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January Storm Term Threat Discussions (Day 3 - Day 7)


WxUSAF
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20 minutes ago, CAPE said:

It was close. Looking at h5, there are some subtle differences between the Euro and GFS. The biggest one may be the spacing between the developing shortwave and the big NA vortex. A bit more on the GFS, and so it is able to develop more ridging out in front. 

Yes, the GFS keeps the 500-mb shortwave mostly coherent as it propagates from AZ on 12z Tuesday to the OH river valley, where it acquires a negative tilt.The shortwave on the Euro loses its coherence over the southwest, keeping some of the energy delayed as the feature moves eastward. The result is a flatter, positively tilted shortwave that produces less favorable interaction with the developing surface low.

There's definitely potential with this system for snow in the mid-Atlantic, but I think there's too much uncertainty right now in how these features will evolve to be confident in any operational model solution.

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1 minute ago, heavy_wx said:

Yes, the GFS keeps the 500-mb shortwave mostly coherent as it propagates from AZ on 12z Tuesday to the OH river valley, where it acquires a negative tilt.The shortwave on the Euro loses its coherence over the southwest, keeping some of the energy delayed as the feature moves eastward. The result is a flatter, positively tilted shortwave that produces less favorable interaction with the developing surface low.

There's definitely potential with this system for snow in the mid-Atlantic, but I think there's too much uncertainty right now in how these features will evolve to be confident in any operational model solution.

Would you consider that to be a bias of the euro with s/w ejection with systems coming out of the southwest like we’ve seen in past storms? 

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This is good info to know. From our Philly board met. 
 

If the GFS went off the rails, it takes about 30 hours of runs to self correct because it uses its own 6 hr forecast to adjust initial conditions.  Hence if it is an error, it gets perpetuated in future runs until a pair of sounding runs expunge it. The Euro starts from scratch each sounding run. So by the 00z run tonight we will know”

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6 minutes ago, Buddy1987 said:

Would you consider that to be a bias of the euro with s/w ejection with systems coming out of the southwest like we’ve seen in past storms? 

Good question; I'm not sure if the differences in the shortwave evolution are caused by something inherent in the model dynamics or differences in the model initial conditions.

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Just now, ryanconway63 said:

The 6z Para GFS seems most realistic to me at this point.   I cant get excited with what the Euro is currently showing.....If a MECS was coming the Euro will definitely pick up on it by 12z today.  If not ill remain extremely skeptical 

Not sure we can make any definitive statements on this one yet... the models have been struggling mightily in this pattern. It’s been really tough to even search for trends... every time it seems there is one, the models shift the next suite. I’d keep an open mind...

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Just now, Ralph Wiggum said:

Admittedly I have an unnerving feeling about this one, especially after the reading above where the GFS if it is wrong takes several runs to adjust. 

Did that rule work when the gfs went from a historic SC storm to a historic NC storm to a historic Lynchburg storm to a historic Norfolk storm to a historic nova storm in 3 days

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15 minutes ago, Wentzadelphia said:

This is good info to know. From our Philly board met. 
 

If the GFS went off the rails, it takes about 30 hours of runs to self correct because it uses its own 6 hr forecast to adjust initial conditions.  Hence if it is an error, it gets perpetuated in future runs until a pair of sounding runs expunge it. The Euro starts from scratch each sounding run. So by the 00z run tonight we will know”

Where is this from?  I dont see it on here... and i've never heard of that before with any model

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Just now, leesburg 04 said:

Did that rule work when the gfs went from a historic SC storm to a historic NC storm to a historic Lynchburg storm to a historic Norfolk storm to a historic nova storm in 3 days

Touche. Would like the know which poster on the other forum said that about the GFS.

In other news, the NAM at range looks consolidated with the sw in the SW about to move out.

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Just now, LP08 said:

I’d bet dollar to donuts that the gfs doesn’t use it’s 6hr forecast for its next run.  It injests new data prior to every run.

I know it used to do that for the 6z and 18z runs.  Thats why back in the day, the 6z and 18z runs could burp out some real outlier solutions.  But I thought that changed long ago.  @high risk?

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10 minutes ago, WxUSAF said:

I know it used to do that for the 6z and 18z runs.  Thats why back in the day, the 6z and 18z runs could burp out some real outlier solutions.  But I thought that changed long ago.  @high risk?

@dtk would be a good one to ask too, I think. To be honest I'm calling BS preliminarily as well. 30 hours to adjust? Why wouldn't it be 24? Or 12? 

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I caught Jay’s FB post late last night after the epic GFS run, so I knew there would be a lot to read through this morning. We always need perfect ingredients to get a nice coastal storm around here, which is what the Euro showed on Wed/Thursday and what the GFS has now shown for a couple of runs.  I  do agree with someone else who says that the Euro often shows a storm in the long-term, loses it in the medium range and then brings it back.  I also recall a few winters recently that the Euro has not done great, which some have attributed to the strong Pacific. I’m hoping that the GFS is on to something because we all could use some purples, pinks, and greens around here. So I guess we all just hold our breath until 12z...

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I'm not a data assimilation scientist although I interact with that community from time to time. So take this fwiw. 

All of the global centers pretty much ingest the same sfc obs, aircraft obs, satellite obs, and radiosondes. ECMWF has a bit of an advantage because they can use some Chinese and Russian satellites that NOAA is prohibited from using, and I think they have a longer time window for when they allow observations to roll in (this is part of why it comes out later). Where they differ is how they adjust the initial state...they all start from the previous forecast but how much impact observations are allowed to have to change this state, and how observations at one time/location impact the fields at different times/locations depend on the assimilation technique.

The radiosondes have the largest impact (https://gmao.gsfc.nasa.gov/forecasts/systems/fp/obs_impact/), so that lends some credence to giving more weight to the 12z/0z runs if they show a big change, but  there is plenty of other independent info going into the 6z/18z runs.

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