First off thanks for reading and checking out my better late than never Winter Forecast. This will be the sixth winter forecast I have partaken in and I enjoy writing them and putting in the effort to learn more about long term forecasting. Of the six forecasts I have issued, I have considered them a success except for last year and I hope to change that this time around.
The key for me has always been to find that one special analog year which unlocks the secret to the future pattern evolution during winter. Given the weak signals in ENSO this year, it has made that almost an impossible venture. Therefore, this years forecast is based a little more on observations in the 2012 global pattern versus just analogs alone.
Global Pattern Observations
One of the main observations that can be made by looking at the summer and fall patterns is the persistent blocking and warm weather over the far north Atlantic. The remnants of this can be seen in the SST’s over this area. The latest global SST map displayed in the image section show's this well. There is a vast warm water pool in this area. Based on statistical SST research I have done in the past, this warm pool during the fall months generally bodes well for blocking in the NAO regions during winter.
Some periods of blocking has been visible in the pattern over the late summer and fall months over SE Canada and the Davis Strait. This is a little displaced to the south of a traditional Greenland block and matches up well with the SST's. This could provide some very favorable scenarios for suppressed systems as we head through winter during -AO periods.
As we turn our attention to the west, we can see the general -PDO pattern still supported by the west-east/warm-cold SST couplet configuration over the North Pacific. This lends support to a HP system over the Aleutians and a general lack of +PNA patterns. The trend has been to weaken this couplet as we have progressed through fall. The CFS2 long range forecast shows this well and the PDO numbers have been steadily increasing. However, regardless of the trend it remains likely we see a -PNA and -PDO pattern in December. This could possibly shift for the first time in several winters, however, as we head into January and February.
The QBO and winter time weather are mostly correlated to the polar vortex and the theory that the reversal of winds aloft from west to east will act to weaken the PV and favor blocking periods. Over time this has proved to be an unreliable tool alone in forecasting PV strength. It is probably better served to use this data in conjunction with ENSO and global patterns as a tool for forecasting the PV strength and AO phase. Some statistical research has correlated low sunspot activity and easterly QBO to negative AO winters. Currently I use this as just another tool to form or support analog years. Which leads us to this winter which will feature a strongly negative QBO trending upwards.
The latest MEI readings from this fall have shown El-Nino decreasing in strength to what we know have, which is a pretty much neutral ENSO environment. There is really no strong signal for El-Nino, nor does the ENSO model guidance suggest we will see any rapid return. This obviously makes forecasting winter time precipitation and temperature anomalies a little more difficult as it takes away many analog years for comparison. However, recent signals over California do show that the STJ is reacting to the Summer and early Fall Nino conditions. The Pineapple Express as it’s called is currently in full force. This STJ will be key for possible winter systems as we head later into December and 2013.
The forecast is based on a slow rise in the PDO as we go through winter, a steady neutral ENSO region, a tendency for periodic falls in the AO at some point(most likely later in winter), and comparisons to a weak but interesting analog in 67-68. This analog is admittedly weak and I am only using it on a progression basis, as I expect winter to gradually become colder from December through February, peaking sometime in Late January to early February. Thanks for reading and the forecast map is attached in the image section.