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|
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: