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Experimental SPC Day 1, 2, 3 Convective Outlook Change Page

Overview of the Experimental SPC Day 1-3 Outlook Change

Product Description Document (PDD): https://products.weather.gov/PDD/SPC_Day_1to3_Cat_Conv_Outlook.pdf.

The public comment period ended on June 17, 2014.

Q: How are the outlooks changing for Day 1, Day 2 and Day 3?

A: The SPC will revise Day 1 through Day 3 categorical severe weather outlooks to better communicate risk and describe the likelihood of severe weather. Format changes will also improve the use of SPC severe weather forecasts for customers who incorporate SPC outlooks into GIS systems.

The SPC is expanding the risk categories from four to five and clarifying the risk previously labeled as "See Text." That descriptor will be replaced by a categorical line and the term "Marginal" to denote areas with a 5 percent probability of severe weather. The upper end of the "Slight Risk" category will be renamed "Enhanced" (short for "Enhanced Slight") to denote a threshold 30 percent probability of severe wind or hail and/or a 10 percent chance of a tornado during the Day 1 period. For Days 2 and 3, the "Enhanced" risk category will denote a 30 percent total severe probability. The Moderate and High risk thresholds will remain essentially unchanged.

Current:

1. See Text
2. Slight (SLGT)
3. Moderate (MDT)
4. High (HIGH)

Proposed:

1. Marginal (MRGL) - replaces the current SEE TEXT and now is described with Categorical line on the SPC Outlook.
2. Slight (SLGT)
3. Enhanced (ENH) - will replace upper-end SLGT risk probabilities, but is not a MDT risk
4. Moderate (MDT)
5. High (HIGH)

The examples below juxtapose the proposed (left) and the current (right) outlook graphics for the marginal (MRGL) and enhanced (ENH) categories as opposed to the current slight (SLGT) category and SEE TEXT labels.

2011/06/01 1300Z Day 1 Outlook Preview Graphics
Proposed 2011/06/01 1300Z Day 1 Categorical Outlook (Proposed Areal Outline Product Example|KMZ|SHP) (Top)
2011/06/01 1300Z Day 1 Outlook Graphics
Current 2011/06/01 1300Z Day 1 Outlook Graphics (Current Areal Outline Product) (Top)

The examples below juxtapose the proposed (left) and the current (right) outlook graphics for the marginal (MRGL) and enhanced (ENH) categories as opposed to the current slight (SLGT) category.

2013/02/10 1630Z Day 1 Outlook Preview Graphics
Proposed 2013/02/10 1630Z Day 1 Categorical Outlook (Proposed Areal Outline Product Example|KMZ|SHP) (Top)
2013/02/10 1630Z Day 1 Outlook Graphics
Current 2013/02/10 1630Z Day 1 Outlook Graphics (Current Areal Outline Product) (Top)

The examples below juxtapose the proposed (left) and the current (right) outlook graphics for the marginal (MRGL) categorie as opposed to the current SEE TEXT labels which does not clearly define the geographical areas of concern.

2013/09/15 1630Z Day 1 Outlook Preview Graphics
Proposed 2013/09/15 1630Z Day 1 Categorical Outlook (Proposed Areal Outline Product Example|KMZ|SHP) (Top)
2013/09/15 1630Z Day 1 Outlook Graphics
Current 2013/09/15 1630Z Day 1 Outlook Graphics (Current Areal Outline Product) (Top)

The examples below juxtapose the proposed (left) and the current (right) outlook graphics for the marginal (MRGL) categorie as opposed to the current SEE TEXT labels which does not clearly define the geographical areas of concern.

2011/05/21 1730Z Day 2 Outlook Preview Graphics
Proposed 2011/05/21 1730Z Day 2 Categorical Outlook (Proposed Areal Outline Product Example|KMZ|SHP) (Top)
2011/05/21 1730Z Day 2 Outlook Graphics
Current 2011/05/21 1730Z Day 2 Outlook Graphics (Current Areal Outline Product) (Top)

Below is an example of a proposed Public Severe Weather Graphic that includes the new categories. This graphic is enlarged on the area of greatest risk and designed for use by media partners and social media.

Proposed 2011/04/27 1630Z Public Severe Weather Outlook Graphic
Proposed 2011/04/27 1630Z Public Severe Weather Outlook Graphic (Top)

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 being made based on customer feedback and to better meet their needs.

Example: Currently, a 10 percent tornado probability including a risk of a significant tornado (>=EF2) is categorized as a Slight Risk. This is the same category used for a "low end" 15 percent risk of severe thunderstorm wind and hail events. In the new scheme, a 10 percent tornado probability that includes the chance of significant tornadoes would be categorized as an Enhanced Risk.

In addition, "See Text" does not currently convey a threat area, due to the lack of a contour in any "See Text" categorical forecast. And the current "Slight Risk" category covers too broad a range of severe weather probability values.

Q: Are there cases where the current categories will change based on the underlying severe weather probabilities?

A: The thresholds for traditional risk categories are essentially unchanged but there is some refinement in the underlying definitions to remain consistent with evolving trends in severe weather reporting. These refinements would only impact a couple of Day 1 tornado and severe wind outlooks during any year. A 15 percent tornado probability without a threat of an EF-2 or greater tornado at Day 1 will qualify as an Enhanced Day 1 tornado risk as opposed to the current scheme where it is a Moderate Day 1 Tornado Risk. Likewise, a 45 percent severe thunderstorm wind probability without a significant threat at Day 1 will qualify as an Enhanced Day 1 wind risk as opposed to the current scheme where it is a Moderate Day 1 wind risk.

Q: Why not a more comprehensive overhaul of all categorical outlook words (i.e. SLGT, MDT, HIGH)?

A: The categorical words Slight, Moderate and High have been used by SPC for nearly 35 years and are generally understood by the weather risk communication community. Making measured changes to the current system, we believe, is more effective than a wholesale change. These measured changes include: 1) moving to de-emphasize the specific words; and 2) working to communicate the level of risk to the public in multiple ways. This includes numerical risk categorization, appropriate colors to indicate severity, and strategic use of icons and symbols. Social scientists have encouraged us to communicate on multiple levels and not just with a single word, label or category.

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 mid-to-late September 2014.

Q: What role did social science play in making 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 Proposed SPC Day 1-3 Outlook Change

The proposed effective date is mid-to-late September 2014. NWS Storm Prediction Center (SPC) Day 1, Day 2, and Day 3 Convective Outlooks for the CONUS will include two new risk categories.

The addition of the new risk categories is based on customer feedback and the need to provide better consistency with other NWS products. Examples of these Outlooks (using historical data), are depicted below.

"MARGINAL" replaces the current SEE TEXT used in these products.

"ENHANCED" is an additional category to delineate areas of risk in the high end of the current SLIGHT risk, but below MODERATE risk.


Click on the links below to view the section:

Proposed Product Text Example Day 1 Outlook Descriptions Day 2, 3 Outlook Descriptions Product IDs To Be Changed

Below is an example of the Convective Outlook text product containing "MARGINAL" (MRGL) and "ENHANCED" (ENH) risk area delineations and Summary section. (Top)

   DAY 1 CONVECTIVE OUTLOOK
   NWS STORM PREDICTION CENTER NORMAN OK
   0110 AM CDT WED APR 27 2011
    
   VALID 271200Z - 281200Z
   
   ...THERE IS A HIGH RISK OF SVR TSTMS OVER PORTIONS OF NRN
   MS...AL...FAR NWRN GA AND SRN MIDDLE TN...
   
   ...THERE IS A MDT RISK OF SVR TSTMS OVER MUCH OF CNTRL AND NRN MS
   AND AL...NWRN GA...MUCH OF TN AND KY...WRN CAROLINAS...
   
   ...THERE IS AN ENH RISK OF SVR TSTMS FROM PARTS OF THE LOWER MS
   VALLEY TO THE UPPER OH VALLEY/CNTRL APPLACHIANS...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CNTRL GULF COAST TO THE
   NRN APPALACHIANS...
   
   ...THERE IS A MRGL RISK OF SVR TSTMS FROM THE LOWER MS VALLEY TO THE
   EAST COAST...
   
   ...SUMMARY...
   AN OUTBREAK OF TORNADOES AND DAMAGING WINDS IS EXPECTED TODAY THROUGH
   THIS EVENING OVER PORTIONS OF NORTHERN MS/AL...TN AND KY. FAST-MOVING
   SUPERCELLS WILL BE CAPABLE OF LONG-TRACKED STRONG TO VIOLENT
   TORNADOES.
   
   ...SYNOPSIS...
   (The rest of the discussion remains unchanged.)


With the addition of "MARGINAL" and "ENHANCED" categories, the new categorical Day 1-3 Outlooks will include contours for up to six (6) categories as follows: (Top)

Day 1: 
   a. General Thunderstorms
      - 10% or greater probability of non-severe or near severe thunderstorms. 

   b. Severe Category 1 - Marginal 
      - 2% or greater tornado probability, or 
      - 5% or greater severe hail or severe wind probability.

   c. Severe Category 2 - Slight 
      - 5% or greater tornado probability, or 
      - 15% or greater severe hail or severe wind probability.

   d. Severe Category 3 - Enhanced 
      - 10% or greater tornado probability, or 
      - 30% or greater severe hail or severe wind probability.

   e. Severe Category 4 - Moderate 
      - 15% or greater tornado probability AND 10% or greater probability 
        of an EF2+ tornado, or
      - 30% or greater tornado probability, or
      - 45% or greater severe wind probability AND 10% or greater 
        probability of a wind gusts 75 mph or greater, or
      - 45% or greater severe hail probability AND 10% or greater 
        probability of hail 2 inches or greater in diameter, or
      - 60% or greater severe wind probability, or
      - 60% or greater severe hail probability.

   f. Severe Category 5 - High 
      - 30% or greater tornado probability AND 10% or greater probability 
        of an EF2+ tornado, or
      - 45% or greater tornado probability, or
      - 60% or greater severe wind probability AND a 10% or greater 
        probability of a wind gust 75 mph or greater.

Day1 probability to categorical conversion table
Day 1 Outlook Probability to Category Conversion Table


Days 2 and 3: (Top)
   a. General Thunderstorms
      - 10% or greater probability of non-severe or near severe thunderstorms.

   b. Severe Category 1 - Marginal 
      - 5% or greater total severe probability.

   c. Severe Category 2 - Slight
      - 15% or greater total severe probability.

   d. Severe Category 3 - Enhanced 
      - 30% or greater total severe probability.

   e. Severe Category 4 - Moderate 
      - 45% or greater total severe probability AND 10% or greater 
        probability of an EF2+ tornado, a wind gust 75 mph or greater, or 
        hail 2 inches or greater in diameter, or
      - 60% or greater total severe probability (Day 2 only).

   f. Severe Category 5 - High (Day 2 only) 
      - 60% or greater total severe probability AND 10% or greater 
        probability of an EF2+ tornado or a wind gust 75 mph or greater.

Day2 probability to categorical conversion table

Day 2 Outlook Probability to Category Conversion Table
Day3 probability to categorical conversion table

Day 3 Outlook Probability to Category Conversion Table

The following products reflect the changes: (Top)

   WMO Header    AWIPS ID    Description
   ACUS01 KWNS   SWODY1      Day 1 Convective Outlook Discussion
   WUUS01 KWNS   PTSDY1      Day 1 Convective Outlook Areal Outline
   PGWE46 KWNS   RBG94O      Day 1 Red Book Graphic Categorical Outlook
   LDIZ17 KWNS               Day 1 NDFD Categorical Outlook
   ACUS02 KWNS   SWODY2      Day 2 Convective Outlook Discussion
   WUUS02 KWNS   PTSDY2      Day 2 Convective Outlook Areal Outline
   PGWK48 KWNS   RBG99O      Day 2 Red Book Graphic Categorical Outlook
   LDIZ27 KWNS               Day 2 NDFD Categorical Outlook
   ACUS03 KWNS   SWODY3      Day 3 Convective Outlook Discussion
   WUUS03 KWNS   PTSDY3      Day 3 Convective Outlook Areal Outline
   PGWI47 KWNS   RBG98O      Day 3 Red Book Graphic Categorical Outlook
   LDIZ37 KWNS               Day 3 NDFD Categorical Outlook

   The "points" products (PTSDY1, PTSDY2, and PTSDY3) will include new labels "MRGL" (Marginal)
   and "ENH" (Enhanced).

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Storm Prediction Center
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Page last modified: June 19, 2014
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