(Reuters) – A heatwave that will blanket the Southwest United States of America starting Wednesday, and pushing temperatures above 100 F the remainder of the week is expected. Forecasters advised residents to avoid being outside and to limit their physical activity.

The National Weather Service (NWS), in multiple advisory, stated that afternoon temperatures will rise to well over 100° Fahrenheit (38 C), across Southern Texas, Arizona, Central California, and Western Nevada. This forecast is good until Sunday night.

It was already 100° in Phoenix on Wednesday morning and would reach 107 degrees by afternoon in Las Vegas. It reached 106 at both Furnace creek and Stovepipe Wells, Death Valley, California around noon.

Morgan Stessman from Las Vegas, a NWS meteorologist said that it is common to observe this phenomenon in June. If you’re thinking of doing outdoor activities in the morning, or late at night, it is best to plan them for either early morning (or later in evening).

According to the weather service, extreme heat can significantly raise the risk of heat-related diseases in people who work outdoors or drink alcohol.

In anticipation of hot weather, health officials from the Phoenix and Las Vegas metros opened cooling stations.

Clark County in Nevada, which is home to Las Vegas, tweeted that “Keep hydrated” and warned against leaving pets and children unattended in cars.