@theguru

I will start using this as well once training is completed.

 

SPC will be introducing new information in Convective Outlooks starting in early March. The following thread will offer some basic information regarding these changes. The TL;DR: Outlook categories (1-5) are not changing! But there will be more info for peak hazard intensity.

The old 10% significant hazard outline is being replaced by three intensity levels (two for hail). These thresholds are not tied to a probability. They are our best estimate of what the maximum hazard intensity could be based on expected storm mode and environmental parameters.

 

 

Let's look at some examples of past outlooks & how they would look under this new intensity paradigm. In this tornado outlook, the old 10% hatched area is on the left. In the new intensity outlook (right), more detail is given showing where the strongest tornadoes are expected.

 

The important thing to remember: outlook categories (Level 1-5: Marginal, Slight, Enhanced, Moderate, High) are not changing! A High risk in 2026 means the same thing as a High risk in 2025. Only now we can graphically show where we expect the most intense storms.

Given the complexity of this change, we have developed a comprehensive training plan to ensure our Core Partners have access to detailed educational/training materials before we go live. This includes: NWS and broadcast meteorologists, emergency managers, and more!

In addition, training information will be available on our YouTube channel later in February with different videos for various user groups. Links and information will be shared here, as well as on our webpage, www.spc.noaa.gov, as it becomes available.

This project has been underway since 2019. It began in the Hazardous Weather Testbed (HWT) and SPC forecasters began drawing conditional intensity outlooks experimentally in 2021.

This final product is the result on multiple iterations based on lessons learned for the HWT, social science research, and forecaster feedback. We are excited to bring higher-resolution outlook and hazard information to you this spring!

 

 

I am ALWAYS learning in this forum.

High-end derechos, stay away!!

"High-end" derechos are exceptionally intense, long-lived, and destructive straight-line windstorms, often referred to as "inland hurricanes" due to their capacity to produce winds exceeding 100-120 mph. These events, which are rare but increasingly recognized for their massive economic impact, can cause widespread, sustained damage similar to a tornado outbreak, covering paths of over 400 miles. 

Here's something else just released today. 

new Data Viewer for Severe Hazards.  The dynamic and customizable data display on this page shows a 30-year history of lightning, wildfires, and severe storms. I can even obtain time-of-day data for one and four hours. Year, month, and day. They include all data or data from the previous 30 years. This provides the likelihood of every tornado or divides it into EF-1+, EF-2+, or EF-3+. 

Here are some maps for illustration. They cover March, April, May, and June.

 

 

 

Here are some maps for illustration. They cover March, April, May, and June.

 

 

I've been studying the changes mentioned in my first post. As I understand it so far, the S.P.C. is keeping the same risk categories and should be issued as in the past.

 

But now they are adding that the intensity of storms will now be conditional.  This means if a tornado/wind gust/hail report occurs, this will be how strong/intense/large they expect it to be. So they have added 3 intensity levels (2 for hail) and the individual graphics.

 

The categorical outlook graphics will have a visual update (including text moving labels from the image to a legend) but will otherwise represent the same expected impacts from each category as before. As I understand it, this means that numbers will no longer be added to the graphics. Just the color codes that correspond with the legend to the right of the graphic.

 

These intensity forecasts will be represented by the SPC as "Intensity Levels" or "Conditional Intensity Groups" (CIG). In the event that severe hazards materialize, these three intensity distributions (CIG1, CIG2, and CIG3) will be used to convey the increasing intensity of significant severe hazards. The current operational "SIGN" label will be replaced by these new Conditional Intensity Groups, which will be displayed on the SPC Severe Weather Outlook Day 1, 2, and 3 graphics and distributed via the SPC Outlook product.

 

This is how the probabilities and conditional intensity will be combined to create the outlook. The first column is the percentage chance of the event occurring. Across the bottom are the intensity levels. This means you can take the percentage row and move to the intensity column to get your risk. These are the same 5 risk levels used in the past, but now they are adding the intensity.

I'm still studying this and will post any changes to how I understand it as I learn more. 

 

 

@theguru

This is how I read the new outlook. For example, if you are in an area with a 15% chance of a tornado and the SPC gives a conditional intensity group of 1 (black arrow). Your area could see a possible tornado max expected of EF-2+. So if the cig increases the max expected strength of the tornado, if one forms, it increases.

I'm using a tornado as an example to try to explain this as I understand it. The same goes for wind and hail. 

 

 

 

The new approach differs from the previous one in that the high-risk area would simply remain high-risk. You would have to say that there is an equal chance of a powerful long-track tornado occurring throughout the entire region.

The new method will indicate which area of the high-risk area is most likely to experience strong tornadoes. They will therefore attempt to identify the area that has the best chance of witnessing a long-track strong tornado, even though there is a large area of high risk. 

This change will take affect on March 3, 2026

 

 

This is merely an illustration of the new SPC cig categories and how they will work. This is the severe hail forecast for portions of Oklahoma and Texas on Thursday. The yellow area may experience severe hail, but the hatched area indicates a supercell environment where the largest hail sizes, more than two inches, may occur. Hail with a diameter of less than two inches is likely to occur in the non-hatched area. 

I thought I would illustrate how this new system will work. I'm using today's SPC outlook for the south-central US.

 

The brown area has a 5–9% chance of seeing a tornado with a CIG 1 intensity level, according to the tornado outlook. This indicates that within 25 miles of a specific location, there is a slight chance of a tornado with the maximum predicted strength of EF2+. EF0-EF1 are primarily in the green hatched area.

 

Here is the hail outlook. Applying this to this map, it shows a red hatched area with a CIG 1 intensity level along with a 30-44% chance of hail. This means an enhanced risk of hail >2 inches in diameter could occur. In the yellow, there is a slight risk of hail of the same diameter. In the brown, there is a marginal risk of >2-inch hail.

 

 

 

Now for the severe wind outlook. Applying the same principle, The yellow is in a CIG 1 intensity level with a 15-29% chance of damaging winds. This translates to all storm modes, with peak wind gusts of 65+ kts. The brown has a 5-14% chance of the same.

 

 

@theguru