Enhanced features of the text-based NWS Severe Thunderstorm Warning
Updated to change implementation date to July 28, 2021, when the National Weather Service (NWS) will implement new and enhanced features in the text products of the Severe Thunderstorm Warning (SVR) and the Special Weather Statement (SPS) for instances of sub-severe convective events. Although there are changes in both products that require different levels of attention by end users, they will be operationally enabled at the same time across all NWS Weather Forecast Offices (WFOs).
The primary addition to SVRs will be the new damage threat categories, as part of the Impact-Based Warning (IBW) coded tags, at the bottom of the product. Depending on the selection of wind and/or hail values in the warning, SVRs will now be assigned one of three threat-level categories. The lowest-end category will not receive a damage threat IBW tag. These coded threat tags will appear below the double ampersand (&&) and just below the supplemental polygon location and storm motion information portion of the alphanumeric/text product.
New definitions and criteria
The container in SVRs for the damage threat categories is the “THUNDERSTORM DAMAGE THREAT” IBW coded tag. The tag for the upper two categories for SVRs will be set to either “CONSIDERABLE” or “DESTRUCTIVE,” depending on hail size and/or wind magnitude. The highest-level category would appear in the tag line, even if both categories are reached through the selected value of either wind or hail. The base-level SVRs will not invoke the damage threat tag and will only display the wind and hail amounts as they appear in the current operational product. SVRs that contain either of the damage threat tags would be based on the following minimum trigger criteria: CONSIDERABLE...1.75 inch diameter hail (golf ball-sized) and/or 70 mph thunderstorm winds.
DESTRUCTIVE...2.75 inch diameter hail (baseball-sized) and/or 80 mph thunderstorm winds.
All changes to the SVR will also be incorporated into the Severe Weather Statement (SVS), which serves as the official update/follow-up alphanumeric product for SVRs.
SVRs containing the “DESTRUCTIVE” tag will be recommended to activate a Wireless Emergency Alert (WEA) to mobile devices through the Federal Emergency Management Agency’s (FEMA’s) Integrated Public Alert Warning System (IPAWS). This added capability is aimed at promoting instant and immediate life preservation actions for this level of hail and/or wind threat. A WEA message would be activated for any SVR, whether in the initial issuance or in any update SVS that carries the “DESTRUCTIVE” tag. This full activation capability should be activated at some point on or after the July 28, 2021 implementation of the change to SVRs and this change to WEA messages will be sent out as a separate Service Change Notice (21-23) that describes the different messages for wind and hail threats.
Additional minor changes to the other IBW tags in the SVR can be found in the Product Description Document, particularly for the wind and hail tags. These changes will also be made to the pertinent tags in the TOR and the sub-severe Special Weather Statement (SPS).
Examples of the Impact-Based Warning (IBW) categories for the Severe Thunderstorm Warning (SVR) are contained in the document linked below:
Information Statement (20-49) describing these changes is online at: https://www.weather.gov/media/notification/pns20-49severe_thunderstorm_IBW.pdf
Special Weather Statements
The primary change to the SPS for sub-severe convective thunderstorm events is the complete reformatting of the text product into the IBW format. As it does with convective warnings, the IBW format separates out key information about the threat(s), including the threat type(s), source of the information, and general impacts from the threat(s) into bulleted sections titled HAZARD, SOURCE, and IMPACT. This format also reiterates the impact information in a succinct format at the end of the text product, using parsable coded tag lines. Formatting of the IBW tags section will follow the new changes to the SVR IBW tags (linked in this notice), not the current operational version.
Additionally, WFOs that currently utilize the subheadline of “Significant Weather Advisory” will revert to a generic headline that succinctly describes that a strong storm/line of strong storms will impact certain counties/parishes through the valid time of the statement. Currently, this subheadline is not used across all WFOs operationally, and this change will baseline the use of headlines in this product.
The SPS will also include two new basis phenomena of landspouts (weaker tornado-like funnels) and waterspouts that occur exclusively over closed, non-marine zoned inland lakes. No changes are being made to the SPS format or issuance criteria for other weather hazards or general usage.
Examples of the IBW-formatted Special Weather Statements are contained in the document, linked below: https://nws.weather.gov/products/PDD/Sub_Severe_SPS_Examples_2021.pdf
The Public Information Statement (20-53) describing these changes is online at: https://www.weather.gov/media/notification/pdf2/pns20-53impact-based_sps.pdf
Additional comments/questions on these changes can be directed to: Gregory.M.Schoor@noaa.govNWS Severe Weather Services Program Manager. National Public Information Statements are online at: https://www.weather.gov/notification/