On July 1, NOAA released its new climate normals - which are used as a baseline for comparison with the current weather. The new climate normals span the period 1981-2010, whereas the old climate normals encompassed 1971-2000. In a post last week, I indicated that across the United States, the new climate normals were warmer than the old climate normals by about 0.5 degree F and that every state’s new normals had warmed.

But what about Washington, D.C.? How have normals in the Nation’s Capitol changed? In short - they have also warmed - and a bit more than the national average. And interestingly, Washington, D.C.’s “normal” snowfall has dropped.

The old normals for the monthly hi, low, and average temperature in D.C. (blue, 1971-2000) compared to the new normals (red, 1981-2010)

Washington, D.C.’s average annual temperature has increased from 57.48 degrees to 58.13, an increase of 0.64 degrees. The average annual low temperatures warmed from 48.59 to 49.53, an increase of 0.94 degrees whereas the annual average high warmed from 66.38 to 66.68, a rise of 0.3 degrees.

Every month’s average high increased except for May, which did not change, and December, which fell 0.2 degrees. Low temperatures increased every month by at least one degree except during March, September, and December which rose 0.3, 0.7, and 0.6 degrees, respectively.

What this all means is that many normal lows each day will be about 1 degree higher, and - in some parts of the year - average highs will warm by about a degree - particularly in January and February. For example, whereas our coldest days in January (from Jan 9-Jan 23) used to have an average high of 42, they will now be 43.

Total annual precipitation increased very modestly, by 0.39” (from 39.35” to 39.74”), but five months had decreases (January, February, March, August, and September), and one month showed no change (December). The biggest precipitation changes occurred in June, which had an increase of 0.65” (no doubt owing to some very wet Junes in recent years), and in August which dropped 0.51” (fewer effects from tropical systems, perhaps?).

Average snowfall dropped every winter month with the exception of December, which saw an increase of 0.8”. The average annual snowfall declined from 15.2” to 14.5” notwithstanding the fact the record-setting 56.1” of snow during 2009-2010 was included in the new normal sample.

Link to new normals for D.C. (DCA, Reagan National)