Tuesday, June 30, 2009

Mid Atlantic June Precipitation Update

Images (click to enlarge): Washington, DC 2008 vs. 2009 monthly precipitation and June 2009 7-day moving average daily precipitation by CapitalClimate from National Weather Service data; June precipitation percentage of average from NWS

Midnight Update: An additional 0.02" this evening brings the monthly total to 5.86".

Original post:
With only a minimal chance of a passing shower through the rest of today, this June will go into the record books with precipitation slightly under 200% of average in Washington, DC. Far from setting any records, however, the official Washington National observation of 5.84" is not enough to put this month in the top 20 wettest Junes. Monthly precipitation for June has reached double digits 3 times in history; this is exceeded only by the 5 Septembers which have seen more than 10". The most recent occurrence was only 3 years ago, when the June monthly record of 14.41" was set.

In a carryover from May's heavy precipitation, the first 10 days of June were the wettest on average, as shown by the chart of the 7-day moving average above (normal daily amounts are shown by the red line). By the middle of the month, only 0.08" of rain fell in the week ending on the 17th. Average daily amounts picked up somewhat from there, but the month ended with only about half the normal daily amount.

Although widespread areas in northern Virginia through central Maryland and the vicinity of Baltimore have had over 150% of their June rainfall, parts of western Virginia and especially the state of West Virginia have seen substantial shortfalls of precipitation for the month.

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