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


WxUSAF
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1 hour 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?

 

1 hour ago, 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.

       

     Both are true.    Yes, the GFS ingests new data for every cycle, but you have to use something as the first guess, and that is the 6-hr forecast from the previous GFS cycle.     You can't just insert obs onto a blank slate - there have to be initial values for all prognostic fields at all grid point at all levels, and you adjust those initial values based on the observations to get a solution that is balanced.    You can't just use blunt force with a data observation and try to just perform straight interpolation of its value in the horizontal and vertical.

    

 

 

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Just now, high risk said:

 

       

     Both are true.    Yes, the GFS ingests new data for every cycle, but you have to use something as the first guess, and that is the 6-hr forecast from the previous GFS cycle.     You can't just insert obs onto a blank slate - there have to be initial values for all prognostic fields at all grid point at all levels, and you adjust those initial values based on the observations to get a solution that is balanced.    You can't just use blunt force with a data observation and try to just perform straight interpolation of its value in the horizontal and vertical.

    

 

 

But wouldn’t all models do that as well?

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1 minute ago, high risk said:

 

       

     Both are true.    Yes, the GFS ingests new data for every cycle, but you have to use something as the first guess, and that is the 6-hr forecast from the previous GFS cycle.     You can't just insert obs onto a blank slate - there have to be initial values for all prognostic fields at all grid point at all levels, and you adjust those initial values based on the observations to get a solution that is balanced.    You can't just use blunt force with a data observation and try to just perform straight interpolation of its value in the horizontal and vertical.

    

 

 

Would this explain trends to a certain degree? 

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Nam looks “diggy” toward the end of its run when comparing to gfs at 90. I’m tempering my expectations as I’m sure most are. Right now threat slightly better for areas to my north and east but I’m far from out of it with para and Canadian looking better region wide.

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4 minutes ago, Wentzadelphia said:

Would this explain trends to a certain degree? 

     Maybe?     If, say, the GFS badly initialized the wave off of the west coast at 18z yesterday, it *could* take a few cycles to undo the damage.     For the 00z cycle, it would start with the specification of the wave from the 18z 6h forecast (the first guess).    If there is new data where that feature resides at 00z, it will take that into account, but it will probably only adjust the first guess partially towards the new obs there.      Then the 06z cycle will adjust further.      It depends how much data is available where the feature is and how different it is from the first guess.

     A famous example is with the NWP failures with the 2000 blizzard.     On the morning before the blizzard, the Peachtree City, GA raob had big wind speeds up at jet level, as a huge jet streak rotated through the trough and helped it go negative tilt.       The first guess value of the jet level wind speed  over GA was about 40 (I can't remember the number) knots lower than the ob, and the models all treated the ob as garbage and pretty much didn't adjust the wind speed there at all.      

 

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1 minute ago, nj2va said:

ICON is a weak POS wave that just slides off the coast. Some very light (less than an inch) snow to CVA.

It’s that ULL in Canada that doesn’t allow it to amplify.  At least in my eyes.

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8ED426CE-06CF-43FF-A902-C4BBE5D2D6BF.png

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36 minutes ago, clskinsfan said:

For those saying the Euro doesn't usually fail inside 5 days. It failed miserably with the December storm inside 3 days. It is the best model for sure. But it isn't perfect.

It fails in New England all the time, FWIW. I have seen it cave to the GFS and even the GGEM twice now. It's not the same Euro as in the past.

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20 minutes ago, high risk said:

     Maybe?     If, say, the GFS badly initialized the wave off of the west coast at 18z yesterday, it *could* take a few cycles to undo the damage.     For the 00z cycle, it would start with the specification of the wave from the 18z 6h forecast (the first guess).    If there is new data where that feature resides at 00z, it will take that into account, but it will probably only adjust the first guess partially towards the new obs there.      Then the 06z cycle will adjust further.      It depends how much data is available where the feature is and how different it is from the first guess.

     A famous example is with the NWP failures with the 2000 blizzard.     On the morning before the blizzard, the Peachtree City, GA raob had big wind speeds up at jet level, as a huge jet streak rotated through the trough and helped it go negative tilt.       The first guess value of the jet level wind speed  over GA was about 40 (I can't remember the number) knots lower than the ob, and the models all treated the ob as garbage and pretty much didn't adjust the wind speed there at all.      

 

Thanks, to me it makes sense why we sometimes see the GFS kind of tick towards other models at times, and then it has one run where it completely caves  on th  overall progression of events. I’d  wager good money the 12z gfs ticks south again, but I suppose the big money will be on the 00z run. This also happens to other models though too so there’s just so many factors well see

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