12Z Model runs Christmas Eve 2010

[SBUWX23]

You have to admit seeing the SREFs jump hugely west is a little compelling.

We are seeing more spread now on the western side and that could be from the members using GFS data.

[TheTrials]

We are seeing more spread now on the western side and that could be from the members using GFS data.

Is there anyway to know how many of these members are actually using the data? there are a lot of heavy hitters in this group.

[baroclinic_instability]

This storm is amazingly sensitive, and I will say it again, the GOM will have to play a role. For nobody that believes me, look at the early ECM runs that were bombing this low out. They developed a much stronger GOM depression/surface low once that weak PV Anomaly ejected NE/phased with the northern stream. Look at the 12Z GFS and compare it to the 12Z NAM. Why is this important? Weak convergence in the GOM, and it can be seen on the GFS, is "priming" the surface low far rapid development by releasing latent heat of condensation in the low levels of the troposphere (generally 850 and below) by hour 36. Also note how the surface low is already beginning to take off inside the GOM by 42, then once the system reaches the Gulf Stream it begins to tank out. This is a positive feedback process, and why the GFS is so much different because of this very small detail results in huge changes with time...it is very non-linear process. So why is this important? Latent heat release in the lower troposphere acts to decrease the static stability by warming the low levels. It also enhances low level warm air advection. You will see this in the upper level height field ahead of the trough manifested in rising upper level heights, aka a building ridge. Height rises are dynamic, and they don't happen by accident. It can be shown rather simply without pulling out long equations if you develop low level warm air advection in the low levels over an area, what happens? The thickness of that layer of air increases (see hypsometric equation), and therefore the heights above it rise. In QG theory, this is differential warm air advection and it results in height rises. VERY important for that process to occur. As for static stability, it plays a prominent role and decreased static stability helps a cylone rapidly intensify because lower statically stable air will rise more efficiently than very stable air, or high static stability air. It can even result in destabilization and the development of convection near the core. If you look at all promient vertical motion equation, including the QG omega eqaution, where is static stability?

It is in the denominator of every major forcing term!

Low static stability is KEY.

Height rises? They are important because an increasing ridge in the mid levels results in a larger magnitude of differential cyclonic vorticity advection which increases sy noptic ascent, but it also results in a much more curved and shorter wavelength tropospheric jet stream which also enhances the divergence aloft associated with the mesoscale jet stream. This is a feedback process! Now what happens? More air converges in the low levels, more latent heat is released, warm air advection increases in magnitude as the low continues to develop, heights rise faster, frontogenesis develops strong mesoscale circulations, the jet curves more, etc etc etc. Throw in air-sea interaction instability and you now have a bomb and this system then "hooks" into the coast, in this case into the SNE/NE region. Mid Atlantic is out of the big snow overall, but the coastal and Delmarva region are definitely still in play. This is positive feedback cyclogenesis, and this is why you have such varying solutions. GFS has a GOM influence, and you need it.

From a forecasting perspective, folks along the EC, especially NE and into NYC/Long Island will be watching development in the GOM with a close eye in 24-30 hours. If the GFS shows what it is now, the potential is there. This is becoming a NOWcasting forecast.

[hckyplayer8]

This storm is amazingly sensitive, and I will say it again, the GOM will have to play a role. For nobody that believes me, look at the early ECM runs that were bombing this low out. They developed a much stronger GOM depression/surface low once that weak PV Anomaly ejected NE/phased with the northern stream. Look at the 12Z GFS and compare it to the NAM. Why is this important? Weak convergence in the GOM, and it can be seen on the GFS, is "priming" the surface low far rapid development by releasing latent heat of condensation in the low levels of the troposphere (generally 850 and below) by hour 36. Also note how the surface low is already beginning to take off inside the GOM by 42, then once the system reaches the Gulf Stream it begins to tank out. This is a positive feedback process, and why the GFS is so much different because of this very small detail results in huge changes with time...it is very non-linear process. So why is this important? Latent heat release in the lower troposphere acts to decrease the static stability by warming the low levels. It also enhances low level warm air advection. You will see this in the upper level height field ahead of the trough manifested in rising upper level heights, aka a building ridge. Height rises are dynamic, and they don't happen by accident. It can be shown rather simply without pulling out long equations if you develop low level warm air advection in the low levels over an area, what happens? The thickness of that layer of air increases (see hypsometric equation), and therefore the heights above it rise. In QG theory, this is differential warm air advection and it results in height rises. VERY important for that process to occur. As for static stability, it plays a prominent role and decreased static stability helps a cylone rapidly intensify because lower statically stable air will rise more efficiently than very stable air, or high static stability air. If you look at all promient vertical motion equation, including the QG omega eqaution, where is static stability?

It is in the denominator of every major forcing term!

Low static stability is KEY.

Height rises? They are important because an increasing ridge in the mid levels results in a larger magnitude of differential cyclonic vorticity advection which increases sy noptic ascent, but it also results in a much more curved and shorter wavelength tropospheric jet stream which also enhances the divergence aloft associated with the mesoscale jet stream. This is a feedback process! Now what happens? More air converges in the low levels, more latent heat is released, warm air advection increases in magnitude as the low continues to develop, heights rise faster, frontogenesis develops strong mesoscale circulations, the jet curves more, etc etc etc. Throw in air-sea interaction instability and you now have a bomb and this system then "hooks" into the coast, in this case into the SNE/NE region. Mid Atlantic is out of the big snow overall, but the coastal and Delmarva region are definitely still in play. This is positive feedback cyclogenesis, and this is why you have such varying solutions. GFS has a GOM influence, and you need it.

From a forecasting perspective, folks along the EC, especially NE and into NYC/Long Island will be watching development in the GOM with a close eye in 24-30 hours. If the GFS shows what it is now, the potential is there. This is becoming a NOWcasting forecast.

Thank you for that. Awesome post.

[Yeoman]

It's water vapor and nowcasting time

[LakeEffectKing]

It's water vapor and nowcasting time

OK, so where's it going???

Sarcastic a bit, of course, but with such a spread in models, we can still deem value on seeing the movements of them.

[Guest someguy]

with all due respect, some of the mets arguing against a big snowstorm were big proponents not long ago. The fact of he matter is this a complex situation and small variations may change the outcome greatly. I think people who have already whiffed on their calls should just stay silent and wait for it to happen b/c they really do not know either.

so b/c the 5 day foreast was wrong you are saying professional meteorologists should NOT be ALLOWED to make any furthere comments?

EVER ?

no argument with being cautious, but it is just as silly to say GFS is definitely wrong as when certain Mets said Euro was correct a few days ago. Certainty gets you burned when it comes to weather..

pay attention stupid

I didnt say it... HPC said it

no issue, just want to see a Met give a forecast w/o citing a model:) Are there any left out there?

WAIT is this one of thos e JB uses the pattern and not the models thing

[stormman]

well for New England its never 100% over becuase the region 'STICK OUT' to almost 70 degrees west longitude

the "its over" refers to the idea of major snow-- not no snow -- but major snow for RIC to NYC

hey dt,

im hearing that the euro ensembles are west of operational, that doesnt concern you at all, that maybe the gfs is onto somethign?

[dtk]

I wish I had more time to reply and not from my phone. The hpc discarded the gfs because they found something that they interpreted as an error (there were no bad obs nor failures that I can tell....so this is largely just their opinion). I am curious to see what they saw, and why....we never draw completely to individual obs, as they too have errors.

[CT Rain]

I wish I had more time to reply and not from my phone. The hpc discarded the gfs because they found something that they interpreted as an error (there were no bad obs nor failures that I can tell....so this is largely just their opinion). I am curious to see what they saw, and why....we never draw completely to individual obs, as they too have errors.

Yeah, exactly. Would like to hear more details.

[snowalot]

Yeah, exactly. Would like to hear more details.

I find that interesting. I just posted under the thread "are models bad" whether all of you guys had been told what exactly was seen as an error and why. I can't imagine that HPC can simply discount a run and not let all of you who have to make these local forcasts the reasons why.

[vinylfreak89]

to correct my earlier statement... i was looking at the 16Z RUC (again blame remoting in and staring at a small screen)... the 12Z GFS 6 hr forecast is about as dead on with the ruc 18z as possible... the only minor change i see is the shortwave is slightly stronger in iowa.