2016-2017 Great Tennessee Valley Winter Discussion

[Met1985]

9 minutes ago, Carvers Gap said:

Glad you mentioned that...I have seen that as well.  Here in Kingsport, we are just too close to the Plateau.  Now, the mountain foothills communities in TN might see some measurable snow.  Decent set-up.

Yeah the best set up so far this season. We need some snow for morale and the ski resorts lol.

[Mrwolf1972]

I know its a ways off but models are still trying to call for some good possible snow 5th thru 9th and some good cold weather hope it pans out we shall see.

[Carvers Gap]

3 hours ago, Mrwolf1972 said:

I know its a ways off but models are still trying to call for some good possible snow 5th thru 9th and some good cold weather hope it pans out we shall see.

 What I am noticing is that an Arctic boundary is draped from the southwest to the northeast generally over or just southeast of our area after d10.  There is growing agreement that high latitude blocking may be in place which will slow storms down and force confluence(borrowed that term from the MA forum). Basically with this last cold spell, there was cold followed by cool wx and rain.  The spacing was poor meaning there was nothing to slow a cold air mass or storm system to wait on the other.  Now, with potential blocking forming in ten days and subsequent cold pressing into our area from the northern Rockies and Plains...one would think there will be chances. It is tough to know how long that window will last.  The morning model runs of the GFS and para and even the Euro now show multiple, potential events.  Well, the Euro shows one around d9.  It has a Nor'easter that somehow has no cold.  It could happen(no cold), but it is nice to see that feature on the model.  The EPS has now turned cold past d10.  The GEFS and EPS show a similar pattern with blocking and colder temps along with active precip.  The GEM has one foot in and one foot out of the cold pattern.  I think the Euro weeklies use the 0z run, so it will be interesting to see where they go this evening.  We have been burned once this winter with models showing extreme cold only to moderate in actuality, but that was with a HP over the Hudson Bay.  This will be a -EPO along with some potential help in the Atlantic.  JB mentioned on his video update yesterday that there is also some potential for the WPO to also go negative.  To sum it up, I think this is just a winter with wild swings, and yes, I agree there is potential on the horizon.  I have cautious but growing optimism.

[Carvers Gap]

6z GEFS meteogram.   The 0z EPS looks similar.  

[Carvers Gap]

Grabbed these images from http://www.daculaweather.com .  The MJO of Madden Juilan Oscillation is basically a measure of thunderstorm activity in the Indian Ocean and western Pacific tropics that correlates to US weather.  This is where it is modeled to go and a "key" for what the weather might be here.  Edit: My definition of the MJO is overly simplistic.  Here is a better one.  Link

[Carvers Gap]

Crazy cold just to our northwest beginning @240 on the 12z GFS.

[Carvers Gap]

The 12z GFS is much colder to the northwest compared to 6z and 0z, remarkably colder over Canada.  I would not take any placement of that air verbatim in this area.  It will be a battle back and forth.  My guess is the models will struggle to find that Arctic boundary, but blocking will do its job.  The further West from the Apps you are...the colder.  The run ends with a trough swinging East w big warmth in front and a massive -NAO centered over the Davis Straights.  Either way, here is a great look post d10.

[John1122]

If that -NAO comes to pass with that much cold lurking, parts of the Valley will have a very high shot at a big winter event within a week of it.

[tnweathernut]

20 minutes ago, John1122 said:

If that -NAO comes to pass with that much cold lurking, parts of the Valley will have a very high shot at a big winter event within a week of it.

Good posts and I agree.  If the Atlantic and Pacific look like the above map you can almost bank on a good winter event in the mid south/southeast.

[Carvers Gap]

See what you all think about the 12z Euro.  I was a bit concerned around d7 until I saw where it went around d9.  Is that a -EPO, -WPO, and weakly -NAO.  Also looks like cross polar flow.  

[Met1985]

7 minutes ago, Carvers Gap said:

See what you all think about the 12z Euro.  I was a bit concerned around d7 until I saw where it went around d9.  Is that a -EPO, -WPO, and weakly -NAO.  Also looks like cross polar flow.  

That's a lot of cold air for the conus. Unless we are just doomed there is no way that will not push through here especially if we have blocking over the top.

[Carvers Gap]

The 12z GEM looks very similar to the 12z Euro at 240.  It begins earlier than this...i.e. It is not just at d10.  I can't post my Euro maps since they are WxBell.

[Carvers Gap]

15 minutes ago, Met1985 said:

That's a lot of cold air for the conus. Unless we are just doomed there is no way that will not push through here especially if we have blocking over the top.

We almost want the cold to spread out a bit per the GEM and Euro.  Have to think that blocking will kick that /trough cold East.  I will add that the heights, while high, are lower than the last few runs near Greenland.  But one would not expect that extreme (like the other runs).  The WPO is looking negative on the GEM as well unless I am misreading it.  The cross polar flow is impressive if I am also reading that correctly.

[John1122]

There's not much in the way of a SE ridge on the Euro and the flow is coming pretty much from Siberia, across the Arctic and down into the lower 48.  It's still out there but it's looking more and more likely that we get some wintry temps and possibly wintry weather in prime time, which to me is January 5th-February 15th. 

Last year everything was hostile to us almost, Super Nino, boiling oceans,  way above average temps everywhere etc. But the NAO went mildly negative from January 8th-22nd and we had two winter storms and nearly had a 3rd in that time frame. 

 

We had a similar Arctic shot to get this cool down for December but with no blocking in the Atlantic to speak of it scooted out. Get the blocking, and sit on the edge of the cold and you get some possible action. 

[Met1985]

2 minutes ago, Carvers Gap said:

We almost want the cold to spread out a bit per the GEM and Euro.  Have to think that blocking will kick that cold East.  I will add that the heights, while high, are lower than the last few runs near Greenland.  But one would not expect that extreme (like the other runs).  The WPO is looking negative on the GEM as well unless I am misreading it.  

Yeah we don't want a direct hit from the PV. A glancing blow really. Let's get temps in the 20's and a system in the Gulf then call it prime time. 

[Met1985]

3 minutes ago, John1122 said:

There's not much in the way of a SE ridge on the Euro and the flow is coming pretty much from Siberia, across the Arctic and down into the lower 48.  It's still out there but it's looking more and more likely that we get some wintry temps and possibly wintry weather in prime time, which to me is January 5th-February 15th. 

Last year everything was hostile to us almost, Super Nino, boiling oceans,  way above average temps everywhere etc. But the NAO went mildly negative from January 8th-22nd and we had two winter storms and nearly had a 3rd in that time frame. 

 

We had a similar Arctic shot to get this cool down for December but with no blocking in the Atlantic to speak of it scooted out. Get the blocking, and sit on the edge of the cold and you get some possible action. 

Yeah I agree. Get some blocking even if transient then a overrunning system or gulf low.

[Carvers Gap]

9 minutes ago, John1122 said:

There's not much in the way of a SE ridge on the Euro and the flow is coming pretty much from Siberia, across the Arctic and down into the lower 48.  It's still out there but it's looking more and more likely that we get some wintry temps and possibly wintry weather in prime time, which to me is January 5th-February 15th. 

Last year everything was hostile to us almost, Super Nino, boiling oceans,  way above average temps everywhere etc. But the NAO went mildly negative from January 8th-22nd and we had two winter storms and nearly had a 3rd in that time frame. 

 

We had a similar Arctic shot to get this cool down for December but with no blocking in the Atlantic to speak of it scooted out. Get the blocking, and sit on the edge of the cold and you get some possible action. 

Agree on all points.  The good thing is that the transition begins during d7, not d10 anymore.  I am watching the heights over Greenland as they weaken from those massive positives during earlier runs.  That is probably an expected correction to reality as the time frame approaches.  The 12z GFS, GEM, and Euro look basically the same as the pattern really begins moving to high latitude blocking around Jan 3rd.

[John1122]

Things can work out here with several different indicies working for us/against us. We managed to do well a couple of years ago due to the -EPO/+PNA even with a +NAO/AO. 

But the -NAO can really make things pop for us. It can be elusive and often runs in long stretches of either positive or negative. At one time it was thought to have flipped to Negative in the late 1990s but I'm not sure it really did. 

If one looks at the most legendary stretch of winter here since the little ice age era, this was why.

Quote

The NAO exhibits considerable interseasonal and interannual variability, and prolonged periods (several months) of both positive and negative phases of the pattern are common. The wintertime NAO also exhibits significant multi-decadal variability (Hurrell 1995, Chelliah and Bell 2005). For example, the negative phase of the NAO dominated the circulation from the mid-1950's through the 1978/79 winter. During this approximately 24-year interval, there were four prominent periods of at least three years each in which the negative phase was dominant and the positive phase was notably absent. In fact, during the entire period the positive phase was observed in the seasonal mean only three times, and it never appeared in two consecutive years.

 

It'd be amazing to see a 3 year -NAO stretch again. But it could be a while with how long it can stay predominantly positive.

[John1122]

The Ensembles are beautiful.

 

[Carvers Gap]

14 minutes ago, John1122 said:

The Ensembles are beautiful.

The 12z GEPS, which has been very stubborn to move to the colder pattern around Jan 5, is noticeably different than 0z as it is adjusting the trough eastward.  Not there yet but significant changes at 500.  It has also incrementally lowered heights along the eastern seaboad over several runs.  

[Carvers Gap]

24 minutes ago, John1122 said:

The Ensembles are beautiful.

The 12z GEPS, which has been very stubborn to move to the colder pattern around Jan 5, is noticeably different than 0z as it is adjusting the trough eastward.  Not there yet but decent changes at 500.  It has also incrementally lowered heights along the eastern half of the US over several runs.  Here is an example.

[Carvers Gap]

Here is another look at Jan 6.  Here the difference in the model initialized on Dec 21 and Dec 26.  On Tropical Tidbits you can see trough adjust eastward for the exact same point in time.  Good trend.

[John1122]

I don't really get the temperature vs anomaly maps.  The GFS/GFES are showing -8c anomalies over my area. That's -14f below normal. My normal low is 24 degrees on the date it's showing that anomaly but it's showing a surface temp of 20-22 degrees over me at the same time. 

[Carvers Gap]

The EPS has finally over the past two days lowered 850 and 2m temps.  Look at the Christmas Eve 12z for d10-15.  Then look at 12z today.  Considerable shift.

[tnweathernut]

And now we will wait to see if the ensembles showing a weaker block are right or if that feature comes back a little more robust in future runs.  I wasn't a fan of the 12z EPS long range, but if right it might mean we fight small windows all winter, which is pretty much where most on our board were from the beginning. 

[Carvers Gap]

CMC ensembles are no longer advertising the massive warm temps that they had at 850 for days 10-15.  Big shifts on the EPS and Canadian ensembles over the past two days.  Not there yet, but significant in terms of good trends.

[Mrwolf1972]

gfs-para 12z is showing some snow the 5th and temps below 32 from 5th to 11th.

[Carvers Gap]

25 minutes ago, tnweathernut said:

And now we will wait to see if the ensembles showing a weaker block are right or if that feature comes back a little more robust in future runs.  I wasn't a fan of the 12z EPS long range, but if right it might mean we fight small windows all winter, which is pretty much where most on our board were from the beginning. 

The heights over Greenland are weaker for sure, but the extreme that was shown was unlikely.  Besides, I have really come to the point I don't believe -NAO signals anymore.  That said, the EPS has looked awful from d10-15 up until yesterday.  Since Christmas Eve, it has dropped 2m temps across the East.  The 12z 12.24.16 run was a torch d10-15.  Almost does not even look like the same model when comparing runs 48 hours ago.  Just glancing...d15 and d13 were warm @on the 12.24.14 12z run for the eastern half of the country.  On the 12z today the eastern half of the country was cold minus the GC for the same two days.  The trough on the Christmas Eve run was in the West...now it is elongated with the SER supressed for a time.  IMO, those are pretty big shifts.  (Basically comparing d13-14 on the 12z Christmas Eve run and the 12z 11-13 today.)

[tnweathernut]

1 minute ago, Carvers Gap said:

The heights over Greenland are weaker for sure, but the extreme that was shown was unlikely.  Besides, I have really come to the point I don't believe -NAO signals anymore.  That said, the EPS has looked awful from d10-15 up until yesterday.  Since Christmas Eve, it has dropped 2m temps across the East.  The 12z 12.24.16 run was a torch d10-15.  Almost does not even look like the same model when comparing runs 48 hours ago.  Just glancing...d15 and d13 were warm @on the 12.24.14 12z run for the eastern half of the country.  On the 12z today the eastern half of the country was cold minus the GC for the same time two days.  The trough on the Christmas Eve run was in the West...now it is elongated with the SER supressed for a time.  IMO, those are pretty big shifts.  (Basically comparing d13-14 on the 12z Christmas Eve run and the 12z 11-13 today.)

Yeah, don't disagree with anything you said,. Just speaking specifically to the blocking.  I have seen too many times in the last four years great blocking show at long leads only to vanish as you got closer to verification.  I guess as long as that area isn't completely hostile we could score in January, but I'd rather see the blocking remain and verify.  Would make me feel better about a potential event if it did.

[Carvers Gap]

1 minute ago, tnweathernut said:

Yeah, don't disagree with anything you said,. Just speaking specifically to the blocking.  I have seen too many times in the last four years great blocking show at long leads only to vanish as you got closer to verification.  I guess as long as that area isn't completely hostile we could score in January, but I'd rather see the blocking remain and verify.  Would make me feel better about a potential event if it did.

Definitely would like to have the EPS fully on board.  I like its trends with it and the CMC, but as you say...blocking has been fleeting all to often on LR models these past few winters.   I think we are going to have to get a -EPO and -WPO and then have a big storm in the NH shake-up the wavelengths and timing.  Confluence does look better for our area.  And yes, definitely think big swings in cold and warm for this area with the window for snow being confined to 4-7 day windows.  You know, one thing I am watching for is a big snow along the GC or SE coasts as these Nina type patterns can produce those.