Wednesday, October 28, 2009

October Rainfall Extremes Set New Record

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Nov. 1 Update: An additional 0.13" on Halloween brings the final monthly total to 5.71", or 2.49" above average. Here are the monthly, seasonal, and year-to-date totals for the region:
Washington National 5.71"/9.02"/35.68"
Washington Dulles 5.70"/7.53"/38.93"
Baltimore BWI 6.24"/9.72"/42.57"
PM Update: Added chart of October 1920-29.

Original post:
With 1.23" of rainfall yesterday, and an additional 0.79" through this morning, the preliminary October rainfall total for Washington stands at 5.59", over 70% above the long-term average for the month. This precipitation excess caps off a decade of October extremes. The 0.02" in 2000 was the second lowest since records began in 1871, and the 9.41" in 2005 was the record highest.

The last 5 consecutive Octobers, and 8 out of the decade 2000-2009, have all been at least 50% above or below the long-term average. The only other decade in which there have been more than 6 such extremes was the 1920s, when there were also 8. This decade's extremes have all been at least +/-55% of average, however, whereas 1925 barely made the 50% level at 50.9%.

Of the 8 extreme Octobers this decade, 5 have exceeded on the up side and 3 on the down side. The 1920s, on the other hand, excelled on the dry side, with 6 of the 8 extreme months below average.

Image (click to enlarge): Washington, DC October 2000-2009 precipitation percentage above or below average; CapitalClimate chart from NWS data

Monday, October 26, 2009

Washington, DC Precipitation Update: Deep Deficit to Solid Surplus

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October 27 Update: The 0.63" from last night through this afternoon brings the monthly total to almost 50% above the average to date. Current month-to-date totals:
Washington National  4.18"
Washington Dulles 4.38"
Baltimore (BWI) 4.85"
Original post:
The nearly 1" of rain which fell on Friday and Saturday, combined with the heavier amount the preceding weekend, has moved October's precipitation in the Washington, DC area from the large deficit of the first half of the month to a solid surplus. The month-to-date total of 3.55" at Washington National is 37% above the average through the 25th and is above the average for the entire month. Along with the 1"+ amounts forecast for the upcoming 5 days ending on Halloween, October has a good chance of joining April, May, and June in being 50% or more above normal.

Here are the storm total, month-to-date, and year-to-date precipitation amounts for the region:
Washington National  0.92"/3.55"/33.52"
Washington Dulles 1.73"/4.03"/37.26"
Baltimore (BWI) 1.00"/4.31"/40.64"

Seasonal Outlook

Latest seasonal forecast: Click here.

Latest 3-month temperature outlook from Climate Prediction Center/NWS/NOAA.