December 16/17 Winter Event

[MillvilleWx]

Just now, Wentzadelphia said:

Low seems to get up to just SE of cape may and then shoots literally due east from there between 78-87 hours

Correct. It's further south than the CMC, so the deformation axis gets into the sub-forum. It's a good middle ground between the CMC and the GFS really. 

[ravensrule]

4 minutes ago, MillvilleWx said:

You mix for a time, then you be whacked really good by a band that develops along the 85H frontogenic placement. 850mb temps crash from ~+1C to -5C in 3 hrs and it rips for like 6 hrs before shutting off. 

Thank you very much for the info. You’re a good man. You need to get back home soon.

[baltosquid]

00z hugs Delmarva far tighter than 18z. Ensembles maybe hinted at his before with a lot of members clustered around there while the operational took a straighter path. I'm kind of concerned that the euro ensembles generally have the tightest cluster around that tucking path while the out-to-sea members are more scattered, even if there are more of those ones overall. But even with this run, I get 6 to 8 or so inches on the snow depth map which is probably the most since March 2018 for me.

Anyone more knowledgeable got an explanation of the tucking behavior and what would stop it? Silver linings?

[MillvilleWx]

Just now, ravensrule said:

Thank you very much for the info. You’re a good man. You need to get back home soon.

Truth. I'm gonna be working on it in the next 2-4 years. Then you'll be stuck with me 

[ravensrule]

2 minutes ago, MillvilleWx said:

Truth. I'm gonna be working on it in the next 2-4 years. Then you'll be stuck with me 

That would be my dream come true. 

[Ruin]

if this pans out it will be funny last year they forecasted way above normal snow way below normal temps it was opposite. this your I am hearing above average tamps just below on the snow. Id like to see them wrong again colder and snowier then normal 

[wizard021]

39 minutes ago, baltosquid said:

00z hugs Delmarva far tighter than 18z. Ensembles maybe hinted at his before with a lot of members clustered around there while the operational took a straighter path. I'm kind of concerned that the euro ensembles generally have the tightest cluster around that tucking path while the out-to-sea members are more scattered, even if there are more of those ones overall. But even with this run, I get 6 to 8 or so inches on the snow depth map which is probably the most since March 2018 for me.

Anyone more knowledgeable got an explanation of the tucking behavior and what would stop it? Silver linings?

Jma looks like gfs

[Maestrobjwa]

1 hour ago, MillvilleWx said:

You mix for a time, then you be whacked really good by a band that develops along the 85H frontogenic placement. 850mb temps crash from ~+1C to -5C in 3 hrs and it rips for like 6 hrs before shutting off. 

What I'm still not getting is why the low on these runs is tucking into the coast...what's making it do that, and what in the overall setup do we need to make it NOT do that? Lol

[MillvilleWx]

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. 

[yoda]

Thank you @MillvilleWx for taking the time for that outstanding post

[Ruin]

Dont know who is still up but the next model is at 4am right?

[Ji]

my best guess right now

Can you just make 6-12 8-12. Sounds better

[Ruin]

Looks like im in the bullseyes for the 20 inch plus on your guess and a lot of models. It will be starting as I go into work in the afternoon. maybe they will give us a heads up tuesday night about not coming in. I get off at 2am and its a bit out of the way in a hilly area. I so need a awd car lol.

[psuhoffman]

my best guess

[yoda]

3 minutes ago, psuhoffman said:

my best guess

I'd take 3 to 6 after last winter... your map looks good... though I'm closer to the 6 inch line after moving lol

[psuhoffman]

1 minute ago, Ji said:

4 minutes ago, psuhoffman said:

my best guess right now

Can you just make 6-12 8-12. Sounds better

You see where the lines are...your closer to the 12 than the 6...call it whatever helps you sleep 

[ravensrule]

7 minutes ago, Ruin said:

Dont know who is still up but the next model is at 4am right?

The GFS starts rolling at 4:30 am

[Ruin]

Thanks I knew it was somewhere around 4am hour just couldnt remember I normally dont go to be till 6am bring it on. 

[MrFreeze6298]

You are lucky in the USA to have snow, we French people rarely have snow.

[Ji]

The nam is almost an apps cutter lol

[Ruin]

last year only snow I got was a snow burst from the lakes that made it over the mountains snowed fast and hard on a day off but i had to go to work for training almost got into a 30 car pilel up. its all the snow we had all year lol. was a fast inch in 10 mins.

[Ruin]

I was about to joke watch it be a lakes cutter or apps or ots models suck so much at times haha

[yoda]

4 minutes ago, Ji said:

The nam is almost an apps cutter lol

Even the SNE mets were tossing it lol

[yoda]

RLX just put up WSWatches for their eastern counties

[psuhoffman]

5 minutes ago, Ji said:

The nam is almost an apps cutter lol

lol its pretty much a non event for our area.  Even up here its about 1" of snow to rain to dryslot.  It mixes almost to state college lol.  Be honest...it does bother you just a little to see it go that far west lol.  I am not overly concerned by an at range NAM run...but I would rather see it going the right way then the wrong way.  

[Ruin]

Just now, psuhoffman said:

lol its pretty much a non event for our area.  Even up here its about 1" of snow to rain to dryslot.  It mixes almost to state college lol.  Be honest...it does bother you just a little to see it go that far west lol.  I am not overly concerned by an at range NAM run...but I would rather see it going the right way then the wrong way.  

Why have models been so bad since they upgraded them? I remember for years king euro was the legit winter model. The upgrade and now it sharts the bed. then nam does good for years gets upgraded then same happens.

[psuhoffman]

2 minutes ago, Ruin said:

Why have models been so bad since they upgraded them? I remember for years king euro was the legit winter model. The upgrade and now it sharts the bed. then nam does good for years gets upgraded then same happens.

The main globals have been crazy consistent with only slight adjustments given the time scale for the last 3 days.  Some of the meso models will bounce around like this at range.  Now...if the globals were to shift to a NAM like inside cutter...that would be a major jump.  

[psuhoffman]

12 minutes ago, Ji said:

The nam is almost an apps cutter lol

SREF looks good lol...I mean if were going to bring up a bad NAM run at range...might as well mention a good SREF

[Ruin]

The main globals have been crazy consistent with only slight adjustments given the time scale for the last 3 days.  Some of the meso models will bounce around like this at range.  Now...if the globals were to shift to a NAM like inside cutter...that would be a major jump.  

 

I have seen major changes like this to often then not sadly. Major snow storm coming tomorrow temps mid 30s 12-18 inchs. wake up its all ready 43 and sun no clouds lol. 

[yoda]

LWX morning disco... mentions FZRA and IP as well

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
Canadian high pressure will build overhead tonight through
Tuesday with blustery and dry conditions with temperatures a
little below normal.

This high will be over Quebec by Wednesday morning and be the
source of cold air into our area for the next storm system.
Weak low pressure over the Ohio Valley will transfer to a
coastal low as an upper trough takes on a negative tilt. As this
low passes near the Delmarva Wednesday afternoon/evening, warmer
air will be drawn into southeastern parts of the area. The
gradient with this storm could be quite stark, with snow totals
approaching a foot versus only a few inches separated by a
county. The potential for mixing looks greatest along the I-95
and US-29 corridor, though worth noting the 00Z NAM brings the
warm intrusion to the Blue Ridge/Catoctins. Ensembles continue
to paint the highest probabilities of 6/12" across the northern
Shenandoah Valley into north central Maryland. For this forecast
package and at this range, have kept the forecast and snow
derivation parameters very close to our blended guidance and
WPC. This probably does not represent the threat for sleet and
freezing rain well enough, but note that is a possibility as
well. Am currently collaborating with our neighboring offices
about a winter storm watch. It looks like precipitation should
largely exit by Thursday morning.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Low pressure is progged to reside along or just east of the Delmarva
and Jersey coast Thursday morning, with lingering snow across the
northern and northeastern portions of the CWA. The low will continue
to push eastward away from the coast as the associated shortwave
aloft shunts eastward as well. This will allow for the steadier
precip across the northern half of the CWA to dwindle Thursday
morning. That being said, broad upper trough will persist over the
Mid Atlantic the remainder of the day and Thursday night, and with
shortwave energy tracking overhead, off and on snow shower/flurry
activity may linger during this time. Temperatures will be on the
chilly side for this time of year, with highs in the 30s to near 40
degrees (20s in the Alleghenies), falling back into the 20s area
wide Thursday night. The primary upper trough axis finally pushes
through the area Thursday night, so any snow shower/flurry activity
will come to an end.