Lower Merion Township residents face dangerous heat conditions this week as the National Weather Service has issued an Extreme Heat Warning for Wednesday, July 15, effective from 10 a.m. to 8 p.m.

The NWS Philadelphia office forecasts a high near 99°F on Wednesday with heat index values as high as 104°F across the Philadelphia and Montgomery County area. Dense areas most affected by the urban heat island effect, including parts of Montgomery and Delaware counties, are under an extreme heat watch for all day Wednesday, meaning the NWS considers life-threatening conditions possible. A broader heat advisory took effect Tuesday afternoon, July 14, and extends into Wednesday evening.

The heat wave arrives less than two weeks after a deadly stretch that killed at least seven people in Philadelphia between July 1 and July 4. That earlier event marked the first time in Philadelphia's recorded history that three consecutive days topped 101°F. Across Pennsylvania, 127 daily temperature records were broken or matched during that July 1–4 period, according to USA Today. Over 128 million Americans were under a heat warning, watch, or advisory as of Tuesday, July 14, according to NWS data.

What the forecast shows

The NWS seven-day forecast for the Lower Merion area as of Tuesday, July 14:

  • Tuesday, July 14: Sunny, high near 92°F, SW wind 5–15 mph
  • Wednesday, July 15: Sunny and hot, high near 99°F, heat index up to 104°F
  • Wednesday night: Partly cloudy, low around 76°F
  • Thursday, July 16: High not specified in NWS forecast; overnight low around 74°F
  • Friday, July 17: Mostly sunny, high near 96°F
  • Saturday, July 18: Sunny, high near 94°F
  • Sunday, July 19: Chance of showers and thunderstorms after 2 p.m., high near 93°F

Highs remain in the 90s through the weekend, with relief possible early next week.

What's driving the heat

The NWS said the heat front is moving in from the Midwest. A dry cold front is expected to pass late Wednesday, which will lower temperatures slightly, but above-normal readings in the upper 80s and low 90s could persist through the weekend.

By late in the week, NWS forecasters said there is a possibility of severe thunderstorms.

How to stay safe

The NWS warns that heat-related illnesses increase significantly during extreme heat and high humidity events. Residents should:

  • Check on elderly neighbors and those without air conditioning
  • Avoid strenuous outdoor activity during peak afternoon hours
  • Never leave children or pets in parked vehicles
  • Watch for signs of heat exhaustion: heavy sweating, weakness, nausea, dizziness

For cooling center locations and emergency information, residents can visit montgomerycountypa.gov/news or call Montgomery County at 610-278-3000.