The largest threat exists across the area shaded in red, which indicates a "moderate risk" for severe weather. The yellow shading indicates a "slight risk" for severe weather. The slight/moderate terminology refers to the probability of severe weather within 25 miles of any point within the shaded area. While the slight risk may see less of a chance for severe weather, it doesn't mean that the storms in that area won't be dangerous.
According to the SPC's technical discussion, the outbreak will begin with discrete supercells across the moderate (red shaded) risk area, capable of producing tornadoes, hail larger than golf balls, and damaging winds. This is where the risk for tornadoes will be greatest.
As the day progresses, the supercells will begin to merge with one another and form a line of severe thunderstorms, and the greatest threat will transition from tornadoes to damaging winds.
Keep up-to-date on the latest severe weather forecasts from the Storm Prediction Center and the National Weather Service today and tomorrow. Make sure you know what to do if your location goes under a tornado warning — scout out the safest part of your home or office, and make a plan in case you're in your car and need to get to quickly the nearest sturdy building.