Dec 8th - 9th (2nd wave/winter storm discussion)

[Zelocita Weather]

_{18z NAM delivers significant snows (4-6") for DC/BALT/S PA/S NJ and accumulating snows (1-3"/2-4") for C/N NJ and NYC before the changeover. One of the better runs yet for this wave.}

[PB GFI]

_{18z NAM delivers significant snows (4-6") for DC/BALT/S PA/S NJ and accumulating snows (1-3"/2-4") for C/N NJ and NYC before the changeover. One of the better runs yet for this wave.}

Yeh  , showing 6 inches from Northeast  DE to just south of Toms River NJ ...  @ the NAM

[Blizzard-on-GFS]

_{18z NAM delivers significant snows (4-6") for DC/BALT/S PA/S NJ and accumulating snows (1-3"/2-4") for C/N NJ and NYC before the changeover. One of the better runs yet for this wave.}

Most likely a hiccup, at least for south PA and Jersey. Seems more reasonable for DC/BALT. If 0z runs support, then it might be on to something.

[Ralph Wiggum]

18z NAM delivers significant snows (4-6") for DC/BALT/S PA/S NJ and accumulating snows (1-3"/2-4") for C/N NJ and NYC before the changeover. One of the better runs yet for this wave.

Most likely a hiccup, at least for south PA and Jersey. Seems more reasonable for DC/BALT. If 0z runs support, then it might be on to something.

18 z runs good for spotting trends. Maybe the finger of qpf is adjusting northward ?

[Storm At Sea]

Same model that was showing 30+ inches of snow for much of the NYC/NJ area just 72 hours out back in February 2013. I stil believe that the Eta was a more reliable model.

[green tube]

Same model that was showing 30+ inches of snow for much of the NYC/NJ area just 72 hours out back in February 2013. I stil believe that the Eta was a more reliable model.

 

if you did a historical breakdown on the % of people who comment on the 18Z GFS/NAM, it would look something like...

meteorologists: 0%

weenies: 100%

[IsentropicLift]

WSW's now for the DC-BWI area. KDIX will likely hoist for a large portion of there cwa tonight, hope I'm included.

[Absolute Humidity]

Same model that was showing 30+ inches of snow for much of the NYC/NJ area just 72 hours out back in February 2013. I stil believe that the Eta was a more reliable model.

I believe it was doing that inside 48 for that one. Laughable

[SnowGoose69]

18 z runs good for spotting trends. Maybe the finger of qpf is adjusting northward ?

 

The NAM may be overdone but its got a better idea I think than the GFS...I said in the SNE thread I'm wondering if perjaps the models are keying in or viewing the high pressure area as a blocking mechanism with this event vs. an overrunning WAA enhancing mechanism....the reason they may be doing that is that a surface low is present and they are generating all of the precipitation based on that surface low, not the isentropic lift or theta E advection that may be occurring...if the surface low was not present the models perhaps would have a better handle on this but I am concerned that perhaps its hindering their ability to see the WAA induced precip that may happen

[earthlight]

I believe it was doing that inside 48 for that one. Laughable

That is something I will not forget for the rest of my career. It was a 18-30 hour forecast for 30+ inches across a vast majority of the area -- and the GFS came in with a completely different solution. One of the few times as a meteorologist that I tossed my hands up.

As it turns out, we got a good storm out of it..just not the biblical storm the NAM was showing.

[earthlight]

18 z runs good for spotting trends. Maybe the finger of qpf is adjusting northward ?

It doesn't really matter where the finger of QPF is (whatever that means). What essentially needs to happen is the depth of cold air needs to be better than modeled, and moisture needs to come in faster and with favorable timing.

We're not only battling the dry air to start, but then warm air advection as well.

[KEITH L.I]

That is something I will not forget for the rest of my career. It was a 18-30 hour forecast for 30+ inches across a vast majority of the area -- and the GFS came in with a completely different solution. One of the few times as a meteorologist that I tossed my hands up.

As it turns out, we got a good storm out of it..just not the biblical storm the NAM was showing.

Was on  Long Island...there were spots that approached 30 inches on the north shore

[IsentropicLift]

The NAM may be overdone but its got a better idea I think than the GFS...I said in the SNE thread I'm wondering if perjaps the models are keying in or viewing the high pressure area as a blocking mechanism with this event vs. an overrunning WAA enhancing mechanism....the reason they may be doing that is that a surface low is present and they are generating all of the precipitation based on that surface low, not the isentropic lift or theta E advection that may be occurring...if the surface low was not present the models perhaps would have a better handle on this but I am concerned that perhaps its hindering their ability to see the WAA induced precip that may happen

The GFS in particular had a closed off 1036mb contour over PA yesterday. If that was reality, nobody north of DC would see anything. We have no blocking and we're not dealing with a suppressing northern jet. The lack of precip frankly makes no sense. The WAA advecting over the cold air to the north creates lift and if you have enough moisture, poof you have precip. I think this has high bust potential in both directions. A very tricky forecast.

[Blizzard-on-GFS]

The NAM may be overdone but its got a better idea I think than the GFS...I said in the SNE thread I'm wondering if perjaps the models are keying in or viewing the high pressure area as a blocking mechanism with this event vs. an overrunning WAA enhancing mechanism....the reason they may be doing that is that a surface low is present and they are generating all of the precipitation based on that surface low, not the isentropic lift or theta E advection that may be occurring...if the surface low was not present the models perhaps would have a better handle on this but I am concerned that perhaps its hindering their ability to see the WAA induced precip that may happen

Good point. We'll have to watch the mesoscale models to see if they sniff that out. We're getting into that range were the NAM can be taken a bit more seriously. WAA could certainly lead to an over performance on the front end dump. I'm tempering my expectations at this point.

[Sn0waddict]

Same model that was showing 30+ inches of snow for much of the NYC/NJ area just 72 hours out back in February 2013. I stil believe that the Eta was a more reliable model.

 

I assume we are talking about the Feb Blizzard? To be fair, spots obviously did get 30+ inches(I was in one of them) It just wasn't in the immediate NYC/NJ area. It's not like it forecasted 30 inches and everybody was smoking cirrus, it just didn't happen in the exact area it was originally projecting it to be.

The NAM may be overdone but its got a better idea I think than the GFS...I said in the SNE thread I'm wondering if perjaps the models are keying in or viewing the high pressure area as a blocking mechanism with this event vs. an overrunning WAA enhancing mechanism....the reason they may be doing that is that a surface low is present and they are generating all of the precipitation based on that surface low, not the isentropic lift or theta E advection that may be occurring...if the surface low was not present the models perhaps would have a better handle on this but I am concerned that perhaps its hindering their ability to see the WAA induced precip that may happen

You've had some great posts here the past few days, really appreciate the insight and I hope you are on to something.

[Weathergun]

The 18z NAM has a warm nose between 700mb-800mb changing the city over to sleet between 3z and 4z Monday.

[IsentropicLift]

The 18z NAM has a warm nose between 700mb-800mb changing the city over to sleet between 3z and 4z Monday.

If the WAA is stronger than modeled two things will happen, the snow will arrive earlier than forecasted and we'll see a prolonged period of mixed or freezing precip, especially inland.

[jm1220]

The GFS in particular had a closed off 1036mb contour over PA yesterday. If that was reality, nobody north of DC would see anything. We have no blocking and we're not dealing with a suppressing northern jet. The lack of precip frankly makes no sense. The WAA advecting over the cold air to the north creates lift and if you have enough moisture, poof you have precip. I think this has high bust potential in both directions. A very tricky forecast.

There's plenty of precip, but it evaporates before hitting the ground because of the dry air. I too hope the NAM's right, on that run even I would see accumulating snow for a few hours.

[earthlight]

The 18z NAM has a warm nose between 700mb-800mb changing the city over to sleet between 3z and 4z Monday.

The warm air advection is driving the precipitation into the drier air to our north in the first place, so I am not too surprised. I think we'll all see a period of snow, changing to sleet and rain fairly quickly (a few hours). Accumulations seem unlikely anywhere close to the coast.

[earthlight]

Was on Long Island...there were spots that approached 30 inches on the north shore

Not trying to take away from the storm at all. But the issue is that the NAM is becoming fairly notorious for an extreme or overdone solution in that time frame. In that storms case, it was too strong and too close to the coast. Ended up slightly more progressive and deepened later, hence the bigger totals farther north and east.

[96blizz]

Not trying to take away from the storm at all. But the issue is that the NAM is becoming fairly notorious for an extreme or overdone solution in that time frame. In that storms case, it was too strong and too close to the coast. Ended up slightly more progressive and deepened later, hence the bigger totals farther north and east.

Exactly. It's one thing to say that a spot or two hit 30", but the name had extremely widespread 30" plus amounts in that range. I was in that range on that 18z run the day before an we got 9". So, yeah, a 21" or so error is rather egregious...

[SnowGoose69]

The 18Z GFS shows slight signs of moving towards the NAM around 21Z Sunday but it then again loses the precip shield to the east off NJ...there are some frontogenetical banding signatures showing up in both the NAM and the GFS on the snow band as it pushes into SRN and CNTRL NJ Sunday afternoon, someone could get hit very hard down that way on the leading edge of the snow band as it moves north.

[UlsterCountySnowZ]

The 18Z GFS shows slight signs of moving towards the NAM around 21Z Sunday but it then again loses the precip shield to the east off NJ...there are some frontogenetical banding signatures showing up in both the NAM and the GFS on the snow band as it pushes into SRN and CNTRL NJ Sunday afternoon, someone could get hit very hard down that way on the leading edge of the snow band as it moves north.

The NAMS Qpf is always bullish but I wouldn't be surprised if the gfs continues to trend towards the NAM in terms of cold signatures and precip shield

[UlsterCountySnowZ]

Can someone post the 18z GFS I'm on my cell and can't get it to work

[PB GFI]

I'm not throwing the NAM out , but its really alone in its WAA solution to its degree. It's true It's QPF is typically higher than most in ths range and too many times its failed .

But more so I will find it hard to believe the 12z Euro is missing a warning type event from NE Deleware thru southern New Jersey 48 hrs out

The GFS didn't buy it either It mayb another hiccup , I'm not gona dismiss it , but I thnk there's other guidance that says it mayb over estimating it again

[ADKweather27]

I'm not throwing the NAM out , but its really alone in its WAA solution to its degree. It's true It's QPF is typically higher than most in ths range and too many times its failed .

But more so I will find it hard to believe the 12z Euro is missing a warning type event from NE Deleware thru southern New Jersey 48 hrs out

The GFS didn't buy it either It mayb another hiccup , I'm not gona dismiss it , but I thnk there's other guidance that says it mayb over estimating it again

I would throw it out, it has little support.

[earthlight]

The Euro's precipitation shield is really lacking on the 12z run. The weatherbell snowfall maps seem like a complete joke based on the total QPF from the second event.

[NorthShoreWx]

That is something I will not forget for the rest of my career. It was a 18-30 hour forecast for 30+ inches across a vast majority of the area -- and the GFS came in with a completely different solution. One of the few times as a meteorologist that I tossed my hands up.

As it turns out, we got a good storm out of it..just not the biblical storm the NAM was showing.

 

Sounds like how we feel about 12/26/10

[NorthShoreWx]

Exactly. It's one thing to say that a spot or two hit 30", but the name had extremely widespread 30" plus amounts in that range. I was in that range on that 18z run the day before an we got 9". So, yeah, a 21" or so error is rather egregious...

 

This is exactly what happened with Boxing day (not withstanding the near term meltdown on some of the models in 2010).  The vast precip fields on the models turn out to be more concentrated in real life depending on where the best banding sets up.  12/2010 and 2/13 are similar in this regard.  The difference in perception is that the ENJ-NYC folks got smoked in 2010 and the LI-SNE folks got smoked in 2013.

 

2013 is no more egregious than what happens with the modeling in many major snowstorms.  Same happened back in 2006.

[Mitchel Volk]

To me the models are showing a weak area of over running that runs into some cold dry air, only the NAM produces a two inch snowfall for NYC, which is suspect since the NAM is not in it;s optimal forecast range of 6-48 hours.  If tonight's NAM does not decrease the snowfall amounts for NYC then it may happen.  I think the period of snow for NYC ends around 10:30 pm Sunday then the warmer air moves in at 750-800 MB level and we start the change over.  I think NYC will see a trace to an 1/2 inch.