Wednesday, December 18, 2013

Analog Seasonal Outlook

As promised a few days ago, I have dug up a number of past years in which Barrow experienced both wet and warm conditions, similar to this year, with a view to creating a new analog forecast for the upcoming months.  The idea here, as with past analog studies, is to explore whether similar past years tended to produce any notable departures from normal weather in the subsequent months; if so, then we have a statistical forecast for the outcome this year.  It turns out that the Barrow analog years do provide some interesting signals for the subsequent January through March.

Using historical data since 1930, I found 10 analog years in which the March through November average conditions in Barrow were both unusually warm and wet; specifically, I required both the mean temperature and total precipitation to be in the top 22 out of 84 years.  Note that March through November 2013 was the fourth warmest and second wettest such period in Barrow's history since 1930.  The analog years are 1950, 1951, 1989, 1997, 2003, 2004, 2009, 2010, 2011, and 2012; obviously we see the long-term trend at play here, with this year being the fifth consecutive year of relatively warm, wet conditions in comparison to the long-term average.

The charts below (click to enlarge) show the number of years (out of 10) in which the subsequent monthly mean temperature and total snowfall occurred in each of the three climatological terciles (below-normal, near-normal, above-normal), based on the 1981-2010 climatology, for Barrow, Fairbanks, and Anchorage.  For example, for Barrow in January, 4 of the analog years produced below-normal temperatures (lower tercile), 2 years produced near-normal temperatures (middle tercile), and 4 years produced above-normal temperatures (upper tercile).

The most striking feature of the analogs is that 7 out of 10 years produced significantly colder than average conditions in Fairbanks in January, and only one analog year (2013) produced a notably warm January.  The probabilities also appear to be shifted away from warm in February and March, though to a lesser extent.

For Barrow and Anchorage, the analog signals are less notable, but it is worth mentioning that warmth seems favored for March in Barrow, and above-normal snowfall seems somewhat likely for Anchorage in February.  The lack of near-normal temperatures in Barrow appears to be mainly a result of the long-term trend; recent years have been unusually warm, but most of the earlier years were unusually cold, relative to the 1981-2010 normals.

It's interesting to look at the broader picture to see what large-scale patterns were characteristic of the analog years.  The maps below show the percentage of years in which the monthly mean values were above or below the 1981-2010 mean for 500 mb height, sea-level pressure, and 2 m temperature.  Note that these data are all from the NCEP/NCAR global reanalysis and the temperature values should be taken with a large pinch of salt.

First, January: the analog years tend to have upper-level ridging over the Bering Sea and high pressure over northern Alaska; this clearly favors colder conditions at the surface over interior Alaska and northwestern Canada.

The analogs show a nearly complete reversal in the pattern for February, with unusually low pressure aloft and at the surface over western Alaska.  Above-normal temperatures are slightly favored in southern Alaska and western Canada, as the highest likelihood of unusual cold is in eastern Siberia.

Finally, for March: there isn't much of a signal for the broad circulation pattern.

To sum up, the history of similar past years based solely on the conditions in Barrow this year provides a hint as to what might transpire in January through March 2014.  While the uncertainty is great, and we can't have high confidence in this kind of forecast, the analogs suggest a cold January may be in store for Fairbanks.  In 9 out of the 10 analog years, the number of days in January with a daily minimum temperature of -20 °F or lower was at or above the 1981-2010 median of 13 days.  However, the January and February weather patterns seem likely to be quite different from each other, with more unsettled conditions in February perhaps leading to a snowy month for Anchorage.


  1. Great work Richard. Do you feel that the additional atmospheric heat due to the recent dramatic reduction in sea ice near Barrow (extent and thickness) in the last 10+ years impacts the analogy analysis?

    1. Brian, Yes I'm sure it must have an impact, but I don't know how to account for it. One could restrict the analog years to only the past decade or so, i.e. throwing out earlier years because of their dissimilarity in terms of ice conditions, but then we would have few years to choose from. Perhaps another approach would be to adjust data from earlier years by the difference in normals from the modern era, so that there is no "bias" from long-term change. However, distinguishing between multi-decadal oscillations and long-term change is very difficult. I suppose the proof is in the pudding: if the simple method produces useful forecasts, then maybe we can proceed without worrying too much about it.

  2. Excellent!

    Unfortunately the CPC doesn't appear to publish WX climate for Canada. No do many of the media, including the Weather Channel. Maybe we have a mutual Treaty of Understanding not to cross our borders when it comes to weather and climate.

    This link I follow ( and the Global WX models surely do. So when the CPC forecasts a 3 month outlook of warmer than normal along Alaska's NW coast, I wonder if we'll experience cold moving west from Canada as shown for January above?


    1. Gary, I suspect the CPC is forecasting warmth in the northwest partly in response to the CFS model forecast. The latest set of runs produces the following:

      However, the previous 10 days of runs gave a cold signal:

      so obviously there is uncertainty. The maps can be accessed from here:

  3. Thank you Richard for the links above. I'd bookmarked them earlier, but they got mixed into other categories. Now they're separated into my blocks of long range forecasts.

    Whether ultimately correct or not, it's important for some of us to plan ahead for heating and inconvenience caused by extreme cold. This type of outlook helps.