NWS Rename of Excessive Heat Watch and Warning

NWS Service Change Notice 24-88 states that Excessive Heat Watch and Warning would be renamed Extreme Heat Watch and Warning effective March 4, 2025. NWSI 10-515 records that transition in its revision history.

This original record-reading guide is a general reading aid, not cited evidence. It does not depict a source record; the article text and source links provide the facts.

Key points

• NWS Service Change Notice 24-88, timestamped “215 PM EDT Thu Sep 5 2024,” announced the rename with the subject line “Renaming of Excessive Heat Watch and Warning to Extreme Heat Watch and Warning: Effective March 4, 2025.”
• The notice retired the underlying VTEC phenomenon code “EH” and replaced it with “XH,” and assigned new alert map colors: Mediumvioletred for Extreme Heat Warning and Maroon for Extreme Heat Watch.
• National Weather Service Instruction 10-515, effective May 16, 2025 and superseding the November 20, 2024 edition, logs “Transition of Excessive Heat Watch/Warning to Extreme Heat Watch/Warning” as a dated revision in its own edition history.
• Neither record sets a nationwide temperature or heat-index threshold for issuing these products — that threshold is set locally.

Rename service notice

NWS Headquarters in Silver Spring, MD issued the change under the standard product header used for such notices:

“NOUS41 KWBC 051815 PNSWSH Service Change Notice 24-88 National Weather Service Headquarters Silver Spring MD 215 PM EDT Thu Sep 5 2024” (Service Change Notice 24-88)

Its subject line states the change and effective date directly:

“Subject: Renaming of Excessive Heat Watch and Warning to Extreme Heat Watch and Warning: Effective March 4, 2025” (Service Change Notice 24-88)

Alert code changes

The rename was not cosmetic text alone — it changed the machine-readable code NWS systems use to track the alert type, and it changed the color assigned to each product on NWS hazard maps.

“The Valid Time Event Code (VTEC) phenomena code “EH” for Excessive Heat Watch and Warning will be decommissioned and will be replaced by the Extreme Heat Watch and Warning VTEC phenomena code “XH”.“ (Service Change Notice 24-88)

“Extreme Heat Warning XH.W Mediumvioletred Extreme Heat Watch XH.A Maroon” (Service Change Notice 24-88)

NWS manual codification

National Weather Service Instruction 10-515 — the directive that specifies NWS non-precipitation weather products — was reissued to reflect the new names.

“NATIONAL WEATHER SERVICE INSTRUCTION 10-515 MAY 16, 2025” (NWSI 10-515)

“This directive supersedes NWSI 10-515, “WFO Non-Precipitation Weather Products (NPW) Specification,” dated November 20, 2024.“ (NWSI 10-515)

The instruction’s own revision history records the rename as the first listed change between those two editions:

“Transition of Excessive Heat Watch/Warning to Extreme Heat Watch/Warning.” (NWSI 10-515)

What this article does not answer

This article documents why and when the name changed — it does not state any nationwide temperature or heat-index number at which a Heat Advisory, Extreme Heat Watch, or Extreme Heat Warning is issued. NWSI 10-515 itself says that “the Extreme Heat Warning/Heat Advisory criteria are highly variable in different parts of the country due to climate variability and the effect of extreme heat on the local population,” and that local weather offices are “strongly encouraged to develop local criteria in cooperation with local emergency and health officials, and/or utilize detailed heat-health warning systems based on scientific research.” Because those thresholds are set locally rather than nationally, no single number applies everywhere. This article also makes no statement about any individual reader’s heat risk, exposure, or health, and readers should not use it to judge their own situation.

Source links

https://www.weather.gov/media/notification/pdf_2023_24/scn24-88_heat_haz_simp.pdf https://www.weather.gov/media/directives/010_pdfs/pd01005015curr.pdf