SACRAMENTO - You will often hear a meteorologist refer to the chance of rain or probability of precipitation. PoP means there will be at least 0.01 inches of measurable rain at a given forecast point.
The National Weather Service forecaster uses verbiage to describe weather conditions in zones, as well as in point or city forecast. A zone forecast gives the average for rain over an area. For example, the interior Northern California zone includes areas from Shasta Lake area, to the Northern, Central and Southern Sacramento Valley, the Delta, Northern San Joaquin County and into the foothills.
With new technology, forecasts can be more specific for cities. That's where point forecasts come into play. Within the zones, there is a breakdown of weather forecasts for major populated cities.
This is an example of an NWS forecast:
SOUTHERN SACRAMENTO VALLEY-
INCLUDING THE CITIES OF...SACRAMENTO
331 PM PST WED MAR 5 2014
.TONIGHT...RAIN SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS.
LOWS AROUND 54. SOUTH WINDS 10 TO 15 MPH WITH GUSTS TO AROUND
.THURSDAY...MOSTLY CLOUDY WITH A CHANCE OF RAIN SHOWERS. HIGHS
64 TO 70. SOUTHWEST WINDS UP TO 10 MPH.
Forecasters have a range for rain percentages. In the text above, the night refers to a slight chance of rain. That slight chance is a range from 0 to 20 percent. Thursday's forecast calls for "a chance of rain". That equals 21 to 50 percent. At 51 to 79 percent, rain is likely. When the percentage reaches 80 percent and above, there will be rain in that given area.
The day forecast period is from 6 a.m. until 6 p.m. The night forecast period is from 6 p.m. until 6 a.m.