December 18-20 Potential Talking Points

[earthlight]

As they often have been in the past for coastal storms.

Yeah I am not too surprised. I'm beginning to get a little more confident in the fact that this comes more northwest, but I want to see the GFS hold on a little longer. Most times, when we see the GFS so stubborn like this in this range (storm developing 84-96 now), it's on to something. I can think of several events the past few years where it's done this. The NAM (DGEX extension showing the results) also presents some possibilities. Still a whole lot of time to go so I think it will be a few days still before we have a better idea--but one things for sure, that upper level jet configuration on the GFS/NAM at hour 72-84 is pretty ominous.

[SnowGoose69]

The Euro is actually a lot more aggressive with the northern stream penetrating southward than the GFS is...the GFS just has a much stronger southern stream than the Euro, and thus a snowier solution.

While the Euro seems way better than the GFS all winter during SW flow events and in January and February with coastal storms it seems to struggle with storms in December for whatever reason based on my memory of the past 10 years or so...it was late picking up on both the 12/5-6 2003 event as well as last year's event as we all remember.

[WeatherX]

so Bill what are you're thoughts?

I believe he wrote the long term AFD this afternoon

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...

-- Changed Discussion --FOR FRI NIGHT INTO SAT EVENING...FAIR WX...WITH CONFLUENT

QUASI-ZONAL FLOW ALOFT TO THE SOUTH OF A RETROGRADING POLAR VORTEX

OVER SE CANADA SETTING UP A NARROW SFC HIGH PRESSURE RIDGE.

FOR LATE SAT NIGHT INTO MON...THE RETROGRADING POLAR VORTEX OVER SE

CANADA WILL BACK THE FLOW ALOFT TO SW ALONG THE EAST COAST...

ALLOWING A DIGGING SHORTWAVE TO INDUCE SFC CYCLOGENESIS IN THE

NORTHERN GULF OF MEXICO OR OFF THE SOUTHEAST COAST SAT INTO SAT

NIGHT...AND THEN TRACK NE. EXACT SFC LOW TRACK...INTENSITY AND

POTENTIAL IMPACTS TO THE AREA ARE STILL UNCERTAIN...AND DEPEND ON

HOW MUCH THE LARGE SCALE FLOW BACKS SW ALOFT AND/OR THE STRENGTH OF

THE VORT...STILL SOMEWHERE OVER EASTERN SIBERIA...AS IT DROPS INTO

THE LONGWAVE TROUGH. A WEAKER VORT AND/OR LESS RETROGRESSION AS PER

THE 12Z ECWMF WOULD STEER ANY DEVELOPING LOW FARTHER OFFSHORE...WITH

A NEAR MISS OR GLANCING BLOW. A STRONGER VORT AND/OR MORE

RETROGRESSION AS PER THE 12Z GFS/GEFS MEAN WOULD ALLOW FOR MORE

AMPLIFICATION... AND A POTENTIALLY SIGNIFICANT SNOWSTORM. MOST OTHER

MODEL GUIDANCE SITS SOMEWHERE BETWEEN THESE TWO CAMPS...WITH MANY

GGEM ENSEMBLE MEMBERS AND THE UKMET ALSO SHOWING AN INTENSIFYING

COASTAL LOW...FAR ENOUGH EAST TO MINIMIZE LOCAL IMPACTS. WITH A

SNOWFALL EVENT AT LEAST WITHIN THE ENVELOPE OF POSSIBLE SOLUTIONS...

IT IS PRUDENT TO INCREASE POP FOR THIS TIME FRAME TO CHANCE.

HIGH TEMPS THROUGH THE PERIOD SHOULD BE IN THE 30S...WITH LOWS IN

THE 20S.-- End Changed Discussion --

[earthlight]

I'll tell you what--the 12z Ukie and 18z GFS aren't too far off valid 12z Monday.

[forkyfork]

the gfs keeps lower heights/more energy over central canada with the polar vortex than the euro... the gfs has a much more split look, while the euro has a concentrated vortex north of maine

notice the 540 dm contour... non existent in west canada on the euro, while it covers the southern half of canada on the gfs

[LocoAko]

how much of the 18z runs are made of 12z data?

I don't know anything quantitatively, but I know that new upper air data is only entered in the system for 12Z and 00Z model runs with the launch of the radiosondes. I believe the 06Z/18Z runs use the 6-hr forecast from the 12Z and 00Z runs to initialize, but from what I understand, radiosonde data is actually a small component of what goes into a model run, especially with the advent of satellites. Not sure about that, though.

[Grothar]

I just got home and saw the Euro....I'll say the one thing I do not like and this may be a surprise to everyone is that based on the orientation of the PV and trough at 500mb from Canada south to the Carolinas at 120 hours...if the low does indeed get better captured it could very well come straight north up the coast which could result in changeover issues.

Snowgoose, sounds familiar? This was over a day ago

Kaner587, on 13 December 2010 - 12:39 AM, said:

ya not really sure what hes looking at...people often make these misinformed posts and all it shows is that they clearly don't know how to analyze a given model solution

At 7 days out, nothing is a sure bet. I am just stating the obvious facts the storm will push west as it has done in the past and when it does- the dry slot will rear its ugly head somwhere. Yes I agree the water temps are in the 40's but unless the wind is out of the north the entire length of the storm- there will be some mixing issues. To compare this to 93 or 96 is way to early. I think alot of us are excited that all the models are being consistent with this potential storm event which is about frickin time

[tombo82685]

are the 18z indiv ens, looks like 2 or 3 members hit the area

http://www.meteo.psu.edu/~gadomski/ENSPRSNE_18z/ensprsloopmref.html#picture

[atownwxwatcher]

Am i the only one that finds these two images interesting

18 Z GFS Operational 114

12 Z ECM means @ 120

[LocoAko]

Am i the only one that finds these two images interesting

18 Z GFS Operational 114

12 Z ECM means @ 120

....What is so interesting about them?

[Ridingtime]

It's discouraging to see the GFS ensemble members look so bleak. Is it really true that with coastal storms the GFS ens have more of a SE bias?

[atownwxwatcher]

....What is so interesting about them?

Almost identical in the low positioning at the same time...GFS might be just a hair west...

[earthlight]

It's discouraging to see the GFS ensemble members look so bleak. Is it really true that with coastal storms the GFS ens have more of a SE bias?

Yes, almost every time at this range.

[am19psu]

I don't know anything quantitatively, but I know that new upper air data is only entered in the system for 12Z and 00Z model runs with the launch of the radiosondes. I believe the 06Z/18Z runs use the 6-hr forecast from the 12Z and 00Z runs to initialize, but from what I understand, radiosonde data is actually a small component of what goes into a model run, especially with the advent of satellites. Not sure about that, though.

Even at 0z/12z most of the data in the models is satellite derived. The only benefit of the sondes (as best I can tell from talking to dtk/wxbadger) is when small perturbations make large differences (e.g. TC tracks, severe wx, tracking s/w across the Pacific). 99% of the time it won't matter, but that 1% is high impact weather.

[Kaner587]

Yes, almost every time at this range.

and when they're nw we dont get a storm a la 2/4-2/5 2010

[LocoAko]

Even at 0z/12z most of the data in the models is satellite derived. The only benefit of the sondes (as best I can tell from talking to dtk/wxbadger) is when small perturbations make large differences (e.g. TC tracks, severe wx, tracking s/w across the Pacific). 99% of the time it won't matter, but that 1% is high impact weather.

Yeah, that was my understanding of it too, but thanks for clarifying. Go figure... I'm guessing this is one of those times when they might matter? I guess that goes a long way into explaining why in recent years 06Z/18Z runs have pretty much matched 12Z/00Z runs in terms of accuracy.

[phlwx]

Ratios on this bufkit run are a bit more believable -- 15:1...still high but better than on the 12z. QPF is a bit less for Philly though 0.73

[Riptide]

It's discouraging to see the GFS ensemble members look so bleak. Is it really true that with coastal storms the GFS ens have more of a SE bias?

The 06z ensemble mean is also similar to the 18z mean. I don't think it is much cause for concern.

[Ridingtime]

Almost identical in the low positioning at the same time...GFS might be just a hair west...

The positioning might be the same, but the flow aloft is pretty different, and that determines what qpf reaches the coast. The Euro has a different positioning with the PV-it's not as split as the GFS, and the southern stream is unable to amplify as well. So while it's interesting the low placement is nearly identical, we need other major features similar as well for the Euro to say storm (and supposedly slight changes in those features in the Euro can enable this to happen).

Edit: Also looking at those two maps again, the GFS low is not just a hair more west, to me its a lot more west by at least 100 miles or so, and that makes a big difference

[Amped]

Will I-95 see major snow this weekend?

Check my new video update for my personal take.

[Absolute Humidity]

Yeah I am not too surprised. I'm beginning to get a little more confident in the fact that this comes more northwest, but I want to see the GFS hold on a little longer. Most times, when we see the GFS so stubborn like this in this range (storm developing 84-96 now), it's on to something. I can think of several events the past few years where it's done this. The NAM (DGEX extension showing the results) also presents some possibilities. Still a whole lot of time to go so I think it will be a few days still before we have a better idea--but one things for sure, that upper level jet configuration on the GFS/NAM at hour 72-84 is pretty ominous.

2-15-2006, GFS held the storm from 8 days out I believe.

[Amped]

2-15-2006, GFS held the storm from 8 days out I believe.

No it was 96hrs

[NEG NAO]

The 06z ensemble mean is also similar to the 18z mean. I don't think it is much cause for concern.

I disagree - 0Z GFS OP will trend toward the Euro - Pacific is unfavorable because of the La Nina .....too progressive little room for amplification

[SnoSki14]

This will probably be our only chance for a good snowstorm so I'd rather be optimistic rather than pessimistic about this threat. OH and yeah, remember how our last rainstorm was originally supposed to be along the coast, instead it went hundred of miles further west through the lakes. There is no denying the NW trend in a La Nina winter, just be patient. In fact it may even trend too much to the NW, I've seen that happen before although I think we're pretty good in this setup.

[Riptide]

I disagree - 0Z GFS OP will trend toward the Euro - Pacific is unfavorable because of the La Nina .....too progressive little room for amplification

I wouldn't be surprised if the Euro and GFS converge in the middle somewhere. Cape Cod will at least get flurries from this storm.

[Absolute Humidity]

No it was 96hrs

True, wrong model , it was the JMA that picked up that one 8 - 10 days out. Thanks.

[LocoAko]

This will probably be our only chance for a good snowstorm so I'd rather be optimistic rather than pessimistic about this threat. OH and yeah, remember how our last rainstorm was originally supposed to be along the coast, instead it went hundred of miles further west through the lakes. There is no denying the NW trend in a La Nina winter, just be patient. In fact it may even trend too much to the NW, I've seen that happen before although I think we're pretty good in this setup.

Our only chance for a good snow storm?

Are you trolling??

[am19psu]

Our only chance for a good snow storm?

Are you trolling??

FWIW, the LR forecast I put out in Nov basically said no sig snow for Philly between mid-Dec and beginning of March. Granted, Dec hasn't verified very well for me yet, but I don't think that was a total troll post.

[LocoAko]

FWIW, the LR forecast I put out in Nov basically said no sig snow for Philly between mid-Dec and beginning of March. Granted, Dec hasn't verified very well for me yet, but I don't think that was a total troll post.

Really? Well sheesh, I hope your forecast verifies (well, not really ) but I just thought that was a bit premature being that it is only Mid-December..

[am19psu]

Really? Well sheesh, I hope your forecast verifies (well, not really ) but I just thought that was a bit premature being that it is only Mid-December..

If it makes you feel any better, we were talking about enhanced probabilities in March with a strong block in place