Uninterrupted sunshine and light winds on Monday allowed temperatures to reach the low 40s. The city’s official high of 42 and low of 32 averaged 10 degrees above normal for the day, and pushed the month’s temperature surplus to 2.1 degrees. Similar weather is slated for Tuesday, with readings well into the 40s. The Chicago area is not the only part of the country experiencing mild conditions. Above normal readings have overspread most of the continental U.S., as suggested by satellite imagery that shows that the nation’s snow cover has shrunk to little more than 20 percent. Forecasts are in close agreement in keeping mild, Pacific-source air flowing through the end of December. Polar air is to make a brief, limited visit to the Great Lakes region Friday and Saturday, but readings are still expected to be above normal. Daytime highs are then forecast to be back near 40 degrees by Christmas.