What is an Extreme Heat Warning and when is it issued in Pennsylvania?
(WHTM) — Much of the Midstate is under an Extreme Heat Warning, a first for the region. Sort of.
The National Weather Service at State College issued two separate Extreme Heat Warnings covering most of our area — one for Mifflin and Juniata counties, and another for Franklin, Perry, Dauphin, Lebanon, Cumberland, Adams, York, and Lancaster counties.
What is a heat dome? Here's what forecasters are talking about
The former is in effect from 10 a.m. to 8 p.m. Monday, and the latter is until 8 p.m. Wednesday with heat index values up to 108°F predicted
It's not the first time we've reached such temperatures, but it is a new term for the warning. Why?
It's part of what the NWS calls 'hazard simplification' which saw two alerts renamed nationwide in March.
WEATHER FORECAST > A hazy, hot, and humid week ahead
Effectively, if these conditions existed this time last year, we would be under an 'Excessive Heat Warning.'
The change of wording from 'Excessive' to 'Extreme,' the National Weather Service says, is part of an effort to 'better convey that heat is dangerous' and improve communication and messaging.
For an Extreme Heat Warning to be issued in all of Pennsylvania outside of metro Philadelphia, heat indexes must exceed 105°F. Metro Philadelphia uses 'Kalkstein Procedures.'
A Heat Advisory, which Mifflin and Juniata counties will be under until 8 p.m. Wednesday outside of when the Extreme Heat Warning is active, requires heat indices between 100°F and 105°F.
Copyright 2025 Nexstar Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
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