Tale of Two Extremes

Now in its final days, this October’s weather can be broken up into two distinct halves.  The month got off to a very dry start, but it will finish as DC’s first wetter than average October since 2014.  It will also finish as a warmer than average month.

Following a very dry August and September, and only 0.14” of rain during the first half of October, moderate to severe drought conditions enveloped the Nation’s Capital and its surrounding suburbs.  Fortunately, there was a dramatic shift in the weather pattern and the last two weeks were quite rainy in Washington, D.C.  A total of 1.6” of rain fell last Sunday, October 20, and that was DC’s largest daily rainfall since July 8.

Excluding today’s rainfall, Washingtonians have seen an impressive 3.53” of rain since October 16.  That’s gone a long way to reducing the intensity of the drought conditions in the Mid-Atlantic Region.  Despite a rainfall deficit of 5.93” for the period of August 1 – October 15, DC still has an overall rainfall surplus of 1.75” as of yesterday.  Given how wet last year was, it’s hard to fathom that his month has already been wetter than October 2018.

This month will also finish as DC’s fourth consecutive warmer than average October.  The two most significant temperatures in the Nation’s Capital this October are noteworthy for different reasons.  The high temperature of 98° on October 2 set a new record for DC’s hottest October temperature.  Meanwhile, the high temperature of only 58° last Sunday – that coincided with the 1.6” of rain – was DC’s chilliest day in more than six months.  Prior to October 20, the last time DC’s high temperature remained below 60° was April 5, 2019 (56°).

Some may wonder whether a correlation exists between a warmer and wetter than average October in the Nation’s Capital and a colder and snowier than average winter.  The short answer is no, but there are some interesting parallels.  October was a cooler and wetter than average month in 2002 and 2009, and it was followed by two of DC’s snowiest winters on record during moderate episodes of El Nino.  On the other hand, October 1995 was a warmer and wetter than average month and the 1995-1996 winter was also quite snowy during a moderate episode of La Nina. 

Forecasting winter weather is quite complex and there are many factors involved.  Simple autumn temperature and rainfall trends aren’t enough to draw conclusions from.  My colleagues and I on the WUSA9 weather team will issue our winter weather outlook soon.