We had below normal temperatures in October and November, then above-normal December into the start of January.
So far we have seen a lack of response from the atmosphere in the U.S. to large-scale drivers such as the El Nino, Madden Julian Oscillation (MJO) and Sudden Stratospheric Warming (SSW) above the North Pole. Put another way the earth system has not yet coupled together.
It is a fallacy that all SSW events automatically disrupt the Polar Vortex and bring it toward North America, it can and does but sometimes the PV is directed away from the U.S. even though a split occurs. Also the SSW and Polar Vortex are in the stratosphere, weather occurs in the troposphere. The feedback from one to the other often takes many weeks to unfold.
Most cold waves occur WITHOUT the involvement of the PV or a SSW event.
STRAT WARM EVENT HAS NOW OCCURRED PV DISRUPTION:
To simplify things the warm air above the North Pole near outer space has to work down to near the surface to displace the arctic air and force it to other regions.
Meanwhile the MJO keeps getting stuck in warmer phases despite models showing it moving into colder ones in their long-range projections.
GFS ENSEMBLE MJO PROJECTION:
The reason may be that the Modoki El Nino is barely a Modoki and the El Nino in general has been not far from neutral and is showing signs of weakening.
Regardless of the Modoki Index, there is basin-wide anomalous warmth in most of the Pacific Ocean.
In addition thanks to the global ocean warmth of the climate there is a lack of temperature gradient north of the El Nino Pacific zones reflected in the Southern Oscillation Index (SOI) suggesting the jet stream has not yet coupled to the oceans or vice versa if you prefer.
WIDESPREAD WARMTH IN THE PACIFIC OCEAN:
Thus we have not seen the weather response normally associated with the large-scale drivers. It has been more like a La Nina base state in the Northern Hemisphere with more of a strong zonal jet stream with embedded transient troughs and closed upper level lows.
The nearly complete circuit of the jet around the globe is both rare and weird. Hence the reason the winter forecast analogs may fail this year.
But it’s worth noting an “early winter” was not the forecast made back in October, so if the back end pattern changes we’ll still be in business, only time will tell.
The models are trending in that direction, but it’s worth noting that they have been flip-flopping for a month now like a fish out of water:
They are suggesting a return to a positive Pacific North America (+PNA) pattern which is supportive of the transport of colder air from North to South by the jet stream so a change is expected going forward the rest of this month and February in one step forward and one step back fashion.
SOME models are even suggesting a snow threat for the Mountains of Tennessee and adjacent states next weekend.
The bottom line is I have not canceled winter (not that it’s up to me) and with a chill in the short term following the unseasonably warm spell, the pattern change is still expected to come before the end of the month and into February. And the split-flow pattern is also expected with the active Sub-tropical jet stream providing moisture and storm track.
The halfway point of the snow season since 1981 for the lower 48 is January 19th, half of snow falls before that date and half after that date. See map below for your area:
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