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Hazardous Inflight Weather Advisory Service (HIWAS)
From SKYbrary Wiki
Hazardous Inflight Weather Advisory Service (HIWAS), available in the United States under Federal Aviation Administration (FAA) sponsorship, is a continuous broadcast of hazardous weather information. This information includes AIRMETs, SIGMETs, Convective SIGMETs, and urgent PIREPs and is transmitted using the voice capability of selected VORs.
Availability of HIWAS information on a specific VOR is indicated on an enroute or terminal area chart by an "H" in the upper right corner of the box surrounding the navaid frequency information.