Today's SPC Convective Outlook
Map showing today's overall severe thunderstorm potential in the continental USA. This map is updated several times during the day. (see below for convective outlook map explanation).
Source: NOAA SPC
Today's Tornado, Hail and High Wind Risk
Maps showing today's risk potential for tornadoes, large hail, and damaging winds in the continental USA. These maps are complements to the Day 1 outlook map shown above. As a general rule, any probabilities greater than 15% indicate a significant risk level. For instance, a 15% or greater risk for tornadoes usually indicates a possible tornado outbreak. NOTE: Color coding on these probability maps does not follow the convention of the main convective outlook maps.
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SPC Convective Outlooks for Upcoming 2 Days
Maps showing the severe thunderstorm potential for tomorrow (Day 2) and the day after tomorrow (Day 3). The Day 2 map is updated twice per day, the Day 3 map is updated once per day. These are thumbnails, click on each map to enlarge: (see below for convective outlook map explanation).
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EXPLANATION OF SEVERE WEATHER OUTLOOK MAPS
Meteorologists at the SPC (NOAA Storm Prediction Center, http://www.spc.noaa.gov) in Norman, Oklahoma issue daily severe thunderstorm forecasts called Convective Outlooks. These outlook maps show where in the United States that severe storms are likely to occur. (A severe thunderstorm is defined as having large hail, damaging winds and/or tornadoes).
Convective outlooks are issued throughout the day for Day 1 (today), Day 2 (tomorrow) and Day 3 (day after tomorrow). The Day 1 outlook is accompanied by probability maps for tornadoes, large hail, and damaging winds. The convective outlooks give us a good idea of the risk of severe weather in a particular area.
The areas of severe thunderstorm risks on the SPC maps are designated by color-coded lines:
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| General Thunderstorm Risk: The areas outlined in orange are at risk for normal garden-variety thunderstorms with lightning, heavy rain, and possibly small hail. Severe weather is slightly possible but not expected in a General Thunderstorm risk zone. If your area is in a General Thunderstorm zone, keep an eye out for potential storm-related dangers in your area such as lightning and heavy rain, especially if you plan to be outdoors. This type of designation is very common, as there is usually a General Thunderstorm zone somewhere in the country almost every day of the year. |
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| Slight Risk: The areas outlined in green are at a slight risk for severe thunderstorms. In a Slight (SLGT) Risk zone, thunderstorms are expected to occur, with a chance for scattered severe thunderstorms. Slight Risk zones are common in the spring and summer and are associated with stronger thunderstorm events. If your area is in a Slight Risk zone, expect a heavy thunderstorm or two sometime during the day or night and plan accordingly. |
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| Moderate Risk: The areas outlined in yellow have a moderate risk for severe thunderstorms. In a Moderate (MDT) Risk zone, thunderstorms are expected to occur, with many of them expected to be severe. Moderate Risks are less common and are associated with more serious, damaging outbreaks of severe weather including tornadoes, large hail and/or damaging winds. If your area is in a Moderate Risk zone, you should monitor news and weather media sources throughout the day for possible warnings, be on the alert for dangerous weather conditions, and have a plan to take appropriate shelter if needed. |
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| High Risk: The areas outlined in red have a high risk for severe thunderstorms. In a High Risk zone, widespread coverage of numerous, very damaging severe thunderstorms is expected. High Risks are rare and are associated with significant, dangerous outbreaks of severe weather, such as multiple strong long-lived tornadoes, very large hail in many locations, and/or very high straight-line winds over a large area. If your area is in a High Risk zone, take the weather situation seriously and be prepared to seek shelter and deal with after-effects such as power outages and blocked roads. Your local media and emergency management will likely already be covering and preparing for the threats, so keep a radio or television on to keep up to date on the situation. A High Risk zone issued for urban areas often signals an impending weather disaster that must be taken seriously. |
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EXAMPLES: A good example of a big severe weather day where all four risk levels were present on the Day 1 outlook was November 10, 2002. On that Sunday afternoon, a large outbreak of tornadoes occured over much of the eastern USA, causing widespread damage and many casualties. Below is the SPC Day 1 Convective Outlook for that day in November. A rare, unusually large High Risk zone was in place that included a large portion of West Virginia. Surrounding the High Risk zone (as is typical) was a Moderate Risk and a Slight Risk zone, followed by a General Thunderstorm Risk zone. This map showed where storms and severe storms were expected to occur that day, and later did occur:
November 10, 2002 was an extreme, very unusual incident, as most High Risk situations cover much smaller areas and mainly are only seen in Tornado Alley (Oklahoma, Kansas, Texas, Nebraska) during the peak springtime severe weather season. [ View photos and video from a Storm Highway storm chasing trip into the High Risk zone in Kentucky on November 10, 2002 ]
A more typical example of a severe weather day in our region was August 26, 2003 when very strong thunderstorms were expected to form over Ohio later in the evening. A small Moderate Risk zone was in place over Ohio, with a large Slight Risk zone covering much of the Ohio Valley and Upper Midwest:
That night, a line of severe storms did form inside the Moderate Risk zone, moving quickly across Ohio into northern West Virginia with very strong winds. [ View photos and video from a Storm Highway storm chasing trip into the Moderate Risk zone in Ohio on August 26, 2003 ]
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