SPC Day 3 Moderates In Context

Posted by on 8 Apr 2011 | 2 comments

UPDATE (25 April 2011): Updated to account for today’s issuance of a Day 3 Moderate Risk

This morning, weather enthusiasts woke to a Storm Prediction Center (SPC) Day 3 Moderate Risk outlook for severe thunderstorms. Most weather enthusiasts already know a Day 3 Moderate Risk outlook is a pretty rare occurrence, but just how rare is it? The simple and misleading answer is that since 2000, and including today’s, only 10 Day 3 Moderate Risk outlooks have been issued. The more precise answer is a bit more complex.

The SPC is continually refining their products based on the state of the science and user feedback. As such the criteria for a Day 3 Moderate Risk outlook has changed over time. Currently, it takes an “Any Severe” probability of 45% and a “Significant Severe” probability of 10% to reach Day 3 Moderate Risk category. Previously it was possible to ascertain the Day 3 Moderate Risk with as little as an “Any Severe” probability as low as 30%, which has happened several more times since the change in probability criteria. Therefore, it is difficult to compare old Day 3 Moderate Risks to current Day 3 Moderate Risks. However, I’ve attempted to break them down below.

Below is a table of the date of issuance for Day 3 Moderate Risk outlooks:

Day 3 Moderate Risk Outlooks (01 January 2000 – 04 April 2010)

** Day 3 Moderate Risk that does not meet the current criteria for a Day 3 Moderate Risk

Broken down by year:

Day 3 Moderate Risk Outlooks Issued By Year
  • 2000: 0
  • 2001: 0
  • 2002: 0
  • 2003: 0
  • 2004: 0
  • 2005: 2
  • 2006: 0
  • 2007: 4
  • 2008: 1
  • 2009: 1
  • 2010: 0
  • 2011: 2 (and counting)

For additional information regarding SPC Outlooks, this time focusing on Day 1, please check out the following posts from earlier this year: