Posted: 7:30 am Wednesday, December 13th, 2017
By Kirk Mellish
The next 5 days temperatures bounce back and forth between a little below normal to a little above and back again, in the 8-12 day stretch there is not much support for cold in the Index tools:
However, we should not discount the -epo as some of the models show that tanking:
Despite the fact that all the lower 48 have now had at least some snow, the far south snow is abnormal for a La Nina winter:
Record snow in our NW suburbs surpassing the Blizzard of March 93 suggests a once in a lifetime event.
There’s unusually strong agreement seen in WSI graphic between the GFS and ECMWF ensembles on pattern change heading toward Christmas, big long-wave trough West with building upper level Ridge East, the Canadian ensemble also on board:
Both showing Christmas week average temps above-normal East and below normal West. Arctic blast NW while record highs possible in the Southeast with a storm track mess in-between, very La Nina:
Analog support is there as well:
Nothing set in stone yet on the warm and rain but significant rain or thunderstorms possible in the Southeast around Christmas… give or take a couple days as indicated by CIPS Analog guidance:
La Nina winters often feature large shifts in the pattern over North America (volatility mentioned in my winter outlook blogs back in November and early Dec). Significant shifts have already occurred and more projected end of this month and next month.
But beyond that a cold snap will be possible as a Stratospheric Warming is occurring above the Arctic:
Research and experience show that can lead to the jet stream taking a dive south again with polar air into the North Central and NE states that MAY be able to bleed into parts of the South in the long-range.
So AROUND and after Christmas is the next potential pattern flip from warm back to cold.
Snowmiser and heatmiser are still doing battle for control of the heart of winter.
The Euro model show January-March averaging warmer than normal, the UKMET and JMA models agree:
Snow after snow?
Did some research and I looked at some stats going back to 1930. Some data is missing so keep that in mind. But I found 43 years with snow in December at the Atlanta airport (although many were just a trace) and of those 42 had more snow later that winter or spring.
On the other hand, those years that had the higher snow amounts in December tended NOT to have more the rest of the season.
Then again “normal” in weather for many years now has been “extremes one way or the other”.