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Holston_River_Rambler

December 8-10 Storm Discussion

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00z Nam looks super cold. The high is at 1041 at the end of the run. The system looks a little more suppressed because of this.

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1 minute ago, Wurbus said:

00z Nam looks super cold. The high is at 1041 at the end of the run. The system looks a little more suppressed because of this.

Rehashing my mind, nam tends to have a cold bias and higher precip bias, correct? 

And for those of us in the northeast tn or southeast ky, we want a little weaker high (but not too weak?)

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I would rather see a trend toward a stronger high personally.  I have seen countless times where precip will make it further north than modeled with a southern stream wave.....  I have also seen countless times where the warm nose makes it further north than modeled.  It’s a tightrope we’ve fallen off of more times than we can count......  high qpf looks almost certain at this point, but the amount and depth of cold is very much in question.

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8 minutes ago, Bango said:

Rehashing my mind, nam tends to have a cold bias and higher precip bias, correct? 

And for those of us in the northeast tn or southeast ky, we want a little weaker high (but not too weak?)

Well to be fair I was just looking at the pressure with that. The actual storm is still out of range anyway. To be honest I'm not sure of what exactly we want to see for that. I would guess it depends on the circumstances of everything else around it and how that would progress outside of it's range. As a general rule though I do believe you want to see a strong high that limits WAA and aids in CAA. As to if that applies in this case? I leave that stuff to Jeff.

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11 minutes ago, Bango said:

Rehashing my mind, nam tends to have a cold bias and higher precip bias, correct? 

And for those of us in the northeast tn or southeast ky, we want a little weaker high (but not too weak?)

LR NAM IMO tends to amp things up just a bit too much late in its run, say after hour 60.  That causes crazy snow totals, systems out of place, but not sure about its bias of high pressure.  That usually causes all kinds of mischief because of that.  But it can give us a clue to how the GFS might look early in its run.  Just my two cents...

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15 minutes ago, Carvers Gap said:

LR NAM IMO tends to amp things up just a bit too much late in its run, say after hour 60.  That causes crazy snow totals, systems out of place, but not sure about its bias of high pressure.  That usually causes all kinds of mischief because of that.  But it can give us a clue to how the GFS might look early in its run.  Just my two cents...

Yeah the NAMs HiRes helps it when dealing with microclimates in short range. When dealing with microclimates even a 5 mi shift can have a dramatic effect so with so much variability when extended out it results in some wild swings.

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I don't pretend to know if this is significant or not, but carver noted the loss of the high as the icon progressed, and some in the se forum were noting this in the latest ukmet late in its run...

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Tonight the GEFS shows a minor improvement over it's last run for Tennessee. The most notable change is an increase in the area of significant snowfall in West Virginia and Virginia. It looks like there is a movement to the north of the heaviest snowfall in the Carolinas but it's pretty insignificant.

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24 minutes ago, John1122 said:

Waiting on the maps from other places that may be more accurate. 

Well temperatures both on the ground and at 850mb seemed good. I saw no ice or sleet so the upper layers seemed to be in agreement with the surface with the exception of a little zr over Kentucky at the beginning. Other than Tropical Tidbits possibly failing to accurately depict snowfall accumulation it would seem to accurately depict what the FV3 was showing. I'm sure the snow depth maps will be less impressive but what else is new? It's funny to think that I am trying to judge the accuracy of something that depicts something that predicts the future condition of the atmosphere with the use of advanced algorithm with countless calculations applied by people who collected data that others observed. Now I have a headache. It's an amazing time to be alive.

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On the Fv3, Some areas of east tn show snow/frozen precip for 55 hours lol. It's a little concerning that the low placement rides up almost into mid alabama, but checking prior runs, they also show it riding considerably north before moving east (not as much).  I would not have thought such a inland path could paint such results for upper east tn, but inversely, some of the money paths on gfs do not, so there's that

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I only have the 24 hour Euro maps right now, but the SE forum just flew off the cliff, apparently not good for them.

Though to look at the 24 hour panels it doesn't look any different than the 00z run last night, actually looks better on them. Once again though with 24 hour panels, can't see many details.

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The Euro was indeed much warmer. I lose around 26 inches off my totals from 12z today. No biggie. It was an epic 24 hours or so of model watching, now the GFS/CMC/Euro have very similar snowfall maps for our region since the Euro folded to the GFS with this run. The mountains still look to do very well. Probably 3-6 inches for the Plateau and border counties with Kentucky and Virginia. SEKY and SW Virginia look like the are still in the game for double digits.

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Not the epic of the last few days, especially today, but not too bad at all for some of us. All in all not terribly off the GFS and CMC, a little more for us than they show but I'll take 6-10 inches any time we can get it. That is 25 percent roughly of the totals from 12z that I said I'd be happy with. We will see if she wobbles back or not, but with every model except the FV3 being fairly similar, we may be close to the track solution. Though I suspect there will be some more shifts, as the majority of the snowfall here is 96-144 hours away.

euromap125.jpg

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For a bit there I wasn't sure how bad the news on the Euro was so I avoided checking and instead watched it as it played out slowly which I often do when I expect to be disappointed.To my surprise there was just a loss of 2 inches give or take another and the storm followed a similar route as the other model guidance. The run acts as a reminder of how shaky they can be over 3 days out.

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So, will be interested in the 12Z suite of models. Looks like the Euro over-corrected too far north imo, seems like allot of the modeling is clustered around the KY/TN border east, just my untrained thoughts!

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06z is good to the far eastern areas, not so great anywhere else. Kills North Carolina. 2 feet in the Piedmont. 

The GFS continues to be far and away the warmest of the models. The NAM is still looking great at 84, but it's the NAM at 84. 

I'm not real clear on why the 850s don't cool here after the low is to our east, but they just don't on the GFS.

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Folks, I went to sleep last night.  I am glad I did, or I would be one grumpy camper this morning after seeing some those runs.  Normally, I would say that the ensembles look good for NE TN, but those edged downwards just a bit overnight in term of snowfall.  Now, the 6z GFS looks somewhat better.   The CMC looks better for NE TN.  The FV3 looked good.   The Euro was north.  One more jog like that, and it is liquid for everyone.  But let's see what the 12z suite says.  This is probably the first morning where I am less enthusiastic about MBY.  That said, here is your morning power nugget from MRX....stellar write-up.

Moving on into Friday night and the rest of the weekend, the pattern
still looks to become increasingly active as the southwest H5
cyclone advects east across the TX, while surface cyclogenesis over
the lower MS valley favors moisture advection/upglide over much of
the deep south.  Meanwhile a second (northern stream) H5 wave will
dive out of Canada, further complicating the pattern through late
weekend.  Although the operational guidance seems to be in fairly
good agreement overall, some of the details remain yet to be
determined.  Most notably timing, which will inherently affect
precipitation onset and ptype characterization across east TN and
southwest VA/NC.  The ECMWF/SREF (as well as the later period of the
00Z NAM) favors a strong OH valley high and eventual eastern
Appalachian wedge, which results in a more southern track of the
eventual Miller A surface low.  This solution would suggest deep
cold air across the southern Appalachians favoring more confidence
in wintry ptypes (SN/IP/ZR), albeit with a transition zone setting
up somewhere. The GFS on the hand has a weaker OH valley surface
ridge, a more northern surface low track across the Gulf Coast, and
thus slightly warmer profiles into the Appalachians.  Of course this
is all relative to the early stages of this system`s impacts on
Saturday, as warm advection will commence into Sunday as deep swly
flow overtakes the region and the surface cyclone slides across the
southeast.  Would expect this to favor a shift in the aforementioned
ptype transition zone northward over SW VA.  Finally, the second
Canadian upper low looks to slide into the picture sometime Sunday
Night into Monday, unphased with the initial southern stream
feature.  With that, any residual moisture wrapped in from the
deformation zone of the initial upper low will encounter deep cool
profiles and thus favorable all snow conditions.

All said, confidence in that a wintry precipitation event across the
cwfa will occur is increasing.  However as stated last night, given
that the system isn`t even being sampled by the RAOB network,
provides at least some uncertainty overall, aside from model
solution discontinuities.  Therefore confidence in timing would be
best stated as moderate, with low/moderate confidence in QPF/ptypes
and placement of such.  Beyond this system, surface high pressure
will advect into the region beneath deep upper ridging, all yielding
dry conditions through midweek.
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After reading MRX, I am going back and looking these.  Going to have to be quick so these may be sloppy and a bit disjointed:

1.  Don't ever want to lose the Euro...and we did on temps.  That said it is run one, and 0z Euro is pretty much the same surface track placement that is has had for several runs.  The high looked good, but the shape was different.  It looked like it lost (to use a football term) containment behind the system.  Basically means there was less high pressure on the backside, and the precip shield jogged north.  Someone mentioned to me that might be a confluence situation.

2.  The 6z GFS is noticeably south with its snow axis compared to 0z.

3.  The 6z FV3 looks about the same, but is slightly south with its snow axis...but not as much as the GFS.

4.  The 0z CMC looks goofy for NE TN and some of central E TN.

5.  If one had never seen the 12z Euro run yesterday, one would say that the overnight 0z mean looks pretty similar to 0z of the night before.  The differences are that the precip shield is further north and it really "wants" to be iffy about lower elevations.  NE TN still looks good...but trends matter right now.

6.  The 0z GEFS was very beefy. The 6z GEFS was maybe beefier and trended south.  It had 6-10" in valley locations of NE TN.

7.  Can anyone post the UKMET...whatever you can get your hands on.  No time to proof...hope it does not look like chicken scratch.   Gotta run.

 

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6 minutes ago, Carvers Gap said:

After reading MRX, I am going back and looking these.  Going to have to be quick so these may be sloppy and a bit disjointed:

1.  Don't ever want to lose the Euro...and we did on temps.  That said it is run one, and 0z Euro is pretty much the same surface track placement that is has had for several runs.  The high looked good, but the shape was different.  It looked like it lost (to use a football term) containment behind the system.  Basically means there was less high pressure on the backside, and the storm jogged north.  Someone mentioned to me that might be a confluence situation.

2.  The 6z GFS is noticeably south with its snow axis compared to 0z.

3.  The 6z FV3 looks about the same, but is slightly south with its snow axis...but not as much as the GFS.

4.  The 0z CMC looks goof for NE TN and some of central E TN.

5.  I one had never seen the 12z Euro run yesterday, one would say that the overnight 0z mean looks pretty similar to 0z of the night before.  The differences are that the precip shield is further north and it really "wants" to be iffy about lower elevations.  NE TN still looks good...but trends matter right now.

6.  The 0z GEFS was very beefy. The 6z GEFS was maybe beefier and trended south.  It had 6-10" in valley locations of NE TN.

7.  Can anyone post the UKMET...whatever you can get your hands on.  No time to proof...hope it does not look like chicken scratch.   Gotta run.

 

Yeah the 6z FV3 was a lot better for me that run, definitely could notice the shift south with the snow axis,  especially in central Arkansas with some big totals that run.  The margin for error with this storm is gonna be so small though.  The rain snow line with this storm looks like it’s gonna be an all out war zone.  Could be great for whoever ends up on the cold side of the rain snow line!

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