Convective Outlooks
The Storm Prediction Center issues convective outlooks (AC) consisting of categorical and probability forecasts describing the general threat of severe convective storms over the contiguous United States for the next 6–192 hours (Day 1–Day 8). They are labeled and issued by day and are issued up to five times a day.
The categorical risks are general thunderstorms (green shaded area/previously brown line before April 2011), "SEE TEXT" (black, textual label on map indicating potential for isolated severe storms or near-severe storms), "SLGT" (yellow shaded area/previously green line indicating slight risk of severe weather), "MDT" (red shaded area/previously red line indicating moderate risk of severe weather), and "HIGH" (pink shaded area/previously fuchsia line indicating high risk of severe weather). Significant severe areas (referred to as "hatched areas" because of their representation on outlook maps) refer to a threat of increased storm intensity that is of "significant severe" (F2/EF2 or stronger tornado, 2 inches (5 cm) or larger hail, or 75 mph (120 km/h) winds or greater) level.
In April 2011, the SPC began issuing new graphics for categorical and probabilistic outlooks. The new format includes shading of risk areas and population, county, and interstate overlays. The colors were changed as mentioned above as well. The new shaded maps also include changes to the probability color shades on each outlook.
Public severe weather outlooks (PWO) are issued when a significant or widespread outbreak is expected, especially for tornadoes. From November to March, it can also be issued for any threat of significant tornadoes in the nighttime hours, noting the lower awareness and greater danger of tornadoes at that time of year.
Read more about this topic: Storm Prediction Center