A picture is worth 1,000 warnings: All NWS Sterling warnings 1986-2013

April 17

Infographic by Kathryn Prociv

Ever wonder what nearly 30 years of severe thunderstorm and tornado warnings looks like if plotted together on a single chart?  …me neither, until I took a stab at it.  In an effort to “think stormy thoughts” during a winter that seemingly won’t end and a severe season that got off to a slow start, I decided what better way to get my head into severe mode than to look at all the severe thunderstorm and tornado warnings ever issued by the Sterling National Weather Service office?  The Iowa Mesonet Watch Warning Archive allowed me to download warnings back to 1986, and that’s where I began.

Now stay with me, because I’m going to take you through Sterling’s history of nearly 30 years of severe thunderstorm and tornado warnings (1986-2013) in less 500 words:

Since 1986, there have been TWO significant benchmarks in the history of issuing warnings, both of which I specifically discuss in the context of the Sterling forecast office.

1) June 12, 1992: Sterling was the FIRST forecast office to install and implement WSR-88D, Doppler Radar, for operational use.  This gave forecasters new tools such as velocity and storm relative velocity which greatly improved the ability to predict and warn for tornadoes.  Check out the infographic above right around 1992:  notice the sudden and marked consistency in the pattern of tornado and severe thunderstorm warnings?

2) On October 1, 2007: All NWS forecast offices transitioned from county-based warnings to polygon or “storm based” warnings.  This movement significantly decreased the areal coverage of warnings resulting in improved accuracy in storm verification.  On the infographic I note the transition occurring from 2002-2007.  In mining through the warning database, polygon warnings began showing up as early as 2002.  Upon further research, Sterling was one of 23 forecast offices that participated in a field evaluation of using short-duration “Warnings by Polygon” that began prior to 2007.

One neat benefit to plotting all the warnings in a single framework is it allowed for an easy way to visualize the largest severe weather outbreaks within Sterling’s county warning area since 1986. 

There have been FOUR very obvious and major severe weather events since 1986:

1) May 10, 2000: A major hailstorm rocked the D.C. area resulting in over 50 hail reports area-wide.  This was not a tornado outbreak, which explains a relatively low number of tornado warnings issued compared to the spike in severe thunderstorm warnings.

2) September 17, 2004: the remnants of Hurricane Ivan spawned 38 tornadoes across the state of Virginia, making it the largest tornado outbreak in Virginia’s history.  See the spike in the number of tornado warnings?

3) June 4, 2008: a major severe weather outbreak occurred at the hands of a large and destructive squall line that caused dozens of damaging wind reports, several large hail reports, and four tornadoes.  70 severe thunderstorm, tornado, and marine warnings were issued during that event.

4) April 27-28, 2011: part of the Super Outbreak of 2011, Sterling issued a total of 38 tornado warnings that night.  NWS Sterling confirmed 19 tornadoes from that event.

So there you have it,  27 years of warning history in less than 500 words.

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Jason Samenow · April 17