If you know the temperature and dew point for your city, you can also calculate the base by this formula for Farenheit: ((Temp - Dew) / 4.4) x 1000 ...For example, currently it's 73F temp with a dew point of 66F, so.... ((73-66) / 4.4) x 1000 = ( 7/4.4) x 1000 = 1.590 x 1000 = 1,590 feet for cloud base. When in celsius just divide by 2.5.