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My capital Weather Blog on the weekend storm


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I wrote the following prior to seeing the 12 GFS ensembles. When I saw them at HPC it really got me worried that maybe I had backed off too much on the probabilities. However, while there I also saw the euro and euro ensembles which if anything shifted a little east and were flatter than the 00Z run. The 18Z gfs now has gone back to a phase too late scenario. All the above makes me think my wild ass, rushed guess for the snow chances for dc were correct.

http://voices.washingtonpost.com/capitalweathergang/2010/12/weekend_snow_threat_down_not_o.html

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You're a class act, Wes. We are fortunate to have folks such as yourself as part of our community.

Wes,

Thanks for this. My question isn't naturally part of this thread, but I'd be interested in knowing if you think the level of model variance 4-7 days out in the last 2 or 3 cases (not including tomorrow's clipper) is (a) unusual (or at least greater than normal), and (b ) if it is, whether this is because of the unusual nature of the conditions we have this December, stuck between a strong Nina and a strong -NAO, to which the models are not used.

Many many thanks.

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I wrote the following prior to seeing the 12 GFS ensembles. When I saw them at HPC it really got me worried that maybe I had backed off too much on the probabilities. However, while there I also saw the euro and euro ensembles which if anything shifted a little east and were flatter than the 00Z run. The 18Z gfs now has gone back to a phase too late scenario. All the above makes me think my wild ass, rushed guess for the snow chances for dc were correct.

http://voices.washin...down_not_o.html

Outstanding piece, Wes.

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Wes,

Thanks for this. My question isn't naturally part of this thread, but I'd be interested in knowing if you think the level of model variance 4-7 days out in the last 2 or 3 cases (not including tomorrow's clipper) is (a) unusual (or at least greater than normal), and (b ) if it is, whether this is because of the unusual nature of the conditions we have this December, stuck between a strong Nina and a strong -NAO, to which the models are not used.

Many many thanks.

Phin, Srain, thanks for the nice words. Phin, my guess could always be wrong.

Eurojosh,

I'm not sure I can answer your question. I think 2007-2008 and 2008-2009 also had some cases with large spreads. Last year, the pattern was a great one but there still was movement of the jan 30th event pretty late in the game. The cases where the ridge upstream is very amplified to start with, I think the models do a better job in handling their forecasts. Strong flow with shorter wavelengths are a big forecast problem. How do you time them? In this case, we need have the timing and amplitude of the two streams work out right. Despite my rater conservative probabilities expressed in the piece, the game isn't over and probably won't be until sometime tomorrow. We can alway hope I'm wrong.

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The 12Z european has come in with the old HPC forecast. Now they don't look so dumb do they. Talk about Craptacular!

It looks like my forecast may have been too conservative.

This. Wes: great write up as always!

This storm is going to be exhibit A as to why one shouldn't go around gloating about a particular model/model forecast BEFORE verification.

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The ECMWF has been showing a progressive pattern, a more east/south polar vortex and offshore phasing for days now.

The GFS is consistent though; consistently wrong.

Why the HPC doesn't emphasize the statistically superior ECMWF ensembles and seemingly "bends" meteorological reasoning to match the GFS is beyond me. Honestly, I thought we got over the AVN/MRF bias 15 years ago. Apparently not.

Statistically superior (i.e. in a time mean sense) does not mean it is always going to be better for a particular forecast. The EC model is a good model, to be sure, but it's not perfect and susceptible to many of the same issues as any model.

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This. Wes: great write up as always!

This storm is going to be exhibit A as to why one shouldn't go around gloating about a particular model/model forecast BEFORE verification.

Of course the euro still could be wrong but I suspect that the 1*Z gfs will edge west towards its solution. It's funny, I would have made a much more aggressive snow probability forecast if I had seen the GFS esnemble mean from yesterday prior to releasing my piece. Then the euro and its ensembles came in and pretty much said don't worry as did the 18Z gfs. Now we're back at square one. lol.

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Of course the euro still could be wrong but I suspect that the 1*Z gfs will edge west towards its solution. It's funny, I would have made a much more aggressive snow probability forecast if I had seen the GFS esnemble mean from yesterday prior to releasing my piece. Then the euro and its ensembles came in and pretty much said don't worry as did the 18Z gfs. Now we're back at square one. lol.

Wes,

From a PHL perspective, there were really a couple of members that stacked the qpf deck, one member (12z yesterday) gave PHL nearly 3 inches of rain. I don't know if I have ever seen such a radical positional change in 24 hours by the ECMWF.

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Rainshadow,

Agreed, I am SHOCKED the EURO has caved in like this in 24 hours especially at this time frame. Other models usually follow EURO trend as we know so I'd expect the 18z GFS to trend again

The 18z gfs to me almost always seems to be a wetter more phased solution, yeah my guess would be a westward shift too. But, the southern stream short wave came into the conus this morning, I think the northern stream one is still offshore, not sure if it comes in tonight or for tomorrow morning's run.

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Rainshadow,

Agreed, I am SHOCKED the EURO has caved in like this in 24 hours especially at this time frame. Other models usually follow EURO trend as we know so I'd expect the 18z GFS to trend again

I know the freebie site doesn't show much, but the ensemble mean showed alot of noise on the west side of the low, kind of a sign that even tho the euro was offshore, there were some ensemble members that probably had a run similar to today's.

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The 18z gfs to me almost always seems to be a wetter more phased solution, yeah my guess would be a westward shift too. But, the southern stream short wave came into the conus this morning, I think the northern stream one is still offshore, not sure if it comes in tonight or for tomorrow morning's run.

So much for my guesses.

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