18z Model Guidance 12/8

[earthlight]

yea it doesnt make sense with how low the pressure is, there really isnt much precip.

It makes plenty of sense given the NVA positioning at 500mb. The PV doesn't phase in until late--and the shortwave orientation just pushes east along the front instead of the phase tugging the entire thing further north and allowing for the PVA to strengthening and develop a CCB in the lower levels.

[LetItSnowInPhilly]

114...benchmark pretty much. This is 800 miles at least from the Euro's positioning...

[yoda]

You must be new here

I am guessing we want that trough to stay positive as long as it can?

[mattinpa]

I have never seen the GFS and the ECMWF this far apart within 100 hours.

Euro showing a cutter while GFS shows out to sea? Never.

One of those models is very clueless. Trends keep getting better on the GFS, though.

[eduggs]

Wow.. big change!!

Finally an exciting run! Of course statistically it's bound to happen as this is clearly represented in the spectrum of 24 hour ensemble runs. But it's always better to see it on the OP run.

[earthlight]

Finally an exciting run! Of course statistically it's bound to happen as this is clearly represented in the spectrum of 24 hour ensemble runs. But it's always better to see it on the OP run.

Look at the lead feature in the Ohio Valley tracking to Northeast PA...it de-amplifies the entire height field across the Northeast.

http://www.meteo.psu.edu/~gadomski/AVN_18z/f84.gif

[KEITH L.I]

114...benchmark pretty much. This is 800 miles at least from the Euro's positioning...

out to sea..lololololol..typical GFS bull..it's funny though

[yoda]

Finally an exciting run! Of course statistically it's bound to happen as this is clearly represented in the spectrum of 24 hour ensemble runs. But it's always better to see it on the OP run.

The ensemble mean and its ensembles should be very interesting to see if they agree with the OP or just toss the OP

[LetItSnowInPhilly]

You must be new here

...have you? Within 100 hours for an east coast storm?

[cleetussnow]

You must be new here

Seriously model agreement at 100 hrs is unique. Last year was an outlier in that there was more consensus because the pattern was can't miss.

These timing scenarios are never handled well right up until the thing as at your front door. No reason to give up - the models are entertaining to say the least.

[tombo82685]

Look at the lead feature in the Ohio Valley tracking to Northeast PA...it de-amplifies the entire height field across the Northeast.

http://www.meteo.psu...AVN_18z/f84.gif

john, if im not mistaken the 84 hr nam had this also. Had one low, the weaker one over the ohio valley, while the main one was back down in mississippi

[phlwx]

interestingly enough, Mount Holly puts chc of snow in the grids:

What I'm mainly surprised about is Monday, and that they went all snow. I mean yeah it's 6 days out and just a gridded forecast, but I expected almost all rain.

You shouldn't be -- it's the backside of the storm and a likely colder solution.

[Kaner587]

The ensemble mean and its ensembles should be very interesting to see if they agree with the OP or just toss the OP

I have a feeling the ensembles will show an I-95 hit but we shall see. The off hour runs of the GFS (6z and 18z) have consistently for the past 2 days been less amplified and further south and east with our s/w and subsequent storm system. Could be the typical bias of the GFS but that deamplifying feature in PA could be the proverbial "fly in the ointment" for any OV or midwestern posters hoping for a blizzard. It could also be our savior if we want to see any white from this.

[eduggs]

Look at the lead feature in the Ohio Valley tracking to Northeast PA...it de-amplifies the entire height field across the Northeast.

http://www.meteo.psu...AVN_18z/f84.gif

And that delays the trof axis from going negative until we stand a chance on the cold side. If the surface low actually starts this far SE, there's a good chance the developing mid-level cutoff holds it in tighter and we're golden. Wouldn't take much from here at all. Of course I still doubt this entire evolution but we needed a major change of some sort.

[earthlight]

And that delays the trof axis from going negative until we stand a chance on the cold side. If the surface low actually starts this far SE, there's a good chance the developing mid-level cutoff holds it in tighter and we're golden. Wouldn't take much from here at all. Of course I still doubt this entire evolution but we needed a major change of some sort.

Exactly. It's something to keep an eye on, at least..especially considering the GFS Ensembles had a handful of members showing solutions like this, with everything later developing and further southeast. I don't believe this will be the final outcome, but it's definitely interesting to watch the guidance struggling with this setup.

[eduggs]

out to sea..lololololol..typical GFS bull..it's funny though

Don't be fooled by the surface specifics

But that is kind of funny to see!

Could the QPF graphics be deceiving just like the 12z? Seems a little dry on the backside based on mid-levels.

[Kaner587]

And that delays the trof axis from going negative until we stand a chance on the cold side. If the surface low actually starts this far SE, there's a good chance the developing mid-level cutoff holds it in tighter and we're golden. Wouldn't take much from here at all. Of course I still doubt this entire evolution but we needed a major change of some sort.

You're describing "threading the needle" as is what needs to occur if we ever want to see snow in an unfavorable pattern. It has happened before, probably in worse patterns than this and will happen again. It is exceedingly unlikely obviously, but throwing a deamplifying s/w into the mix will definitely push it in the direction of threading the needle.

[earthlight]

Could the QPF graphics be deceiving just like the 12z? Seems a little dry on the backside based on mid-levels.

I think it makes sense given the cyclones evolution. See the below frame..not conducive for a developing cold conveyor belt over our area. That being said..it looks like it might be struggling with some convective feedback issues off the coast there. Who knows.

[Kaner587]

interestingly enough, this solution would fit the seasonal bias so far since we've switched to the -NAO

[earthlight]

interestingly enough, this solution would fit the seasonal bias so far since we've switched to the -NAO

Sure, but it would be a real accomplishment to get a storm this far off the coast given how diminished the NAO and Atlantic blocking is at the time of the storm system.

[eduggs]

Exactly. It's something to keep an eye on, at least..especially considering the GFS Ensembles had a handful of members showing solutions like this, with everything later developing and further southeast. I don't believe this will be the final outcome, but it's definitely interesting to watch the guidance struggling with this setup.

Thank god the model gods threw us a bone. Now if only we could string together two positive runs in a row.

Every run for a week had pissed me off until the crazy DGEX looked interesting and now the GFS. 0z is likely to disappoint based on recent history. But for sure this GFS run buys us more time because it keeps the envelope of viable outcomes at least as wide as the ensembles.

[Edge Weather]

Wow, amazing differences! Unreal. From rain to snow in one model run. Well, maybe not all snow, but pretty close in NW NJ. The concern before was that it would be too far west and rain, now I am worried about it being too far east and a near miss of the big event. Have to wait and see. Very interesting turn of events. This does go against La Nina though, so it is really interesting if it really does this.

[eduggs]

I think it makes sense given the cyclones evolution. See the below frame..not conducive for a developing cold conveyor belt over our area. That being said..it looks like it might be struggling with some convective feedback issues off the coast there. Who knows.

When I looked again I see you're right. I'm merging previous runs' evolution with this one to imagine a more favorable QPF result.

[Kaner587]

Sure, but it would be a real accomplishment to get a storm this far off the coast given how diminished the NAO and Atlantic blocking is at the time of the storm system.

agreed...the other storm threats were when our -NAO was raging and more west based.

[earthlight]

Thank god the model gods threw us a bone. Now if only we could string together two positive runs in a row.

Every run for a week had pissed me off until the crazy DGEX looked interesting and now the GFS. 0z is likely to disappoint based on recent history. But for sure this GFS run buys us more time because it keeps the envelope of viable outcomes at least as wide as the ensembles.

I'm still perplexed as to where that lead shortwave came from (probably not a good thing). I think it has some to do with the initial clipper which was further south this run as well. The initial energy coming out of the Pacific escaped east towards the Ohio Valley and de-amplified the heights. Also, it's important to note that even around 60-72 hours the energy was slower. These two things combined led to the de-amplification and the trough going negatively tilted later.

I couldn't believe what I was looking at when we still had a positively tilted trough past Arkansas. If that does occur, this thing is not going to wrap up inland.

[earthlight]

A small footnote..it's at least another 36-42 hours before we get the main features of this entire setup into better sampling or data ingestion areas, so it may be a grab bag of solutions until that point.

[Ericjcrash]

A small footnote..it's at least another 36-42 hours before we get the main features of this entire setup into better sampling or data ingestion areas, so it may be a grab bag of solutions until that point.

Yeah, expect everything possible till the clipper is handled.

[tombo82685]

this is what john is talking about the s/w that deamplifies everything. I circled the areas and compared the two in the 12z and 18z gfs runs. On the 12z gfs you can see how the pieces of energy are most closer together ready to begin phasing....the 18z gfs the pieces of energy are spread out a good bit which deamplifies it, almost like a kicker

heres the 18z gfs

12z gfs

[phlwx]

For all of the griping about the models in general they're all performing relatively well at Day 5 wrt 500 mb pattern..the problem is with all the amplification a small difference means a huge change in final result.

http://www.emc.ncep.noaa.gov/gmb/STATS/html4x/acz5.html

[tombo82685]

I'm still perplexed as to where that lead shortwave came from (probably not a good thing). I think it has some to do with the initial clipper which was further south this run as well. The initial energy coming out of the Pacific escaped east towards the Ohio Valley and de-amplified the heights. Also, it's important to note that even around 60-72 hours the energy was slower. These two things combined led to the de-amplification and the trough going negatively tilted later.

I couldn't believe what I was looking at when we still had a positively tilted trough past Arkansas. If that does occur, this thing is not going to wrap up inland.

john i think thats a northern stream feature. Look at how far south the low is over center of the country, but look how place like wisconsin and minnesota still get some snow....i think its that feature. thats just my guess