December 8/9 wave

[SnowLover22]

I would say so

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[BristowWx]

1 minute ago, Philadelphia Snow said:

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What is it with e11?  The weenie member of the group always.  

[MountainGeek]

Curious to know what folks think is driving the still-sharp NW cutoff --- is it the NS vort still messing things up a bit on the precip shield, modeling just underdoing it, dry air, or....

I remember with the Jan 2017 southern slider someone kept hollering about "dry air" every other post and they turned out to be correct.  

[RVAman]

2 minutes ago, MountainGeek said:

Curious to know what folks think is driving the still-sharp NW cutoff --- is it the NS vort still messing things up a bit on the precip shield, modeling just underdoing it, dry air, or....

I remember with the Jan 2017 southern slider someone kept hollering about "dry air" every other post and they turned out to be correct.  

Seriously, I've told people several times throughout the day today dry air could play a major role in the VA/DC area. There always seems to be a slot develop between Richmond that continues NE. 

[Jebman]

We do have dewpoints in the teens. Something to take into consideration. I am pulling for a cartopper - IF I see even that much.

[poolz1]

Long day at work today but been following closely...I really am surprised that even in mby I may see first flakes!  Good trends...and a good sign that our first threat in early Dec may continue to trend in the right direction up to game time.  

[mitchnick]

Dry air with this one will NOT be a particular problem. Average issue, if at all.

[psuhoffman]

17 minutes ago, Bob Chill said:

The thing that gives me the most confidence is where in the model runs the nw trend is happening. You can literally start seeing it at hour 6. Lol. Models are catching up to the atmosphere in real time it seems. That's not really that common honeslty. It's one of the reasons the EPS made a very large shift at short range.  That's not common either. 

 

I suppose we can say the ukie saw the potential first but it backed right off at 0z last night so I don't think any model has done well with the evolution of the southern wave. When you see notable shifts in heights at 6-12 hour leads it's pretty clear that this event is unfolding at unusually short leads and models probably aren't done shifting. 

The way it's gone today, I don't think the nw trend is done but big shifts are probably over. The short story of my long post is that your yard will do well enough to be happy. This has always been a SE jackpot setup. Thankfully us folks to the north and west don't have any ptype worries. Everything that falls will be snow. If I lived in southern VA I would be hating the trends though. I know how it feels watching the danger zone approaching and it sucks. 

This certainly has the feel of something that's going to keep trending northwest until the end.  Once these things start they usually don't stop.  We've been burned plenty of times watching something that looked great 48-72 hours out slowly slip away as it nudged North a bit more each run. 

ETA:  the last few years it seems they stabilize some at the very end around 12-18 hours before the event.  But we have several more runs to see this bleed north more before then. 

[Cobalt]

9 minutes ago, MountainGeek said:

Curious to know what folks think is driving the still-sharp NW cutoff --- is it the NS vort still messing things up a bit on the precip shield, modeling just underdoing it, dry air, or....

I remember with the Jan 2017 southern slider someone kept hollering about "dry air" every other post and they turned out to be correct.  

Jan 2017 storm was colder by 13-14 degrees

[WxUSAF]

Don't look at the GEFS mean for precipitation totals on the NW edge.  It's going to smear out the gradient.  Look at low position/strength.  

[osfan24]

If this keeps trending this way with each run leading up to the event, we are going to be under Winter Storm Warnings.

[Bob Chill]

14 minutes ago, MountainGeek said:

Curious to know what folks think is driving the still-sharp NW cutoff --- is it the NS vort still messing things up a bit on the precip shield, modeling just underdoing it, dry air, or....

I remember with the Jan 2017 southern slider someone kept hollering about "dry air" every other post and they turned out to be correct.  

Think about what's happening overhead. This isn't a pivoting coastal storm. It's a tight highway being driven by the southern jet. The highway is loaded up good but pull off on the shoulder and there's nothing going on. 

Coastal storms with hp to the north are very different. Pressure gradient and circulation will push precip inland with e-ne flow. This setup doesn't have that sort of spin. It's just a wave of deep moisture running a defined boundary. However, the boundary appears to be shifting west in front of the digging tough. 

There is no cold/dry hp to the north either so not much worry about a snow eating pacman taking bites out of the nw edge either. You just need to be in the highway traffic and you're good. 

[BTRWx's Thanks Giving]

1 minute ago, Bob Chill said:

Think about what's happening overhead. This isn't a pivoting coastal storm. It's a tight highway being driven by the southern jet. The highway is loaded up good but pull off on the shoulder and there's nothing going on. 

Coastal storms with hp to the north are very different. Pressure gradient and circulation will push precip inland with e-ne flow. This setup doesn't have that. Sort of spin. It's just a wave of deep moisture running a defined boundary. However, the boundary appears to be shifting west in front of the digging tough. 

When was our last decent snow without NE hp?

[yoda]

3 minutes ago, WxUSAF said:

Don't look at the GEFS mean for precipitation totals on the NW edge.  It's going to smear out the gradient.  Look at low position/strength.  

Just to clarify, do you mean us in DC as well or just those out west of the BR?

[BristowWx]

1 minute ago, Bob Chill said:

Think about what's happening overhead. This isn't a pivoting coastal storm. It's a tight highway being driven by the southern jet. The highway is loaded up good but pull off on the shoulder and there's nothing going on. 

Coastal storms with hp to the north are very different. Pressure gradient and circulation will push precip inland with e-ne flow. This setup doesn't have that. Sort of spin. It's just a wave of deep moisture running a defined boundary. However, the boundary appears to be shifting west in front of the digging tough. 

Would you consider this overrunning type scenario vice a storm?

[Cobalt]

0z GFS:
 

 

[WxUSAF]

2 minutes ago, yoda said:

Just to clarify, do you mean us in DC as well or just those out west of the BR?

Everyone in our area except maybe RIC-Salisbury and points SEward.  

[Cobalt]

Biggest storm of the winter so far coming up. Am excited 

[BTRWx's Thanks Giving]

1 minute ago, Cobalt said:

0z GFS:
 

 

It's more like a leaf than a comma head.

[MillvilleWx]

Yeah like I said earlier, the NAM (and hi-res) can be useful in certain scenarios. But really, the answer should always be that a good forecaster looks at the totality of the guidance, analyzes the environment, and blends or forecasts accordingly. Leaning on one model all the time and not looking at an overall synoptic or mesoscale setup objectively and critically is a recipe for a bust. 

This is 100% spot on. I’m not the biggest fan of the NAM either, but over the past 36 hours, it’s been leading the charge with the handling of the upstream pattern across the Western and Central US when it comes to mesoscale properties and regional dynamics. A lot of times, NAM really drops ball on synoptic patterns and 3km does well once within a certain range. Once we get inside 48 hrs, I do try to put a little more credence in the run for certain areas, but General H5 and H25 looks I look more at the globals. It’s important to blend guidance because each model has their own strengths and weaknesses. After looking at everything, it’s certainly very positive to see globals adjust NW with the jet structure over the NE US. There should a pretty decent area of upper divergence in the right entrance region of the jet, placing the Mid Atlantic within a good zone of vertical ascent. This is where GFS/Euro and NAM differ as to the western extent of the precip field.

GFS and Euro expand the NW side of the QPF much better than the NAM, which is more believeable when looking at upper level panels. The amplified look East of the Rockies should help bring heights downstream in the Western Atlantic up, and cause the feature to slow down some in timing. This will also allow for a more north-south orientation of the precip field. The NAM will come into play when we talk about banding structures as it will handle the mesoscale and dynamic properties better than a global close in. The 3km nest is especially good at this once within 24 hours and HRRR can do it as well, but sometimes it can be too aggressive at range (> 8 hrs). This will be a fun storm to track. Thermals look great outside surface for many people. It’ll be a case of snow or no for most. Possibly some mixing out by the Atlantic due to an easterly component trying to push a warm nose aloft. Water off coast is still a bit warm, so that doesn’t help the coastal gang.


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[RVAman]

Just now, BTRWx's Thanks Giving said:

It's more like a leaf than a comma head.

I think the thing to watch is the southern edge near the Florida peninsula in the bottom picture, I guess it could turn to something if conditions are right. 

[Bob Chill]

2 minutes ago, BristowWx said:

Would you consider this overrunning type scenario vice a storm?

Overrunning is typically warm moist air hitting cold and lifting so not exactly the same. This is a deep (and narrow) jet driven moisture plume with embedded waves. We're lucky the antecedent airmass supports snow because there is no cold feed to the north.   

[Paleocene]

This is mildly off topic, but my friend in Austin, TX reports that they're getting sleet right now. That's a notable event in any winter in that city, not to mention in early December.  That energy and precip is headed our way :-)

[Cobalt]

Only time I will ever get a forecast correct 5 days in advance (I called this on Monday) ever. I saw it coming, called it off like everyone, and woke up to a surprising change in the models

 

 

 

[Cobalt]

Just now, Paleocene said:

This is mildly off topic, but my friend in Austin, TX reports that they're getting sleet right now. That's a notable event in any winter in that city, not to mention in early December.  That energy and precip is headed our way :-)

Not that off topic really. Still good information 

[BristowWx]

1 minute ago, Bob Chill said:

Overrunning is typically warm moist air hitting cold and lifting so not exactly the same. This is a deep (and narrow) jet driven moisture plume with embedded waves. We're lucky the antecedent airmass supports snow because there is no cold feed to the north.   

Roger.  Seems we are lucky on several fronts.  Been around a long time like you and not often do things trend in our favor so close to game time 

[poolz1]

4 minutes ago, MillvilleWx said:

 

This is 100% spot on. I’m not the biggest fan of the NAM either, but over the past 36 hours, it’s been leading the charge with the handling of the upstream pattern across the Western and Central US when it comes to mesoscale properties and regional dynamics. A lot of times, NAM really drops ball on synoptic patterns and 3km does well once within a certain range. Once we get inside 48 hrs, I do try to put a little more credence in the run for certain areas, but General H5 and H25 looks I look more at the globals. It’s important to blend guidance because each model has their own strengths and weaknesses. After looking at everything, it’s certainly very positive to see globals adjust NW with the jet structure over the NE US. There should a pretty decent area of upper divergence in the right entrance region of the jet, placing the Mid Atlantic within a good zone of vertical ascent. This is where GFS/Euro and NAM differ as to the western extent of the precip field.

GFS and Euro expand the NW side of the QPF much better than the NAM, which is more believeable when looking at upper level panels. The amplified look East of the Rockies should help bring heights downstream in the Western Atlantic up, and cause the feature to slow down some in timing. This will also allow for a more north-south orientation of the precip field. The NAM will come into play when we talk about banding structures as it will handle the mesoscale and dynamic properties better than a global close in. The 3km nest is especially good at this once within 24 hours and HRRR can do it as well, but sometimes it can be too aggressive at range (> 8 hrs). This will be a fun storm to track. Thermals look great outside surface for many people. It’ll be a case of snow or no for most. Possibly some mixing out by the Atlantic due to an easterly component trying to push a warm nose aloft. Water off coast is still a bit warm, so that doesn’t help the coastal gang.


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Great post, Millville!  Exactly what makes this site enjoyable..compared to "others." 

[yoda]

18z RGEM decent... looks like .5 QPF total

[Jebman]

6 minutes ago, Paleocene said:

This is mildly off topic, but my friend in Austin, TX reports that they're getting sleet right now. That's a notable event in any winter in that city, not to mention in early December.  That energy and precip is headed our way :-)

Relatives in Buda TX 20 miles SSW of AUS just hit my email about sleet/rain mix in Buda. Their forecast just went over to wintry mix overnight into early Fri.

[Cobalt]

2 minutes ago, yoda said:

18z RGEM decent... looks like .5 QPF total

RGEM keeps temps below freezing throughout the storm. You think this is possible? I hope so