The images depicted on the
Day 1-3 page
represent forecast probabilities that freezing rain or drizzle will fall within the 3-hour
period ending at the valid time of the product. There is no conditional dependency on accumulation
of precipitation above a threshold greater than zero.
The probability of freezing rain is based on the precipitation type diagnosed using output from several
medium-to-high resolution models along with output from the Short Range Ensemble Forecast (SREF) system.
The individual models include the Global Forecast System (GFS) model, the North American Mesoscale (NAM) model, and
the global model at the European Centre for Medium Range Weather Forecasts (ECMWF). The relative frequency of
occurrence of freezing rain in each 3-hour period is computed initially from the combined output of the GFS, NAM, and
ECMWF; then, the frequency of occurrence is determined among the members of the SREF. The displayed probability
at each point on the domain is a weighted average of 25% of the GFS-NAM-ECMWF frequency and 75% of the SREF
frequency. The probabilities are displayed in percent.
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