Washington: Today - Partly cloudly, hot and humid with a slight chance of a thunderstorm, high in the mid 90s, low near 70. The chance of rain is 20 percent through tonight. Wednesday - Hot, with a chance of thundershowers, high in the mid 90s. Winds will be from the south at 8 mph.

Maryland and Virginia: Today - partly cloudy, hot and humid, high in the mid 90s, low in the 60s or low 70s. Wednesday - Hot again with a chance of thundershowers, high in the 90s.

Extended Area Forecast for Thursday through Saturday - Partly cloudy and warm through the period. Highs will average in the 80s to low 90s, lows in the 60s to mid 70s. Normal Washington temperatures are a high of 87 and a low of 68.

Lower Potomac and Chesapeake Bay - Thunderstorms likely. Winds will be from the southwest at 12 to 18 knots. Waves will average 1 to 2 feet. Visibility will be 5 miles or more diminishing to less than 1 mile in showers.

Atlantic Ocean Beaches from New Jersey to North Carolina: Today and Wednesday - Hot and humid with a chance of thundershowers both days, highs in the mid 80s to low 90s. Water temperatures will range from the low to mid 60s in the north to the low 70s in the south.

West Virginia: Today - Warm and humid with a chance of showers or thundershowers, high in the mid 80s to low 90s, lows from mid 60s to low 70s. Wednesday - Humid, high near 90.

The national weather forecast for today - Scattered thundershowers will move eastward to cover much of the lower Great Lakes region, the Ohio Valley. New England and the Atlantic Coast states. A few thundershowers will also develop along the eastern Gulf coast and southern Florida will be covered with thundershowers once again. Sunny weather will prevail over the western half of the nation Temperatures will be a little warmer in the Pacific Northwest, with high near 80, but the Plains will not be as warm as they have been. The southwest will bake with highs in the 100s.

The Council of Government's Air Index for yesterday showed the high reading in the Washington area during the 3 p.m. period was 50 for the pollutant, photochemical oxidants. Index values between 50 and 99 indicate unhealthy air quality. When the index exceeds 100 the air is considered very unhealthy and individuals with lung, heart and eye ailments are urged to restrict their activity. The forecast for today indicates that the air quality will improve.

The National Weather Service forecast the Potomac River Stage high at Little Falls should decrease slightly to 3.4 feet today.

Almanac Data for today: The sun rises 5:45 a.m. sets 8:37 P.m.; moon sets 1:27 p.m. Tides: high 2:16 a.m. and 1:36 P.m.; low 9:03 a.m. and 9:23 p.m. High and low tides at the following locations may be obtained by subtracting the hours indicated from the hours above: Annapolis (3 1/4), Bloody Point Lighthouse (4 1/2), Deale, Md., (4 1/2), Colonial Beach (5 1/4), Norfolk (1), Virginia Beach (3/4), Solomons Island (6 1/4), Point Lookout (7).

Washington data for yesterday: Highest temperature since midnight yesterday, 88 degrees at 4:52 p.m. Lowest temperature since midnight 73 degrees at 1:01 a.m. Excess of temperature since June 1, 27 degrees. Deficiency of temperature since Jan. 1, 173 degrees. Record high temperature for today, 98 degrees in 1952. Record low temperature for today, 57 degrees in 1927. Relative humidity: maximum, 76 percent at 7 a.m.; minimum, 65 percent at 2 p.m. 24-hour precipitation, none. Deficiency of precipitation since June 1, 1.70 inches. Excess of precipitation since Jan. 1, 1.88 inches. Local Temp., Humidity(TABLE) Time(COLUMN)T.(COLUMN)L. 12 midn.(COLUMN)76(COLUMN)62 1 a.m.(COLUMN)75(COLUMN)64 2 a.m.(COLUMN)73(COLUMN)68 3 a.m.(COLUMN)73(COLUMN)71 4 a.m.(COLUMN)73(COLUMN)71 5 a.m.(COLUMN)73(COLUMN)71 6 a.m.(COLUMN)73(COLUMN)71 7 a.m.(COLUMN)73(COLUMN)76 8 a.m.(COLUMN)74(COLUMN)76 9 a.m.(COLUMN)76(COLUMN)74 10 a.m.(COLUMN)77(COLUMN)72 11 a.m.(COLUMN)77(COLUMN)74 12 noon(COLUMN)81(COLUMN)69 1 p.m.(COLUMN)82(COLUMN)72 2 p.m.(COLUMN)85(COLUMN)65 3 p.m.(COLUMN)86(COLUMN)68 4 p.m.(COLUMN)85(COLUMN)68 6 p.m.(COLUMN)86(COLUMN)70 7 P.m.(COLUMN)86(COLUMN)68(END TABLE) Temperatures ending 8 a.m. (EDT) yesterday:(TABLE) City(COLUMN)H.(COLUMN)6. Albany(COLUMN)83(COLUMN)61 Albuquerque(COLUMN)99(COLUMN)64 Amarillo(COLUMN)101(COLUMN)73 Anchorage(COLUMN)58(COLUMN)50 Asheville(COLUMN)84(COLUMN)66 Atlanta(COLUMN)92(COLUMN)71 Atlantic City(COLUMN)74(COLUMN)63 Austin(COLUMN)97(COLUMN)77 Baltimore(COLUMN)85(COLUMN)65 Billings(COLUMN)65(COLUMN)52 Birmingham(COLUMN)94(COLUMN)74 Bismarck(COLUMN)80(COLUMN)54 Boise(COLUMN)68(COLUMN)45 Boston(COLUMN)79(COLUMN)63 Brownsville(COLUMN)97(COLUMN)81 Buffalo(COLUMN)82(COLUMN)68 Burlington, Vt.(COLUMN)80(COLUMN)63 Casper(COLUMN)77(COLUMN)40 Charleston, S.C.(COLUMN)87(COLUMN)78 Charleston, W. Va.(COLUMN)88(COLUMN)68 Charlotte(COLUMN)87(COLUMN)72 Cheyenne(COLUMN)85(COLUMN)48 Chicago(COLUMN)76(COLUMN)64 Cincinnati(COLUMN)87(COLUMN)67 Cleveland(COLUMN)87(COLUMN)69 Columbia, S.C.(COLUMN)90(COLUMN)72 Columbia(COLUMN)84(COLUMN)68 Dal.-Ft. Worth(COLUMN)100(COLUMN)75 Dayton(COLUMN)86(COLUMN)69 Denver(COLUMN)93(COLUMN)52 Des Moines(COLUMN)91(COLUMN)68 Detroit(COLUMN)85(COLUMN)68 Duluth(COLUMN)64(COLUMN)55 El Paso(COLUMN)109(COLUMN)83 Fairbanks(COLUMN)61(COLUMN)50 Fargo(COLUMN)73(COLUMN)51 Flagstaff(COLUMN)83(COLUMN)74 Great Falls(COLUMN)63(COLUMN)51 Harford(COLUMN)86(COLUMN)57 Helena(COLUMN)62(COLUMN)55 Honolulu(COLUMN)87(COLUMN)75 Houston(COLUMN)93(COLUMN)78 Indianapolis(COLUMN)89(COLUMN)71 Jackson(COLUMN)97(COLUMN)71 Jacksonville(COLUMN)88(COLUMN)72 Juneau(COLUMN)52(COLUMN)50 Kansas City(COLUMN)95(COLUMN)77 Las Vegas(COLUMN)101(COLUMN)73 Little Rock(COLUMN)94(COLUMN)75 Los Angeles(COLUMN)84(COLUMN)61 Louisville(COLUMN)93(COLUMN)72 Memphis(COLUMN)94(COLUMN)79 Miami Beach(COLUMN)88(COLUMN)78 Midland(COLUMN)100(COLUMN)74 Milwaukee(COLUMN)81(COLUMN)65 Mpls.-St. Paul(COLUMN)85(COLUMN)66 Nashville(COLUMN)95(COLUMN)74 New Orleans(COLUMN)93(COLUMN)74 New York(COLUMN)82(COLUMN)65 Norfolk(COLUMN)81(COLUMN)63 North Platte(COLUMN)96(COLUMN)62 Oklahoma City(COLUMN)97(COLUMN)77 Omaha(COLUMN)92(COLUMN)68 Orlando(COLUMN)93(COLUMN)75 Philadephia(COLUMN)85(COLUMN)64 Phoenix(COLUMN)110(COLUMN)81 Pittsburgh(COLUMN)84(COLUMN)68 Portland, Me.(COLUMN)76(COLUMN)53 Portland, Ore.(COLUMN)67(COLUMN)53 Providence(COLUMN)79(COLUMN)57 Raleigh(COLUMN)89(COLUMN)66 Rapid City(COLUMN)86(COLUMN)49 Reno(COLUMN)79(COLUMN)55 Richmond(COLUMN)85(COLUMN)66 St. Louis(COLUMN)91(COLUMN)79 St. Prbg.-Tampa(COLUMN)92(COLUMN)76 Salt Lake City(COLUMN)72(COLUMN)42 San Antonio(COLUMN)97(COLUMN)77 San Diego(COLUMN)78(COLUMN)64 San Francisco(COLUMN)69(COLUMN)53 San Juan(COLUMN)88(COLUMN)75 St. Ste. Marie(COLUMN)79(COLUMN)63 Seattle(COLUMN)67(COLUMN)52 Shreveport(COLUMN)99(COLUMN)75 Sioux Falls(COLUMN)86(COLUMN)62 Spokane(COLUMN)71(COLUMN)51 Syracuse(COLUMN)84(COLUMN)67 Topeka(COLUMN)33(COLUMN)36 Tucson(COLUMN)105(COLUMN)78 Tulsa(COLUMN)95(COLUMN)80 Washington(COLUMN)88(COLUMN)73 Wichita(COLUMN)102(COLUMN)79(END TABLE) Temperatures (Western Hemisphere)(TABLE) City(COLUMN)(COLUMN)H.(COLUMN)L. Acapulco(COLUMN)fair(COLUMN)92(COLUMN)77 Barbados(COLUMN)Cloudy(COLUMN)88(COLUMN)74 Bermuda(COLUMN)Cloudy(COLUMN)81(COLUMN)74 Calgary(COLUMN)Cloudy(COLUMN)70(COLUMN)52 Edmonton(COLUMN)pt. cldy.(COLUMN)73(COLUMN)46 Havana(COLUMN)pt. Cldy.(COLUMN)88(COLUMN)77 Kingston(COLUMN)pt. cldy.(COLUMN)90(COLUMN)79 Montego Bay(COLUMN)fair(COLUMN)90(COLUMN)74 Mexico City(COLUMN)pt. cldy.(COLUMN)81(COLUMN)55 Monterrev(COLUMN)clear(COLUMN)103(COLUMN)77 Montreal(COLUMN)cloudy(COLUMN)81(COLUMN)63 Nassau(COLUMN)pt. cldy.(COLUMN)90(COLUMN)76 Ottawa(COLUMN)pt. cldy(COLUMN)79(COLUMN)59 Regina(COLUMN)cloudy(COLUMN)75(COLUMN)57 St. Kitts(COLUMN)fair(COLUMN)88(COLUMN)75 Toronto(COLUMN)cloudy(COLUMN)77(COLUMN)63 Vancouver(COLUMN)pt. cldy.(COLUMN)68(COLUMN)54 Veracruz(COLUMN)fair(COLUMN)88(COLUMN)79 Winnipeg(COLUMN)cloudy(COLUMN)72(COLUMN)52(END TABLE) Temperatures Abroad Yesterday(TABLE) City(COLUMN)Weather(COLUMN)Time(COLUMN)Temp. Aberdeen(COLUMN)pt. cldy.(COLUMN)1 p.m.(COLUMN)57 Amsterdam(COLUMN)rain(COLUMN)1 p.m.(COLUMN)54 Ankara(COLUMN)clear(COLUMN)3 p.m.(COLUMN)79 Athens(COLUMN)clear(COLUMN)2 p.m.(COLUMN)84 Auckland(COLUMN)pt. cldy(COLUMN)midn.(COLUMN)50 Berlin(COLUMN)rain(COLUMN)1 p.m.(COLUMN)52 Birmingham(COLUMN)cloudy(COLUMN)1 p.m.(COLUMN)55 Bonn(COLUMN)cloudy(COLUMN)1 p.m.(COLUMN)55 Brussels(COLUMN)rain(COLUMN)1 p.m.(COLUMN)54 Cairo(COLUMN)clear(COLUMN)2 p.m.(COLUMN)93 Casablanca(COLUMN)clear(COLUMN)noon(COLUMN)70 Copenhagen(COLUMN)rain(COLUMN)1 p.m.(COLUMN)70 Dublin(COLUMN)cloudy(COLUMN)1 p.m.(COLUMN)55 Geneva(COLUMN)clear(COLUMN)1 p.m.(COLUMN)59 Hong Kong(COLUMN)cloudy(COLUMN)8 P.m.(COLUMN)82 Lisbon(COLUMN)cloudy(COLUMN)noon(COLUMN)72 London(COLUMN)cloudy(COLUMN)1 p.m.(COLUMN)55 Madrid(COLUMN)pt. cldy.(COLUMN)1 p.m.(COLUMN)70 Malta(COLUMN)clear(COLUMN)1 P.m.(COLUMN)82 Manila(COLUMN)pt. Cldy.(COLUMN)8 P.m.(COLUMN)81 Moscow(COLUMN)cloudy(COLUMN)3 p.m.(COLUMN)77 New Delhi(COLUMN)cloudy(COLUMN)5 p.m.(COLUMN)86 Nice(COLUMN)pt. Cldy.(COLUMN)1 p.m.(COLUMN)68 Oslo(COLUMN)cloudy(COLUMN)1 p.m.(COLUMN)64 Paris(COLUMN)pt. Cldy.(COLUMN)1 p.m.(COLUMN)63 Peking(COLUMN)clear(COLUMN)8 p.m.(COLUMN)84 Rome(COLUMN)clear(COLUMN)1 p.m.(COLUMN)77 Saigon(COLUMN)cloudy(COLUMN)8 p.m.(COLUMN)82 Sofia(COLUMN)clear(COLUMN)2 P.m.(COLUMN)77 Stockholm(COLUMN)pt. cldy.(COLUMN)1 P.m.(COLUMN)68 Sydney(COLUMN)pt. cldy.(COLUMN)10 p.m.(COLUMN)54 Tokyo(COLUMN)rain(COLUMN)9 p.m.(COLUMN)77 Tunis(COLUMN)clear(COLUMN)1 p.m.(COLUMN)81 Vienna(COLUMN)pt.cldy.(COLUMN)1 p.m.(COLUMN)66 Warsaw(COLUMN)rain(COLUMN)1 p.m.(COLUMN)52(END TABLE)