* Brownout in parts of New York City
* Power grids expect to have enough power
* Temperatures could reach record Thursday
By Scott DiSavino
NEW YORK, June 21 (Reuters) - A heat wave blanketed the U.S. Mid-Atlantic and Northeast, sparking a brownout in New York City an d forced utilities to ask customers to conserve electricity.
Despite local transmission problems, regional power grid operators in New York, New England and the 13 states served by a regional transmission group expected to have enough power to meet soaring demand on Thursday, the second day of the mini heat wave.
After reaching 94 degrees Fahrenheit (34 Celsius) on Wednesday, temperatures in New York, the nation's biggest metropolitan area, were expected Thursday to match the record high for the day of 97 degrees before slipping to 92 degrees on Friday and into the 80s over the weekend.
The National Weather Service issued a heat advisory until Thursday night.
Average highs in New York at this time of year are about 81.
New York utility Consolidated Edison Inc continued to reduce power in neighborhoods in Queens and Brooklyn Thursday morning due to equipment problems.
About 600 customers in Queens, Brooklyn and the Bronx had no power early Thursday, Con Edison spokesman Chris Olert told Reuters.
Wednesday night, Con Edison reduced power and asked customers to curtail use of non-essential appliances in affected neighborhoods to protect equipment and maintain service as crews work to solve the problem.
In brownouts, incandescent lights are dimmer, water is warm rather than hot, and motors move slower.
The New York Power Authority (NYPA) and New York's power grid operator, the New York Independent System Operator, activated programs in the city and parts of the state Wednesday afternoon to curb peak demand. NYPA said it may activate the demand response program again on Thursday.
Under the programs, subway cars lose air conditioning, people wait longer for elevators, and office lobby lights are dimmed.
Still, utilities say they keep the lights on and air conditioners humming for everyone as well as keep power prices from climbing too high.
Besides reducing usage, demand-response participants can run onsite power generators to take the load off the grid.
The PJM regional transmission grid issued a hot-weather alert for Wednesday and Thursday, telling generators and transmission owners to delay maintenance on plants and power lines until the heat wave passes.
PJM is the biggest power grid in the United States, serving 60 million people in 13 Mid-Atlantic and Midwest states.
Power prices in PJM, the most active hub in the United States, jumped about 70 percent on Wednesday to the $150s per megawatt hour for Thursday delivery. New England prices jumped almost 80 percent to the $170s for Thursday.
New England's grid operator also asked generators and transmission owners to put off maintenance during the heat wave.