2016-2017 Great Tennessee Valley Winter Discussion

[Mrwolf1972]

00z gfs para showing it to

[ShawnEastTN]

3 hours ago, Mrwolf1972 said:

00z gfs para showing it to

The Para is a dream track for the low, though would like to see the low a tad lower pressure, but beautiful.  Maybe we get a late christmas night, boxing day treat.

[John1122]

You never want to see lower pressure unless it's way south. Weak lows = big snows. Stronger lows pump up warm air and cause mixing issues.

[ShawnEastTN]

25 minutes ago, John1122 said:

You never want to see lower pressure unless it's way south. Weak lows = big snows. Stronger lows pump up warm air and cause mixing issues.

True, though I guess I like to see a weaker low while its to the south of us to limit WAA but as its rounding the bend up through the carolina's for it to strengthen.  I always look back at that 990's mbar low cranking up through the Carolina's during the Blizzard of 93 as my standard barer.

[Mrwolf1972]

12z gfs makes it to warm for snow the 26th takes the low to ohio hope it will change back in the models to come.

[Daniel Boone]

5 hours ago, John1122 said:

You never want to see lower pressure unless it's way south. Weak lows = big snows. Stronger lows pump up warm air and cause mixing issues.

Good point John. More times than not that's the case especially in the great valley. Also, strong lows produce more wind therefore, increasing downsloping for the valley. Many of this areas big snows came by way of either weak lows or over running events. Those exceptions with the big lows such as '93 were because of the strong arctic air mass coming down ahead and behind it. The valley did see downsloping effects as totals were much lower in it than what would have been with the amount of moisture the storm carried. i.e.,London , Ky on the back edge of the storm received over 20" while TRI and KNOX. received 14" further into the storm.

   I've always said if it weren't for the Cumberlands to our west and the app spine to our east(Smokies in particular) we'd get more snow alot of the time.

[Carvers Gap]

Past d10, virtually every ensemble is warm.  Interestingly, the OPs and controls do not necessarily agree.  But post d10, it is usually wise to go with the ensembles, and those ensembles portray a 500mb pattern that is not conducive to snow or BN temps.   The MJO is not favorable after d10.  The EP, WPO, NAO, PNA and AO all point to warmer weather which will be debatable to the degree it shows.  Those some ensembles and teleconnections pointed to extreme cold.  They were right about that, but were wrong in how far south the cold could hold.  I still cannot tell if this is a new pattern or a reloading of the same pattern that originated in Nov. Mostly, this is weak Nina climo.  Strong cold fronts.  Bouts with the SER. Extremes.  If this is '89, we are out of luck.  Admittedly, it has some striking similarities with the extreme cold for Dec. However, the weeklies have generally suggested a return of winter after wk 2 in January.  I have no idea if this is true.  I am going to roll with climo that generally suggests chances for snow with normal temps(basically an average of two extremes).   New pattern or not, weak Ninas are generally a good thing for the forum area.  Hey, we're BN at TRI so far for Dec.  But it has been my experience that snow prior to Dec 20th is not the norm unless we find a -NAO.   So, if one were not to look at LR models one would say that winter is off to a good start.  When those models are factored in, then I get concerned that we are going to lose the first half of Jan which is normally prime for snow chances.  So, making an assumption that post-d10 is correct...we have at least 2-4 week break from the cold.  So, for me I am now watching to see if the cold can steal some of those days, and if it will snow during the warm-ish pattern.  The one bonus on all models is that the GOM is open for business with of rain which was so badly needed.  If somehow one of those LPs can be supressed(and not cut) the precip pattern is there with plentiful cold in the northern Rockies.  I do have doubts about the accuracy of the LR models and ensembles.  I think the cold is causing them problems.  We will learn some good lessons during the next few weeks.  The JAMSTEC has flipped cold for the season and the weeklies do point to cold around mid-Jan.  

[1234snow]

Some volatile swings today on the GFS with regards to the Christmas storm. 6z run this morning gave the valley a nice little snow. Fast forward to the 0z run tonight and the low is tracking thru Minnesota giving them a blizzard. I don't remember this many wild swings in the medium range from the GFS.

[1234snow]

Some volatile swings today on the GFS with regards to the Christmas storm. 6z run this morning gave the valley a nice little snow. Fast forward to the 0z run tonight and the low is tracking thru Minnesota giving them a blizzard. I don't remember this many wild swings in the medium range from the GFS.

[nrgjeff]

Christmas we have a better chance of severe weather than snow this year, but it is still 7 days out.

AO is super positive at the moment. Usually a +AO in late December is a mild signal for January. However I do not believe a sustained super warm pattern will develop.

Right at the New Year all ensembles have the +AO fading as the PV gets disorganized again. Even now a stubborn ridge is noted over Scandinavia. While it should fade, theme of the PV not completely buttoned up should continue.

After 2-3 mild weeks I favor a return to this forecasting regime. Cold variable weather pattern may feature sharp cold fronts with mild breaks in the cold. Worst cold may still dive into the Plains and Midwest, oozing south and east. 

Could mean continued shots at severe, but I would think less so during January. As some have noted, snow season really starts after Christmas. An active pattern with lots of baroclinicity can't be bad in January.

[Carvers Gap]

Great video by DT.  It is a great breakdown of the pattern for those learning and for those who have been following wx for many years.  Explains where we are and where we are heading.  

 

[Carvers Gap]

22 minutes ago, nrgjeff said:

Christmas we have a better chance of severe weather than snow this year, but it is still 7 days out.

AO is super positive at the moment. Usually a +AO in late December is a mild signal for January. However I do not believe a sustained super warm pattern will develop.

Right at the New Year all ensembles have the +AO fading as the PV gets disorganized again. Even now a stubborn ridge is noted over Scandinavia. While it should fade, theme of the PV not completely buttoned up should continue.

After 2-3 mild weeks I favor a return to this forecasting regime. Cold variable weather pattern may feature sharp cold fronts with mild breaks in the cold. Worst cold may still dive into the Plains and Midwest, oozing south and east. 

Could mean continued shots at severe, but I would think less so during January. As some have noted, snow season really starts after Christmas. An active pattern with lots of baroclinicity can't be bad in January.

Thanks, Jeff.  Great commentary as usual.  Excellent info.

[tnweathernut]

I agree, Jeff.  Thank you for taking the time to share your thoughts!

[tnweathernut]

Well, at least at the end of the recent GFS runs we are modeled to change our severely positive NAO to a severely negative NAO.  I'm not sure the NAO can actually find its negative state much anymore though.  haha

[John1122]

Granted it's nearly impossible to trust them beyond day 5, but the overall pattern looks like it might be transient. Warm will have about 7 or 8 days and below normal will have 7 or 8 days in the next 16 days per the gfes. It tries to build a bridge from Scandinavia across the pole towards Alaska. It also has some height rises in the NAO region. Pacific never quite gets on board on the run though.  

[John1122]

Actually just looked at the 18z.  Looks like the PV gets dropped to the Hudson Bay and a big ridge dominates the West after day 10. 

[JayCee]

24 minutes ago, John1122 said:

Actually just looked at the 18z.  Looks like the PV gets dropped to the Hudson Bay and a big ridge dominates the West after day 10. 

Reminiscent of January 1994

[John1122]

2 hours ago, JayCee said:

Reminiscent of January 1994

I haven't looked at the 500mb maps for then but I know that January was fierce winter during the Olympics. -10s and plenty of snow on the ground.

[jaxjagman]

The Big Ice Storm Feb 1994

[Carvers Gap]

50 minutes ago, John1122 said:

I haven't looked at the 500mb maps for then but I know that January was fierce winter during the Olympics. -10s and plenty of snow on the ground.

I finally remember that winter.  We did miss a ton of chances in Knoxville.  But man, the interstate was one lane for like three days because it wouldn't melt.  I was a senior at UT.  Just brutal cold.   We had snow which turned to an ice storm and froze on top of the snow.  (Seems like one of those winters near that time frame featured afternoon thunderstorms as snow squalls with lightning.) We had water running into our apartment  on Papermill, because it was backing-up under the shingles.   If the cold were ever to lock w the GOM open...some nice analogs show.  Right now, the transient nature of the trough/ridge makes it tough to really bank on anything cold or warm.

[John1122]

5 minutes ago, Carvers Gap said:

I finally remember that winter.  We did miss a ton of chances in Knoxville.  But man, the interstate was one lane for like three days because it wouldn't melt.  I was a senior at UT.  Just brutal cold.   We had snow which turned to an ice storm and froze on top of the snow.  (Seems like one of those winters near that time frame featured afternoon thunderstorms as snow squalls with lightning.) We had water running into our apartment  on Papermill, because it was backing-up under the shingles.   If the cold were ever to lock w the GOM open...some nice analogs show.  Right now, the transient nature of the trough/ridge makes it tough to really bank on anything cold or warm.

That was actually thunderstorms that turned to freezing rain in Knox and ended with a couple inches of snow on top of it. I can remember watching WATE live coverage of the freezing rain in the Central Valley. We had heavy snow and less freezing rain but the winds were powerful. Temp dropped into the single digits that afternoon behind the system. I lost power and my water line froze as well. It didn't get above 20 for a week with lows in -10s a couple mornings with two days of lower 10s for highs. 

[John1122]

00z was transient again, not real locked in warmth or cold. Seems basically a continuation of the pattern we've been in, warm up, Lakes cutter, cold. Not the best for winter weather but at least not a locked in heat wave like we had from December 1st til mid to January last year.

[JayCee]

11 hours ago, John1122 said:

That was actually thunderstorms that turned to freezing rain in Knox and ended with a couple inches of snow on top of it. I can remember watching WATE live coverage of the freezing rain in the Central Valley. We had heavy snow and less freezing rain but the winds were powerful. Temp dropped into the single digits that afternoon behind the system. I lost power and my water line froze as well. It didn't get above 20 for a week with lows in -10s a couple mornings with two days of lower 10s for highs. 

I lived in London, KY at the time, and we were buried in snow during that storm from the TN-KY border north through Lexington, KY, and westward to Bowling Green.  Most, if not all, interstate highways were shut down because they could not be cleared due to the extreme cold.  The salt & brine simply wouldn't work.  I believe London set a new record low around -24.  I also remember California was basking in warmth under a strong ridge at the same time.  The only reason I remember that is because of the Northridge earthquake--January 17, 1994.  I was watching coverage of the quake while having a snowstorm. 

[Carvers Gap]

These types of occurances seems to really shake-up wx patterns.  

 

[Carvers Gap]

11 hours ago, John1122 said:

That was actually thunderstorms that turned to freezing rain in Knox and ended with a couple inches of snow on top of it. I can remember watching WATE live coverage of the freezing rain in the Central Valley. We had heavy snow and less freezing rain but the winds were powerful. Temp dropped into the single digits that afternoon behind the system. I lost power and my water line froze as well. It didn't get above 20 for a week with lows in -10s a couple mornings with two days of lower 10s for highs. 

The lightning squalls were a different event.  I got caught on the interstate near Cherry St. One of those squalls passed through and the interstate was white in less than sixty seconds.  They were afternoon storms with snow.  The snow left pretty quickly.

Now, the ice/snow event was a total mess.  Fortunately, I did not get caught on the interstate.  I remember trying to get to class that week. Was awful.  After several meh winters(not counting the blizzard, it was a shock to commute for days in that.  We had water pooling in our apartment attic because the snow and ice would not let melting water run-off.  I went to free my car from the ice.  The ice on the windshield cracked...I thought I had broken my windshield.  Thankfully, it was just the ice shattering,. 

[nrgjeff]

Glad you posted the picture! Yes the AO is exceptionally positive today, but I think the picture tells more than the index does. Low pressure bomb east of Greenland has spiked the AO, just a measure of pressure difference between the latitudes. Low press northeast of Siberia is also contributing to the index.

However right at the North Pole, temperatures are 50 degrees warmer than normal! That is not a typo. Actually wide swings can and do happen up there in winter due to low pressure bombs over the oceans. We can discuss the current sea ice and implications in the Climate Forum, but here we will just worry about the rest of this winter. 

While a +AO correlates with a mild start to January, it may not be so this year. Picture tells me the cold air is not bottled up at the pole. Way upstairs the stratospheric PV is tight right now, but may not remain so buttoned up in January. Then in between, the 500 mb pattern gets choppy in January with more high latitude ridging.

After a Florida like Christmas, a couple cold fronts are forecast New Year's weekend. However I'm not sure that is the change back to a colder pattern. Maybe give it until January 10-15? Hard to guess timing this far out, but we still have plenty of winter ahead of us.

[tnweathernut]

1 minute ago, nrgjeff said:

Glad you posted the picture! Yes the AO is exceptionally positive today, but I think the picture tells more than the index does. Low press bomb east of Greenland has spiked the AO, just a measure of pressure difference between the latitudes. Low press northeast of Siberia is also contributing to the index.

However right at the North Pole, temperatures are 50 degrees warmer than normal! That is not a typo. Actually wide swings can and do happen up there in winter due to low pressure bombs over the oceans. We can discuss the current sea ice and implications in the Climate Forum, but here we will just worry about the rest of this winter. 

While a +AO correlates with a mild start to January, it may not be so this year. Picture tells me the cold air is not bottled up at the pole. Way upstairs the stratospheric PV is tight right now, but may not remain so buttoned up in January. Then in between, the 500 mb pattern gets choppy in January with more high latitude ridging.

After a Florida like Christmas, a couple cold fronts are forecast New Year's weekend. However I'm not sure that is the change back to a colder pattern. Maybe give it until January 10-15? Hard to guess timing this far out, but we still have plenty of winter ahead of us.

I have been looking at the strat maps and noticed while it remains fairly tight you can notice an occasional elongation in the various 10 day forecasts (gefs and euro).  

Nothing appears to be locked and much is changing. Combine this with a continued sinking of the jet as we head deeper into winter, along with a shortening of the wavelengths, it's probably just a matter of time before we have an opportunity, even in a pattern that features some nagging hostility.  

In short, it just becomes a little (key word little, this is the mid-south) easier to snow in the mid and late winter period...

[PowellVolz]

I don't post much on here but thought I'd share that this morning in the Nortwest area of Knoxville the fog condensed and it started snowing. You could see the blue skies but had moderate, very fine snow. It coated the roads.


Sent from my iPhone using Tapatalk

[JayCee]

Thanks for posting!  We had some very heavy fog, and the ground was white with frost...but it didn't coat the roads.

[Knoxville Horn]

Long time lurker; first time poster.

What pic of NW Knox is crazy.  I live and teach near downtown and didn't even think that was in the realm of possibilities.  Just heard about possibly freezing fog.

Here's to much more of that stuff in January.