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Kuchera snow totals.   One thing to notice is that bigger snow totals extend a bit more on the western edge(compared to 6z).  I think this is because the system is not as sharp.  A couple of days ago, the system was so sharp(go back and look at the post about the buckle), that it produced a narrower swath due to the snow axis be nearly vertical.  Now, the axis is "leaning" more SW to NE(over the forum area) and includes more surface area.  That has been a trend on modeling since yesterday.  

1831988895_ScreenShot2020-12-23at10_22_20AM.png.958cdd3580bb2cb9b2af7701beaf8400.png

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The 12z RGEM and 12z NAM sort of get to the same point via two paths.  The RGEM is quicker with the changeover and the NAM produces a lee side low which very temporarily backs flow...but that extra thump of precip and backing was enough to up totals.  For higher confidence, really would like to see modeling continue to be aggressive like the RGEM in bring in cold air.  The NAM setup is finesse stuff.  Now, if we got both an earlier changeover and a lee side low...you get the GFS from a few days ago.

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1 minute ago, Blue Moon said:

Wouldn't jump at this if I were me. The Canadian models are a joke like the SREF plumes.

The RGEM(especially within 30 hours) as a general rule does well w E TN snow storms, but it is not infallible(no model is in these microclimates). And who knows...it may miss this time as it is definitely a western outlier with strong snow totals, but it has been persistent.  I actually prefer the RGEM(not the CMC global) to the NAM.  I really don't use SREF plumes - woefully inconsistent.  For me the SREF and RGEM are world's apart in reliability.  The toughest part of this storm is whether the cold reaches the back side of the precip.  So, I don't really fault modeling one way or the other.  In E TN, we all know the drill.  Sometimes it hangs up on the Plateau and sometimes it is faster.   "Low confidence" is a term I have been using lately.  There are a wide range of options on the table right now ranging from a whiff to heavy snow.  I do like looking at trends right now more than actual totals.  Seeing models "bump up" or hold is obviously preferred.  

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13 minutes ago, Blue Moon said:

Wouldn't jump at this if I were me. The Canadian models are a joke like the SREF plumes.

I don't know if I would jump either, just based on climo as well as a  common sense and level-headed evaluation of the bust potential, but I don't think the RGEM is a joke.  

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And anybody that uses the SREF plumes for anything other than a curious interest in the NAM or just out of pure weather weenie snow lust, is not too bright. I know I post them sometimes, but I try to be judicious about how I do it. I hope I haven't given anyone the idea that I take them seriously. If so, apologies. 

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Just now, Holston_River_Rambler said:

I don't know if I would jump either, just based on climo as well as a  common sense and level-headed evaluation of the bust potential, but I don't think the RGEM is a joke.  

Right, I don't think anyone is jumping one way or another.  We all know the drill.  LOL.  During the late 90s, we were once under a heavy snow warning(you may remember this!) at TRI for like 10-15" of snow.  Nothing.  So, yeah I get disappointed when snow forecasts don't verify...but I have seen enough to remain skeptical until even sometimes right in the middle of a winter storm!  LOL.  I have learned to enjoy different model runs if not just for entertainment and also for learning.  However, trends right now are good.  Let's hope they continue to hold.  This a tough system as evidenced by the wide range of solutions still out there with under 36 hours to go.  Glad to see the GFS trending away from the nada solution.

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2 minutes ago, Holston_River_Rambler said:

And anybody that uses the SREF plumes for anything other than a curious interest in the NAM or just out of pure weather weenie snow lust, is not too bright. I know I post them sometimes, but I try to be judicious about how I do it. I hope I haven't given anyone the idea that I take them seriously. If so, apologies. 

Oh, I look at them.  If a storm is going to fizzle, they will drop like a hot rock.  I just don't take them overly seriously.  Like any model, once you know the biases...they can be useful.  I just don't use them, because I don't know all of the biases.  MRX actually mentioned them on FB yesterday.  

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7 minutes ago, Carvers Gap said:

Right, I don't think anyone is jumping one way or another.  We all know the drill.  LOL.  During the late 90s, we were once under a heavy snow warning(you may remember this!) at TRI for like 10-15" of snow.  Nothing.  So, yeah I get disappointed when snow forecasts don't verify...but I have seen enough to remain skeptical until even sometimes right in the middle of a winter storm!  LOL.  I have learned to enjoy different model runs if not just for entertainment and also for learning.  However, trends right now are good.  Let's hope they continue to hold.  This a tough system as evidenced by the wide range of solutions still out there with under 36 hours to go.  Glad to see the GFS trending away from the nada solution.

Off topic, but I remember that event.  Went to bed under a WSWarning calling for 8-12 the next day.  Woke up and had been upped to 12-16" and thought "here we go"...........  Ended with a trace.  lol

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Just now, tnweathernut said:

Off topic, but I remember that event.  Went to bed under a WSWarning calling for 8-12 the next day.  Woke up and had been upped to 12-16" and thought "here we go"...........  Ended with a trace.  lol

Me too. I keep trying to remember that one, but can't.  I remember the weather channel met Bruce Edwards coming on and saying something like, "Well we were expecting the moisture to come north and it just didn't happen." I vaguely remember the radar image and I think convection parallel to the Gulf cut off the moisture feed?? 

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Back on this storm note, I'm really looking forward to @BuCoVaWx obs for this. If you can take some pictures please do. I think you are as close to the bull's eye as anyone on here. 

I'll be with the Kingsport crew tomorrow to see my folks for Christmas, hoping I can get home in time to see the changeover, but expect it may have already happened when I get home around 4. I will be driving down 81 as the changeover works it's way east and NE. 

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This is an example of how I use trends.  6z is on the right.  12z is on the left.  I look at the snow axis to see if it moves.  While I don't "think" I am getting that much IMBY, the bump up or down and position of axis does give some hints as to how the storm developed on a particular run.  For this run, totals went up(tells me cold might have gotten there sooner or a lee side low helped or both) and heavier snow accumulations trended westward - very close to the RGEM and 0z/6z Euro.  And of course, we know all of this can go "poof."  LOL.  I have seen that movie too many times.  The GFS was persistent yesterday of nearly a total whiff, so a change here is notable - but obviously never a certainty. If it were to trend westward with heavier snow totals one more time, that would be significant. The only certainty with snow storms is measuring after it is over.  

1607534373_ScreenShot2020-12-23at11_06_29AM.png.a797f0a7a8287ee451e833af4a6da0eb.png

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Off topic, but I remember that event.  Went to bed under a WSWarning calling for 8-12 the next day.  Woke up and had been upped to 12-16" and thought "here we go"...........  Ended with a trace.  lol

Right! Also seen the inverse in recent memory, think in February same year plateau got major icing event a snow event preceded it I think in 2015 or 16 NWS started the day with knoxville forecast of .5" - 1" as the event neared they continually updated amounts all day by that night they issued a graphic of 10"-12" knoxville, Chattanooga got 10" was a huge bust in the positive. 

Sent from my SM-G965U using Tapatalk

 

 

 

 

 

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I didn't even recognize you had posted them, but that's okay, no need to apologize at all, especially to me if my post came across as provocative. I sometimes glance at them to see where the amounts over the last four runs have trended, but I never pay attention to the actual amounts, if that makes sense. 

It's a cynical view of mine, but I pay little mind to the CMC and RGEM. Its cold bias is so overdone that I disregard it just about every time. It's good to show what's possible, but when does that ever pan out?
Personally I pay little attention to amounts just watch for evolution. I am very partial to RGEM for it's uncanny ability to sense energy and features that often it's closest equal the NAM doesn't sniff out.

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5 minutes ago, Blue Moon said:

I didn't even recognize you had posted them, but that's okay, no need to apologize at all, especially to me if my post came across as provocative. I sometimes glance at them to see where the amounts over the last four runs have trended, but I never pay attention to the actual amounts, if that makes sense. 

It's a cynical view of mine, but I pay little mind to the CMC and RGEM. Its cold bias is so overdone that I disregard it just about every time. It's good to show what's possible, but when does that ever pan out?

Skepticism and conservative calls are wise in this hobby.  And we don't mind discussion or disagreement.  None of that is taken then wrong way.  There are a lot of new folks on the forum, so it is healthy to talk about how things are used - biases and what not.

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Problem with the plumes is they are basically an "ensemble" view of the NAM (use that loosely)...and they are like any other models ensembles at close range (jump more due to not being able to get a mean spread since it is so close to the event)...and in the fact they like to really overamp members, they arent good for totals. But they are one way to see a precursor of what the upcoming NAM run may do. They are for trend purposes only.

As far as the RGEM, it used to be horrible IMBY..but the last year or so it has done a remarkable job on borderline events here. The more micro climates are at play, the more I pay attention to it.

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For those new to the forum, I like to use a side-by-side comparison(an overlay would be better...but don't have access to that) of storm totals.  12z CMC is on the left.  6z is on the right.  I say "held serve" in a sense that it still has the storm, similar accumulation amounts(we know those will likely be lower or even much lower), and the storm is still vigorous as it exits.  Totals are down a hair which is to be expected.   What we don't want to see are large scale drop-offs as this could indicate a change in intensity, track, moisture transport(I do worry that storms along the GOM could cut off some precip into our forum area), etc.  The green axis is roughly the old "purple 6" line.  So, one can see that the precip axis to our north moved east slightly.  The pivot in south middle TN has stayed nearly the same.  Overall storm totals have been circled - a slight decrease is noted.  This is upper end of the envelop as cold arrives more quickly.  It definitely has a bias for cold, so that tells us changeover will likely occur further east in the forum area - so cut totals and shift east.  Lastly, the ARW mesoscale model shows how none of us could get snow - again, lots of options on the table.  I actually like the ARW and RGEM inside of 24 hours - so not having the ARW is of note.

1916533386_ScreenShot2020-12-23at11_42_28AM.png.ad60ee449fb8ea40288e347ccb042a34.png

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