The National Weather Service has issued a tornado watch is in effect throughout the region until 11 p.m.

Showers and thunderstorms are likely, mainly before 1 a.m. Some storms could be severe, with large hail and damaging winds. Mostly cloudy, with a low around 65. South wind 5 to 10 mph. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.

Greater Pennsylvania Red Cross disaster teams are on standby to respond to needs across the 61-county region including mobilizing vehicles to provide emergency assistance or sheltering if severe weather significantly impacts communities.

It is critical that residents know the difference between a watch and warning and when to act.

A watch means severe weather such as a Thunderstorm, Tornado, or Flash Flooding event is possible. A warning means conditions are expected within 36 hours and immediate action is necessary.

A thunderstorm is considered severe if it produces hail at least 1 inch in diameter or has wind gusts of at least 58 mph. Every thunderstorm produces lightning, which kills more people each year than tornadoes or hurricanes. Heavy rain from thunderstorms can cause flash flooding, and high winds can damage homes and blow down trees and utility poles, causing widespread power outages.

The Red Cross advises:

• If a severe thunderstorm warning is issued, take shelter in a substantial building or in a vehicle with the windows closed. Get out of mobile homes that can blow over in high winds.

• If you are outside and cannot reach a safe building, avoid high ground; water; tall, isolated trees; and metal objects such as fences or bleachers. Picnic shelters, dugouts and sheds are NOT safe.

• Listen to local news or NOAA Weather Radio for emergency updates. Watch for signs of a storm, like darkening skies, lightning flashes or increasing wind.

• Postpone outdoor activities if thunderstorms are likely to occur. Many people struck by lightning are not in the area where rain is occurring. Stay indoors; avoid beaches, riverbanks and floodwaters.

• If you can hear thunder, you are close enough to be in danger from lightning. If thunder roars, go indoors! The National Weather Service recommends staying inside for at least 30 minutes after the last thunderclap.

• If you are driving, try to safely exit the roadway and park. Stay in the vehicle and turn on the emergency flashers until the heavy rain ends. Avoid touching metal or other surfaces that conduct electricity in and outside the vehicle.

• Avoid electrical equipment and telephones. Use battery-powered TVs and radios instead.

• Shutter windows and close outside doors securely. Keep away from windows.

• Do not take a bath, shower or use plumbing.

• Use flashlights in the dark if the power goes out. Avoid using candles.

• Keep cell phones charged as power outages may occur because of the storm.

• Find important documents and keep them safe from water. Consider photographing important documents in case of loss.

The rest of the forecast:

Friday: Mostly sunny, with a high near 83. West wind 10 to 15 mph, with gusts as high as 30 mph.

Friday Night: Mostly clear, with a low around 55. Northwest wind around 10 mph.

Saturday: Mostly sunny, with a high near 65. Northwest wind around 15 mph, with gusts as high as 30 mph.

Saturday Night: Mostly clear, with a low around 47.

Juneteenth: Sunny, with a high near 70.

Sunday Night: Mostly clear, with a low around 48.

Monday: Sunny, with a high near 75.

Monday Night: Mostly cloudy, with a low around 55.

Tuesday: A chance of showers. Partly sunny, with a high near 75. Chance of precipitation is 30%.

Tuesday Night: A chance of showers. Partly cloudy, with a low around 60. Chance of precipitation is 40%.

Wednesday: A chance of showers. Mostly sunny, with a high near 82. Chance of precipitation is 30%.

Wednesday Night: A chance of showers. Mostly cloudy, with a low around 63. Chance of precipitation is 30%.

Thursday: A chance of showers. Mostly sunny, with a high near 81.