Washington Today -- Mostly cloudy and cooler with a chance of occasional rain, high near 60, low in the mid 40s. The chance of rain is 40 percent today and 50 percent tonight.Winds will become northesterly at 10 to 15 mph. Thursday -- Cloudy, high in the 50s.

Maryland and Virginia: Today -- Mostly cloudy and cooler with a chance of occasional rain, highs in the 50s to low 60s, lows mostly in the 40s. Thursday -- Cloudy and continued cool, highs from the 40s in the west to the 60s in the southeast.

West Virginia: Today -- Partial clearing, high in the 50s, low in the 40s. Thursday -- Increasing cloudiness with periods of rain likely, high in the 50s.

Extended Area Forecast for Friday through Sunday -- Chance of rain through the period with partial clearing on Saturday. Highs will range from the 50s to low 60s, lows will be in the 10s and 40s. Normal Washington temperatures are a high of 56 and a low of 38.

Lower Potomac and Chesapeake Bay -- Chance of rain. Visibility will be 5 miles or more diminishing to less than 1 mile in rain. Winds will shift to the northeast at 8 to 15 knots. Waves will average 1 to 2 feet.

The National Weather Forecast for today -- Rain is probable across most of the southern half of the nation. Snow will return to the southern Rocky Mountains and spread eastward into the Texas Panhandle and western Kansas. Rain will spread across Texas and Louisiana into the southern Plains and the Ohio Valley. Rain is also forecast for the middle Atlantic Coast states. Sunshine across the northern half of the nation will bring the temperatures above freezing. The Gulf Coast will have partly sunny skies with mild temperatures. The Pacific Northwest will be cool as will New England. Almanac Data for today: The sun rises 6:50 a.m., sets 4:55 p.m; moon rises 5:56 p.m., sets 7:22 a.m. Tides: high 8:18 a.m. and 8:39 p.m., low 2:40 a.m. and 2:50 p.m. High and low tides at the following locations may be obtained by substracting 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 (1/4), Solomons Island (6 1/4), Point Lookout (7).

The Council of Government's Air Quality Index for yesterday showed the high reading in the Washington area during the 3 p.m. period was 31 for the pollutant, photochemical oxidants. Index values between 25 and 49 indicate fair air quality. When the index exceeds 1-10 the air is considered very unhealthy and individuals with lung, heart and eye aliments are urged to restrict their activity. The forecast for today indicates that the air quality will improve.

The National Weather Service forecasts the Potomac River stage at Little Falls should remain between 2.3 and 2.9 feet today.

Washington data for yesterday: Highest temperature since midnight yesterday, 69 degrees at 1:40 p.m. Lowest temperature since midnight, 53 degees at 6:40 a.m. Excess of temperature since Nov. 1, 87 degrees. Excess of temperature since Jan. 1, 181 degrees. Record high temperature for today, 79 degrees in 1973. Record low temperature for today, 20 degrees in 1905. Relative humidity: maximum, 83 percent at 7 a.m.; minimum, 51 percent at 3 p.m. 24 hour precipitation, none. Deficiency of precipitation since Jan. 1, 94 inches. Highest observed wind since 7 a.m., 18 miles per hour from the south-southwest at 3:02 p.m. Peak gust since 7 a.m., 25 miles per hour from the south at 3:20 p.m. Local Temp., Humidity(TABLE) Time(COLUMN)T.(COLUMN)H. 12 midnite(COLUMN)57(COLUMN)69 1 a.m.(COLUMN)57(COLUMN)69 2 a.m.(COLUMN)57(COLUMN)72 3 a.m.(COLUMN)56(COLUMN)74 4 a.m.(COLUMN)56(COLUMN)74 5 a.m.(COLUMN)55(COLUMN)77 6 a.m.(COLUMN)54(COLUMN)80 7 a.m.(COLUMN)53(COLUMN)63 8 a.m.(COLUMN)54(COLUMN)83 9 a.m.(COLUMN)58(COLUMN)72 10 a.m.(COLUMN)60(COLUMN)67 11 a.m.(COLUMN)62(COLUMN)63 12 noon(COLUMN)65(COLUMN)58 1 p.m.(COLUMN)68(COLUMN)55 2 p.m.(COLUMN)69(COLUMN)53 3 p.m.(COLUMN)69(COLUMN)51 4 p.m.(COLUMN)69(COLUMN)51 5 p.m.(COLUMN)66(COLUMN)61 6 p.m.(COLUMN)65(COLUMN)65 7 p.m.(COLUMN)65(COLUMN)63(END TABLE) Temperature ending 7 a.m. (Est) yesterday:(TABLE) City(COLUMN)H.(COLUMN)L. Albany(COLUMN)43(COLUMN)41 Albuquerque(COLUMN)57(COLUMN)36 Amarillo(COLUMN)64(COLUMN)41 Anchorage(COLUMN)32(COLUMN)11 Asheville(COLUMN)68(COLUMN)45 Atlanta(COLUMN)71(COLUMN)59 Atlantic City(COLUMN)54(COLUMN)51 Austin(COLUMN)82(COLUMN)65 Baltimore(COLUMN)54(COLUMN)51 Billings(COLUMN)19(COLUMN)10 Birmingham(COLUMN)76(COLUMN)53 Bismarck(COLUMN)26(COLUMN)20 Boise(COLUMN)37(COLUMN)14 Boston(COLUMN)43(COLUMN)40 Brownsville(COLUMN)87(COLUMN)70 Buffalo(COLUMN)58(COLUMN)53 Burlington, Vt.(COLUMN)42(COLUMN)38 Casper(COLUMN)22(COLUMN)-10 Charleston, S.C.(COLUMN)71(COLUMN)63 Charleston, W.V.(COLUMN)77(COLUMN)58 Charlotte(COLUMN)70(COLUMN)49 Cheyenne(COLUMN)37(COLUMN)15 Chicago(COLUMN)67(COLUMN)33 Cincinnati(COLUMN)72(COLUMN)60 Cleveland(COLUMN)64(COLUMN)57 Columbia, S.C.(COLUMN)76(COLUMN)51 Dal.-Ft. Worth(COLUMN)75(COLUMN)65 Dayton(COLUMN)68(COLUMN)54 Denver(COLUMN)50(COLUMN)23 Des Moines(COLUMN)59(COLUMN)26 Detroit(COLUMN)63(COLUMN)32 Duluth(COLUMN)38(COLUMN)27 El Paso(COLUMN)66(COLUMN)45 Evansville(COLUMN)78(COLUMN)55 Fairbanks(COLUMN)29(COLUMN)-2 Fargo(COLUMN)33(COLUMN)17 Flagstaff(COLUMN)35(COLUMN)28 Great Falls(COLUMN)20(COLUMN)5 Hartford(COLUMN)46(COLUMN)40 Helena(COLUMN)26(COLUMN)-4 Honolulu(COLUMN)80(COLUMN)71 Houston(COLUMN)78(COLUMN)70 Indianapolis(COLUMN)73(COLUMN)46 Jackson(COLUMN)81(COLUMN)64 Jacksonville(COLUMN)76(COLUMN)62 Juneau(COLUMN)33(COLUMN)31 Kansas City(COLUMN)63(COLUMN)29 Las Vegas(COLUMN)55(COLUMN)44 Little Rock(COLUMN)80(COLUMN)64 Los Angeles(COLUMN)53(COLUMN)45 Louisville(COLUMN)77(COLUMN)64 Memphis(COLUMN)79(COLUMN)66 Miami Beach(COLUMN)80(COLUMN)75 Midland(COLUMN)71(COLUMN)55 Milwaukee(COLUMN)80(COLUMN)32 Mpls.-St. Paul(COLUMN)50(COLUMN)29 Nashville(COLUMN)77(COLUMN)59 New Orleans(COLUMN)81(COLUMN)57 New York(COLUMN)51(COLUMN)48 Norfolk(COLUMN)63(COLUMN)14 North Platte(COLUMN)35(COLUMN)16 Oklahoma City(COLUMN)65(COLUMN)45 Omaha(COLUMN)51(COLUMN)20 Orlando(COLUMN)87(COLUMN)67 Philadelphia(COLUMN)52(COLUMN)50 Phoenix(COLUMN)66(COLUMN)51 Pittsburgh(COLUMN)59(COLUMN)52 Portland, Ore.(COLUMN)44(COLUMN)20 Raleigh(COLUMN)69(COLUMN)55 Rapid City(COLUMN)25(COLUMN)-5 Reno(COLUMN)33(COLUMN)22 Richmond(COLUMN)60(COLUMN)44 St. Louis(COLUMN)78(COLUMN)42 St. Prbg-Tampa(COLUMN)81(COLUMN)63 Salt Lake City(COLUMN)40(COLUMN)24 San Antonio(COLUMN)82(COLUMN)68 San Diego(COLUMN)62(COLUMN)56 San Francisco(COLUMN)51(COLUMN)45 San Juan(COLUMN)86(COLUMN)73 St. Ste. Marie(COLUMN)50(COLUMN)35 Seattle(COLUMN)44(COLUMN)28 Shreveport(COLUMN)81(COLUMN)68 Sioux Falls(COLUMN)43(COLUMN)21 Spokane(COLUMN)28(COLUMN)11 Syracuse(COLUMN)50(COLUMN)46 Topeka(COLUMN)61(COLUMN)28 Tucson(COLUMN)65(COLUMN)52 Tulsa(COLUMN)73(COLUMN)45 Washington(COLUMN)57(COLUMN)53 Wichita(COLUMN)59(COLUMN)33(END TABLE) Temperatures (Western Hemisphere)(TABLE) City(COLUMN)Weather(COLUMN)High(COLUMN)Low Acapulco(COLUMN)clear(COLUMN)87(COLUMN)72 Bogota(COLUMN)rain(COLUMN)66(COLUMN)46 Calgary(COLUMN)cloudy(COLUMN)23(COLUMN)07 Culiacan(COLUMN)cloudy(COLUMN)90(COLUMN)64 Edmonton(COLUMN)pt. cldy.(COLUMN)25(COLUMN)12 Kingston(COLUMN)cloudy(COLUMN)87(COLUMN)75 Montego Bay(COLUMN)fair(COLUMN)85(COLUMN)73 Mexico City(COLUMN)haze(COLUMN)73(COLUMN)50 Monterrey(COLUMN)cloudy(COLUMN)79(COLUMN)64 Montreal(COLUMN)rain(COLUMN)41(COLUMN)37 Nassau(COLUMN)pt. cldy.(COLUMN)85(COLUMN)73 Ottawa(COLUMN)drizzle(COLUMN)41(COLUMN)32 Regina(COLUMN)snow(COLUMN)21(COLUMN)18 St. Kitts(COLUMN)fair(COLUMN)87(COLUMN)73 Toronto(COLUMN)cloudy(COLUMN)44(COLUMN)46 Vancouver(COLUMN)clear(COLUMN)43(COLUMN)25 Vera Cruz(COLUMN)pt. cldy.(COLUMN)86(COLUMN)73 Winnipeg(COLUMN)snow(COLUMN)27(COLUMN)19(END TABLE)