Washington: Today - Cloudy, high near 70, low near 50. Chance of rain 30 per cent today, 40 per cent tonight. Saturday - Cloudy with chance of rain, high near 70.

Maryland: Today - Cloudy, high in 60s, low in mid 40s to near 50. Chance of rain throughout state through tonight. Saturday - Cloudy with chance of rain, high in 60s.

Virginia Today - Cloudy, high near 70, low in mid 40s to near 50. Chance of rain tonight throughout the commonwealth. Saturday - Cloudy with chance of rain, highs near 70.

Lower Potomac and Chesapeake Bay: Today - Cloudy with chance of rain through tonight.Visibility should be 5 miles or more, decreasing to 2 miles or less at times. Winds should be southeast at 10 to 18 knots today and easterly at 10 knots or less tonight.

Extended Areas Outlook: For Sunday through Tuesday - Chance of rain through Monday with partial clearing Tuesday. Highs should average near 70, lows in mid 40s to mid 50s. Washington's normal temperature range for this time of year is from 54 to 34.

West Virginia: Today - Rain, high in upper 60s to mid 70s, lows in mid 40s to mid 50s. Saturday - Rain, highs in upper 60s to upper 70s.

The National Weather Forecast for Today - Rain will be widespread from the Great Plains to the Atlantic Coast except for the northern Atlantic Coast states and Florida. Thunderstorms will be scattered from the lower and middle Mississippi Valley across the south and central Plains. Snow will be scattered from western South Dakota into the central Rockies. Rain will spread along the northern Pacific Coast. Elsewhere, fair or partly cloudy skies are forecast. It will be much cooler from the north and central Plains across the northern half of the Mississippi Valley and the western Great Lakes region. Elsewhere, little temperature chance is forecast.

The Council of Governments' Air Quality Index for yesterday showed the high reading in the Washingtion area during the 2 to 3 p.m. period was 40 for the pollutant, photochemical oxidants index exceeds 100 the air becomes hazardous and persons with lung, heart and eye problems should restrict their activity. The forecast for today indicates the air quality will improve.

The National Weather Service forecasts that the Potomac River stage at Little Falls will fall slowly to near 4.4 feet today.

Washington Data at 7 p.m. (EST) yesterday: Highest temperature since 7 a.m. yesterday, 68 degrees at 4:10 p.m. Lowest temperature since midnight, 46 degrees at 6:13 a.m. Excess of temperature since March 1, 83 degrees. Deficiency of temperature since Jan. 1, 174 degrees. Record high temperature, 15 degrees in 1960. Relative humidity: Maximum, 66 per cent at 1 a.m.; Minimum, 32 per cent at 3 p.m. 24-hour precipitation, non. Deficiency of precipitation since March 1, 1.01 inches. Deficiency of precipitation since Jan. 1, 3.92 inches. Highest observed wind since 7 a.m. 15 miles per hour from the south at 2 p.m. Peak gust since 7 a.m., 23 miles per hour from the S.W. at 4 p.m. Local Temp., Humidity(TABLE) Time(COLUMN)T.(COLUMN)H. 12 midngt.(COLUMN)54(COLUMN)57 1 a.m.(COLUMN)52(COLUMN)66 2 a.m.(COLUMN)54(COLUMN)51 3 a.mn(COLUMN)53(COLUMN)53 4 a.m.(COLUMN)50(COLUMN)66 5 a.m.(COLUMN)50(COLUMN)61 6 a.m.(COLUMN)48(COLUMN)66 7 a.m.(COLUMN)47(COLUMN)66 8 a.m.(COLUMN)51(COLUMN)59 9 a.m.(COLUMN)54(COLUMN)53 10 a.m.(COLUMN)56(COLUMN)53 11 a.m.(COLUMN)58(COLUMN)49 12 noon(COLUMN)62(COLUMN)46 1 p.m.(COLUMN)67(COLUMN)34 2 p.m.(COLUMN)67(COLUMN)33 3 p.m.(COLUMN)67(COLUMN)32 4 p.m.(COLUMN)67(COLUMN)32 5 p.m.(COLUMN)66(COLUMN)33(END TABLE)