Washington: Today - Partly cloudy, high in mid to upper 70s, lows in low to mid 60s. Chance of rain 40 per cent today, 50 per cent tonight. Sunday - Rain, high in low to mid 70s.

Maryland and Virginia: Today - Chance of rain east, rain likely west, highs in 70s, lows near 60. Sunday - Rain, highs from 50s west to 70s in south and east.

Lower Potomac and Chesapeake Bay: Today - Chance of rain this afternoon and evening with generally good visibility. Winds should be southwesterly at 10 to 20 knots today and 10 to 15 knots tonight.

Extended Area Outlook: For Monday through Wednesday - Chance of rain Monday followed by partly cloudy skies through remainder of period. Highs should average in mid 60s to low 70s, lows in mid 40s to near 50 through period. Washington's normal temperature range for this time of year is from 71 to 49.

West Virginia: Today and Sunday - Chance of rain, highs in mid 60s to mid 70s, lows in 60s.

The National Weather Forecast for Today - Showers and thunderstorms will be widespread from the Atlantic to the Mississippi River except in Illinois and southern Michigan. There will be some showers in western Oregon and extreme northwest California. The remainder of the nation will be mostly sunny. Seasonal temperatures are expected over most of the nation with cooling to seasonal levels forecast over much of the Ohio Valley and New England.

Almanac Data For April 23, 1977: Sun rises 5:21 a.m., sets 6:53 p.m.; moon rises 9:48 a.m. Tides: High 11:01 a.m. and 11:29 p.m. Low 5:30 a.m. and 6:10 p.m. High and low tides at the following locations can be obtained by substracting 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).

The Council of Governments' Air Quality Index for yesterday showed the high reading in the Washington area during the 2 to 3 p.m. period was 42 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 forecast for today indicates the air quality will improve.

The National Weather Service forecasts that the Potomac River stage at Little Falls will remain near 3.9 feet through today.

Washington data at 7 p.m. (EST) yesterday: Highest temperature since 7 a.m. yesterday, 85 degrees at 2:30 p.m. Lowest temperature since midnight, 65 degrees at 1:25 a.m. Excess of temperature since April 1, 109 degrees. Excess of temperature since Jan. 1, 90 degrees. Record high temperature for today, 95 degrees in 1960. Record low temperature for today, 33 degrees in 1933. Relative humidity: Maximum, 90 per cent at 2 a.m.; Minimum, 46 per cent at 4 p.m. 24 hour precipitation, none. Deficiency of precipitation since April 1, .83 inches. Deficiency of precipitation since Jan. 1, 4.90 inches. Highest observed wind since 7 a.m. 18 miles per hour from the S.S.W. at 5 p.m. Peak gust since 7 a.m., 28 miles per hour from the S.W. at 3:46 p.m. Temperatures ending 7 a.m. (EST) yesterday:(TABLE) City(COLUMN)H.(COLUMN)L. Albany(COLUMN)82(COLUMN)59 Albuquerque(COLUMN)67(COLUMN)42 Amarillo(COLUMN)48(COLUMN)38 Anchorage(COLUMN)53(COLUMN)36 Asheville(COLUMN)73(COLUMN)59 Atlanta(COLUMN)74(COLUMN)61 Atlantic City(COLUMN)62(COLUMN)56 Austin(COLUMN)75(COLUMN)55 Baltimore(COLUMN)80(COLUMN)60 Billings(COLUMN)67(COLUMN)40 Birmingham(COLUMN)75(COLUMN)68 Bismarck(COLUMN)58(COLUMN)39 Boise(COLUMN)76(COLUMN)50 Boston(COLUMN)82(COLUMN)58 Brownsville(COLUMN)85(COLUMN)64 Buffalo(COLUMN)80(COLUMN)61 Burlington, Vt.(COLUMN)83(COLUMN)67 Casper(COLUMN)65(COLUMN)39 Charleston, S.C.(COLUMN)80(COLUMN)68 Charl'tn, W.V.(COLUMN)85(COLUMN)66 Charlotte, N.C.(COLUMN)79(COLUMN)58 Cheyenne(COLUMN)57(COLUMN)33 Chicago(COLUMN)69(COLUMN)47 Cincinnati(COLUMN)77(COLUMN)64 Cleveland(COLUMN)79(COLUMN)62 Columbia, S.C.(COLUMN)84(COLUMN)55 Columbus, O.(COLUMN)80(COLUMN)62 Dal.-Ft. Worth(COLUMN)72(COLUMN)56 Dayton(COLUMN)79(COLUMN)63 Denver(COLUMN)61(COLUMN)38 Des Moines(COLUMN)65(COLUMN)51 Detroit(COLUMN)80(COLUMN)62 Duluth(COLUMN)63(COLUMN)35 El Paso(COLUMN)73(COLUMN)44 Fairbanks(COLUMN)52(COLUMN)34 Fargo(COLUMN)60(COLUMN)39 Flagstaff(COLUMN)67(COLUMN)28 Great Falls(COLUMN)60(COLUMN)38 Hartford(COLUMN)83(COLUMN)55 Helena(COLUMN)64(COLUMN)39 Honolulu(COLUMN)82(COLUMN)70 Houston(COLUMN)79(COLUMN)64 Indianapolis(COLUMN)70(COLUMN)64 Jackson, Miss.(COLUMN)69(COLUMN)64 Jacksonville(COLUMN)81(COLUMN)60 Juneau(COLUMN)57(COLUMN)34 Kansas City(COLUMN)61(COLUMN)52 Las Vegas(COLUMN)86(COLUMN)54 Little Rock(COLUMN)73(COLUMN)60 Los Angeles(COLUMN)81(COLUMN)58 Louisville(COLUMN)73(COLUMN)65 Memphis(COLUMN)74(COLUMN)65 Miami Beach(COLUMN)77(COLUMN)75 Midland(COLUMN)68(COLUMN)41 Milwaukee(COLUMN)64(COLUMN)43 Mpls.-St. Paul(COLUMN)64(COLUMN)43 Nashville(COLUMN)74(COLUMN)66 New Orleans(COLUMN)80(COLUMN)64 New York(COLUMN)75(COLUMN)40 Norfolk(COLUMN)81(COLUMN)59 North Platte(COLUMN)61(COLUMN)31 Oklahoma City(COLUMN)59(COLUMN)51 Omaha(COLUMN)66(COLUMN)46 Orlando(COLUMN)85(COLUMN)63 Philadelphia(COLUMN)81(COLUMN)59 Phoenix(COLUMN)90(COLUMN)62 Pittsburgh(COLUMN)81(COLUMN)62 Portland, Me.(COLUMN)75(COLUMN)49 Portland, Or.(COLUMN)59(COLUMN)42 Providence(COLUMN)77(COLUMN)52 Raleigh(COLUMN)81(COLUMN)58 Rapid City(COLUMN)68(COLUMN)43 Reno(COLUMN)74(COLUMN)38 Richmond(COLUMN)85(COLUMN)61 St. Louis(COLUMN)71(COLUMN)60 St. P'bg.-Tampa(COLUMN)87(COLUMN)70 Salt Lake City(COLUMN)74(COLUMN)43 San Antonio(COLUMN)75(COLUMN)54 San Diego(COLUMN)72(COLUMN)56 San Francisco(COLUMN)60(COLUMN)49 San Juan, P.R.(COLUMN)84(COLUMN)74 St. Ste. Marie(COLUMN)61(COLUMN)38 Seattle(COLUMN)61(COLUMN)50 Shreveport(COLUMN)74(COLUMN)56 Sioux Falls(COLUMN)63(COLUMN)35 Spokane(COLUMN)59(COLUMN)43 Syracuse(COLUMN)81(COLUMN)64 Topeka(COLUMN)60(COLUMN)54 Tucson(COLUMN)82(COLUMN)53 Tulsa(COLUMN)65(COLUMN)48 Washington(COLUMN)80(COLUMN)65 Wichita(COLUMN)52(COLUMN)51(END TABLE) Temperatures Abroad Yesterday(TABLE) City(COLUMN)Weather(COLUMN)Time(COLUMN)Temp. Aberdeen(COLUMN)rain(COLUMN)1 p.m.(COLUMN)45 Amsterdam(COLUMN)cloudy(COLUMN)1 p.m.(COLUMN)54 Ankara(COLUMN)rain(COLUMN)3 p.m.(COLUMN)41 Athens(COLUMN)cloudy(COLUMN)2 p.m.(COLUMN)54 Auckland(COLUMN)clear(COLUMN)mid.(COLUMN)59 Berlin(COLUMN)rain(COLUMN)1 p.m.(COLUMN)54 Birmingham(COLUMN)rain(COLUMN)1 p.m.(COLUMN)55 Brussels(COLUMN)rain(COLUMN)1 p.m.(COLUMN)50 Cairo(COLUMN)cloudy(COLUMN)2 p.m.(COLUMN)91 Casablanca(COLUMN)clear(COLUMN)noon(COLUMN)70 Copenhagen(COLUMN)rain(COLUMN)1 p.m.(COLUMN)48 Dublin(COLUMN)cloudy(COLUMN)1 p.m.(COLUMN)55 Geneva(COLUMN)pt. cldy(COLUMN)1 p.m.(COLUMN)68 Hong Kong(COLUMN)clear(COLUMN)8 p.m.(COLUMN)77 Lisbon(COLUMN)clear(COLUMN)noon(COLUMN)75 London(COLUMN)cloudy(COLUMN)1 p.m.(COLUMN)59 Madrid(COLUMN)clear(COLUMN)1 p.m.(COLUMN)72 Malta(COLUMN)clear(COLUMN)1 p.m.(COLUMN)63 Manila(COLUMN)clear(COLUMN)8 p.m.(COLUMN)82 Moscow(COLUMN)cloudy(COLUMN)3 p.m.(COLUMN)45 New Delhi(COLUMN)clear(COLUMN)5 p.m.(COLUMN)99 Nice(COLUMN)pt. cldy(COLUMN)1 p.m.(COLUMN)63 Oslo(COLUMN)clear(COLUMN)1 p.m.(COLUMN)55 Paris(COLUMN)pt. cldy(COLUMN)1 p.m.(COLUMN)66 Peking(COLUMN)cloudy(COLUMN)8 p.m.(COLUMN)70 Rome(COLUMN)pt. cldy(COLUMN)1 p.m.(COLUMN)63 Saigon(COLUMN)clear(COLUMN)8 p.m.(COLUMN)82 Sofia(COLUMN)clear(COLUMN)2 p.m.(COLUMN)54 Stockholm(COLUMN)rain(COLUMN)1 p.m.(COLUMN)46 Sydney(COLUMN)cloudy(COLUMN)10 p.m.(COLUMN)64 Tel Aviv(COLUMN)cloudy(COLUMN)2 p.m.(COLUMN)90 Tokyo(COLUMN)cloudy(COLUMN)9 p.m.(COLUMN)61 Tunis(COLUMN)rain(COLUMN)1 p.m.(COLUMN)59 Vienna(COLUMN)pt. cldy(COLUMN)1 p.m.(COLUMN)63 Warsaw(COLUMN)rain(COLUMN)1 p.m.(COLUMN)52(END TABLE) Temperatures (Western Hemisphere)(TABLE) City(COLUMN)Weather(COLUMN)High(COLUMN)Low Acapulco(COLUMN)haze(COLUMN)90(COLUMN)79 Barbados(COLUMN)cloudy(COLUMN)84(COLUMN)73 Bermuda(COLUMN)clear(COLUMN)69(COLUMN)63 Calgary(COLUMN)pt. cldy(COLUMN)54(COLUMN)30 Cullacan(COLUMN)pt. cldy(COLUMN)91(COLUMN)63 Edmonton(COLUMN)clear(COLUMN)52(COLUMN)19 Havana(COLUMN)pt. cldy(COLUMN)84(COLUMN)72 Kingston(COLUMN)cloudy(COLUMN)80(COLUMN)76 Montego Bay(COLUMN)pt. cldy(COLUMN)88(COLUMN)73 Mexico City(COLUMN)haze(COLUMN)70(COLUMN)46 Monterrey(COLUMN)cloudy(COLUMN)84(COLUMN)63 Montreal(COLUMN)rain(COLUMN)79(COLUMN)59 Nassau(COLUMN)pt. cldy(COLUMN)82(COLUMN)72 Ottawa(COLUMN)rain(COLUMN)77(COLUMN)61 Regina(COLUMN)clear(COLUMN)54(COLUMN)36 St. Kitts(COLUMN)cloudy(COLUMN)84(COLUMN)68 St. Thomas(COLUMN)rain(COLUMN)84(COLUMN)50 Toronto(COLUMN)rain(COLUMN)72(COLUMN)57 Vancouver(COLUMN)cloudy(COLUMN)59(COLUMN)46 Veracruz(COLUMN)cloudy(COLUMN)84(COLUMN)73 Winnipeg(COLUMN)pt. cldy(COLUMN)57(COLUMN)36(END TABLE)