(WHTM) — With spring here, the battle of warm and cold air masses begins, which means severe weather in portions of the country. In Pennsylvania, we really do not see an uptick in crazy weather until late April or early May, though many parts of the country are facing constant threats of severe weather.

The National Weather Service has a department called the Storm Prediction Center, or SPC for short. This center issues all of the severe thunderstorm watches and tornado watches we see throughout the country.

A Day 1 Convective Outlook showing the HIGH-risk level of severe weather (Courtesy: NWS)

The SPC also has something called convective outlooks. These outlooks are catered to meteorologists at local National Weather Service offices and local meteorologists who are in charge of telling their communities about the weather.

The SPC issues Day 1Day 2, and Day 3 Convective Outlooks that depict non-severe thunderstorm areas and severe thunderstorm threats across the contiguous United States, along with a text narrative. The SPC states the categorical forecast specifies the level of the overall severe weather threat via numbers (e.g., 5), descriptive labeling (e.g., HIGH), and colors (e.g., magenta).

The probabilistic forecast directly expresses the best estimate of a severe weather event occurring within 25 miles of a point. The text narrative begins with a listing of severe thunderstorm risk areas by state and/or geographic region.

There are six categories and colors that the SPC can issue regarding thunderstorms. They are:

General or Non-Severe Thunderstorms:- Delineates, to the right of a line, where a 10% or greater probability of thunderstorms is forecast during the valid period. This area is outlined in light green.

1. Marginal Risk: An area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity. This area is out outlined in dark green

2. Slight Risk: An area of organized severe storms, which is not widespread in coverage with varying levels of intensity. This area is outlined in yellow.

3. Enhanced Risk – An area of greater (relative to Slight risk) severe storm coverage with varying levels of intensity. This area is outlined in orange.

4. Moderate Risk – An area where widespread severe weather with several tornadoes and/or numerous severe thunderstorms is likely, some of which should be intense. This risk is usually reserved for days with several supercells producing intense tornadoes and/or very large hail, or an intense squall line with widespread damaging winds. This area is outlined in red.

5. High risk- An area where a severe weather outbreak is expected from either numerous intense and long-tracked tornadoes or a long-lived derecho-producing thunderstorm complex that produces hurricane-force wind gusts and widespread damage. This risk is reserved for when high confidence exists in widespread coverage of severe weather with embedded instances of extreme severe (i.e., violent tornadoes or very damaging convective wind events). This area is outlined in magenta or pink.

The categories are shaded on a map of the United States. Included in the day one and day two outlooks are separate risks for wind, hail, and tornadoes.

Along with the colors, the SPC also uses something called a “Hatched Area” which is marked by the black outline with lines inside. This represents that there is a risk of significant severe weather for either tornadoes, wind, or hail.

The significant severe risk is only put on the outlooks if:

  • Tornadoes with an intensity of EF2 or higher are expected
  • Wind speeds of 75 miles per hour or greater are expected
  • Hail that is 2 inches in diameter or larger is expected.

You can see from the maps above, that the SPC has put this hatched area in all three categories, tornadoes, wind, and hail.

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With the severe weather season fast approaching here in the Midstate, it is important to know about these risks. The abc27 weather team uses this on air on occasion to explain the risk for you and your family.