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June severe weather in Washington, D.C.: the month of the derecho

So far this year I’ve reviewed monthly severe weather climatology for the months of March, April, and May.  How does June, a month rooted in the summer season, compare?

After reading through the previous month reviews, you know the drill: I used the Storm Prediction Center’s datasets for all hail, high wind, and tornado reports from 1950-2011 and parsed out all the reports for each that happened during the month of June for the Washington, D.C. region.

All June severe weather reports (tornado, wind, and hail) from 1950-2011. Storm data courtesy of the Storm Prediction Center. Map by Kathryn Prociv

Examining the map, a tally of all reports (1950-2011) west of the Chesapeake Bay include:

45 confirmed tornadoes

440 hail reports

1200 wind reports

June tornado climatology

The 45 confirmed tornadoes during the month of June are lower than May’s 100 and April’s 67.  The lower tornado number in comparison to the previous two months is likely due to the more summer-like pattern experienced during June.  Typically a more zonal (west to east) pattern of heat and humidity dominates with less big temperature clashes (due to south to north flow) conducive for tornado outbreaks – patterns more characteristic of spring.  However, due to June’s heat – which serves as thunderstorm fuel – , it features more thunderstorm days overall. Thus, despite June’s lower tornado numbers, there can be more hail and damaging wind reports.

Tornadoes by Fujita/Enhanced Fujita (EF) category during the month of June:

F/EF0: 20

F/EF1: 16

F/EF2: 8

F/EF3: 1

The one F3 and strongest tornado to strike the area during the month of June was on June 9, 1961 – south of Baltimore and near Glen Burnie, Md.

Notable June tornado days featuring five or more tornadoes include:

June 2, 1996 – 6 tornadoes

June 18, 1997 – 5 tornadoes

June 1998 was an active year, with 7 tornadoes occurring between the 2 and 16

June 4, 2008 – 8 tornadoes

All June tornado reports from 1950-2011. Storm data courtesy of the Storm Prediction Center. Map by Kathryn Prociv

June hail climatology

June is one “hail” of a month.  (Sorry I couldn’t resist).  June not only features one of the higher number of total monthly hail reports in the calendar year, but also boasts one of the largest hail stone ever reported for the D.C. region.  In fact, June has so many days featuring major hail events that the list of “ten or more hail reports in a day” was so long I decided to omit it all together.

All June hail reports from 1950-2011. Storm data courtesy of the Storm Prediction Center. Map by Kathryn Prociv

Here is the breakdown of hail reports by size (in diameter) for the month of June:

Less than 1 inch: 52 percent (below severe criteria)

1 to 2 inches: 46 percent

Greater than inches : 2 percent

There have been five hail reports of 3 inches in diameter or larger.  The largest hail reported was 4.5 inches in diameter and occurred on June 18, 1970 near downtown Baltimore!

June wind climatology

As mentioned above, Junes between 1950 and 2011 the D.C. region have experienced around 1200 damaging wind reports.  While that is already an insane amount, that does not take into account the damaging wind reports that resulted from last summer’s derecho on June 29, 2012.

Since the Storm Prediction Center has not yet released severe report data through 2012, I used the Iowa Environmental Mesonet’s Archived National Weather Service (NWS) Watch/Warning page to gather all the local wind reports as well as severe thunderstorm warning polygons for the derecho event so I could include it in the June wind climatology discussion.

All June wind reports from 1950-2011. Storm data courtesy of the Storm Prediction Center. Map by Kathryn Prociv

The map above shows the approximately 1200 wind reports from 1950-2011.  The June 29, 2012 derecho alone produced an impressive 190 damaging wind reports across the D.C. region.  Putting that number in perspective, that number is equivalent to 10 percent of all the damaging wind events that have occurred in our region in the last 60 years… happening in one night, and more realistically in less than one hour.

A zoomed out map of all severe thunderstorm warnings and wind reports from the June 29th, 2012 derecho. Data courtesy of the Iowa Environmental Mesonet. Map by Kathryn Prociv

The map above shows the full extent of the derecho’s impact last June, causing damaging wind reports all the way from central Iowa early in the morning on the 29th to the Atlantic Ocean just before midnight.

A zoomed in map shows the impact locally on the Washington, D.C. metro area and surrounding counties.  Notice the entire map is blue?  Every single county around the District was under a severe thunderstorm warning that night.

Severe thunderstorm warnings and wind reports around the D.C. area from the June 29th, 2012 derecho. Data courtesy of the Iowa Environmental Mesonet. Map by Kathryn Prociv

Related: Derecho: Behind Washington, D.C.’s destructive thunderstorm outbreak, June 29, 2012


While June may not claim as many tornadoes as April or May, it still features plenty of severe weather to go around.  Thanks to last summer, June will likely be known as the “month of the derecho” in the years to come.

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