What Can Washingtonians expect in October?

Great Falls, MD

October is a fine month in the Nation’s Capital.  Average temperatures range from a high/low of 74°/56° on October 1 to 64°/46° by Halloween.  Washingtonians can also expect an average of 3.4” of rain in October.  NOAA’s forecast for October is for a warmer and drier than average month.

Such a forecast doesn’t differ much from recent years.  Four of the last five Octobers have been warmer than average.  The warmest October on record in the Nation’s Capital occurred ten years ago in 2007.  Washington, D.C.’s hottest October temperature on record was on October 5, 1941 (96°).  90° temperatures in October are relatively rare in the Nation’s Capital.  No 90° heat has occurred in October in the Nation’s Capital since October 6, 2013 (91°).  The latest in the season Washingtonians have had 90° heat is October 11 (90° in 1919).

By comparison, the coolest October temperature on record in Washington, D.C. is 26° that occurred twice (on October 30, 1873 and October 31, 1917).  Official weather observations for the Nation’s Capital have been made at National Airport since it opened in 1941.  Prior to that, they were made downtown.  Washington, D.C.’s coolest October temperature at National Airport occurred on October 24, 1969 (29°).  The earliest in the season measureable snowfall has occurred in the Nation’s Capital was on October 10, 1979 (0.3”).

Some current or former tropical systems have impacted the Mid-Atlantic Region in October.  Memorable ones in recent decades include the remnants of Hurricane Opal in 1995 and the remnants of Hurricane Sandy in 2012.  By the time Sandy made landfall, it was considered a “post-tropical” storm since it had lost its tropical characteristics over cooler waters.  However, the gusty winds and heavy rainfall that occurred with the remnants of Sandy were virtually identical to that of a tropical storm.

The DC Metro Area could actually use some rainfall.  No measureable rainfall has occurred in the Nation’s Capital since September 13 (0.04”).  Washington, D.C.’s current streak of 18 consecutive days without measureable precipitation is significant, but not record-setting.  DC’s longest streak of dry weather is 34 days (ending October 18, 2007) according to the National Weather Service.  The current streak would have to reach 27 days just to crack the Top 5.  

Although NOAA expects a drier than average month, there is some precedent for a wetter than average October to follow a drier than average September.  September 2005 was DC’s driest on record (0.11”) and that was followed by the wettest October on record (9.41”), largely because of the 7.3” of rain on October 5-6.  For perspective, the record 7.3” of rain that occurred during that two-day period is more than rain than occurred during all of August and September 2017 combined (6.01”).