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December 18-20 Winter Storm Discussion


Chicago WX

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I just saw that post...a real head scratcher

Basically what I meant is I'm starting not to trust them anymore than the GFS OP runs. I used to think looking at the GFS Ensembles, even 84-144 hours out was a decent sign if they had agreement amongst most of their members, but unless it is every single one, I'm not convinced they are that accurate. It was somewhat facetious as well.

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Basically what I meant is I'm starting not to trust them anymore than the GFS OP runs. I used to think looking at the GFS Ensembles, even 84-144 hours out was a decent sign if they had agreement amongst most of their members, but unless it is every single one, I'm not convinced they are that accurate. It was somewhat facetious as well.

So it's like being a little bit pregnant.

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Basically what I meant is I'm starting not to trust them anymore than the GFS OP runs. I used to think looking at the GFS Ensembles, even 84-144 hours out was a decent sign if they had agreement amongst most of their members, but unless it is every single one, I'm not convinced they are that accurate. It was somewhat facetious as well.

If I'm not mistaken, ensembles are only as good as their initialization of current parameters. I think BI used to mention garbage in/garbage out when it came to the initialization of guidance in general. So as long as there aren't too many initialization errors the ensembles should have a much better grasp if you take an average of the more dominant members. Ensembles certainly aren't perfect, but they usually do pretty good at showing which side the op run should be leaning towards.

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The Brazilian shows the storm missing the MW/OV by a close shave.

Ahh I needed the good laugh, nice one.

As for the storm the GFS is having issues with the first storm, it is weak yet completely stops and sits NE of here. It is trying to force a block that won't be there, I expect corrections from the GFS. As for the GGEM with both vorts diving as far South as they do I would be highly skeptical of any solution the GGEM has, it has a known bias for having issues with systems that dive far South into the SW part of USA.

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Let me preface by saying I am only an observe and harldy understand most of this weather lingo. But wasn't the Euro going a little to far north in previous years?

I like to think that every winter has its own model "biases" in the medium/long range. Really, the general pattern probably dictates this...and the more "chaos", the better (or worse) the model disagreement. But just as there may be some truth to the Euro over amplifying storms outside 6+ days, the reverse can be said for the GFS.

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Basically what I meant is I'm starting not to trust them anymore than the GFS OP runs. I used to think looking at the GFS Ensembles, even 84-144 hours out was a decent sign if they had agreement amongst most of their members, but unless it is every single one, I'm not convinced they are that accurate. It was somewhat facetious as well.

Bad move to double down, typically when there is agreement even in the mid/long range that the ensembles tend to be closer to correct than not. Rarely will you ever get all the ensembles to agree though.

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If I'm not mistaken, ensembles are only as good as their initialization of current parameters. I think BI used to mention garbage in/garbage out when it came to the initialization of guidance in general. So as long as there aren't too many initialization errors the ensembles should have a much better grasp if you take an average of the more dominant members. Ensembles certainly aren't perfect, but they usually do pretty good at showing which side the op run should be leaning towards.

This would be correct, If they get in bad data they will more than likely pump out bad solutions.

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This would be correct, If they get in bad data they will more than likely pump out bad solutions.

The numerical weather prediction article on Wikipedia sums this up pretty well.

Factors affecting the accuracy of numerical predictions include the density and quality of observations used as input to the forecasts, along with deficiencies in the numerical models themselves. Although post-processing techniques such as model output statistics (MOS) have been developed to improve the handling of errors in numerical predictions, a more fundamental problem lies in the chaotic nature of the partial differential equations used to simulate the atmosphere. It is impossible to solve these equations exactly, and small errors grow with time (doubling about every five days). In addition, the partial differential equations used in the model need to be supplemented with parameterizations for solar radiation, moist processes (clouds and precipitation), heat exchange, soil, vegetation, surface water, and the effects of terrain.
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I would expect there to be another 12 hour to 24 hour slow down on the system for this thread...if i'm not mistaken (useing the ECMWF just for consistency sake) that it has already slowed a bit since it started showing up 3 or so days ago? Aren't there typically larger speed/timing issues with systems of this nature (as shown via ECMWF)?

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I would expect there to be another 12 hour to 24 hour slow down on the system for this thread...if i'm not mistaken (useing the ECMWF just for consistency sake) that it has already slowed a bit since it started showing up 3 or so days ago? Aren't there typically larger speed/timing issues with systems of this nature (as shown via ECMWF)?

I would say it is possible considering the scope and magnitude of the potential system.

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12z Euro looks like it will go harmlessly out to sea. That lead wave sorta came out of nowhere...something to watch in future cycles.

Not to mention the massive block across Eastern Canada that blew up this run. Neither one of those things have been on previous runs.

Edit: upon further examination that wave that creates the coastal in the 144-168 range seems to be a piece of the first system that is left in the SW, it is weak and disorganized until it hits the SE coast after sitting in the SW for 2 days. Seems like a very suspect solution all together with respect to that weak vort that somehow manages to smash down the SE ridge to allow for an escape route for this system.

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Not to mention the massive block across Eastern Canada that blew up this run. Neither one of those things have been on previous runs.

Which is why it's just one run and I wouldn't worry about it. For the euro to be consistent for 6 straight runs and just back off now makes total scence because this is still a week out. Euro ensembles should be interesting

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wow...talk about a kiljoy euro run.

Question: Assume for a moment that the euro and ggem are correct and this thing slides harmlessly OTS. Does that have significant repercussions on the pattern as a whole moving into Xmas? ie, major spoiler?

DT alluded to this in his latest post...saying it would basically fck up cold and wintry chances for the rest of the month

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