Potential 12/8 Event Discussion Part I

[earthlight]

It's not artificial cooling. It's synoptic cooling. CAA. Winds are out of the west and northwest south of around 700mb. Whether this boundary to a supportive airmass sags far enough south in the first place is a question I still have. If the shortwave (which is really superimposed on the longwave before 48hrs or so) is actually a bit stronger than currently modeled, the surface low could make an early run towards the Ohio Valley. The resulting southerly flow would initially taint the boundary layer airmass (something like the UKMET depiction), but it should definitely cool if and when a surface low forms or tracks southeast of the metro.

Well I think the thing that has me (and you) most concerned about this set up is how small the window is to get any accumulations. It's not about meaningful snow, it's about snow at all. If the shortwave changes orientation or timing just slightly, this storm could bring much warmer air in to the low levels very easily.

The other side of it is that we have a frontal boundary offshore, so you have to wonder about positioning, model QPF along the front (sometimes overdone), and the interaction with the shortwave itself.

The airmass entering behind the front is definitely fresh and cold. So that helps. I just think we are walking a serious tightrope here.

[eduggs]

I'm actually surprised it's this wet given how weak a vort this is overall. Not a tremendous amount of forcing or dynamics.

The shortwave and vortmax are strong initially. Good precip influx and overrunning, hence the high QPF in the south and parts of Mid-Atlantic. But I think precip will decrease as you move northeast since the wave will be weakening. The few GEFS members that blow the low up off SNE are a little curious though.

[Isotherm]

woa, it was cold on 12/5/03, ice cold with a strong hp to the north. Not even close to this setup.

Here is the setup.

Thicknesses for the 12/03 event were essentially the same as progged for this Thursday. Between 534-540 across the area, with much colder air near the Canadian border this time.

[eduggs]

The synoptic cooling doesn't kick in until after the precip is well underway and almost over, especially with only a small 6 hour window here.

That's not how I see it. Per the models, it looks like gradual CAA most of the day Wednesday and continuing...

[ag3]

The synoptic cooling doesn't kick in until after the precip is well underway and almost over, especially with only a small 6 hour window here.

It has a 4-5 hour period of snow. That's just fine for a 1"-3" type snowfall.

And euro is too dry anyway. It will increase in qpf with the upcoming runs.

[TheTrials]

Thicknesses for the 12/03 event were essentially the same as progged for this Thursday. Between 534-540 across the area, with much colder air near the Canadian border this time.

Hold on, you are comparing the thicknesses prior to the storm on 12/03 and the thicknesses shown on the gfs as the current storm pulls away. And the 534 line is much further south already at the begining of 12/03.

and i disagree about the temps near canada. Maybe central, but not north of our area on the NY and Maine border. It was very cold for the 12/03 storm.

[SBUWX23]

And you know this because why? This is not a bombing out low that the model should have increased QPF.

It has a 4-5 hour period of snow. That's just fine for a 1"-3" type snowfall.

And euro is too dry anyway. It will increase in qpf with the upcoming runs.

[TheTrials]

And you know this because why? This is not a bombing out low that the model should have increased QPF.

if anything, it could be over done as is right now.

[earthlight]

That's not how I see it. Per the models, it looks like gradual CAA most of the day Wednesday and continuing...

Agreed.

[eduggs]

Well I think the thing that has me (and you) most concerned about this set up is how small the window is to get any accumulations. It's not about meaningful snow, it's about snow at all. If the shortwave changes orientation or timing just slightly, this storm could bring much warmer air in to the low levels very easily.

The other side of it is that we have a frontal boundary offshore, so you have to wonder about positioning, model QPF along the front (sometimes overdone), and the interaction with the shortwave itself.

The airmass entering behind the front is definitely fresh and cold. So that helps. I just think we are walking a serious tightrope here.

I agree with all points. I was really doubtful yesterday but today seems more optimistic. GFS, Euro, NAM, and probably GGEM all support at least some snow. And there is some continuity to the runs. We are within 72hours. It's December. Temps don't look great but not dreadful (track depending obviously). Even the latest ensembles lend support. Haven't seen the recent SREFs though.

I know everybody's been really down on the pattern, which creates lingering pessimism. And storms with a limited ceiling aren't too exciting, but I definitely don't think this is hopeless, even along the coast. Somebody will probably get accumulating snow. Maybe a hilltop in WV, Va, or Md. Maybe even Logan up on the ridge in Knox. We waited more than a month for a threat to track, and it's finally here!

[psv88]

I agree with all points. I was really doubtful yesterday but today seems more optimistic. GFS, Euro, NAM, and probably GGEM all support at least some snow. And there is some continuity to the runs. We are within 72hours. It's December. Temps don't look great but not dreadful (track depending obviously). Even the latest ensembles lend support. Haven't seen the recent SREFs though.

I know everybody's been really down on the pattern, which creates lingering pessimism. And storms with a limited ceiling aren't too exciting, but I definitely don't think this is hopeless, even along the coast. Somebody will probably get accumulating snow. Maybe a hilltop in WV, Va, or Md. Maybe even Logan up on the ridge in Knox. We waited more than a month for a threat to track, and it's finally here!

wait..are you the same eduggs as before? This def doesnt sound like you/him?

[earthlight]

I know everybody's been really down on the pattern, which creates lingering pessimism. And storms with a limited ceiling aren't too exciting, but I definitely don't think this is hopeless, even along the coast. Somebody will probably get accumulating snow. Maybe a hilltop in WV, Va, or Md. Maybe even Logan up on the ridge in Knox. We waited more than a month for a threat to track, and it's finally here!

This post is awesome, man. Locker room pump up speech.

[ag3]

This post is awesome, man. Locker room pump up speech.

I can't wait until the inevitable weenie run and a classic mother of god post.

[atownwxwatcher]

And you know this because why? This is not a bombing out low that the model should have increased QPF.

Its a low pressure that is deepening as it moves NE along the coast..

At 60 hours it is around 1006-1008 MBS and by 72 hours it is down to 996 mbs.

Have seen plenty of cases where the ECM is too dry...

Will this be one not sure at this point and time but yesterday everyone was on the no snow bandwagon and now today ...well I will leave it at that...

[ag3]

And you know this because why? This is not a bombing out low that the model should have increased QPF.

Seeing the gefs mean so amped up and so wet, is usually a sign of increased qpf coming.

Strange seeing the operational gfs with almost nothing and the usually less amped up ensembles with nearly 1.50" of precip.

http://raleighwx.americanwx.com/models/gfsensemble/12zgfsensemblep72096.gif

[eduggs]

This post is awesome, man. Locker room pump up speech.

:weight_lift:

[earthlight]

I can't wait until the inevitable weenie run and a classic mother of god post.

I don't think that's coming with this storm, but we will see.

[jm1220]

I can't wait until the inevitable weenie run and a classic mother of god post.

I can't imagine what this board would be like if it were around in 1997-2000. It would be more like demon of hell than mother of God.

[eduggs]

GEFS have a signal for something around 120 hr. Just FWIW.

I just went and checked and you're right - nice catch. They are wildly divergent at day 5, which is great because the operational run was boring. At quick glance I think I notice at least three distinct camps among the GEFs members. And one of those camps hints at a developing low in the SE evolving into a coastal threat. It's definitely a meager threat, but it's not completely illusory. Keep em coming!

[eduggs]

wait..are you the same eduggs as before? This def doesnt sound like you/him?

Same one. But I'm the new and improved version.

[Edge Weather]

JMA looks exactly like the Euro but just a little more north and west and with a bit more moisture. The JMA told the story several days ago really, but very few people looked at what it was saying. That is why it's verification scores are better than the GFS but many people are in denial of that fact.

[Edge Weather]

The JMA, with higher verification scores than the GFS at 8 days, has a low in the Gulf of Mexico next Tuesday, that may or may not come north as 500mb energy is coming south into the central states.

[Isotherm]

A 2-4" event before Dec 15th is a good deal in any winter, regardless of the pattern. Many years we're snowless until the 3rd week of December, sometimes the last week or later.

I'm hoping it verifies so it finally shuts up all the "no blocking no snow!" people, who seem to think we can't get even minor snows in this pattern (no one in particular, just seems to be the popular catch phrase these days). Transient +PNA/-EPO periods can do it for minor/mdt snows at this time of year.

[atownwxwatcher]

THE ONLY CHANGE TO THE UPDATE PACKAGE MADE FOR THE FINAL ISSUANCE

WAS TO SLOW THE WAVE APPROACHING THE SOUTHERN TIP OF NOVA SCOTIA

SLIGHTLY DAY 3...TOWARD THE CENTER OF THE 12Z/05 GUIDANCE. THIS

POSITION ENDS UP BEING BETWEEN THE 00Z/05 AND 12Z/05 DETERMINISTIC

ECMWF SOLUTIONS. THE 12Z/05 GFS...GEFS MEAN...AND GEM GLOBAL HAVE

ALL TRENDED TOWARD A MORE NEGATIVELY TILTED WAVE EMERGING OFF THE

VIRGINIA CAPES AT THE START OF THE MEDIUM RANGE PERIOD...WHICH

APPEARS TO BE VIGOROUS ENOUGH TO DYNAMICALLY COOL PORTIONS OF THE

INTERSTATE 95 CORRIDOR FROM WASHINGTON DC TO BOSTON TO THE POINT

WHERE THE PRECIPITATION WOULD END AS SNOW. THE EARLIER THE

TURNOVER...THE MORE ACCUMULATION IS POSSIBLE

[Sundog]

A 2-4" event before Dec 15th is a good deal in any winter, regardless of the pattern. Many years we're snowless until the 3rd week of December, sometimes the last week or later.

I'm hoping it verifies so it finally shuts up all the "no blocking no snow!" people, who seem to think we can't get even minor snows in this pattern. Transient +PNA/-EPO periods will do it for minor/mdt snows at this time of year.

AMEN!

Edit: Sorry I though this was the banter thread otherwise I wouldn't have made a one word response post.

I agree it has been taken to an extreme by several posters on how it's simply impossible to get snow just because an index isn't favorable atm. The pattern we will find ourselves in IS good enough for some snow. There's no raging SE ridge to say that it's simply not possible. Yes it's difficult but we've seen similar setups produce in the past.

[earthlight]

Should be interesting to see the SREF's...they were almost all whiffs at 09z.

[Snow_Miser]

Looks like the HPC is on board:

THE ONLY CHANGE TO THE UPDATE PACKAGE MADE FOR THE FINAL ISSUANCE

WAS TO SLOW THE WAVE APPROACHING THE SOUTHERN TIP OF NOVA SCOTIA

SLIGHTLY DAY 3...TOWARD THE CENTER OF THE 12Z/05 GUIDANCE. THIS

POSITION ENDS UP BEING BETWEEN THE 00Z/05 AND 12Z/05 DETERMINISTIC

ECMWF SOLUTIONS. THE 12Z/05 GFS...GEFS MEAN...AND GEM GLOBAL HAVE

... ALL TRENDED TOWARD A MORE NEGATIVELY TILTED WAVE EMERGING OFF THE

VIRGINIA CAPES AT THE START OF THE MEDIUM RANGE PERIOD...WHICH

APPEARS TO BE VIGOROUS ENOUGH TO DYNAMICALLY COOL PORTIONS OF THE

INTERSTATE 95 CORRIDOR FROM WASHINGTON DC TO BOSTON TO THE POINT

WHERE THE PRECIPITATION WOULD END AS SNOW. THE EARLIER THE

TURNOVER...THE MORE ACCUMULATION IS POSSIBLE

http://www.hpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdepd

[earthlight]

SREFs are nice. Much more precipitation compared to the 09z run and you can see the gradual CAA taking over as the event occurs.

[ag3]

srefs came on board.

850's plenty cold throughout. Looks like surface is in the 30's and coming down as the precip expands.

[ag3]

Looks like close to .50" of precip on the srefs.