2010-2011 Winter weather outlook for Tennessee.

[StormNine]

  I wouldn't underestimate the threat of a Ice/Wintry Mix event or a few during the duration of the winter. Depending on where the battleground sets up, and how cold we get.  07-08 featured two potent ice-storms in Western Kentucky, that would get overshadowed by that historic one that occurred the year after.  Like 09 those storms came very close to hitting TN.  Then you had Dec 23rd-24th 1998 Ice/Sleet fest. 

  Overall this winter is not looking good for snow lovers, except for maybe a second half of Feb to March.  Which will be our best chance I think for a mostly to all snow event.

[Adam]

Im not saying the track would be too our north im saying it could be to our south. But just a little more northward.

[snowdog]

Ahh it feels good to talk winter weather....just makes me giddy thinking about those cool crisp fall mornings...I dont know if there is anything worse than August weather. 

Most of your major mets are going to point towards a warm and dry winter for us considering the La Nina.  They are probably going to be right.  But at some point it would seem we would go through a period of below normal winters seeing as how we have been in a period of generally warmer than normal winters.  I dont know, last winters cold gave me hope we may be entering a period of colder winter weather. 

[StormNine]

Our favorite snow weenie JB from our favorite weather source Hacccuuuuweather issued his winter weather forecast.  He calls for Warmer and drier than average for all of TN and the KY counties bordering TN.  With North Kentucky(Henderson to Louisville to Covington) and IL,IN, and the Northeast to be the Winter Weather battle-zone between the air-masses.

To give them some credit they did call last winter relatively well.

[tennessee storm09]

well that means one thing. everyone should get a noaa radio now if that dont. looks like there could be some chasing going on. and for some reason in the winter time with a nina the nite naders are what you have to really watch.

[Curt]

Latest CPC ENSO outlook.

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml

Official forecast for LN is slightly different depending on dynamical and statistical models:

Dynamical models- height of winter(DJF) is a declining La Nina with avg of about (- 0.9) = moderate
Statistical models- height of winter (DJF)is a declining La Nina with avg of about (-   0. 8  )= moderate

La Nina goes weak by spring.Lots of things to consider besides LN such as PDO, NAO, etc...
Some similar comparisons just based on past La Nina stregnth (not necessarily declining or inclining):

Year/ Stregnth/Snow and ice at KMEM
49-50 (0.7) (declining) Trace
50-51 (1.0) (declining) 7.9in including one of the worst ice storms to hit the area
54-55 (1.0) (declining) 0.3in
64-65 (0.8 ) (declining) 7.9in
67-68 (0.7) (increasing)23.8in
71-72 (0.7) (declining) 1.2in
74-75 (0.6) (declining) 6.0in
84-85 (0.9) (declining) 20.7in amazing winter snow totals in January
95-96 (0.7) (declining) 0.4in this was a blockbuster winter for many, not KMEM
00-01 (0.6) (declining) 2.6in very cold December with ice and snow;Jan-Mar mild
08-09 (0.8 ) (declining) 8.0 Late Feb-early March snowstorm

[snowdog]

Interesting info ctb...thanks for posting that.   

[mempho]

Didn't 1995-96 have a huge sleet storm that stayed on the roads for over a week?  I was living in N. Miss. at the time and we were out of school for like 6 days.  It was very cold after the storm...did Memphis not get much out of that?

[Curt]

Didn't 1995-96 have a huge sleet storm that stayed on the roads for over a week?  I was living in N. Miss. at the time and we were out of school for like 6 days.  It was very cold after the storm...did Memphis not get much out of that?

Memphis got zilch. the precip line made it to the state line, and dry air eroded it from moving any further north. This one was one of the most frustrating events ever. To make matters worse, it got down into the single digits with nothing on the ground. I think that storm went on to give Knoxville 8 inches.

[mempho]

Also, thanks for the write-up.  In looking at those values, I think we may be missing something.  The La Nina values do not seem to have a strong correlation to anything really.  In those 21 winters, we see:

-2 of KMEM's snowiest winters (95th percentile or greater) (and this out of only 60 years of data); so the chance of a superb winter would appear to be roughly double the normal

-10 winters greater than 5" (the mean snowfall being greater than the median snowfall, this is fairly impressive)

-7 winters less than 1"  (7/21 chance of <1" (33%) is also much higher than a random winter)

-3 of the coldest months in recent memory (January 1985, January 1996, & December 2000...may be others but this is off the top of my head)

-Yet, a propensity for mostly mild months.  Most of these winters (as alluded to) feature a winter of extremes often with a very cold 2-4 week period and the rest of the winter being quite mild.

So, there is, somewhat paradoxically, both an above average chance of a good to great winter while also an above average chance of a very poor winter.  In other words, the normal or moderate winters are the ones that appear to be much less likely, both from a snowfall and a temperature perspective.

The key seems to be "catching the sweet spot" on the transition storms between the shifts between extremes.  Once the cold pattern is established, it seems to be very dry until it is time for cessation of the cold pattern which seems to be normally a one-shot deal as the cold does not often return after it has paid its visit.


If there is anything more that we could glean from the data, I think it may come in the additional factors.

In other words, if:

La Nina= in terms of snowfall

then, perhaps, we could find something like:

La Nina+?= Lots of snow

May I suggest....





Go and look at the numbers by month here:

http://www.cpc.noaa.gov/products/precip/CWlink/pna/norm.nao.monthly.b5001.current.ascii.table

and you will find that the key to big snow in La Nina winters is the transition from a positive NAO to a negative NAO.  Also, the larger transitions (in values) correlate strongly with large snowfalls.  

Also, winters that feature the full DJF period with positive NAOs are all snowless.  

Exceptions:  Very recent....the only two were the 07-08 (that was almost entirely the March snowstorm which occurred in a transition from an NAO +0.73 in February to an almost neutral 0.08 in March) and the ...

08-09 (another late season storm but there is nothing from a climatic index perspective that suggests this should have ever happened).  



Winters that feature one or more of the months with a -NAO significantly negative (<=-.50)are all greater than 5"

Exceptions:

1954-55

1995-96...but featured large-scale significant winter storms within the mid-south

2000-01...December only siginficantly negative month but very cold.  The famed "Snow Bowl" in Shreveport, LA occurred that year when a bowl game featuring MS State was played in heavy snow.


In any case, unless you want to try to recoup all your missed snow in a late-season and last-ditch effort, you should root for a -NAO.

In almost all cases,

(La Nina) + (Significantly strong -NAO) = (Lots of snow in the region)

Normally, you will get it but, as is the case with weather, you can sometimes miss when everything else is in your favor.  Also, strongly -NAO months during La Nina periods are heavily correlated with "jackpot" snow totals.

However, if the NAO remains positive or weakly negative throughout the DJF period during a La Nina, the snow nazi says..."No snow for you."

So, while we must wait a lot longer for the NAO data to come in, at least you know what to watch for....and watch, we will.  

[Curt]

Great write up Mempho! Adding the NAO data to the mix really does shed some light on the issue. I think you said it best...

a. nina plus sig NAO= cold and winter type precip possibilities
b. nina plus pos NAO = warm with severe possbilities

Most nina's see a mix of both, especially in the northwest parts if the SE, including a good chunk of Tennessee. One could also look at east vs west based ninas and its effect on any bias. I dont have a lot to offer here other than we may see a slightly more east based than west, although all regions of the pacific are negative at this time.

Even the the best winter of my lifetime, 1985, showed some similarities to a typical Nina:

December '84 = Much above normal and dry. 10-15 days in the 70's, including mid and upper 70's. There were only 6 days that recorded temps below freezing overnight. NAO = neutral

January '85= Weather literally changed to cold almost overnight on New Years Eve. Much below normal and below normal precip. Most all of the precip was in the frozen form, including nearly 20 inches of snow at KMEM. Highest temp of the month is 54, lowest is -4. (BTW, the 54 occurred just ahead of the most significant arctic cold front of my lifetime where the temp plummeted 58 degrees over the next 36 hours!) There were 27 days with overnight lows below freezing, including 17 days with high temps below 40. NAO= sig negative

Feb '85- Transition back to less sig NAO. First part of the month was cold and snowy, last half was back to temps in the 60-70s.

March '85- back to positive NAO. There were ZERO days below freezing, thus no frozen prepcip occurred. Most days were warm and dry with temps in the 60-70s and little precip.

I dont remeber any significant severe weather episodes during this winter, even with the abnormally warm December. So winter basically occurred over a 4-5 week period in Jan and early Feb, then poof...it was over just as fast as it arrived. Overall, my guess is that winter 84-85 was about normal on temps, maybe even slightly above given December and March warmth. So one doesnt have to have a significantly below normal winter temp wise to have a good winter snow-wise. Lets face it..one or two events a winter is a good winter these days!

So bottom line...there are several factors that will play into the mix. the NAO will flucuate from time to time and we will see at least periods of negative in which winter type weather would be a possibility. We will most likely see quick changes in the weather as mentioned. I have a feeling we wil see "mini versions" of the '84-85 scenario where the transition may be quick and tumultuous. While it may be hard to repeat Jan 85, there are possibilities for all kinds of weather. We shall see!

[snowdog]

mempho, what is the graph showing?  I'm a little confused.   

[StormNine]

A good winter that was 84-85 ish was also 50-51 another Moderate La Nina.

After a record cold November, and cold December.  January and February were quite warm.  Both months were about 2 to 4 degrees above average, in contrast with a November, and December that were chilly.  The real kicker is a big time Ice Storm of 1951 occurred, along with a quick, but intense cold snap in Early Feb. 1951.  Which happened right in the middle of the warmest part of the winter.  By the link there after the cold shot happened temps. in the second half of the month were well above average.   

Even an overall blowtorch period, can provide hope if you can get a storm in one of the short cold windows.  Another example is that even Hopkinsville and Clarksville TN got two little 1 to 2 inch events in the ultimate blowtorch of Jan. 2006.

http://www.wunderground.com/history/airport/KBNA/1951/2/6/MonthlyHistory.html?req_city=NA&req_state=NA&req_statename=NA
^^ Feb. 1951^^

[John1122]

La Nina winters can be all over the place here and as has been pointed out, the NAO, which is independant of La Nina has a signifigant impact.

The NAO cooperated very well in 1995/1996 and my area had one of it's coldest and snowiest winters ever with several major snow events and temps in the minus 20 range in early Feb 1996. Most of Jan and Feb had snow on the ground here and we picked up almost 36 inches of snow that winter.

1985 also featured a fearsome bout of winter in Jan and early Feb. With the famous -24 degrees at Knoxville on Jan 21st 1985.

So the two times I can recall -20 or colder here were La Nina -NAO years.

On the other hand, the last La Nina a couple years ago had no cooperation from the NAO and was one of the worst winters of my lifetime. Of course it was part of a string of several horrible winters in a row if you like snow.

I am hoping last year started a transition, as snowy conditions seem to run in packs here. You don't often have just one snowy and cold winter, it's usually several in a row. Much like realitively mild, snowless patterns tend to run together too.

[John1122]

Looking at some data in the other thread about the 10 snowiest winters on record for parts of the state at Nashville for instance all the snowiest years from the 20th century were either La Nina or neutral. No El Nino years in the top 10.

Winters which featured the most brutal cold were La Nina. 1917-1918, 1985, 1996, all those years parts of Tennessee featured temps as low as the -20s. 

Several of those years also featured early starts to cold. 1917 had record early frosts in the East and September and October were well below average. La Nina in 1950-1951 featured a brutal cold outbreak in November an heavy snows across Tennessee. Most record lows for November in Tennessee came in 1950.

Also there was some very cold and snowy weather at times during the La Nina dominant phase from 1970-1973, I seem to recall there are a few record lows for Knoxville in January from this time frame as well.

All in all I am not ready to write this winter off due to La Nina.