is maxed over York County into the Coal country of eastern PA. That's why the clown maps show insane totals for that general region. The Euro shows the best axis of heavy snow out towards 81 with secondary max displaced to the east over Pars Ridge as they get in on the 85H frontgen band and rip for several hrs before the storm pulls away.

General QPF distribution is similar for all guidance, but the Euro and Canadian show distinct maxes intersecting the areas where lift is maximized, as well as where the WCB pushes ashore along the Delmarva coast. PWATs are well above normal with Euro coming in between 1.5-2.5 StD above normal on Wednesday and Wednesday night with up to 3 StD where the deformation axis is located, so the precip potential is absolutely there to breach 1.5" with local 2" spots possible within the best areas of lift.

Bringing this all together, I think we're beginning to see where the max potential will be realized for the sub-forum, and the storm overall. The Blue Ridge from Front Royal on north along I-81 over into south-central PA will likely be ground zero with a relative axis of heaviest snowfall extending east into the Catoctins, Northern Carroll, and perhaps northern Balt county, pending the deformation extension to the east. 10-16" of snow with local 20"+ totals will be realized in parts of the sub with incremental decreases further east from the line I mentioned. The urban corridors will likely mix and end up either high end Advisory or low end Warning criteria snowfall. Pars Ridge will have a secondary max of 8-14" with potential for more pending localized banding structures. I'll have a final call Tuesday night into early Wednesday. 

I guess the nightmare scenario would be if we get dryslotted right after a change over and then get fringed on the pivot.. other than that. I will take my chances with the a stronger storm as depicted by the euro and roll the dice with temps.. did you notice how the GFS has been keeping precip around for a couple 6 hour periods after the main shield exits.. is that one of those "upper level lows rotating through" things? 

[WeatherShak]

Sigh.  Ok.  So for all that don't know where I live I am just under the bottom of the beltway in VA about 6 pixels from the Potomac river.  I am initially in the 1-2" 6hr panel.  Then from that point on its the very first shading which is 0-1"  
So when that first 1-2" falls I will flip to sleet and rain.  My storm total on the ground won't be 3-6".  

Where at? I just moved to Hollin Hills.


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[aldie 22]

5 minutes ago, wxtrix said:

i stole this from a post Will made in the SNE forum just now.

 

Darn

[MillvilleWx]

The 06z Euro wasn't a NAM carbon copy at all. It was a slightly further west extension of the SLP once it gets to ORF lat. The dynamics between 00-09z on Thursday are ridiculous. It would be puking fatties for northern neck of VA, C MD, and into PA. Verbatim, the I-81 crew get raked on this run with the northern tier also firmly in 12+". 

[aldie 22]

3 minutes ago, mappy said:

nah. im not going to apologize for the snow i get. move north if you don't like your climo. 

Some of us did

[Ji]

Great.  Can't wait for you to bitch about a model run that takes you from 16" to 12" while I can't even get 4. 

Lol relax...just trying to give you hope for the next one and per hm there should be a next one

[catoctin wx]

4 minutes ago, mappy said:

nah. im not going to apologize for the snow i get. move north if you don't like your climo. 

Is it bad that I have actually considered moving to higher elevations just for this reason?  My catoctin ridge rain / snow shadow can be a frustrating.

[MillvilleWx]

2 minutes ago, 40westwx said:

I guess the nightmare scenario would be if we get dryslotted right after a change over and then get fringed on the pivot.. other than that. I will take my chances with the a stronger storm as depicted by the euro and roll the dice with temps.. did you notice how the GFS has been keeping precip around for a couple 6 hour periods after the main shield exits.. is that one of those "upper level lows rotating through" things? 

I don't think that's too much of a worry here. The bigger concern would be 7H fronto too far to the north, but nothing shows that right now. GFS stacks a little further south than other models, so there's a more uniform eastward motion of the comma head. Euro and CMC are bit further north, so the drier air undercuts the backside like it normally does and the back edge is further north a bit. 

[H2O]

3 minutes ago, WeatherShak said:

Where at? I just moved to Hollin Hills.


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Just a bit east of Rose Hill neighborhood

[jayyy]

4 minutes ago, MillvilleWx said:

The 06z Euro wasn't a NAM carbon copy at all. It was a slightly further west extension of the SLP once it gets to ORF lat. The dynamics between 00-09z on Thursday are ridiculous. It would be puking fatties for northern neck of VA, C MD, and into PA. Verbatim, the I-81 crew get raked on this run with the northern tier also firmly in 12+". 

Forgive me if I’m wrong here, but aren’t we out of euro’s “good range” at this point? 48 hours or less usually isn’t it’s sweet spot. GFS/RGEM and other medium range are probably better to lean on at this juncture, no? (Not the NAM - seems to have lost touch with reality) Or has that changed?

[MillvilleWx]

06z ECMWF was a Fall Line special. Ever wanted to know where that was, look at that Clown snow map. There it is! Pretty textbook actually. 

[osfan24]

Surprised we haven't seen the Euro move to a less amped solution yet. Maybe this thing will be more amped and it will have lead the way on this one.

[mappy]

3 minutes ago, catoctin wx said:

Is it bad that I have actually considered moving to higher elevations just for this reason?  My catoctin ridge rain / snow shadow can be a frustrating.

ha, no!  

[frd]

 

Interesting 

 

 

 

 

[jayyy]

... we ALL know this can be a cutthroat hobby and business. Let’s try not to get personal over snow in our backyards, shall we? We’re looking at a 3-6+ snowfall area wide outside of the immediate coast before winter has officially begun on the calendar - with more storms and an active winter pattern to track behind it. Cheer up buttercups!

[WeatherShak]

Just a bit east of Rose Hill neighborhood

Nice! I’m technically in White Oaks. I’m about a mile away from you! Just on the other side of 1.


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[MillvilleWx]

Just now, jayyy said:

Forgive me if I’m wrong here, but aren’t we out of euro’s “good range” at this point? 48 hours or less usually isn’t it’s sweet spot. GFS/RGEM and other medium range are probably better to lean on at this juncture, no? (Not the NAM - seems to have lost touch with reality)

I never move from the Euro since it's got a great resolution and is good with large scale forcing mechanisms. The mesoscale is definitely not good for it, but that's where our short term guidance will come in play. It gets mixed more with other guidance for decision making and review for trends. GFS is in the same boat as the Euro since it has fairly similar properties for large scale ascent depictions.

[jayyy]

2 minutes ago, MillvilleWx said:

I never move from the Euro since it's got a great resolution and is good with large scale forcing mechanisms. The mesoscale is definitely not good for it, but that's where our short term guidance will come in play. It gets mixed more with other guidance for decision making and review for trends. GFS is in the same boat as the Euro since it has fairly similar properties for large scale ascent depictions.

Ah. Should have known something was updated / different when the euro has 6z runs. Been “outta the game” so to speak. As always, thank you for sharing your wisdom my friend. 

[WxUSAF]

3 minutes ago, MillvilleWx said:

I never move from the Euro since it's got a great resolution and is good with large scale forcing mechanisms. The mesoscale is definitely not good for it, but that's where our short term guidance will come in play. It gets mixed more with other guidance for decision making and review for trends. GFS is in the same boat as the Euro since it has fairly similar properties for large scale ascent depictions.

Seems like we've seen 0z/6z euro runs bump NW and then 12z runs move SE.  All-in-all, these are ultimately small differences, even if this was 24hrs before start time, but it obviously makes a big difference to most of us in snow totals.  

[Fozz]

30 minutes ago, ravensrule said:

I’m definitely not one to defend @H2O but it has to be extremely annoying and frustrating when people think they know your climate better than you and on top of it a large majority of the forum gets a lot more snow than you. I would be cranky as hell. 

I feel kinda bad for Wes... I hope he’s doing well but I bet he really hates this storm.

[Fozz]

27 minutes ago, 40westwx said:

this is an incendiary post.. you should be more sensitive to those south of you

Don’t be a snowflake over snowflakes.

[jayyy]

This storm is going to be insanely close on the margins. Could have a situation where folks around owings mills (N of 70 / W of 695) see 8” while folks in middle river / Essex see 2”. Difference in 50 miles in track could mean the world to folks along 95

[MillvilleWx]

3 minutes ago, WxUSAF said:

Seems like we've seen 0z/6z euro runs bump NW and then 12z runs move SE.  All-in-all, these are ultimately small differences, even if this was 24hrs before start time, but it obviously makes a big difference to most of us in snow totals.  

For sure. This has Fall Line special written all over it. Massive increases the further north and west you go with this one. Then pinning down the CCB will be another fun task. That's where the real fun totals will come out. 

[osfan24]

6 minutes ago, WxUSAF said:

Seems like we've seen 0z/6z euro runs bump NW and then 12z runs move SE.  All-in-all, these are ultimately small differences, even if this was 24hrs before start time, but it obviously makes a big difference to most of us in snow totals.  

I keep hoping we see the Euro back off these NW pushes and get closer to the GFS solution. It will really make a huge difference for us. I've seen my totals around 16 inches on some runs with bigger totals not all that far NW of me but then closer to 8 on others with much smaller totals not that far to my SE.

[WxUSAF]

1 minute ago, MillvilleWx said:

For sure. This has Fall Line special written all over it. Massive increases the further north and west you go with this one. Then pinning down the CCB will be another fun task. That's where the real fun totals will come out. 

I really, really want that CCB.  Seems like the front half of the storm is pretty well set for MBY.  3-5" of snow+sleet.  

[stormtracker]

1 hour ago, H2O said:

That says 1-2" for me.  Tops.  Oh well.  Time to look for the next one

Yeah, this one is getting away from us.  Time to start measuring expectations here or make plans to chance west.   Still like my earlier call of 2 to 4" for beltwayers.    You can keep your dress stored away.

[ravensrule]

Just now, WxUSAF said:

I really, really want that CCB.  Seems like the front half of the storm is pretty well set for MBY.  3-5" of snow+sleet.  

A Ravens win tonight and some CCB loving and I’ll be quite excited. 

[jayyy]

5 minutes ago, MillvilleWx said:

For sure. This has Fall Line special written all over it. Massive increases the further north and west you go with this one. Then pinning down the CCB will be another fun task. That's where the real fun totals will come out. 

Going to be really interesting to see where that CCB sets up. It could help some places just west of 95 “catch up” a bit with their snowfall totals on the backside. I see it setting up in a spot near the R/S line. As a member of the “northern crew”, am rooting for that to occur along 95 for you folks as we seem pretty set up this way

[WxUSAF]

2 minutes ago, osfan24 said:

I keep hoping we see the Euro back off these NW pushes and get closer to the GFS solution. It will really make a huge difference for us. I've seen my totals around 16 inches on some runs with bigger totals not all that far NW of me but then closer to 8 on others with much smaller totals not that far to my SE.

Every model, even the GFS, has this baggy area of low pressure stretching from onshore to well offshore as it approaches and pass our latitude.  Where the "L" gets put on the surface map isn't always a fine science.  All comes down to how convection plays in (we really won't know this until tomorrow or Wednesday) and where the surface low starts to get stacked with the upper level energy. That later detail just keeps wobbling just onshore and just offshore.