Thursday night, a combination of clear skies and diminishing wind over fresh snow cover was a recipe for maximum heat loss. This set-up gave the city its first official subzero temperatures of the winter, and led to our coldest Valentine’s day since 1943. Temps across rural areas of northern Illinois dipped to -20 degrees at Odell, in Livingston county, -17 at Roscoe, north of Rockford, and -15 at Kirkland in northern DeKalb county. These will be the lowest readings we experience for some time if forecasts prove correct. Late Friday’s south winds were on the increase across Iowa and points to the west, signaling the approach of milder air. Building southwest winds are expected to propel our temps to the low and mid 30s Saturday, but the transition to milder air will likely be accompanied by clouds and a period of snow. Thawing daytime readings are then forecast to extend into Tuesday.