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SPC Day 4-8 Severe Thunderstorm Outlook Change Page

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

Multimedia briefing for the Day 4-8 outlook changes: http://www.spc.noaa.gov/misc/2014_D48_OutlookChanges.mp4.

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.

Q: How have the outlooks changed for Day 4-8?

A: Starting on December 16, 2014, additional information has been 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, has been 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 helps SPC communicate threats earlier in the forecast process.

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

Below: Day 4-8 Severe Weather Outlook Overview. This animated gif is only available on the SPC website
Day 4-8 Severe Weather Overview Graphics

More examples are below in the example section.

Q: Why is the SPC doing 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: What role did social science play in 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 SPC Day 4-8 Severe Thunderstorm Outlook Change

Starting December 16, 2014, the NWS Storm Prediction Center (SPC) Day 4-8 Severe Weather Outlook includes five separate outlook graphics, one for each individual day. Previously, a single graphic for all five days was produced.

Areas are 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 are also 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 change, only areas of probabilities of 30% were available. The labels "D4", "D5", "D6", "D7", "D8" are no longer 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 are no longer produced as of December 16, 2014 at 1500 UTC:

   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) now includes labels of "0.15" (15 percent) and "0.30" (30 percent).

Product graphics and points product examples:

Below: Day 4 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48|KML|shapefile)
Day 4 Severe Weather Preview Graphics
Below: Day 5 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48|KML|shapefile)
Day 5 Severe Weather Preview Graphics
Below: Day 6 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48|KML|shapefile)
Day 6 Severe Weather Preview Graphics
Below: Day 7 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48|KML|shapefile)
Day 7 Severe Weather Preview Graphics
Below: Day 8 Severe Weather Outlook example (Areal Outline Product Example WUUS48 KWNS PTSD48|KML|shapefile)
Day 8 Severe Weather Preview Graphics
Weather Topics:
Watches, Mesoscale Discussions, Outlooks, Fire Weather, All Products, Contact Us

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National Centers for Environmental Prediction
Storm Prediction Center
120 David L. Boren Blvd.
Norman, OK 73072 U.S.A.
spc.feedback@noaa.gov
Page last modified: December 19, 2014
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