SPC Day 3 Moderates in Context
This post is from April 2011. It is part of the archive of my original blog, so its data, links, and conclusions may be out of date.
UPDATES
(28 April 2013): Updated to add 16/17 April 2013 outlooks. Also added verification for all days.
~~(15 April 2013): Updated to account for today’s Day 3 Moderate Risk~~
~~(12 April 2012): Updated to account for today’s Day 3 Moderate Risk~~
(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 11 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 2005 – Present)
* 08 June 2005 -> Day 2 Moderate -> Day 1 Moderate -> Storm Reports
* 31 December 2005 -> Day 2 Moderate -> Day 1 Moderate -> Storm Reports
22 April 2007 -> Day 2 Moderate -> Day 1 High -> Storm Reports
04 June 2007 -> Day 2 Moderate -> Day 1 Moderate -> Storm Reports
05 June 2007 -> Day 2 Moderate -> Day 1 High -> Storm Reports
* 16 October 2007 -> Day 2 Moderate -> Day 1 Moderate -> Storm Reports
08 April 2008 -> Day 2 Moderate -> Day 1 Moderate -> Storm Reports
11 May 2009 -> Day 2 Moderate -> Day 1 Moderate -> Storm Reports
08 April 2011 -> Day 2 Moderate -> Day 1 Moderate -> Storm Reports
25 April 2011 -> Day 2 Moderate -> Day 1 High -> Storm Reports
12 April 2012 -> Day 2 High -> Day 1 High -> Storm Reports
15 April 2013 -> Day 2: Moderate -> Day 1: Moderate -> Storm Reports
* Day 3 Moderate Risk that does not meet the current criteria for a Day 3 Moderate Risk