It is worth noting that Metro Atlanta has now experienced three consecutive winters with 3 inch+ snowfalls, you have to go back to 1892 to 1895 to find the same thing!

It's also interesting that despite last year being remembered as a harsh winter, once past Feb 12 it was over and done! In fact last winter turned warmer than normal in February and March as I forecast, and Atlanta recorded its EARLIEST last freeze since 1945! Hardly a long winter, but it was bad for a good stretch. 

This winter will again be a La Nina winter, but more than La Nina will regulate the season.

According to Klause Wolter of the CDC: “The current rank of the MEI has dropped further from 16th last month to 13th this month, just a little weaker than moderate La Niña rankings. The 2010-11 portion of this La Niña event had been classified as strong (top 6 rankings since 1950) from July-August 2010 through March-April 2011, tied with 1975-76 for 2nd place in terms of strong duration, and only behind 1955-56 (15 months).

ENSO is comprised of both El Nino and La Nina and La Nada or neutral phases. El Niño/Southern Oscillation (ENSO) is the most important coupled ocean-atmosphere phenomenon to cause global climate variability on interannual time scales. Here we attempt to monitor ENSO by basing the Multivariate ENSO Index (MEI) on the six main observed variables over the tropical Pacific. These six variables are: sea-level pressure (P), zonal (U) and meridional (V) components of the surface wind, sea surface temperature (S), surface air temperature (A), and total cloudiness fraction of the sky (C).

La Nina, an episodic cooling of the tropical Pacific Ocean is expected to be significant player influencing winter weather this year La Nina events tend to favor a strong and dominant polar branch of the jet stream, and a weaker sub-tropical jet.  I expect the primary polar jet stream storm track to set up slightly north and west of where it did last year. Signals from the solar cycle, Arctic sea ice and a high altitude wind pattern called the QBO suggest more jet stream blocking than normal (-AO, NAM/-NAO) especially in the front part of winter, conducive to colder air masses as the mean trough sets up over the central and Eastern US (+PNA), but late in the winter the back end looks to have high pressure building over FL shifting the polar jet storm track more to the Northwest (-PNA) while the blocking pattern (AO/NAO) relaxes allowing for a milder than normal trend with the mean trough farther NW and SE ridging. Second year La Nina events like this one typically reach an early peak in cooling water and then the intensity of the cooling fades by the end of winter.  Second year La Ninas are almost always weaker. This is what most but not all statistical and dynamical models are projecting in the months ahead. The American CFS model for example is now projecting a strong to very strong La Nina.

La Ninas tend to have big swings in temperatures. The complication is what the NAO will do. It has been running negative for decent chunks during the last several winters. The same will probably hold this winter, as we seem to have cycled into a period with more blocking in the North Atlantic than we had in the 1990s and early part of the decade. That blocking [negative NAO] probably will give us some chances for snow even with a La Nina. But with such a strong northern stream, we may only get fringed with storms.

This hurricane season and the previous featured a similar path congregation and high numbers of storms but with lower than average land impact, so this weighs into expecting some similar behavior between last winter and this winter in the large scale patterns.

Cold SST are building South of Alaska and in the equatorial Pacific, while warm SST are building North of Alaska, on Hudson Bay, Off the New England Coast and around Greenland. These are blocking signals.

I suspect that the La Nina and its associated lower AAM Atmospheric Angular Momentum will allow periods of blocking, but with the affects of volcanic particles being less than the previous few years and the very modest uptick in sun activity it should not be as extreme as last winter. This is a key assumption and if wrong it will be another cold and snowy winter. If on the other hand the blocking is even less than anticipated and the La Nina much stronger or weaker then it will be a mild winter. Some commodity researchers and private forecasters are calling for a winter just like last year with super blocking. We won’t know until March.

Characteristics expected of winter 2011-2012:

LESS COLD AND LESS SNOW THAN LAST WINTER…Precipitation averaging near normal to below normal with temperatures averaging out near normal to slightly above-normal with a cold start and mild finish.  

Fall (October and November) temperatures near normal plus or minus a half to one degree for the 60-day period. October will swing back and forth but November may end below normal by the final week or two after being warmer than normal in the middle. Autumn rainfall expected to remain below average.

November, an autumn month, looks to have a bi-polar personality, a bit of chill at the start then milder than normal only to end below normal.

Look for an early start to winter by December as another round of early season blocking is anticipated, but a warmer than normal turn by March well before the spring equinox as blocking fades and the La Nina takes over, even as it too begins to fade in strength by March.

Cold weather less persistent than last winter, more like it comes and goes with episodes of normal in-between and maybe even brief milder than normal spells. The cold that occurs will still be noteworthy (more than a handful of analog years saw a light freeze in central Florida) but so will some of the winter season warm-ups.

Not a long winter thanks to temperatures milder than normal in March if not February, but April looks near normal to slightly cooler than normal.  The two northern jet stream branches (arctic and polar) will be the strongest and most active with the southern sub-tropical jet weak or nil. This lessens the opportunities for Gulf of Mexico lows or “Miller A” storms. This is the type that brings Georgia most of its best snowfalls. The best chance for one to form will be December and January with little chance in February or March.

If it turns out to be a colder than normal winter I would expect it will only be by about one degree below-normal for the 3-month period.  That would be less than half as cold as last winter.

Autumn severe weather season looks quiet, and winter severe weather threat looks average to below average. But severe weather next March and April looks more active (normal to above-normal) with the jet stream storm track nearby between troffing in the NW US and SE upper level ridging producing more of a late winter zonal upper-air pattern for the Southern US.

Something of a blend of the last four winter seasons, especially 2008 and 2010, as we should have a weak to moderate La Nina and episodic high latitude blocking of the jet streams.

To forecast long-range we look at the antecedent conditions and the EXPECTED conditions of the various teleconnections to then FORECAST the seasonal weather from those. But these are based on correlations to the signals and not every year will follow, or in scientific and mathematical terms there is “a nonlinearity to the climate response”, so it just tells us which way the odds are tilted.

Statistically a third or fourth consecutive cold and snowy winter is improbable in Georgia, but not impossible.

To be honest, my outlook is somewhat like what I expected last year to be like but was wrong about due to the unexpectedly deep and persistent high latitude blocking (-AO/-NAO Greenland block).

ICE ice baby: the last time we had a serious ice storm was 2005 (CAD event), yet the long term repeat period is about once every 5 years.  So at least statistically you might say we are overdue for a major ice storm. But weaker La Nina years have not produced many, so I think odds this winter are normal to below-normal for a big ice storm. But this is just an educated guesstimate. Data for ice storms is very hard to find and what can be found is often lacking detail.  At least 4 of my analog years had some kind of “ice event”, two listed as damaging. But there is no way to know definitively if any other analog years did or did not have ice.

I am expecting a weak to moderate La Nina and moderate to strong negative PDO with less persistent blocking to allow more of a RNA jet stream pattern… in the means… a trough west ridge southeast pattern. Not a mega heat ridge but enough to deflect the deepest cold air intrusions north of GA. The difference from an average –ENSO this winter being more significant blocking early in the winter, which after it relaxes allows for a more traditional La Nina pattern with the above-normal temperature anomalies becoming more prevalent in February and March. This loads the weather dice for normal or less than normal snowfall. But as I’ve pointed out in the past, climatology of Atlanta snow being so small (2 inches) it only takes A SINGLE small storm to reach or exceed “average” snow amount.

This forecast represents what I think is MOST LIKELY to occur, since there are methods and analog sets that are substantially warmer and drier as well as colder and snowier than my outlook. Any unexpected changes in the months ahead (such as major volcanic eruption, stratospheric wind change or warming, or change in ocean temperatures) will require an update and revision to my outlook.

Patterns revealed in October and November can give important clues for the coming winter. We look at moisture-temperature patterns in the US and the mean position of upper-level ridges and troughs. These can sometimes signal what’s ahead in winter. We also look at Northern Canada and Siberia-Eurasian snow cover for clues. Snowfall build up to early October in the Northern Hemisphere is much less than 2009 and last year at this time, and close to 2008 IF these vary greatly from expectations as I write this on the first weekend of October, then a future update will be needed.

I should point out that my statements on severe weather are just best guesses as I have not deeply researched the teleconnection correlations to severe weather but instead used what seemed intuitive from the expected synoptics.

There are climate models that project monthly and seasonal weather and I look at them but weigh them lightly compared to analogs.

Short term indications the third week of October point to an increase in snow cover in Eur-Asia and Canada to levels close to 2010. We also have seen since Sept 1^st quite a few closed upper level lows and deep troughs east of the Mississippi River. Now some of the ensemble progs are indicating the polar vortex will drop into SE Canada for the first time this autumn in the days ahead, and that blocking may form over Greenland in the medium range. These are both red flags for a cold winter and raise the alarm to monitor that possibility as we watch developments the rest of the fall season that could change the long-range outlook for this coming winter. As it stands as of early October:

FOR ATLANTA for the period December-February…

TEMPERATURE AVERAGE plus or minus .50F (half degree)

PRECIPITATION AVERAGE plus or minus 1” (one inch)

SNOWFALL ESTIMATE 1.2 inches or less (normal is 2)

How does this compare to last winter? Last Dec.-Feb at the airport averaged -2.4F and precipitation was -1.4 inches. Snowfall was +5.2

December was -7F and -2.28 inches. January was -3.1F and -1.57 inches. February was +2.9F and -.42 inches of precipitation.

Dec snow 1.4 inches, Jan snow 4.4 inches, February snow 1.4 inches.  Total 7.2 inches of snow.

Georgia has never before in recorded history had a strong La Nina winter that was colder than normal. Truly a "black swan event".  As I've written previously, the reason for the abnormal cold was the record negative NAO/AO. Speculation on what caused the extreme blocking of the -AO/NAO centers on the 11-year sunspot cycle and the long term low solar minimum, combined with stratospheric aerosols over the northern hemisphere from high latitude volcanic eruptions in Siberia and Alaska over the past 3-4 years.

The total winter analog list for winter 2011-2012: 1880, 1893, 1904, 1917, 1933, 1944, 1950, 1954,1955, 1956, 1961, 1962, 1963, 1964,1967,1969, 1970,1971, 1972, 1974, 1984, 1985, 1989, 1991, 1995, 1996, 1998,1999, 2000, 2003, 2006,2007, 2008, 2010. Maps constructed using weighted best-fit years.