Winter Forecast 2010-2011

National Weather Service Winter 2010-2011 Outlook

For Southwest Lower Michigan

By William Marino
Forecast Overview

The official National Weather Service forecast for December 2010 through February of 2011 for Southwest Lower Michigan from the Climate Prediction Center (CPC) calls for an equal chance (EC) for above, below, or near normal temperatures (Fig. 1). There is a greater chance for above normal precipitation (Fig. 2) and snowfall. 

 

Forecast Reasoning

 

The forecast for this winter is primarily based on the interaction of the El Niño / Southern Oscillation (ENSO) with the polar jet stream, whose dominant position affects the weather patterns over Southwest Lower Michigan. Beside the ENSO factor, the persistence of seasonal trends is strongly considered in these forecasts as were dynamical models and soil moisture anomalies. Higher frequency oscillations like the North Atlantic Oscillation (NAO), the Arctic Oscillation (AO) and the Pacific North American Oscillation (PNA) are significant players in the Southwest Michigan winter weather pattern, but they are difficult to forecast several seasons in advance so are not considered in this forecast.

 
Normals

Normal temperatures are calculated averages from the 30-year period of record from 1971 to 2000. Table 1 lists normal values of temperature and precipitation for the winter months of December, January and February for the primary climate stations at Grand Rapids, Lansing, and Muskegon. Lake Michigan has a significant effect on the local climate. Muskegon, being closest to the lake, has the mildest temperatures and the greatest snowfall amount and frequencies of occurrence. Lansing is the farthest from Lake Michigan and is colder and drier (Table 1).

 

Temperature
             

The most significant factor in forecasting the winter temperature for Southwest Lower Michigan for this winter is the state of ENSO. By mid October, moderate to strong La Niña  conditions prevailed across the tropical Pacific Ocean with sea surface temperature anomalies as much as 2.5 degrees Celsius below normal.  La Niña is expected to continue to strengthen into late fall and then persist through the northern hemisphere winter of 2010-11 (Fig. 3). This box and whiskers forecast in Fig. 3 shows various model forecasts for the future state of La Niña. The impact of La Niña on the climate over Southwest Lower Michigan is expected to be greatest during the winter season.  

There are only six recorded winters with a strong La Niña since 1949 (1949-50, 1954-55, 1964-65, 1970-71, 1973-74, 1988-89, and 2010-2011).  It should be noted that except for the 1949-50 winter, all the other strong La Niña cases were preceded by a moderate or strong El Niño the previous winter.

 

             

             The latest forecast from the various forecast models for the state of ENSO this winter all show the sea surface temperature anomaly for Niño 3.4 (the primary monitoring area for the strength of ENSO) remaining below -1.5 degrees Celsius during the winter of 2010-2011, meaning a strong La Niña is expected to continue (Fig. 3).   

During a typical La Niña winter, colder than normal temperatures prevail across the Northern Plains and western United States (Fig. 4). Over the southern United States, a La Niña winter typically results in warmer than normal temperatures. As for Southwest Lower Michigan, temperatures average near normal. While not shown here, the stronger the La Niña, the farther north and west is the boundary between the colder than normal winter and the warmer than normal winter.

Our next tool to consider is the trend tool (Fig. 5). This shows that over most of the country, the trend over the past 10 years is for warmer than normal winter temperatures. Looking at all winters when there was a moderate or strong El Niño the previous winter (7 winters) then a moderate or strong La Niña the next winter, using composite analysis the result comes very close to classic La Niña winter result (Fig. 5). 

           This trend is shown strongly by looking at the mean winter temperatures for southwest Lower Michigan using our 36 long term climate stations from the winter of 1949-50 to 2009-2010 (Fig. 6). Here, using the 10 year running mean temperature, the winters in Southwest Lower Michigan have been warmer than normal since 1988-89. In the 22 winters since then, 10 winters have been warmer than normal, while only 4 have been colder than normal.  So, in the past 5 years we have had only two cold seasons, the winter of 2008-2009 and the summer of 2009. All of this would seem to point to a warmer than normal winter for 2010-2011.

 

 

 

 

Most climate tools are evenly divided between warmer than normal and colder than normal for Southwest Lower Michigan, even in the individual months.  As seen in the case of Muskegon, the near normal case seems to have the greatest frequency. The Coupled Model (not shown) is the only tool forecasting a colder than normal winter for Southwest Lower Michigan this winter, but it has known cold biases. The case for warmer than normal winter has stronger support than does the case for a colder than normal winter since the trend has been toward warmer winters over the past 10 years. Over the past five years, less than 10% of all our seasons have been colder than normal while 76% have been warmer than normal.  In fact, since October 2009, there have been no colder than normal months in Southwest Michigan.  Also supporting warmer than normal is the composite map that looks only at strong La Niña events (not shown).

However, there are too few of those to build a strong case for that outcome. That leaves us with the remainder of the tools, like the El Niño to La Niña composites and all 20 past La Niña composites, which both show an equal chance for above normal, near normal or below normal. It is that forecast which we will then go with. The monthly graphs show some suggestion of a colder than normal December away from the Lake Michigan shore, with a warmer than normal January followed by a colder than normal February (not shown). There are enough indicators to warrant an EC forecast for temperature.  As a result of all these factors and trends, the forecast for Southwest Michigan this winter is for an equal chance for above, near or below normal temperatures.

 
 
Precipitation
 

The classic CPC precipitation anomaly composite map for La Niña winters shows above normal precipitation over the southern Great Lakes (Fig. 7). Aside from this, our climate station data (Fig. 8) shows a trend toward wetter winters during the past 15 years. During the past 15 years, there were 7 winters that were wetter than normal, 3 winters with below normal precipitation and 5 were near normal. The official CPC trend for winter over the southern Great Lakes confirms the trend toward wetter winters over Southwest Lower Michigan (Fig. 9). As it turns out for all moderate or strong La Niña winters (of which there were 12), half of them were wetter than normal, with only 25% drier than normal and 25% near normal. Clearly, the frequency of wet winters is double that of a dry winter for moderate or strong La Niñas.

 

Precipitation over the past fifteen years compared to the 1971 to 2000 normal period shows a trend toward wetter winters. Again, this can be seen in Fig. 8 which shows the winter precipitation departure from normal for the 36 long term climate stations from 1949-1950 through 2009-2010.  Note the frequency of dry winters from 1975-1976 through 1994-1995 was much greater than was the frequency of wet winters. Dry winters dominated from the mid 1970s through the mid 1990s, and then wet winters have dominated since then.

 

The station data for the individual climate sites (Grand Rapids, Lansing, and Muskegon) for each month (not shown) show a large preference for near normal precipitation in December, then above normal precipitation in January and February. January seems to have the lowest frequency for below normal precipitation at all three sites. This idea of a wet January and February are supported by the overall La Niña signal and our composted maps for January and February (not shown).

 

            Putting this all together, a strong argument could be made for a wetter than normal winter. The strongest argument for that is the recent lack of dry winters in Southwest Michigan over the past 15 years. The primary storm track will be through the Ohio Valley, which is typical for La Niña winters; thus, the wetter than normal outcome is most likely. Therefore, we are going with a wetter than normal forecast, suggesting January as the wettest month.

 
 
Snowfall
 

Snowfall will likely start out the season below normal.  This is suggested by the CPC composite for DJF (Fig. 10).  However, looking at the FMA snowfall composite, note the snowfall is well above normal (Fig. 11).  What this suggests is snowfall is expected to be below normal early in the winter, then at some point between mid December and mid January the tide will turn toward a more persistent pattern featuring more snow. This will be the result of a change in the primary wave pattern.  The upper level wave pattern will change, being more conducive to above normal snowfall. Once set up, the pattern will be rather persistent into March.

 

For Southwest Lower Michigan, there is a below normal snowfall anomaly by the lake shore for the DJF period (Fig. 10).  The map adjacently on the right shows an above average frequency for that anomaly. For all of our analog years at all three of our primary climate sites, December snowfall was below normal. This increases our confidence that the total snowfall along the Lake Michigan shore will be below normal for the DJF time frame.

 

We are expecting most of our snowfall to occur in the January to March time frame as opposed to early snowstorms and lake effect snows. Of course, that is not to say we won’t see any measurable snow before the end of 2010! But, a later start to winter is likely. Overall, above normal snowfall is expected for Southwest Lower Michigan given a more impactful storm system track and the historical trends that show above normal snowfall in general occurs more frequently in La Niña winters for Southwest Lower Michigan.     

 

 

Summary

When all of these influences are considered together for Southwest Lower Michigan, there is an equal chance (EC) for above, below, or near normal temperatures for the winter of 2010-2011. Temperatures will likely start out in December with large fluctuations between above and below normal. There is likely to be an extended warm period in late December into mid January, then it will largely be colder than normal the rest of the winter into the early spring.  There is an increased chance for above normal precipitation and snowfall. However, most of the snow will likely be during the 2011 part of the season.

USEFUL WEB LINKS ON LONG RANGE FORECASTING:
 

Three month downscaled outlooks for selected cities in Southwest Lower Michigan:

http://www.weather.gov/climate/calendar_outlook.php?wfo=grr
 
 

The Climate Prediction Center’s (CPC’s) forecast:

http://www.cpc.ncep.noaa.gov/products/predictions/90day/
 
 

Additional information about past and current climate conditions:

http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing/
 
 
Other CPC forecasts:
http://www.cpc.ncep.noaa.gov/products/predictions/
 
 
CPC’s ENSO page:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/
 
 
Additional ENSO information:
http://www.pmel.noaa.gov/tao/elnino/nino-home.html
 
 
Information on the PDO:
http://www.wrh.noaa.gov/fgz/science/pdo.php
 
 
Information on the AMO:
http://www.aoml.noaa.gov/phod/amo_faq.php
 
 

Persistent Patterns that Shape Weather and Climate Variability- a glossary for them:

http://www2.ucar.edu/news/backgrounders/arctic-oscillation-pineapple-express-weather-maker-glossary

 

 



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