A deeper look at Washington, D.C.’s tornado history

If you’ve been following the 2013 severe weather season, you know it has been quite a roller coaster ride.  Before this week, we had been flirting with records for the lowest number of tornadoes (so far this year) and tornado fatalities (in the past year).  Unfortunately, after the last several days of severe weather and Monday’s devastating EF5 tornado that struck Moore, Okla., the tornado season has suddenly taken on a much different feel.

While tornado numbers have jumped significantly across the Great Plains states in the last week, the D.C. area is still having a much lower-than-average year with only one tornado warning issued so far, and two confirmed tornadoes.  Using the Iowa Environmental Mesonet’s Archived National Weather Service (NWS) Watch/Warning page, I investigated the number of tornado warnings issued by the NWS office serving Washington, D.C. and Baltimore between 2002 and 2013 (so far) and compared the number of warnings to actual confirmed tornado reports during that same timeframe.

Link: The 8 tornadoes recorded in D.C.

In addition to analyzing tornado climatology from this perspective, I also discuss some basic figures by breaking down D.C.’s tornado history by the intensity of tornadoes (Fujita/Enhanced Fujita rating) and by month.

Tornado “warning” climatology

All tornado warnings issued by the Sterling NWS 2002-2013. Tornado warning data courtesy of the Iowa Environmental Mesonet archive page. Map by Kathryn Prociv

All tornado warnings issued by the Sterling NWS 2002-2013. Tornado warning data courtesy of the Iowa Environmental Mesonet archive page. Map by Kathryn Prociv

From January 1, 2002 to present day our local NWS office has issued 360 tornado warnings within their county warning area (blue outline).  What is the average number of tornado warnings issued by the office each year, and how does the number of tornado warnings correlate to actual confirmed tornado reports?

The animated slideshow below displays tornado warnings issued by year starting with 2002 and ending with 2013 so far.  Watch as the yellow polygons change by year.  2004 and 2011 should stick out due to the high number tornado warnings issued during those years; 2004 saw many tornado warnings due to the remnants of Hurricane Ivan, and 2011 featured the April 25th-28 Super Outbreak.

Tornado warnings issued for Washington and Baltimore region 2002-2013 (Kathryn Prociv)

Animation of tornado warnings issued for Washington and Baltimore region 2002-2013 (Kathryn Prociv)

From January 2002-May 2013, the NWS has issued 360 total tornado warnings:

2013: 1; 2012: 43; 2011: 94; 2010: 31; 2009: 12; 2008: 36; 2007: 14; 2006: 13; 2005: 9; 2004: 72; 2003: 30; 2002: 5

Due to the incredibly high number of tornado warnings issued in 2004 and 2011, calculating the average seemed inappropriate as that would skew the average too high.  Instead, I simply looked at the mode of the numbers and it appears the typical number of tornado warnings issued each year by the NWS Sterling is in the 15-30 range.

Verification: tornado warnings vs. confirmed tornadoes

Since 2002, 360 tornado warnings have been issued, and 179 confirmed tornadoes have been reported (including the tornado that struck Fredericksburg last month on April 19th).  This equates almost exactly to a 2:1 warning to confirmed tornado ratio (although a number of tornadoes have occurred for which no warning was issued).  Below is a map showing all tornado warnings and all confirmed tornado reports within the Sterling NWS county warning area 2002-2011.

All tornado warnings and tornado reports within the Sterling CWA.  Tornado data courtesy of the Storm Prediction Center. Map by Kathryn Prociv

All tornado warnings and tornado reports within the D.C. and Baltimore NWS region 2002-2011. Tornado data courtesy of the Storm Prediction Center. Map by Kathryn Prociv

Tornado climatology quick facts

While the above information discussing tornado warnings included 2002-2013 (the watch/warning database only provided archived information back to 2002), below are some facts regarding the full tornado climatology of the Sterling NWS county warning area provided by the Storm Prediction for 1950-2011.

By Fujita/Enhanced Fujita rating since 1950

Tornadoes by F/EF Rating. Chart by Kathryn Prociv

Tornadoes in the D.C. and Baltimore regions by F/EF Rating 1950-2011. Chart by Kathryn Prociv

Total: 443 confirmed tornadoes within the our region between 1950-2011

Weak tornadoes in the F/EF0-F/EF1 range make up the vast majority of the tornadoes in the D.C. area at 83%.  Significant tornadoes, defined as F/EF3 or stronger, comprise only 3% of the area tornadoes.  Recall this map from Jason’s article yesterday on D.C. tornado history:

All tornadoes from 1950-2011 rated by F/EF Scale. Tornado data courtesy of the Storm Prediction Center. Map by Kathryn Prociv

All tornadoes from 1950-2011 rated by F/EF Scale in the D.C. and Baltimore regions. Tornado data courtesy of the Storm Prediction Center. Map by Kathryn Prociv

By month since 1950

Tornadoes by month. Chart by Kathryn Prociv

Tornadoes by month in the D.C. and Baltimore regions 1950-2011. Chart by Kathryn Prociv

An interesting tri-modal pattern to tornado reports since 1950.  Surprisingly July has had the most tornadoes across the area with June, September, and April not far behind. CWG’s Ian Livington has a more detailed tornado climatology article in the making where he will dive deeper in the details.

Conclusion

Tornado climatology across the D.C. area is very interesting when comparing actual confirmed tornado reports to warnings issued, and when breaking down reports by intensity and monthly occurrence. Tornadoes across the region are much less intense and certainly less prolific overall than across the Great Plains and South, but that does not mean we are immune to tornado outbreaks (September 2004 and April 2011) or significant tornadoes (La Plata, Md. F4 tornado).  There has only been one tornado warning issued so far in 2013, but we have a long way to go.

With that I will leave you with one more map.  The map fails to illustrate any new information as it is just showing tornado warnings issued color-coded by year.  I just thought it looked rad.

Chart by Kathryn Prociv

Chart by Kathryn Prociv

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D.C. area forecast: Humidity still here through tomorrow, then cool and dry into weekend