The National Oceanic and Atmospheric Administration (NOAA), the parent organization of the National Weather Service (NWS), has released its official 2009-2010 Winter Outlook. (Steve at wxtalk.wordpress.com recently posted about the winter forecast in NOAA Releases Official Winter Outlook.)
Precipitation Forecast
NOAA winter outlook--precipitation
Temperature Forecast
NOAA winter forecast--temperatures
El Nino
The main factor cited in the forecast is the presence of an El Nino–although the release makes reference to other climate factors that cannot be predicted more than a couple of weeks in advance, which will allow for some variability of the season.
Where Is the Snow Forecast?
The NOAA outlook does not include what is, arguably, the most important part of the winter forecast–the amount of snowfall. The West depends on winter snowfall for summer water. In addition, snow is a major factor country-wide in the winter, ranging from skiing to the cost of snow removal to the cost of lost days of production and school.
A forecast of higher precipitation than normal is not the same as a forecast of more snow than normal since it depends on whether the precipitation falls when it’s cold enough for snow; similarly, a pattern with less precipitation than normal can have more snowfall than normal if most of the precipitation-producing storms occur during cold periods.
NOAA should include snowfall amounts in its outlook.
Outlook, Not Forecast
I believe that NOAA calls their prediction an “outlook” rather than a forecast because they use a probability scheme. If you look at the forecast closely, it is a projection of the percentage chance of certain outcomes, not a prediction of a specific type of weather.
For instance, the forecast calls for a greater than 40% chance that precipitation will be greater than normal in California, which means that there is a 60% chance that precipitation will be normal or below normal. The forecast of “equal chances” is not a forecast of “near normal” temperatures (or precipitation); it’s a statement that there are equal chances of temperatures (or precipitation) either being above or below normal, which is not terribly useful.
–Paul Yeager
