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Experimental SPC Day 4-8 Severe Thunderstorm Outlook Change Page

Overview of the Experimental SPC Day 4-8 Severe Thunderstorm Outlook Change

Public Information Notice (PNS): http://www.nws.noaa.gov/om/notification/pns14spcday4-8outlooks.htm.

Product Description Document (PDD): http://products.weather.gov/PDD/spc_day4-8outlooks_pdd.doc.

The public comment period ended on June 17, 2014.

Q: How are the outlooks changing for Day 4-8?

A: Additional information is being added to extended range severe weather forecasts to better characterize the risk to our partners and the public. Traditionally, the threshold for denoting a "Severe" area in the Day 4 through 8 timeframe was based on a 30 percent total severe threshold. That threshold will be retained, and another probability, 15 percent, will be added for areas where organized severe weather is possible. The addition of the 15 percent threshold will result in more consistency between the Day 4-8 graphic and corresponding text discussion, and will help SPC communicate threats earlier in the forecast process.

Here is an example of the proposed Day 4-8 outlook with 15% and 30% probability areas:

Below: Proposed Day 4 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48)
Day 4 Severe Weather Preview Graphics

More examples are below in the example section.

Q: Why is the SPC proposing to do this?

A: A primary goal of these changes is to bring better consistency to the risks communicated in SPC outlooks, from the short-range Day 1 outlooks through the extended range Day 4-8 outlooks. The changes are based on customer feedback and to better meet their needs.

Q: When will this change occur?

A: A 45-Day Public Comment Period regarding the proposed outlook changes ended on June 17, 2014. After assessing the feedback and incorporating any needed adjustments, a Service Change Notice will be issued at least 75 days prior to the implementation of changes to the outlook categories. Currently, a change is most likely to occur in September 2014.

Q: What role did social science play in proposing this change?

A: The NWS has a strong commitment to engaging the social sciences in evolving our services, and this community has helped inform our decision making for this change.


Technical Details of the Experimental SPC Day 4-8 Severe Thunderstorm Outlook Change

If the outcome of the experiment results in the proposal being implemented, the effective date would be mid-to-late September 2014. At that time, the NWS Storm Prediction Center (SPC) Day 4-8 Severe Weather Outlook will include five separate outlook graphics, one for each individual day. Currently, a single graphic for all five days is produced.

Areas will be delineated by a line labeled 15% where the total severe weather probabilities are at least 15 percent within 25 statute miles of any point. Areas will also be delineated by a line labeled 30% where the total severe weather probabilities are at least 30 percent within 25 statute miles of any point. Prior to the proposed change date only areas of probabilities of 30% are available. The labels "D4", "D5", "D6", "D7", "D8" will no longer be used.

The following products would reflect these changes:

   WMO Header    AWIPS ID   Description:
   ACUS48 KWNS   SWOD48     Days 4-8 Convective Outlook Discussion
   WUUS48 KWNS   PTSD48     Days 4-8 Convective Outlook Areal Outline
   PGNW49 KWNS   RBG44O     Day 4 Red Book Graphic Total Probability of Severe Thunderstorms
   LDIZ48 KWNS              Day 4 NDFD Total Probability of Severe Thunderstorms
   PGNW50 KWNS   RBG55O     Day 5 Red Book Graphic Total Probability of Severe Thunderstorms
   LDIZ58 KWNS              Day 5 NDFD Total Probability of Severe Thunderstorms
   PGNW51 KWNS   RBG66O     Day 6 Red Book Graphic Total Probability of Severe Thunderstorms
   LDIZ68 KWNS              Day 6 NDFD Total Probability of Severe Thunderstorms
   PGNW52 KWNS   RBG77O     Day 7 Red Book Graphic Total Probability of Severe Thunderstorms
   LDIZ78 KWNS              Day 7 NDFD Total Probability of Severe Thunderstorms
   PGNW53 KWNS   RBG88O     Day 8 Red Book Graphic Total Probability of Severe Thunderstorms
   LDIZ88 KWNS              Day 8 NDFD Total Probability of Severe Thunderstorms

The following products would no longer be produced:

   WMO Header    AWIPS ID   Description:
   PGNM98 KWNS   RBG48O     Days 4-8 Red Book Graphic Categorical Outlook
   LDIZ47 KWNS              Day 4 NDFD
   LDIZ57 KWNS              Day 5 NDFD
   LDIZ67 KWNS              Day 6 NDFD
   LDIZ77 KWNS              Day 7 NDFD
   LDIZ87 KWNS              Day 8 NDFD
The "points" product (PTSD48) would include labels of "0.15" (15 percent) and "0.30" (30 percent).

Product graphics and points product examples:

Below: Proposed Day 5 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48)
Day 5 Severe Weather Preview Graphics
Below: Proposed Day 6 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48)
Day 6 Severe Weather Preview Graphics
Below: Proposed Day 7 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48)
Day 7 Severe Weather Preview Graphics
Below: Proposed Day 8 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48)
Day 8 Severe Weather Preview Graphics
Weather Topics:
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Page last modified: June 19, 2014
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