June Delivers a Severe Weather Punch

NOAA's Severe Weather Outlook for June 22

June is one of the most active severe weather months in the United States.  It averaged 243 tornadoes over the 20 year period ending in 2010 according to NOAA.  Although Texas, Kansas and Nebraska are the three states with the highest average number of tornadoes in June, Maryland and Virginia both average 1 to 2 tornadoes.  In fact, a tornado was confirmed in Howard County, Maryland, just yesterday.  “Severe weather” is defined as a thunderstorm with any of the following hail 1” in diameter or greater, wind gusts of at least 58 mph or greater, or a tornado. 

Some other terminology to be familiar with are “weather watches” and “weather warnings.”  A severe thunderstorm “watch” is issued if conditions are expected to be favorable for severe thunderstorms in a given area during a given time.  A watch usually lasts for several hours.  But, if the situation is more urgent and a severe thunderstorm is imminent or is occurring, than a severe thunderstorm “warning” is issued.  A “warning” typically lasts for only a few minutes to an hour.  If a severe thunderstorm is producing a tornado, than a tornado “warning” is issued.  In this case, only a tornado warning is issued in order to minimize confusion.

Large severe weather outbreaks during the spring are commonly related to the position of the jet stream.  Spring storms typically develop in conjunction with a trough – or dip – in the jet stream.  This helps create favorable conditions for supercell thunderstorms (i.e. long lasting thunderstorms that rotate) from which the strongest tornadoes tend to develop.  However, during the summer when the jet stream retreats northward into Canada, severe weather in the United States tends to be more dependent on smaller scale weather systems.  This includes clusters of thunderstorms known as mesoscale convective complexes.  “MCCs” are long-lasting clusters of showers and thunderstorms and can produce severe wind gusts and hail.  

There were over 400 reported cases of severe weather nationally, on June 4, 2008, with dozens of confirmed cases of severe wind gusts, hail and a few tornadoes in the Mid-Atlantic Region.  Fortunately, there were no fatalities but there was extensive damage and record rainfall at both National and Dulles Airports.  More recently, on June 1, 2012, another severe weather outbreak occurred with nearly three dozen confirmed tornadoes from Pennsylvania to North Carolina.  

Severe weather can be tough to predict since each outbreak is unique.  That underscores the importance of keeping up to date on the latest weather forecasts and taking shelter in an interior room when a severe thunderstorm or tornado warning is issued for your location.  You can rely on my colleagues and I on the WUSA9 weather team for the latest weather forecasts both on-air and on the free WUSA9 app for your mobile devices.