CREATE TABLE "train" (
    "id" int,
    "train_number" int,
    "name" text,
    "origin" text,
    "destination" text,
    "time" text,
    "interval" text,
    primary key ("id")
)

CREATE TABLE "station" (
    "id" int,
    "network_name" text,
    "services" text,
    "local_authority" text,
    primary key ("id")
)

CREATE TABLE "route" (
    "train_id" int,
    "station_id" int,
    primary key ("train_id", "station_id"),
    foreign key ("train_id") references `train`("id"),
    foreign key ("station_id") references `station`("id")
)

CREATE TABLE "weekly_weather" (
    "station_id" int,
    "day_of_week" text,
    "high_temperature" int,
    "low_temperature" int,
    "precipitation" real,
    "wind_speed_mph" int,
    primary key ("station_id", "day_of_week"),
    foreign key ("station_id") references "station"("id")
)
SELECT avg(high_temperature) ,  day_of_week FROM weekly_weather GROUP BY day_of_week
What is the average high temperature for each day of week?