2016-2017 Great Tennessee Valley Winter Discussion

[John1122]

If the modeling is correct on the temps, I can see the cold catching and undercutting the moisture causing the anafrontal precip. The NAM out to 84 has the freezing line getting to the Plateau with temps in the single digits in Southern Illinois and Missouri. It's 40 degrees colder in NW Tn than NE Tn at that hour.

The NAM won't show as much on freezing rain accum maps because it's rolling sleet as the precip type for now.

 

[Carvers Gap]

The 0z GFS op continues the trend of getting colder in the LR.  Tries to build a strong -EPO after d10ish.  2m temps are not continuous warmth.  GEFS says not so fast.  If one rolled the 0z Euro forward past d10, have to think that EC ridge is going to get pushed out in the LR.  Hard to discount the ensembles, but the past few operational runs certainly make things interesting.  Remember, the operationals a few days ago basically were an unrelenting torch if I remember correctly.  Huge anomalies.  If one looks at the 2m temps on the operational, not too shabby(nod to Adam Sandler).  By the time d13 rolls around on this GFS run, high latitude blocking is moving into place.  

[John1122]

06z NAM is going bonkers.

 

 

[John1122]

Some of that that is showing up as snowfall could be from sleet falling as well.  The breakdown of it by p-type shows .2-.4 of precip falling as sleet from the Plateau to Middle Tennessee down into Northern Alabama. Sleet is usually 3:1 vs 10:1 standard for snow. So some areas could see some freezing rain, 3/4ths to 1.25 inches of sleet and maybe some snow on top of that if the NAM is to be believed.  Just west of Chattanooga into NE Alabama the NAM is showing some .25+ freezing rain totals through 84 with the precip still falling. The snow/sleet line is from Knox County north at that point with probably 1-2 hours of precip to go.

 

Is the NAM out to lunch? It has some decent agreement with the Canadian and the GFS. Not sure on the Euro.

[weathertree4u]

2 hours ago, John1122 said:

Some of that that is showing up as snowfall could be from sleet falling as well.  The breakdown of it by p-type shows .2-.4 of precip falling as sleet from the Plateau to Middle Tennessee down into Northern Alabama. Sleet is usually 3:1 vs 10:1 standard for snow. So some areas could see some freezing rain, 3/4ths to 1.25 inches of sleet and maybe some snow on top of that if the NAM is to be believed.  Just west of Chattanooga into NE Alabama the NAM is showing some .25+ freezing rain totals through 84 with the precip still falling. The snow/sleet line is from Knox County north at that point with probably 1-2 hours of precip to go.

 

Is the NAM out to lunch? It has some decent agreement with the Canadian and the GFS. Not sure on the Euro.

We just need a good system! Seems like there have been so many of the past few years dominated by this SER, which in part, causes all these systems to head to the lakes. Forgive my synopsis it may not be exactly correct. I have about decided to see snow on a regular basis I need to move to the Tug Hill Plateau area of New York!

[nrgjeff]

The following lines up better with Page 10 discussion:

Totally agree torch talk is wrong in the variable pattern. So the weeklies show all warm charts? Sure as the sun comes up in the East we will still have cold fronts. I still like a generally mild pattern from Christmas through about January 10; however, blowtorch is absurd.

Been a while, like 2-3 years, but the MJO will have a big role this winter. The said EPO flip will eventually happen when the MJO convection shifts from the IO to West Pac. Timing is up in the air but I think before the first third of January elapses.

Weeklies average out things too much this pattern. Cold fronts will still pass through. I am going to assume the Euro weeklies stay mild (not hot) tonight, but that's OK. Operational models struggling with the 11-15 day tells us variability should continue. The 11-15 follies kind of reminds me of 2010-11.

[JayCee]

4 hours ago, John1122 said:

Some of that that is showing up as snowfall could be from sleet falling as well.  The breakdown of it by p-type shows .2-.4 of precip falling as sleet from the Plateau to Middle Tennessee down into Northern Alabama. Sleet is usually 3:1 vs 10:1 standard for snow. So some areas could see some freezing rain, 3/4ths to 1.25 inches of sleet and maybe some snow on top of that if the NAM is to be believed.  Just west of Chattanooga into NE Alabama the NAM is showing some .25+ freezing rain totals through 84 with the precip still falling. The snow/sleet line is from Knox County north at that point with probably 1-2 hours of precip to go.

 

Is the NAM out to lunch? It has some decent agreement with the Canadian and the GFS. Not sure on the Euro.

As always, thanks for the analysis.  It looks like things might at least be a little interesting for east TN this Sunday.  I'll be at home watching the thermometer all day. 

[PaEasternWX]

Philly is apparently going to merge with you guys. I am completely against.

[Carvers Gap]

31 minutes ago, PaEasternWX said:

Philly is apparently going to merge with you guys. I am completely against.

I think they were trolling you guys.  They went through several forums that evening.  Now, they may merge you...but highly doubtful w the TN Valley unless they are just trying to hurt AmWx.  Besides, it's not like you couldn't start your own forum on social media.  Heck, could be done pretty cheaply on GoDaddy.  Always remember, you are the customer.  This day and age, there are other options.  I like the AmWx community quite a bit...but business is business.

[jaxjagman]

IMME for Jan

 

 

 

[nrgjeff]

The above looks like cold chasing rain all month. Just kidding!

Sunday has my interest in parts of Western and Middle Tennessee. Looks like a morning wintry mix should follow overnight rain. QPF below freezing should be light. A fast moving strong front should bring a pretty quick change from rain straight to sleet, but I have some concerns about freezing rain.

GFS sounding, lol, has a fairly deep layer of cold air which would imply sleet. Two problems there. First the GFS is coarse, so that cold air might not be so thick. Second, the GFS does not pick up well on the back (3rd) ripple wave along the front Sunday. Euro and extended NAM see it better. Said wave would slow down CAA just above the surface, while shallow dense CAA goes on ahead on the ground. Yields shallower cold air and freezing rain.

Partial thickness on all 3, but esp Euro/NAM, shows quite a spread between the 1000-850 line and the 850-700 line, from which I infer some freezing rain risk. So, we have some risks for freezing rain. Again, fortunately QPF below freezing is pretty light either way. Simple pattern recognition would put it over to sleet pretty quick before ending. However the devil may be in the details. Unfortunately this may be my last post for the event if work gets crazy. Cheers!

[jaxjagman]

1 hour ago, nrgjeff said:

The above looks like cold chasing rain all month. Just kidding!

Sunday has my interest in parts of Western and Middle Tennessee. Looks like a morning wintry mix should follow overnight rain. QPF below freezing should be light. A fast moving strong front should bring a pretty quick change from rain straight to sleet, but I have some concerns about freezing rain.

GFS sounding, lol, has a fairly deep layer of cold air which would imply sleet. Two problems there. First the GFS is coarse, so that cold air might not be so thick. Second, the GFS does not pick up well on the back (3rd) ripple wave along the front Sunday. Euro and extended NAM see it better. Said wave would slow down CAA just above the surface, while shallow dense CAA goes on ahead on the ground. Yields shallower cold air and freezing rain.

Partial thickness on all 3, but esp Euro/NAM, shows quite a spread between the 1000-850 line and the 850-700 line, from which I infer some freezing rain risk. So, we have some risks for freezing rain. Again, fortunately QPF below freezing is pretty light either way. Simple pattern recognition would put it over to sleet pretty quick before ending. However the devil may be in the details. Unfortunately this may be my last post for the event if work gets crazy. Cheers!

Actually it does,doesn't it? Cutters cutting on the wrong side up the Ozarks with the heavier precip on the eastern side.Hopefully it's cutters cutting around Montgomery with colder air in place

[nrgjeff]

17 hours ago, jaxjagman said:

Actually it does,doesn't it? Cutters cutting on the wrong side up the Ozarks with the heavier precip on the eastern side. Hopefully it's cutters cutting around Montgomery with colder air in place

Actually I am half serious, taking the charts verbatim. I wish for your adjustment though. 

In other news the Euro weeklies are warm, but not torch. Looking under the hood the clusters show plenty of uncertainty weeks 3-4. Those weeks from 1/4 to 1/3 of the members show a cold pattern completely opposite the main charts. While the cold clusters are in the minority, some of them are quite cold. Temperature forecasting will remain about like day trading the stock market on days the Fed concludes a meeting. 

[jaxjagman]

 

 

Well below normal so far.Pic from Michael Ventrice

[jaxjagman]

 

rognostic Discussion for Experimental Week 3-4 Outlook 
NWS Climate Prediction Center College Park MD 
300PM EST Fri Dec 16 2016 

Week 3-4 Forecast Discussion Valid Sat Dec 31 2016-Fri Jan 13 2017 

Consensus is notably high among guidance regarding this present Week 3-4 period, while also exhibiting consistency with the Week-2 outlook. Dynamical guidance has trended more amplified than last week, featuring a dipole of 500-hPa ridging equatorward of troughing in the Pacific that projects well onto the positive phase of the North Pacific Oscillation/West Pacific Pattern (NPO). Pronounced anomalous 500-hPa ridging is also consistent among dynamical model guidance for the eastern CONUS. The forecast is made against the background La Nina state, with observed sea surface temperature (SST) and outgoing longwave radiation (OLR) patterns being largely archtypical, despite a limited footprint observed over the U.S. thus far. Given the consistent, amplified solutions among dynamical model guidance, these forecasts are primarily relied upon in this outlook. Confidence is adjusted slightly to account for the background low-frequency state, decadal trends, and a near-orthogonal solution from the constructed analog conditioned on observed 200-hPa streamfunction. 

Weakness is generally apparent in Madden-Julian Oscillation (MJO) indices that appears related to a complicated tropical pattern with multiple modes of variability. Filtered 200-hPa velocity potential anomalies suggest a signal in the MJO band near the Maritime Continent, with Kelvin wave activity in the Indian Ocean and Western Hemisphere, and low-frequency signatures over the Maritime Continent and Pacific. Nino 3.4 region SST anomalies cooled slightly over the past week, but values over the past month continue to be on the weak end of the La Nina spectrum. Given modest observed signals from intraseasonal and seasonal tropical modes of variability, limited inferences can be drawn for their roles in the Week 3-4 period. Furthermore, dynamical model guidance appears to be having difficulty in portraying high-latitude teleconnection patterns, with Arctic Oscillation forecasts exhibiting poor skill over the last several months and having several periods where observed values fell entirely outside of the ensemble spread. Nevertheless, short-term dynamical model guidance is consistent with portraying a building positive phase of the NPO over the North Pacific which appears to linger through the forecast period. 

In addition to the 500-hPa circulation forecast in the Pacific, CFS and ECMWF ensemble guidance is also consistent in forecasting pronounced anomalous ridging centered over the eastern Great Lakes during Week-3 with slight weakening the following week. The JMA solution also features anomalous ridging in the East, albeit further south over the Mid-Atlantic while also extending westward across the CONUS. The JMA solution limits anomalous troughing to the Pacific during the forecast period, while the CFS and ECMWF bring the troughing eastward towards the Rockies. Given the broad consistency of the circulation pattern, the CFS and ECMWF forecasts were favored across the west, while the JMA scenario regarding the trough placement was also considered. In general dynamical model solutions largely exhibited consistency and a continuation of Week-2 guidance enabling a smooth transition between the two forecast periods. 

The temperature outlook supports below-normal temperatures associated with anomalous 500-hPa troughing for portions of Alaska and the West, centered on the northern Great Basin and Alaska Panhandle. Above-normal temperatures associated with the persistent 500-hPa ridging are generally favored form the Great Plains eastward. Highest probabilities of above-normal temperatures are focused on the Central Appalachians, with sufficient consistency in anomaly sign and amplitude to warrant an area of 70% confidence over this region. Equal chances are generally forecast across the High Plains and Rockies, where the extent of progression of the anomalous troughing eastward and southward introduces uncertainty. 

The precipitation outlook is generally developed based on the CFS and ECMWF ensemble circulation patterns favored during Weeks 3-4, as model output precipitation has been shown to be skill-less in general. Above-median precipitation is favored from the Lower Mississippi Valley through the Ohio Valley, associated with expectations of a storm track tied to anomalous southerly flow into the anomalous 500-hPa ridging anticipated over the East. Below-median precipitation is forecast adjacent to this area across the High Plains and the Southeast. Above-median precipitation is also favored for the Alaska panhandle and into the Pacific Northwest associated with anomalous 500-hPa troughing favored in this vicinity. Potential for anomalous southerly flow across the Aleutians and southwestern mainland Alaska also introduces a chance of above-median precipitation for these areas. 

Hawaii is forecast to have marginally enhanced chances of above-normal temperatures due to expectations of anomalous southerly flow, despite SSTs generally being near climatological values. Ensemble guidance indicates an increased likelihood of below-median precipitation for Hawaii with the exception of the big island. 

 

[weathertree4u]

1 hour ago, jaxjagman said:

 

rognostic Discussion for Experimental Week 3-4 Outlook 
NWS Climate Prediction Center College Park MD 
300PM EST Fri Dec 16 2016 

Week 3-4 Forecast Discussion Valid Sat Dec 31 2016-Fri Jan 13 2017 

Consensus is notably high among guidance regarding this present Week 3-4 period, while also exhibiting consistency with the Week-2 outlook. Dynamical guidance has trended more amplified than last week, featuring a dipole of 500-hPa ridging equatorward of troughing in the Pacific that projects well onto the positive phase of the North Pacific Oscillation/West Pacific Pattern (NPO). Pronounced anomalous 500-hPa ridging is also consistent among dynamical model guidance for the eastern CONUS. The forecast is made against the background La Nina state, with observed sea surface temperature (SST) and outgoing longwave radiation (OLR) patterns being largely archtypical, despite a limited footprint observed over the U.S. thus far. Given the consistent, amplified solutions among dynamical model guidance, these forecasts are primarily relied upon in this outlook. Confidence is adjusted slightly to account for the background low-frequency state, decadal trends, and a near-orthogonal solution from the constructed analog conditioned on observed 200-hPa streamfunction. 

Weakness is generally apparent in Madden-Julian Oscillation (MJO) indices that appears related to a complicated tropical pattern with multiple modes of variability. Filtered 200-hPa velocity potential anomalies suggest a signal in the MJO band near the Maritime Continent, with Kelvin wave activity in the Indian Ocean and Western Hemisphere, and low-frequency signatures over the Maritime Continent and Pacific. Nino 3.4 region SST anomalies cooled slightly over the past week, but values over the past month continue to be on the weak end of the La Nina spectrum. Given modest observed signals from intraseasonal and seasonal tropical modes of variability, limited inferences can be drawn for their roles in the Week 3-4 period. Furthermore, dynamical model guidance appears to be having difficulty in portraying high-latitude teleconnection patterns, with Arctic Oscillation forecasts exhibiting poor skill over the last several months and having several periods where observed values fell entirely outside of the ensemble spread. Nevertheless, short-term dynamical model guidance is consistent with portraying a building positive phase of the NPO over the North Pacific which appears to linger through the forecast period. 

In addition to the 500-hPa circulation forecast in the Pacific, CFS and ECMWF ensemble guidance is also consistent in forecasting pronounced anomalous ridging centered over the eastern Great Lakes during Week-3 with slight weakening the following week. The JMA solution also features anomalous ridging in the East, albeit further south over the Mid-Atlantic while also extending westward across the CONUS. The JMA solution limits anomalous troughing to the Pacific during the forecast period, while the CFS and ECMWF bring the troughing eastward towards the Rockies. Given the broad consistency of the circulation pattern, the CFS and ECMWF forecasts were favored across the west, while the JMA scenario regarding the trough placement was also considered. In general dynamical model solutions largely exhibited consistency and a continuation of Week-2 guidance enabling a smooth transition between the two forecast periods. 

The temperature outlook supports below-normal temperatures associated with anomalous 500-hPa troughing for portions of Alaska and the West, centered on the northern Great Basin and Alaska Panhandle. Above-normal temperatures associated with the persistent 500-hPa ridging are generally favored form the Great Plains eastward. Highest probabilities of above-normal temperatures are focused on the Central Appalachians, with sufficient consistency in anomaly sign and amplitude to warrant an area of 70% confidence over this region. Equal chances are generally forecast across the High Plains and Rockies, where the extent of progression of the anomalous troughing eastward and southward introduces uncertainty. 

The precipitation outlook is generally developed based on the CFS and ECMWF ensemble circulation patterns favored during Weeks 3-4, as model output precipitation has been shown to be skill-less in general. Above-median precipitation is favored from the Lower Mississippi Valley through the Ohio Valley, associated with expectations of a storm track tied to anomalous southerly flow into the anomalous 500-hPa ridging anticipated over the East. Below-median precipitation is forecast adjacent to this area across the High Plains and the Southeast. Above-median precipitation is also favored for the Alaska panhandle and into the Pacific Northwest associated with anomalous 500-hPa troughing favored in this vicinity. Potential for anomalous southerly flow across the Aleutians and southwestern mainland Alaska also introduces a chance of above-median precipitation for these areas. 

Hawaii is forecast to have marginally enhanced chances of above-normal temperatures due to expectations of anomalous southerly flow, despite SSTs generally being near climatological values. Ensemble guidance indicates an increased likelihood of below-median precipitation for Hawaii with the exception of the big island. 

 

Translation please? I noticed the 18Z GFS was not nearly as warm

[Carvers Gap]

1 hour ago, weathertree4u said:

Translation please? I noticed the 18Z GFS was not nearly as warm

The 18z GFS is no warm-up at all.  Even the GEFS is not near as warm.  The control run of the GEM ensemble is pretty cold.  Not where we need to be w many models cosensus warm.  I would be more than satisfied to see at least once in my life....a wam pattern not verify.   

[weathertree4u]

30 minutes ago, Carvers Gap said:

The 18z GFS is no warm-up at all.  Even the GEFS is not near as warm.  The control run of the GEM ensemble is pretty cold.  Not where we need to be w many models cosensus warm.  I would be more than satisfied to see at least once in my life....a wam pattern not verify.   

here here!

[jaxjagman]

It's not a big deal RIGHT NOW.The MJO is in the Meridonal,where it goes from there is in question.The GEFS shows some signs of a Scandinavian ridge and signs by the look the PV could making some noise again towards NA,that's long range though.I'm with the rest here,it looks like a roller coaster ride right now,dont see any huge warmup

[John1122]

The picture it paints imo is terrible modeling activity. The ensemble spread is usually a big window beyond day 10 and when indices are falling outside of that range in the long range, they are performing badly. I don't trust either cold or warm forecasts right now in the long term. 

[Carvers Gap]

10 hours ago, John1122 said:

The picture it paints imo is terrible modeling activity. The ensemble spread is usually a big window beyond day 10 and when indices are falling outside of that range in the long range, they are performing badly. I don't trust either cold or warm forecasts right now in the long term. 

The 0z Euro and GFS operationals are now colder through d10.  The GFS was flat-out cold through 16 days.  Interesting to see the ensembles continue to promote a warm pattern.  Obviously, the ensembles are a different tool, but the OPs and the ensembles are out of sync.  Some runs of the OPs are even trying to develop a +PNA/-NAO pattern.  

[Carvers Gap]

Great post by Jon in the SE forum...click the title to link there.

 

[Carvers Gap]

The 12z para GFS was interesting around 192....I remain unconvinced about the strength of the modeled warm-up.  It has yet to get inside of d10 on operationals.  Now, there is no denying that the structure of high latitude blocking in the NH at some point is going to make us pay-up.  The question I have is can we steal some days from the warmth?  And, Bob Chill mentioned this in the MA and I also see the resemblance....It almost looks like the pattern is about to repeat itself.  Either way, the LR models are showing some chances on a few runs though not consistent enough to be excited.  I am optimistic about Jan and Feb. Daniel Boone, what do you say?

[ShawnEastTN]

Love the feature placement on the 18Z GFS for this storm, strong high to the north good moisture flow, could be an interesting setup as it gets closer.

[Daniel Boone]

Yeah Carver, I think you're right. That's the reason of the huge run to run op. flip flopping. The huge cold deposit that came over to our side of nh is affecting the pattern and like you said, the high lat. condition will make us pay up but, will prob. be less realized due to the cold reservoir, imo. Also of note, the models continue to poke that atlantic ridge all the way up to far eastern Canada at times. That can allow for troughiness here as some models are showing in 10 day. If it weren't for that +ao that feature could eventually pop a -nao. 

  January and February are looking better to me irt cold and snow. Weakening la nina, n. atlantic sst's look pretty favorable for -nao. ssw looking more likely again of which would prob. do away the + ao. That's what we need with the predicament n pac's sst structure, imo. Too bad that big warm blob eroded. Wqbo is prob. some problem now and may be hindering mjo. It too(Qbo) should become less influential Jan/feb. I think.

  I had been worried of a '73-74 type winter and still feel a little uneasy but, the la nina differences have me optimistic of a better outcome.

[Carvers Gap]

7 minutes ago, ShawnEastTN said:

Love the feature placement on the 18Z GFS for this storm, strong high to the north good moisture flow, could be an interesting setup as it gets closer.

If you think that looks good, take a look at the 12z para GFS for the same potential event....that high is in a great spot.  Still a long ways out there....but better than having nothing to track.

[ShawnEastTN]

9 minutes ago, Carvers Gap said:

If you think that looks good, take a look at the 12z para GFS for the same potential event....that high is in a great spot.  Still a long ways out there....but better than having nothing to track.

Para is beautiful placement.  As modeled small shifts could make quite an event.

[John1122]

3 hours ago, ShawnEastTN said:

Love the feature placement on the 18Z GFS for this storm, strong high to the north good moisture flow, could be an interesting setup as it gets closer.

That's a snow set up for here 90 percent of the time. When this event was showing up in the long long range with that same placement I said the same. But the high ended up over Eastern Montana and Wyoming and the low was way west. The GFS runs a storm from the southern Gulf almost due north towards that 1040+ HP.

[ShawnEastTN]

7 minutes ago, John1122 said:

That's a snow set up for here 90 percent of the time. When this event was showing up in the long long range with that same placement I said the same. But the high ended up over Eastern Montana and Wyoming and the low was way west. The GFS runs a storm from the southern Gulf almost due north towards that 1040+ HP.

Yeah it looks strange how it does that, you look at the path of least resistance and it seems to defy that.

[Mrwolf1972]

06 gfs shows good snow in valley on the 26th.