April Gets Off to a Chilly Start !

The first three days of April felt more like March in the Nation’s Capital.  That coincided with the National Park Service’s declaration that the famous cherry blossoms along the Tidal Basin reached “peak bloom” on April 1.  The chilly temperatures are actually good for the blossoms once they reach peak bloom.  Their primary enemies are gusty winds, hot weather or heavy rainfall.

High temperatures on April 1 and 2 were 51° and 50°, respectively, at National Airport while they remained in the upper 40s at Dulles Airport.  That’s more characteristic of late-February than early April.  It also made for the chilliest first two days of April in the Nation’s Capital since 2011.  Low temperatures remained in the 30s at National Airport on the first three days of the month.  That was the first instance of at least three consecutive days with temperatures in the 30s during April in Washington, D.C. since April 2 – 5, 2013.

It was even colder at Dulles Airport, where low temperatures were in the 20s on the first three days of the month.  Although not record-setting, it was the first time it’s been that cold at Dulles in early-April since the same time period in April 2013.  However, it doesn’t typically remain chilly for very long in April given the increasing sun angle and amount of daylight.  Despite a low temperature of 38° at National and 27° at Dulles yesterday, high temperatures reached the low 70s.

Whenever there is a difference in low temperature of 5° or more between two relatively close geographic locations, one should compare the difference in urbanization and proximity to water between them.  National Airport is on the Potomac River by the Nation’s Capital and the heavily urbanized northern Virginia suburbs.  Meanwhile, Dulles Airport is in the more rural Sterling, Virginia area away from any body of water.  The principal known as the “urban heat island effect” explains how one area in a more rural location will become much cooler than a more urban area on a night with clear skies and calm winds.  Bodies of water can also influence temperature by keeping it a little warmer at night and cooler during the day depending, on wind direction.

Relative humidity was also low yesterday and that helped temperatures to rise significantly.  It’s not uncommon for there to be a large swing in temperature between the daily high and low temperatures on a sunny day with a dry air mass.  There was a 44° temperature swing at National Airport yesterday and a 43° difference at Dulles Airport.  Humidity is “relative” to a given temperature since warmer air can hold more water vapor than cold air.  Think of the atmosphere as a sponge where the higher than temperature is, the larger the sponge.  That’s why a humid day in the summer feels much more oppressive than in the winter.