Posted: 10:59 am Wednesday, December 6th, 2017
By Kirk Mellish
Note this outlook was made a couple weeks ago for publication today.
There are enough differences in the sea-surface temperature patterns around the world this year compared to last year to expect a different kind of winter.
The past two winters were quite warm. This one is expected to be more normal when averaged over the 90 day period.
Waters west of Australia are cooler than normal but warmer around India, this can impact how much energy gets injected into our jet streams for the winter. Likewise, this year there is warmer than normal waters off the coast of California and Mexico, but there is cool water in the ENSO regions, especially east making for an East based La Nina. There has also been a warming of waters NW of Hawaii which can influence jet stream ridges and troughs downstream this winter in ways more favorable for some cold shots east of the Rockies.
There are all indicators for a cooler weighted La Nina compared to the average of all La Ninas.
Combine a weak La Nina with a low solar period, a moderate negative QBO, and a warm pool growing South of Alaska all indicate a boiler plate La Nina winter can’t be counted on safely at least not constantly.
When looking at northern and southern hemisphere warm and cold ocean pools the signals for winter are most consistent north of I-70 and more contradictory south of I-70.
Highlighted areas are where warmer or colder than normal sea-surface temperatures can impact the face of winter, one even makes a face:
A changeable 3-month period is expected nationally, winter volatility is greater in a weak to moderate La Nina as seen in this research from Dr. Dew Point:
Based on climate data, the coldest time of year in ATLANTA runs from November 28th to February 27th.
Among the analog years considered: 1950, 1981, 1985, 1989, 1992, 1993, 1995, 1998, 1999, 2000, 2005, 2007, 2008, 2009, 2010, 2011, 2013, 2014.
In weather and climate “analogs” ask, when patterns have looked like this in the past, what type of weather has occurred?
Using the best SST analog matches and projected indices the analog matches plus model trends here is the final winter forecast estimate:
MEAN TEMPERATURES FOR 3-MONTH AVERAGE DECEMBER-FEBRUARY 2017-18
MEAN PRECIPITATION FOR 3-MONTH AVERAGE DECEMBER-FEBRUARY 2017-18
The variability and volatility of the winter and the analogs suggest the odds of having at least some snow in Atlanta are above normal.
Most Common Winter Storm Types:
For Georgia and much of the Southeast a “Miller” storm is required for substantial snow or ice. (Named after the researcher J.E. Miller who came up with this system in 1946)
There are OTHER ways for Atlanta to get snow and ice and there are variations on Miller storms here as well. But below represents the “classic or idealized” schematic for Miller type winter storms provided by the PA NWS:
Gray= snow, Green= rain, Red= sleet/freezing rain.
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