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The relation between present weather and concurrent daily 700‐mb circulation is studied for the winter season in the United States. All weather data are averaged within 40 climatologically homogeneous circles and expressed as a numerical index giving the proportion of precipitation or cloudiness within each circle at map time. The synoptic climatology of the resulting weather index is analyzed, and schematic models are constructed showing preferred parts of the 700‐mb contour pattern for general precipitation or clear skies in different parts of the country. By means of the screening method of multiple regression, specification equations are derived for each circle, giving the weather index as a linear function of selected 700‐mb heights located over North America or adjacent oceans. On the average, about 36% of the variance of the weather index is explained by five heights, but there is considerable geographical variation. Similar equations are derived to specify the occurrence or nonoccurrence of precipitation within a 24‐hour period. Both sets of equations are tested by applying them to 36‐hour baroclinic prognostic heights prepared in the National Meteorological Center during the past two winters. The resulting objective forecasts of weather and precipitation are consistently better than persistence, but they are not quite as good as predictions made by experienced forecasters.

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