If in summer, a themal low is near the ground whereas westerlies are in high attitude. As a result of the speedy velocity of wind in high attitude, the heat energy momentum of the ground conveys downward to quicken the wind speed near the ground.
In summer, thermal low is on the ground, and westerlies are in the high altitude, because the wind speed is greater in the high altitude and the theraml energy-momentum is transfered downwards on the ground, which can increase the wind speed on the ground.