(Reuters) - California's power grid operator on Monday issued an alert to homes and businesses to conserve electricity on Tuesday and Wednesday when a heat wave is expected to blanket the state.

The California Independent System Operator (ISO), the grid operator, said it issued the so-called "Flex Alert" due to high temperatures across the western United States, reduced electricity imports into the state, tight natural gas supplies in Southern California and high wildfire risk.

The ISO's alert followed an earlier notice by Southern California Gas Co (SoCalGas), the gas utility for the southern part of the state.

SoCalGas issued a gas curtailment watch on Monday, notifying customers to be prepared to reduce gas use if needed, with power generators expected to burn more fuel this week than usual to keep air conditioners humming.

SoCalGas, a unit of California energy company Sempra Energy, said the watch would remain in effect until further notice.

High temperatures in Los Angeles were forecast to top 90 degrees Fahrenheit (32 Celsius) Monday-Friday with the mercury expected to reach 97 degrees on Wednesday, according to AccuWeather. The normal high in the city at this time of year is 84 degrees.

The ISO said consumers "can help avoid power interruptions" by turning off all unnecessary lights, using major appliances before 5 p.m. and after 9 p.m., and setting air conditioners to 78 degrees or higher.

Gas supplies are expected to remain tight in Southern California this summer and winter due to reduced availability from SoCalGas' Aliso Canyon storage facility in Los Angeles, following a massive leak between October 2015 and February 2016, and ongoing shutdowns of several pipelines.

SoCalGas projected gas demand would rise from 3.0 billion cubic feet per day (bcfd) on Monday to 3.1 bcfd on Tuesday and 3.2 bcfd on Wednesday and Thursday, while receipts of the fuel via pipelines into California would only total about 2.6 bcfd.

That means SoCalGas will have to tap storage fields to make up the difference, which could hurt the utility's ability to stockpile enough fuel to avoid curtailments for some power and industrial customers on the coldest days during the winter heating season.

State and federal agencies have projected SoCalGas will only be able to deliver about 3.6 bcfd from non-Aliso storage fields due to the Aliso limitations and pipeline outages, which has only occurred once in the summer in the past five years but is fairly common in the winter.

(Reporting by Scott DiSavino; editing by Jonathan Oatis and Susan Thomas)