The Arctic Oscillation and Snow in the Ohio Valley

The Arctic Oscillation (AO) is a measure of the difference in pressures near the surface between the North Pole and 40 degrees latitude. When this index is very negative, as it is currently, indicated by the time series chart below, the Ohio Valley tends to have a better chance for measuring snowfall and colder temperatures. This contrast is more pronounced during a strong El Nino, as we also currently have.

Note that for much of this cool season, the values has been near zero or positive (the black line on the plot above). Consequently, the region has not seen any measurable snowfall until now. Where the black line ends and the red lines begin are the forecast for the possible values of the AO based on model data. These forecasts are indicating the AO will stay negative at least for the next 7 days. Consequently our forecasts call for a couple of chances for measurable snowfall.

If you're interested in more study of these large-scale patterns check out this webpage from the Climate Prediction Center, http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml.

Louisville Trimarc Camera Image of potentially icy roads after morning snows along the Gene Snyder (I-265) and Taylorsville Road.