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Jan 15-16 Winter Storm


Brick Tamland
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Regarding the Icon and the low pressure position.  Yes, it looks like the low has shifted south based on the "L" positions.  However, if you look at the pressure circles, I think the "L" can sometimes be a bit misleading as they sometimes look a bit off center.  Does anyone know how they determine exactly where to put the "L" on the map as sometime it seems to be a bit off center compared to the circle of lowest pressure.  Just trying to get educated here.    Also, I do see the stronger High and that there's stronger ridging going on east of the mountains.

TW

 

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2 minutes ago, tarheelwx said:

Regarding the Icon and the low pressure position.  Yes, it looks like the low has shifted south based on the "L" positions.  However, if you look at the pressure circles, I think the "L" can sometimes be a bit misleading as they sometimes look a bit off center.  Does anyone know how they determine exactly where to put the "L" on the map as sometime it seems to be a bit off center compared to the circle of lowest pressure.  Just trying to get educated here.    Also, I do see the stronger High and that there's stronger ridging going on east of the mountains.

TW

 

If you look at the 500 map you can clearly see that the vort was more reminiscent of the icons 6z/12z runs. Energy is strong and closed over southwestern Missouri and more in line with guidance. 

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1 hour ago, ILMRoss said:


TBH those ensemble graphics are manna from forecasting gods at this range. There’s a shape, you get to communicate a pseudo-snowmap well before it’s responsible to put together an actual map but you also get to absolve blame to the model in case things go wrong. I can blame them. I interned there back in the day and one of my good met friends (no comment on who) is on the team; they’re smart cookies and I generally think they thread the needle pretty well of tipping their hand while also being responsible with what they put out.

 

46 minutes ago, Cold Rain said:

They heavily use ensembles, which have been been trending from flatter and weaker to stronger and more wintry as the Ops have trended from adequately strong and favorable to more amped warmer aloft.  If the Ops continue to trend in that direction, you can expect the ensembles to follow and WRAL to follow that.

If you guys think I am arguing against using ensembles in forecasting, I am not.  I am arguing against displaying a map that gives precision probabilities.  If WRAL derives their “probabilities” from ensembles, I still disagree with their language.  If they said “14 out of 50 ensemble members indicated 3 inches or more of snow for Clinton” or even “28% of ensemble members indicated 3 inches or more of snow for Clinton”, I would have no issue with those statements.  Those are indisputable facts based off model output.  But equating such fractions of ensemble members to probabilities is a misuse of statistics, in my opinion.

The probability of a success (getting three inches of snow or more, in this case) is equal to the number of successes divided by the number of possible outcomes (failures + successes).  The ensemble members do not represent all the possible outcomes; they only represent approximately 50 of the infinite number of possible outcomes.  Thus, we can’t really say there is a 28% probability of something happening based off ensemble members.  In fact, I would argue there’s really no way to calculate such a probability, because it’s impossible to account for all the possible outcomes that arise from tweaking just one minuscule atmospheric condition somewhere over the entire globe.

It’s the language that I take issue with, not the use of ensembles.  If they were to change their title to “Percent of Ensemble Members that Predict 3 Inches of Snow”, I would see that as much more transparent.  As it is, I think it’s a misleading graphic.

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If you guys think I am arguing against using ensembles in forecasting, I am not.  I am arguing against displaying a map that gives precision probabilities.  If WRAL derives their “probabilities” from ensembles, I still disagree with their language.  If they said “14 out of 50 ensemble members indicated 3 inches or more of snow for Clinton” or even “28% of ensemble members indicated 3 inches or more of snow for Clinton”, I would have no issue with those statements.  Those are indisputable facts based off model output.  But equating such fractions of ensemble members to probabilities is a misuse of statistics, in my opinion.
The probability of a success (getting three inches of snow or more, in this case) is equal to the number of successes divided by the number of possible outcomes (failures + successes).  The ensemble members do not represent all the possible outcomes; they only represent approximately 50 of the infinite number of possible outcomes.  Thus, we can’t really say there is a 28% probability of something happening based off ensemble members.  In fact, I would argue there’s really no way to calculate such a probability, because it’s impossible to account for all the possible outcomes that arise from tweaking just one minuscule atmospheric condition somewhere over the entire globe.
It’s the language that I take issue with, not the use of ensembles.  If they were to change their title to “Percent of Ensemble Members that Predict 3 Inches of Snow”, I would see that as much more transparent.  As it is, I think it’s a misleading graphic.

I agree with all of this. I see the point. It’s not a perfect graphic but on a snow week in news when you have 100 people asking you about the storm in social, when you have to coordinate messaging, when you have to produce a couple of afternoon/evening shows and oh on top of all of that do a bit of forecasting it’s a time saver and a “don’t let perfect get in the way of good” kind of graphic.

I’m tuning out the 00z ICON I thought it looked kind of wonky
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