Washington: Today - sunny, high in the low 70s, low in the mid 50s. The chance of rain is 20 per cent today and near zero tonight. Thursday - Fair, high in the low 70s.

Maryland and Virginia: Today - Sunny, highs from the upper 60s to the low 70s, lows in the 50s. Thursday - Fair throughout the area, except for a chance of rain in western Virginia. Highs will be from the 60s to the mid 70s.

Lower Potomac and Chesapeake Bay: Today - Cloudy during the morning fair through the remainder of the day. Visibility will be more than five miles in fair weather. Wind will be variable at less than 10 knots. Waves in unprotected waters will be less than 1 foot.

Extended Area Forecast for Friday through Sunday: Chance of showers on Friday and Sunday, fair on Saturday. Highs will be from the 60s on Friday to the 50s on Saturday and Sunday. Lows will be from the 30s to the 40s. Normal Washington temperatures for the period are a high of 59 and a low of 40.

West Virginia: Today - partly cloudy, highs from the mid 60s to the low 70s, lows from the 40s to the mid 50s. Thursday - Partly cloudy, highs from the mid 60s to the low 70s.

The National Weather Forecast for today - Thundershowers will fall from the western Gulf Coast into the middle and lower Mississippi Valley with showers extending into Alabama and the western and central sections of the Great Lakes and Ohio Valley. Showers will also fall over the upper MIssissippi Valley, and there will be some rain and snow in the central Plains. Rain will remain over New England, and showers will spread from Washington and northern Oregon into north-western Montana. Skies elsewhere in the west will be mostly sunny and in the east, partly cloudy. Temperatures will be cool in the western [WORD ILLEGIBLE] of the nation and in the northern Plains. It will be colder from the western Great Lakes into the southern Plains. Mild temperatures will prevail in the eastern third of the nation.

Almanac Data for today - Sun rises 6:10 a.m., sets 5:40 p.m., moon rises3:31 a.m., sets 3:27 p.m. Tides: high 4:57 a.m. and 5:27 p.m., low 11:49 a.m. High and low tides at the following locations can be obtained by subtracting the hours indicated from the tides above. Annapolis (1 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 show and the high reading in the Washington area during the 2 p.m. to 3 p.m. period was 15 for the [WORD ILLEGIBLE] carbon monoxide. Index values between zero and 24 indicate good 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 be good.

The National Weather Service forecasts the Potomac River stage at Little Falls shuld be near 5.5 feet today.

Washington data at 8 p.m. (EDT) yesterday: Highest temperature since 8 a.m. yesterday, 64 degrees at 11:45 a.m. Lowest temperature since midnight, 61 degrees at 6:20 a.m. Excess of temperature since November 1, 106 degrees. Excess of temperature sine Jan. 1, 529 degrees. Record high temperature for today, 77 degrees in 1975. Record low temperature for today, 26 degrees in 1972. Relative humidity: Maximum, 87 per cent at 3 a.m.; Minimum, 78 per cent at noon, 24 hour precipitation; 26 inches. Excess of precipitation since November 1, 1.26 inches. Deficiency of precipitation since Jan. 1, 5.22 inches. Highest observed wind since 8 a.m., 9 miles per hour from the northeast at 8:31 a.m. Peak qust since 8 a.m. 14 miles per hour from the northeast at 8:07 a.m. Local Temp., Humidity(TABLE) Time(COLUMN)T.(COLUMN)H. 12 midn't(COLUMN)63(COLUMN)84 1 a.m.(COLUMN)63(COLUMN)84 2 a.m.(COLUMN)63(COLUMN)84 3 a.m.(COLUMN)63(COLUMN)84 4 a.m.(COLUMN)62(COLUMN)87 5 a.m.(COLUMN)62(COLUMN)87 6 a.m.(COLUMN)62(COLUMN)87 7 a.m.(COLUMN)61(COLUMN)87 8 a.m.(COLUMN)61(COLUMN)87 9 a.m.(COLUMN)61(COLUMN)87 10 a.m.(COLUMN)62(COLUMN)87 11 a.m.(COLUMN)63(COLUMN)81 12 noon(COLUMN)64(COLUMN)87 1 p.m.(COLUMN)63(COLUMN)81 2 p.m.(COLUMN)64(COLUMN)81 3 p.m.(COLUMN)64(COLUMN)81 4 p.m.(COLUMN)64(COLUMN)78 5 p.m.(COLUMN)63(COLUMN)81 6 p.m.(COLUMN)62(COLUMN)81 7 p.m.(COLUMN)62(COLUMN)81(END TABLE) Temperatures ending 8 a.m. (EST) yesterday:(TABLE) City(COLUMN)H.(COLUMN)L. Albany(COLUMN)55(COLUMN)44 Albuquerque(COLUMN)45(COLUMN)34 Amarillo(COLUMN)57(COLUMN)37 Anchorage(COLUMN)23(COLUMN)10 Asheville(COLUMN)63(COLUMN)46 Atlanta(COLUMN)64(COLUMN)57 Atlantic City(COLUMN)61(COLUMN)58 Austin(COLUMN)79(COLUMN)55 Baltimore(COLUMN)64(COLUMN)58 Billings(COLUMN)55(COLUMN)25 Birmingham(COLUMN)66(COLUMN)52 Bismarck(COLUMN)59(COLUMN)37 Boise(COLUMN)49(COLUMN)24 Boston(COLUMN)54(COLUMN)50 Brownsville(COLUMN)85(COLUMN)77 Buffalo(COLUMN)60(COLUMN)51 Burlington(COLUMN)52(COLUMN)43 Casper(COLUMN)58(COLUMN)25 Charleston, S.C.(COLUMN)74(COLUMN)61 Chrl'ton, W.Va.(COLUMN)62(COLUMN)59 Charlotte(COLUMN)68(COLUMN)53 Chevenne(COLUMN)54(COLUMN)24 Chicago(COLUMN)60(COLUMN)53 Cincinnati(COLUMN)65(COLUMN)58 Cleveland(COLUMN)69(COLUMN)57 Columbia, S.C.(COLUMN)74(COLUMN)50 Columbus(COLUMN)66(COLUMN)58 Dal,-Ft, Worth(COLUMN)77(COLUMN)54 Dayton(COLUMN)64(COLUMN)58 Denver(COLUMN)61(COLUMN)34 Des Moines(COLUMN)61(COLUMN)56 Detroit(COLUMN)59(COLUMN)56 Duluth(COLUMN)46(COLUMN)45 El Paso(COLUMN)53(COLUMN)40 Fairbanks(COLUMN)5(COLUMN)-2 Fargo(COLUMN)56(COLUMN)48 Flagstaff(COLUMN)41(COLUMN)29 Great Falls(COLUMN)51(COLUMN)21 Hartford(COLUMN)54(COLUMN)45 Helena(COLUMN)50(COLUMN)25 Honolulu(COLUMN)87(COLUMN)71 Houston(COLUMN)76(COLUMN)68 Indianapolis(COLUMN)67(COLUMN)61 Jackson, Miss.(COLUMN)77(COLUMN)54 Jacksonville(COLUMN)77(COLUMN)55 Juneau(COLUMN)36(COLUMN)31 Kansas City(COLUMN)59(COLUMN)53 Las Vegas(COLUMN)71(COLUMN)47 Little Rock(COLUMN)77(COLUMN)58 Los Angeles(COLUMN)72(COLUMN)53 Louisville(COLUMN)68(COLUMN)62 Memphis(COLUMN)69(COLUMN)55 Miami Beach(COLUMN)82(COLUMN)70 Midland-Odessa(COLUMN)64(COLUMN)47 Milwaukee(COLUMN)53(COLUMN)52 Mpls. St. Paul(COLUMN)56(COLUMN)53 Naahville(COLUMN)66(COLUMN)62 New Orleans(COLUMN)76(COLUMN)60 New York(COLUMN)55(COLUMN)51 Norfolk(COLUMN)70(COLUMN)57 North Platte(COLUMN)54(COLUMN)51 Oklahoma City(COLUMN)73(COLUMN)52 Omaha(COLUMN)60(COLUMN)53 Orlando(COLUMN)80(COLUMN)60 Philadelphia(COLUMN)59(COLUMN)55 Phoenix(COLUMN)64(COLUMN)50 Pittsburgh(COLUMN)66(COLUMN)52 Portland, Ma.(COLUMN)49(COLUMN)41 Portland, Ore.(COLUMN)51(COLUMN)29 Providence(COLUMN)53(COLUMN)47 Raleigh(COLUMN)73(COLUMN)52 Rapid City(COLUMN)57(COLUMN)32 Reno(COLUMN)57(COLUMN)18 Richmond(COLUMN)71(COLUMN)53 St. Louis(COLUMN)60(COLUMN)56 St. Prbq-Tmpa(COLUMN)80(COLUMN)59 Salt Lake City(COLUMN)54(COLUMN)26 San Antonio(COLUMN)80(COLUMN)55 San Diego(COLUMN)70(COLUMN)55 San Francisco(COLUMN)67(COLUMN)55 San Juan(COLUMN)85(COLUMN)75 St. Ste. Marie(COLUMN)52(COLUMN)49 Seattle(COLUMN)51(COLUMN)35 Shreveport(COLUMN)78(COLUMN)59 Sioux Falls(COLUMN)58(COLUMN)55 Spokane(COLUMN)45(COLUMN)22 Syracuse(COLUMN)60(COLUMN)47 Topeka(COLUMN)60(COLUMN)50 Tucson(COLUMN)56(COLUMN)45 Tulsa(COLUMN)68(COLUMN)56 Washington(COLUMN)68(COLUMN)61 Wichita(COLUMN)63(COLUMN)55(END TABLE) Temperatures (Western Hemisphere)(TABLE) City(COLUMN)Weather(COLUMN)High(COLUMN)Low Acapulco(COLUMN)pt. cldy(COLUMN)90(COLUMN)79 Barbados(COLUMN)pt. cldy.(COLUMN)86(COLUMN)81 Bermuda(COLUMN)pt. cldy.(COLUMN)79(COLUMN)72 Bogota(COLUMN)cloudy(COLUMN)63(COLUMN)51 Calgary(COLUMN)pt. cldy.(COLUMN)45(COLUMN)23 Edmonton(COLUMN)snow(COLUMN)41(COLUMN)18 Havana(COLUMN)sunny(COLUMN)86(COLUMN)68 Kingston(COLUMN)pt. cldy.(COLUMN)88(COLUMN)75 Montego Bay(COLUMN)pt. sunny(COLUMN)88(COLUMN)75 Mexico City(COLUMN)fair(COLUMN)72(COLUMN)54 Monterrey(COLUMN)sunny(COLUMN)84(COLUMN)63 Montreal(COLUMN)rain(COLUMN)46(COLUMN)41 Nassau(COLUMN)pt. sunny(COLUMN)82(COLUMN)68 Ottawa(COLUMN)rain(COLUMN)45(COLUMN)37 Regina(COLUMN)clear(COLUMN)52(COLUMN)18 St. Kitts(COLUMN)pt. cldy(COLUMN)87(COLUMN)75 St. Thomas(COLUMN)pt. cldy.(COLUMN)90(COLUMN)77 Toronto(COLUMN)cloudy(COLUMN)54(COLUMN)46 Vancouver(COLUMN)clear(COLUMN)48(COLUMN)34 Veracruz(COLUMN)fair(COLUMN)86(COLUMN)67 Winnipeg(COLUMN)clear(COLUMN)54(COLUMN)37(END TABLE)