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Holston_River_Rambler

NAM vs the Euro cage match storm, Feb 20 - 21

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To the tune of All along the Watchtower (Hendrix version) 

 

There must be some kind of way out of winter

said the Rambler to met Jeff

there's too much confusion

can't get no relief

The southeast ridge, it flexes north

troughs dump in the west

the Euro won't level with my mind

will the NAM prove its worth? 

 

No reason to get excited

nrgjeff he kindly spoke

there are many in the valley,

who think that snow is but a joke

but you and I, we've been through that

and this is not our fate

so let us not trust the Euro

the hour's getting late...

 

All along the river valleys

snowhounds kept their view

while model runs came and went

SREF plumes too

outside and up to the north

a big HP dropped down

two shortwaves were approaching

and the wind began to howl....

 

 

 

 

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4 minutes ago, Holston_River_Rambler said:

Yeah, kind of/ sort of worried given that. It was overzealous with the early December bit and here is only very gradually ticking north. 

Doesnt it have a cold bias (could be wrong)..jw if it is keying on the HP too much.

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This may mean nothing, on the globals at 00z Monday my 24 hour rain ending at 1am tonight was .25 on the Euro, .3 on the GFS and .6 on the Canadian. On the meso models it was .25 in the NAM and .35 in the RGEM. I just checked my rain gauge for the night. .57 fell between around 12am last night and now.  The Canadian models we much heavier to the West. The other models were too far south and east with the heavier precip. 

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Strictly in terms of precip totals, there was a decent jump in the right direction for East Tn on the 00z UKMET vs 12z.

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2 minutes ago, PowellVolz said:

And just like that, MRX updates their map just now to pretty much remove all snow in Knoxville.


.

Ironic because in their overnight forecast discussion, they seemed to be coming around to the idea that Knox would see some snow.

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@PowellVolz They had an interesting AFD this AM and expressed a lot of uncertainty for areas 40 north  to bust high or low. 

"A lot to discuss in the extended period with chances of rain and
snow, some of which could be accumulating snowfall. Models are in
good agreement regarding the overall synoptic pattern but
differences are apparent in the overall thermal profiles with the
NAM/EURO a bit colder than the GFS/CMC in the Thursday time frame.
By 12Z Thursday, the h50 pattern will feature a trough extending
from the Great Lakes westward into the Rockies. Nearly zonal h50
flow will traverse the Tennessee valley. At the surface an area of
surface low pressure will develop across the Gulf coast with a
frontal zone extending northeast and a strong high moving out of the
northern plains. The eventual strength of this high will likely have
a great influence on how far north the precip can move north and how
quickly the cold air will arrive. Favorable upper level dynamics
will overspread much of the southeast including the Tennessee valley
12Z onward which along with overrunning will lead to an expansive
zone of precipitation from the TN/GA state line southward. It is
expected that this precipitation will gradually make its way north
through the day Thursday in response to a strengthening 850-700mb
frontal zone as the surface low lifts northeast. However as
mentioned above the strength of the surface high will play a role in
the overall northward progression of the precipitation field.

Forecast soundings, and 2-D planviews indicate the thermal profile
will be sufficient for much of the precipitation to start as snow
before warmer air moves north changing the snow to rain. Much
uncertainty still resides in how cold the lower troposphere becomes
during the day Thursday. The ECMWF and NAM12 show rather strong CAA
as the surface high slides south into the Tennessee valley. This may
actually offset the normal increasing diurnal temperature trend.
This results in much lower confidence in snow accumulations in the
southern and central valley, but believe if any accumulations would
indeed occur they would be on grass and elevated surfaces. As far as
model guidance is concerned the NAM/EURO are in agreement regarding
overall max temperatures in the 925-700MB layer while the GFS and
CMC mirror each other more. Decided to favor a model blend of the
ECMWF/GFS along with the GEFS means. Ensemble plumes still show a
great deal of spread regarding snow amounts but am seeing some
clustering around a dusting to a half inch for locations such as
CHA, and TYS. Even more spread is being observed across SW Virginia
and extreme NE TN where no noticeable clustering can be seen
indicating higher uncertainty across these areas.

Nonetheless confidence is high enough that most locations will
likely see snow fall especially from 12Z - 18Z Thursday as Omega and
RH are most favorable in the DGZ during this time period. However,
warming near surface temperatures and an increasing February sun
angle will be working against heavier snow accumulations especially
for the southern and central valley. Areas further north across SW
Virginia, the Cumberland Plateau will likely see the snow last
longer and could receive upwards of a dusting to a half inch of
snow. The higher terrain of the Tennessee mountains will see the
heaviest accumulations where 1-3 inches of snow could fall.
Confidence in forecast snow amounts are still fairly low, and
because of this, decided against issuing any winter weather
advisories at this time. Additional changes to the forecast are most
certainly going to occur and later shifts may need to issue an
advisory across portions of the area."

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[mention=14393]PowellVolz[/mention] They had an interesting AFD this AM and expressed a lot of uncertainty for areas 40 north  to bust high or low. 
"A lot to discuss in the extended period with chances of rain andsnow, some of which could be accumulating snowfall. Models are ingood agreement regarding the overall synoptic pattern butdifferences are apparent in the overall thermal profiles with theNAM/EURO a bit colder than the GFS/CMC in the Thursday time frame.By 12Z Thursday, the h50 pattern will feature a trough extendingfrom the Great Lakes westward into the Rockies. Nearly zonal h50flow will traverse the Tennessee valley. At the surface an area ofsurface low pressure will develop across the Gulf coast with afrontal zone extending northeast and a strong high moving out of thenorthern plains. The eventual strength of this high will likely havea great influence on how far north the precip can move north and howquickly the cold air will arrive. Favorable upper level dynamicswill overspread much of the southeast including the Tennessee valley12Z onward which along with overrunning will lead to an expansivezone of precipitation from the TN/GA state line southward. It isexpected that this precipitation will gradually make its way norththrough the day Thursday in response to a strengthening 850-700mbfrontal zone as the surface low lifts northeast. However asmentioned above the strength of the surface high will play a role inthe overall northward progression of the precipitation field.Forecast soundings, and 2-D planviews indicate the thermal profilewill be sufficient for much of the precipitation to start as snowbefore warmer air moves north changing the snow to rain. Muchuncertainty still resides in how cold the lower troposphere becomesduring the day Thursday. The ECMWF and NAM12 show rather strong CAAas the surface high slides south into the Tennessee valley. This mayactually offset the normal increasing diurnal temperature trend.This results in much lower confidence in snow accumulations in thesouthern and central valley, but believe if any accumulations wouldindeed occur they would be on grass and elevated surfaces. As far asmodel guidance is concerned the NAM/EURO are in agreement regardingoverall max temperatures in the 925-700MB layer while the GFS andCMC mirror each other more. Decided to favor a model blend of theECMWF/GFS along with the GEFS means. Ensemble plumes still show agreat deal of spread regarding snow amounts but am seeing someclustering around a dusting to a half inch for locations such asCHA, and TYS. Even more spread is being observed across SW Virginiaand extreme NE TN where no noticeable clustering can be seenindicating higher uncertainty across these areas.Nonetheless confidence is high enough that most locations willlikely see snow fall especially from 12Z - 18Z Thursday as Omega andRH are most favorable in the DGZ during this time period. However,warming near surface temperatures and an increasing February sunangle will be working against heavier snow accumulations especiallyfor the southern and central valley. Areas further north across SWVirginia, the Cumberland Plateau will likely see the snow lastlonger and could receive upwards of a dusting to a half inch ofsnow. The higher terrain of the Tennessee mountains will see theheaviest accumulations where 1-3 inches of snow could fall.Confidence in forecast snow amounts are still fairly low, andbecause of this, decided against issuing any winter weatheradvisories at this time. Additional changes to the forecast are mostcertainly going to occur and later shifts may need to issue anadvisory across portions of the area."


And I’d like to know what they have seen to change their mind, especially how the euro jumped in.


.

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I think they're lowballing it for now, with that bolded caveat at the end. 

Can't remember how to look at the GEFS plumes, but SREFs for Knoxville and TRI look fairly similar. 

giphy.gif

Sorry that there are no totals on the screenshots I used, but the high end plume is around 7"

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MRX...... the NAM and Euro are together on this, they actually get better overnight and our boys lower the snow amount across most of the CWA? I feel like I read this every time there’s a chance for snow.


.

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This is the sounding that 3km NAM is showing as rain for KTYS:
49556721492_2e4bc288a3_b.jpg&key=2422b1883d94eeebc333520e6b48878f932afd953b94733086068fc959f53b9d To me, that looks like it might more likely be big old snowflakes

Maybe I’m reading this wrong but everything looks +0c. What am I missing?


.

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6 minutes ago, PowellVolz said:

Maybe I’m reading this wrong but everything looks +0c. What am I missing?

You're not missing anything, as far as I can tell. That's why I said it looks more like wet snow, than what the NAM was depicting as rain. 

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With the last system, this area got lucky with accumulations because we spent several hours below freezing before precip started. This will not be the case for this system. I predict a RN/SN mix with no accumulation for the valley south of 40, light accumulations in the grassy areas above 1500'. 

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