Pattern Winter Discussion

[GaWx]

With the consensus showing for the SE US near normal when averaging days 1-10 (warmer more SE, cooler more NW), and warmer than normal 11-15 all despite much colder much of the country to our NW including the MW, the current projections for Dec as a whole reflect a SE ridge pattern with warmest relative to normal there vs most of the rest of the country with above normal most likely nearer to the coast and near normal further NW in the SE. I looked at Dec's with a similar pattern and found these 9 with ENSO noted:

Here's how the nine averaged for Dec.: http://www.esrl.noaa.gov/psd/tmp/climdiv/cd73.182.20.43.344.13.47.44.prcp.png

1897 (WLN), 1916 (SLN), 1919 (WEN), 1924 (WLN), 1926 (NP), 1961 (NN), 1983 (WLN), 2008 (WLN), 2013 (NN)


So, interestingly enough, an impressive 6 of these 9 (bolded) were near our current ENSO (NN/WLN). I'll concentrate on those 6. How were those 6 for the rest of winter?


Temp's:
Jan: 1898 was mild; 1925 was near normal to mild; 2009 was near normal; 1962, 1984, and 2014 were cold...so a crapshoot
Feb: 1925 and 1962 were mild; 1984, 2009, and 2014 were near normal; 1898 was cold..again a crapshoot

So, for Jan-Feb: 1925 remained mild while 1984/2014 didn't have another mild month. 1962 & 1898 were on a rollercoaster. 2009 was near normal. So, a crapshoot!

Wintry precip at ATL for these 6:

Dec: 1961 had 1" SN. No other Dec had sig wintry precip.
 
Jan: 1898 had 0.8" SN. 1962 was a great month with a 3.5" SN followed by a major ZR (yes, it was neutral negative ENSO) just 10 days later! 2014 had the memorable snowjam from 2.6" of SN. The other three had no measurable. Overall though, the 6 Jan's averaged more wintry than average with 1.15" of SN & a major ZR. Two of the three cold Jan's were well above the average of wintry precip.

Feb.: 1984 had 1.3" of SN. 2014 had a major ZR on the south and east sides (yes, during the other NN ENSO) with 2" of IP/SN though 3"+ was measured on the northside. The other 4 had no measurable though the 6 Feb.'s averaged more wintry than normal.

Mar: 2009 had a 4.2" SN. Though the other 5 had no sig wintry, the 6 averaged 0.7", which is nearly double the longterm avg.

Dec-Mar (normal SN/IP is 2"): 1897-8 had 0.8" SN (below normal). 1924-5 had 0". 1961-2 was a banner season with 4.5" of SN & a major ZR. 1983-4 had 1.3" of SN (not terrible but below normal). 2008-9 had 4.2" of SN, making it well above normal. 2013-4 was the other banner year with 4.6" of SN/IP & a major ZR. So, the two NN ENSO's were the two banner winters for ZR/IP. Coincidence? I don't know.

So, of the 6, only one was a shutout. Two had below normal SN. But three had well above normal SN/IP and 2 of those 3 also had a major ZR. The 6 averaged 2.6" of SN/IP (vs normal of 2") with 1/3 of them having a major ZR (vs 1 every 4.5 years). So, overall good enough stats to at least give ATL and much of the SE US hope.

 

[WeatherLC]

I'd be ecstatic if we could get a nice little snow starting on Christmas Eve with temps 20-25 degrees.  I just can't recall anytime in my life that it snows here that cold, or at least starts that way.  Usually we are just above freezing and the melting flakes cool it down on the surface and we see a changeover.  It really would be nice to not have to worry about temperatures for a change.

That's why I love a reinforcing high.  Funneling in that extra cold stuff, although that can lead the zmonster in too, if the second high isn't cold enough.  That was what made that 80's storm that shut down Atlanta's in town thruways so good/ bad.  It stayed super cold while a gom low was working up. Everything froze instantly at mid day.  Perfecto!! Just doesn't happen enough...down here it's always on the edge, it seems. In that space where patterns change.  What I hate is we often get the best snows in Spring, when the ground just melts it as fast as it falls.  Six, seven, eight inches onto warm ground...it's heartbreaking while being beautiful, lol.
[/quote]Remember the white Christmas of 2010?

 

[WeatherLC]

ATL over the last hundred years has averaged only 0.3" of SN/IP in Dec (0.1" 1st half and 0.2" 2nd half). That is only ~15% of its average seasonal total of ~2". Only 18 of the last 100 ATL Decembers have had measurable SN/IP. In contrast, 0.8" has fallen on average in Jan over the last 100 years with 45 of them having had measurable. In Feb, 0.4" avg/30 of them had measurable. Mar: 0.4" avg/15 of them. Note that most of this is based on the airport, which is south of town. A few of the years are based on downtown. The northside is obviously higher in freq/amts though I have no hard stats. My guess would be that the northside gets ~3"/year on avg. Regardless, this gives one the idea about Dec being relatively quiet.

Aside: Back in the late 1800's/early 1900's, Feb was a big SN/IP month with close to 1.5"/month!! Jan was near 1.4". Dec was near 0.7". (Mar was only near 0.1".). So, seasonal SN/IP was ~3.8" or about double the subsequent 100 years' rate! One reason: it was colder then on average, esp. in Feb. Also, the station was in the city, not south of town.

  Looking at history, ZR's don't pick up there too much in frequency til the last week of Dec. I will reiterate that due to us being in neutral negative ENSO that this winter's chances for a major ZR or IP are ~50%, which is about 3 times the chance for other winters. Most major ZR's there have occurred between late Dec and early Feb.

Larry, have you found any correlation with years that have had major at in the N GA area? (2001,2005,2015,etc)

 

[GaWx]

[quote author=GaWx link=topic=3.msg1144#msg1144 date=1481383059]
ATL over the last hundred years has averaged only 0.3" of SN/IP in Dec (0.1" 1st half and 0.2" 2nd half). That is only ~15% of its average seasonal total of ~2". Only 18 of the last 100 ATL Decembers have had measurable SN/IP. In contrast, 0.8" has fallen on average in Jan over the last 100 years with 45 of them having had measurable. In Feb, 0.4" avg/30 of them had measurable. Mar: 0.4" avg/15 of them. Note that most of this is based on the airport, which is south of town. A few of the years are based on downtown. The northside is obviously higher in freq/amts though I have no hard stats. My guess would be that the northside gets ~3"/year on avg. Regardless, this gives one the idea about Dec being relatively quiet.

Aside: Back in the late 1800's/early 1900's, Feb was a big SN/IP month with close to 1.5"/month!! Jan was near 1.4". Dec was near 0.7". (Mar was only near 0.1".). So, seasonal SN/IP was ~3.8" or about double the subsequent 100 years' rate! One reason: it was colder then on average, esp. in Feb. Also, the station was in the city, not south of town.

  Looking at history, ZR's don't pick up there too much in frequency til the last week of Dec. I will reiterate that due to us being in neutral negative ENSO that this winter's chances for a major ZR or IP are ~50%, which is about 3 times the chance for other winters. Most major ZR's there have occurred between late Dec and early Feb.

Larry, have you found any correlation with years that have had major at in the N GA area? (2001,2005,2015,etc)
[/quote]

Dustin,
I haven't done an analysis of major ZR well N/NE of ATL though many of these major ATL ZR's likely extended NE to Gainesville and east to Athens.

 

[WeatherLC]

Word

Welcome. Glad you are here.

 

[GaWx]

For those hoping for a cold SE US Jan., it is better that Dec. be cold than warm because there is a decent correlation between Dec temps and Jan temps.

Looking at ATL since 1950 as a proxy for the SE as a whole:

When Dec was 42 or colder (3.5 or more colder than normal), Jan was 42 or colder 10 out of 14 times.
When Dec was 40 or colder (5.5 or more colder than normal), Jan was 42 or colder 6 out of 7 times.

When Dec was 49 or warmer (3.5 or more warmer than normal), Jan was 42 or colder only 2 out of 15 times.
When Dec was 51 or warmer (5.5 or more warmer than normal), Jan was 42 or colder only 1 out of 5 times.

Well, per progs as well as actuals for 12/1-25, it looks like Atlanta will end up with near 48-49 for December. Based on winters since 1950, that means that the odds of a 42 or colder Atlanta January are low for 2017. Normal there is 43. However, low chance doesn't mean no chance and I still am hoping for a 2013-4 type of sudden change. That winter had a mild Dec (48 F, which means December of 2016 will be very close) due to dominating SE ridge but then a quite cold January including significant wintry precip as the SE ridge gave way. The longterm based odds are against this though and, therefore, I can't bet on it. But I will continue to hope for it based on the strong similarities to Dec of 2016: mild temperatures in SE due to ridge, much colder in the Midwest, strong +AO, and neutral negative ENSO.

 

[GaWx]

I don't know if the Atlanta area is going to get a ZR and/or IP out of the mess ~1/6-10 but I continue to think they have a much above average chance for one sometime this winter because we're in a neutral negative (NN) ENSO. I counted a total of 36 ATL major ZR and/or IP. It is very impressive that half of these (18) were during NN ENSO, alone, when one considers that NN have occurred only about 1 every 5 years. I counted 28 NN's. Of these 28, 16 (57%) had at least one major ZR and/or IP. In contrast regarding the other 109 winters, only 15 (14%) had at least one major ZR and/or IP. So, the % of NN winters with a major ZR and/or IP is a whopping four times as high as those for non-NN winters!

Dates of 18 ATL major ZR and/or IP during NN ENSO:

12/11-3
12/14-5
12/24-5
12/25
1/13-4
1/17-8
1/18-9
1/21
1/23
1/30
1/30-1
2/6-7
2/9-11
2/12
2/14-5
2/17-8
3/2
3/9

 

[GeorgiaGirl]

Looks like I missed out on the 12z GFS fun. Geez that's a classic southern winter storm there but its kind of in lala land.

 

[GaWx]

For those hoping for a cold SE US Jan., it is better that Dec. be cold than warm because there is a decent correlation between Dec temps and Jan temps.

Looking at ATL since 1950 as a proxy for the SE as a whole:

When Dec was 42 or colder (3.5 or more colder than normal), Jan was 42 or colder 10 out of 14 times.
When Dec was 40 or colder (5.5 or more colder than normal), Jan was 42 or colder 6 out of 7 times.

When Dec was 49 or warmer (3.5 or more warmer than normal), Jan was 42 or colder only 2 out of 15 times.
When Dec was 51 or warmer (5.5 or more warmer than normal), Jan was 42 or colder only 1 out of 5 times.

Based on the above, I think it is pretty clear that betting on a cold January right now would be going out on a limb at this stage despite some pretty strong cold that appears to be on the way for late week and into the weekend. However, that doesn't mean we should give up on that chance and even a near normal January, which would still be possible, can easily allow for a big SE wintry event. For that matter, even a warm January could allow for it.