Looking back at October, the freakish snow event that hit the Northeast hard and grazed our region stands out most. The Washington, D.C. region experienced its first marginally measurable snowfall in October since 1979.
Outside of the snow event, the month of October can be defined as slightly wetter (3.91” vs. 3.29” normal) and cooler-than-normal overall. The latter was a bit of a surprise as we tracked most of October in the warmer-than-normal category.
Though not terribly far above average, this was the third month in a row with more precipitation than normal. Bolstered heavily by the August and September rains, the 21.67” falling during the Aug-Oct 2011 period ranks as the third rainiest on record at D.C., behind 1934’s 23.41” and 1942’s 22.43”. Average for that same period is 10.05”, so if you think it’s been pretty wet throughout--you’re right.
The month began and ended much colder than average, anywhere from 9-17F below the norm.
The high of 52 at Reagan National Airport (DCA) on October 2 tied for the coldest maximum temperature on record for the date and Dulles’ 50 and BWI’s 51 both set records for coldest high temperature. The highs averaged across the first three days of the month (61, 52, and 53) marked the coolest start to the month on record (for highs).
Rounding out the month, the brutal cold high of 42 last Saturday on October 29 was an impressive 22-degrees colder than normal. It also set a record for the lowest maximum temperature for the date, and was the 6th time in history D.C. has seen a high of 42 degrees or less in October, most recently occurring in 2002 with 41. These two dates are the only two of the top-10 coldest in October that have happened since the switch to National as the recording station in the 1940s.
This late month cold surge pushed the month colder than the new 1981-2010 normal. The October 2011 average temperature of 58.4F is about 1.1F cooler than normal and 3.1F cooler than October 2010. We spent most of our days in the 60s and 70s (12 apiece), but also spend more recent time in the 50s with one day in the 40s (last Saturday) and only one day in the 80s (way back on Oct 10!). We only logged one 80-degree day compared to the average of four continuing our “cool” end to the torrid warm season this year. This is after logging zero 90-degree days in September, also below the recent climatological norm.
I was fascinated how similar October was year-on-year when looking at the daily average temperatures. It seems like we followed a similar theme through the month, hitting our spikes and valleys all around the same periods, but keeping 2011 cooler than 2010. Perhaps our most enjoyable similar period year-to-year occurred from the 6th through the 10th when CWG handed out 5 perfect 10s in a row with the daily digit. Last year we had four from the 7th to the 10th!
The big picture pattern themes between this year and last year were also similar. We still have a La Niña in the tropical Pacific (but weaker than last year). We still have a cold Pacific and warm Atlantic base state too. These similarities help explain the similar year-to-year weather .
Looking ahead: November 2011
November is shaping up to be a very mixed month with a variable to warm first half and then more potential for stronger cold events in the second part. After a chilly end of October, it does seem like we will have intermittent periods of warmer temperatures with 60s to maybe some Indian Summer-like 70s at times.
But some key patterns are expected to develop toward mid-to-late month that are quite reminiscent of last winter, which could start sending in some colder weather once again. Temperatures for November should be slightly below normal overall (mainly due to a colder late-month again) with near normal precipitation. You can see the National Weather Service’s final November temperature and precipitation outlooks here
For further information
The National Weather Service publishes nice monthly assessments usually within a week of the close of each month (should be available shortly):
You can click on your closest airport location here:
Historical Washington, DC data provided by NOAA.
Check out Ian’s excellent rundown on October climatology: What is Washington, D.C.’s weather like in October? Breaking down norms and extremes
(CWG’s Ian Livingston contributed to this piece)