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:

As many already know, the southern plains is in the midst of a fairly pronounced drought. The drought reminds me of the drought we experienced in Norman during 2005-2006. During the drought, the rain stopped in late summer of 2005 and remained that way through November of 2006, when a very intense cyclone helped to alter the prevailing storm track.

As we head into the spring storm season, I’ve been getting asked more and more frequently how the lack of precipitation in the southern plains will affect storm season. The answer to this question is highly complex, and poorly understood at this time. However, I’ll offer one possible outcome.

The lack of southern plains precipitation, and more importantly, the dry soil, might allow the dryline to mix eastward faster than if the soil held more moisture. This, coupled with warm air aloft being advected over the southern plains from the higher elevations of New Mexico (which has also been extremely hot and dry of late), will help suppress thunderstorm and tornado development across much of western Oklahoma and the Texas Panhandle.

This is what happened in 2006, and you can see based on the graphic below, most of the tornadoes were to the north and east of western OK.

As we head into April, it’s time to update the plot of tornadoes by county for the current month. These data have been updated to include tornadoes in 2010. (Please note the modified color scale compared to January, February, and March.)

As you can see, the southern plains is becoming more as we approach late spring!

Greg Carbin, Warning Coordination Meteorologist at the Storm Prediction Center (SPC), informed me today that he has updated the SPC tornado database up through 2010. Thus, in the coming days, I’ll updated the graphics to include the last 2 years worth of tornadoes. I look forward to playing with the updated data!

After a long hiatus from blogging for most of February, I’m back at it as things appear to be slowing down just enough to let me have coherent thoughts again. This is fortunate since we’ve entered a new month and I need to post the March tornado graphics! This post should do the trick!

Above is a choropleth map of tornadoes by county. As we head into spring, warmer temperatures and more moisture begins making its way farther north and west than January and February. This allows for surface-based thunderstorms to develop farther north and west, and consequently we see a considerable expansion north and westward in the number of tornadoes. However, numerous tornadoes have been reported in the central valley of California.

If we break the tornado numbers down by state, we can see that Texas is the big winner (or loser depending on your point of view), with the other southern plains states having high numbers of tornadoes. The southeastern states have little change with the February numbers, making this area one favored area for tornado development.

The actual counts by state are broken down below.

What about injuries? Keeping the same state ordering above (namely, in decreasing order of tornadoes), we can see the breakdown of injuries by state. For the third month in a row, Mississippi leads the nation in injuries, with Arkansas not far behind.

Examining the number of fatalities, Mississippi no longer leads the nation. Arkansas has the most number of March tornado fatalities, thanks in part to the 1 March 1997 tornado outbreak.

Lastly, here is a summary figure combining the last three figures.