Don’t worry, there is no high risk outlook today.
But when the SPC issues them, they do get lots of people’s attenton.
Rich Thompson is a highly respected forecaster at the Storm Prediction Center in Norman, Oklahoma. He spoke at the National Storm Chasers Convention in Denver in February. His topic: why high risk severe weather outlooks sometimes don’t pan out.
Many storm chasers believe that high risk outlooks always doom a day of chasing. They generally howl when they hear a high risk has been issued because some of them believe that the SPC always busts n high risk outlooks.
Thompson went back and researched all of the high risk outlooks issued by SPC between 2003-2008. In that six year period, there were 24 high risk days.
A high Risk implies that major severe weather is expected with a large coverage of severe weather and a high chance of extreme severe weather, including violent tornadoes. Thompson said that a High Risk generally signified a 30% or higher probability of tornadoes or a 60% probability of significant wind damage. For the purposes of his study, Thompson considered the High Risks to have verified if there were significant long track tornadoes.
Thompson found that High Risk outlooks busted for the following reasons:
1. Early season events turn into squall line scenarios early in the situation.
2. Situations with marginal moisture but strong shear. Outbreaks can’t happen without moisture.
3. Clouds limit destabilization.
4. Forecasters follow bad model guidance. (The same staff has been at SPC since 2003, so turnover is not a problem.
5. Taking a worst case scenario without considering the uncertainty involved. (The Dallas Metroplex scenario – where forecasters don’t want to downplay a situation that could threaten a major metro area.)
6. Thompson said that sometimes the issuance of a High Risk might be influenced by a significant headline tornado from the day before.
The team at SPC does an incredible job day in, day out. Hats off to the professionals there.
