Washington: Today - Sunny, high in the mid 70s, low near 50. The chance of rain is 10 per cent. Tuesday - Partly cloudy, high near 80.

Maryland and Virginia: Today - Partly cloudy, high in the 70s, low in the 40s. Tuesday - Partly cloudy, high in the 70s.

Lower Potomac and Chesapeake Bay: Today - Fair with early morning haze. Winds will become southerly at 12 knots by afternoon. Visibility will be good. Waves in unprotected waters will average 2 feet.

Extended Area Forecast for Wednesday through Friday: Fair and warm through the period. Highs will average from the 70s to the low 80s, lows from the mid 40s to the mid 50s. Normal Washington temperatures for the period are a high of 69 and a low of 48.

West Virginia: Today - Partly cloudy, high in the 70s. Tuesday - partly cloudy, high in the 70s.

THE NATIONAL WEATHER FORECAST for today - Ralnsheers will continue over the Pacific Northwest. Showers and occasional thundershowers will extend from the central Great Lakes across the Ohio Valley, the lower half of the Mississippi Valley, through the central Gulf of Mexico coast and east portions of the lower half of the plains. Temperatures will be warm through much of southeast. It will be cool over the northwest as well as the south and central plains. Elsewhere, temperatures over the nation will remain seasonably mild.

The Council of Governments' Alt Quality Index for yesterday showed the high reading in the Washington area during the 10 a.m., period was 25 for the pollutant, photochemical oxidants. Index values between 25 and 49 indicate fair air quality. When the index exceeds 100 the air becomes hazardous and persons with lung, heart and eye problems should restrict their activity.

The National Weather Service forcasts that the Potomac River stage at Little Falls will fall to 42 feet.

Sun rises 5:26 a.m., sets 6:49 p.m.; moon rises 6:09 a.m. sets 8:08 p.m. Tides: High 8:10 a.m. and 8:32 p.m.; low 2:23 a.m. and 2:54 p.m. High and low tides at the following locations can be obtained by subtracting the hours indicated from the tides above. Annapolis (3 1/2); Bloody Point Lighthouse (4 1/2); Deale, Md. (4 1/2); Colonial Beach (6); Norfolk (1 1/2); Virginia Beach (1); Solomons Island (6 1/2); Point Lookout (7).

Washington data at 7 p.m. (EST) yesterday: Highest temperature since 7 a.m. yesterday, 75 degrees since midnight, 50 degrees at 5:40 a.m. Excess of temperature since April 1, 56 degrees. Excess of temperature since Jan. 1, 37 degrees. Record high temperature for today, 95 degrees in 1976. Record low temperature for today, 25 degrees in 1875. Relative humidity: Maximum, 72 per cent at 1 a.m. Minimum, 21 per cent at 11 a.m. 24 hour precipitation, none. Deficiency of precipitation since April 1, 37 inches. Deficiency of precipitation since Jan. 1, 4.44 inches. Highest observed wind since 7 a.m. 9 miles per hour from the west at 3 p.m. Peak gust since 7 a.m., 16 miles per hour from the west at 4:22 p.m. Local Temp., Humidity(TABLE) Time(COLUMN)T.(COLUMN)H. 12 midn't(COLUMN)60(COLUMN)50 1 a.m.(COLUMN)55(COLUMN)72 2 a.m.(COLUMN)56(COLUMN)59 3 a.m.(COLUMN)56(COLUMN)55 4 a.m.(COLUMN)53(COLUMN)64 5 a.m.(COLUMN)51(COLUMN)69 6 a.m.(COLUMN)51(COLUMN)66 7 a.m.(COLUMN)55(COLUMN)51 8 a.m.(COLUMN)60(COLUMN)44 9 a.m.(COLUMN)64(COLUMN)29 10 a.m.(COLUMN)66(COLUMN)24 11 a.m.(COLUMN)68(COLUMN)21 12 noon(COLUMN)70(COLUMN)24 1 p.m.(COLUMN)72(COLUMN)22 2 p.m.(COLUMN)74(COLUMN)23 2 p.m.(COLUMN)75(COLUMN)25 4 p.m.(COLUMN)75(COLUMN)24 5 p.m.(COLUMN)75(COLUMN)26 6 p.m.(COLUMN)73(COLUMN)32(END TABLE) Temperatures ending 7 a.m. (EST) yesterday:(TABLE) City(COLUMN)H.(COLUMN)L. Albany(COLUMN)62(COLUMN)29 Albuquerque(COLUMN)67(COLUMN)44 Amarlllo(COLUMN)67(COLUMN)52 Anchorage(COLUMN)37(COLUMN)24 Asheville(COLUMN)80(COLUMN)44 Atlanta(COLUMN)85(COLUMN)55 Atlantic City(COLUMN)68(COLUMN)46 Austin(COLUMN)67(COLUMN)58 Baltimore(COLUMN)73(COLUMN)45 Billings(COLUMN)78(COLUMN)42 Birmingham(COLUMN)89(COLUMN)53 Bismarck(COLUMN)63(COLUMN)44 Boise(COLUMN)69(COLUMN)37 Boston(COLUMN)67(COLUMN)48 Brownsville(COLUMN)76(COLUMN)63 Buffalo(COLUMN)63(COLUMN)40 Brulington, Vt.(COLUMN)58(COLUMN)29 Casper(COLUMN)65(COLUMN)47 Charleston, S.C.(COLUMN)85(COLUMN)66 Charleon, W.V.(COLUMN)76(COLUMN)51 Chalotte(COLUMN)82(COLUMN)55 Cheyanne(COLUMN)57(COLUMN)36 Chicago(COLUMN)84(COLUMN)49 Cincinnati(COLUMN)90(COLUMN)52 Cleveland(COLUMN)63(COLUMN)49 Columbia, S.C(COLUMN)89(COLUMN)53 Columbus(COLUMN)75(COLUMN)52 Dal Ft. Worth(COLUMN)67(COLUMN)69 Dayton(COLUMN)80(COLUMN)57 Denver(COLUMN)65(COLUMN)44 Des Molnss(COLUMN)87(COLUMN)59 Detrolt(COLUMN)42(COLUMN)44 Duluth(COLUMN)62(COLUMN)42 El Paso(COLUMN)69(COLUMN)49 Fakbanks(COLUMN)33(COLUMN)24 Fargo(COLUMN)73(COLUMN)54 Flagstaff(COLUMN)67(COLUMN)28 Great Falls(COLUMN)74(COLUMN)30 Hartford(COLUMN)64(COLUMN)34 Helena(COLUMN)68(COLUMN)32 Honolulu(COLUMN)83(COLUMN)71 Houston(COLUMN)71(COLUMN)62 Indianapolis(COLUMN)83(COLUMN)57 Jackson(COLUMN)86(COLUMN)55 Jacksonville(COLUMN)86(COLUMN)53 Juneau(COLUMN)42(COLUMN)35 Kansas City(COLUMN)80(COLUMN)60 Las Vegas(COLUMN)86(COLUMN)57 Louisville(COLUMN)83(COLUMN)54 Memphis(COLUMN)89(COLUMN)56 Miami Beach(COLUMN)76(COLUMN)73 Midland(COLUMN)62(COLUMN)52 Milwaukee(COLUMN)65(COLUMN)44 Mpls St. Paul(COLUMN)74(COLUMN)59 Nashville(COLUMN)87(COLUMN)53 New Orleans(COLUMN)84(COLUMN)67 New York(COLUMN)70(COLUMN)49 Norfolk(COLUMN)67(COLUMN)49 North Platte(COLUMN)68(COLUMN)47 Oklahoma City(COLUMN)73(COLUMN)59 Omaha(COLUMN)82(COLUMN)57 Orlando(COLUMN)85(COLUMN)54 Philadelphia(COLUMN)74(COLUMN)48 Phoenix(COLUMN)86(COLUMN)60 Pittsburgh(COLUMN)65(COLUMN)41 Portland, Me.(COLUMN)62(COLUMN)38 Portland, Or.(COLUMN)55(COLUMN)34 Providence(COLUMN)67(COLUMN)45 Raleigh(COLUMN)81(COLUMN)49 Rapid City(COLUMN)68(COLUMN)40 Reno(COLUMN)79(COLUMN)41 Richmond(COLUMN)77(COLUMN)45 St. Louis(COLUMN)88(COLUMN)57 st. Prbg.-Tampa(COLUMN)86(COLUMN)58 Salt Lake City(COLUMN)71(COLUMN)43 San Antonio(COLUMN)71(COLUMN)57 San Diego(COLUMN)64(COLUMN)58 San Francisco(COLUMN)62(COLUMN)50 San Juan(COLUMN)91(COLUMN)76 St. Ste. Marie(COLUMN)66(COLUMN)35 Seattle(COLUMN)54(COLUMN)39 Shreveport(COLUMN)83(COLUMN)62 Sloux Falls(COLUMN)73(COLUMN)61 Spokane(COLUMN)56(COLUMN)28 Syracuse(COLUMN)59(COLUMN)32 Topeka(COLUMN)82(COLUMN)58 Tucson(COLUMN)77(COLUMN)54 Tulsa(COLUMN)79(COLUMN)63 Washington(COLUMN)74(COLUMN)50 Wichita(COLUMN)63(COLUMN)58(END TABLE) Temperatures (Western Hemisphere)(TABLE) City(COLUMN)Weather(COLUMN)High(COLUMN)Low Acapulco(COLUMN)pt. cldy(COLUMN)88(COLUMN)73 Barbados(COLUMN)cloudy(COLUMN)83(COLUMN)78 Bermuda(COLUMN)sunny(COLUMN)70(COLUMN)62 Cullacan(COLUMN)pt. cldy.(COLUMN)86(COLUMN)55 Havana(COLUMN)cloudy(COLUMN)78(COLUMN)69 Kingston(COLUMN)pt. cldy.(COLUMN)86(COLUMN)77 Montego Bay(COLUMN)pt. cldy.(COLUMN)86(COLUMN)75 Mexico City(COLUMN)pt. cldy.(COLUMN)77(COLUMN)44 Monterrey(COLUMN)cloudy(COLUMN)83(COLUMN)62 St. Kitts(COLUMN)pt. cldy.(COLUMN)87(COLUMN)70 St. Thomas(COLUMN)pt.cldy(COLUMN)84(COLUMN)75 Veracruz(COLUMN)pt. cldy(COLUMN)90(COLUMN)75(END TABLE)