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Posted at 10:45 AM ET, 04/08/2011

What is Washington, D.C.’s weather like in April? Breaking down norms and extremes


April 5, 2009. Photo by author.
Following early-spring’s roller coaster ride from cold to warm and back, April is typically when more consistent periods of temperate weather are established (though it can still be a rough go some years). We begin with “normal” daytime readings above 60 degrees and the 70-degree average daily high appears during the final portion of the month.

And of course, the saying goes that, “April showers bring May flowers.” In D.C. (as recorded at National Airport -- DCA), while April is a moderately wet month, at least in number of days with precipitation, it’s not super wet. Just enough to get the growing season going though!

Keep reading for more in this first installment of a year-long series of posts detailing specific statistics on climate norms, extremes, and averages for the each month in Washington, D.C…

PRECIPITATION

The April average* rainfall of 3.06” (previously 2.77” from 1971-2000) is not astounding compared to some of the months that follow during the warm season, when thunderstorms can drop several inches in hours or tropical remnants threaten. But the clash of cool and warm air masses can still create memorable storm events during the month.


April rainfall, in inches, at Washington, D.C. since records began. (See sources for data)
April’s maximum monthly precipitation is 9.13”, way back in 1889. The low point for monthly rainfall is a measly 0.03” in 1985. If you count every day with at least a heavy sprinkle (trace of rain or more), D.C. averages 15 days with precipitation during the month. On a more stringent “disruptive” rainfall note, days with .1” or greater occur about seven times per April.

The maximum daily rainfall for April is 3.21”, falling on the 26th in 1889. There has been only one other day surpassing 3” in the month -- 3.04” on the 14th in 1970. A recent comparative, the 4.66” that fell on September 30, 2010, was only the third-greatest daily rainfall in that month. And for further comparison, the greatest all-time daily rainfall is 6.39” on August 23, 1933. 13 days in April have had daily totals of 2” or greater.


Change in monthly rainfall averages from 1971-2000 to 1981-2010. April’s change equaled +0.29”. (See sources for data)
With the showers of April in better perspective, the month is one of several (five) which saw an increase in rainfall from the 1971-2000 to the 1981-2010 averages. Its 0.29” increase in monthly precipitation catapulted it from the 11th wettest month to the 8th. The noteable increase was in part thanks to five Aprils during the 2000-2009 period tallying 4”+ (well above average) monthly totals.

Snowfall in the month is almost non-existent at the lowest elevations in the area, like DCA. There have been eight days in the entire climate record of D.C. with greater than 1” of snow in April. The last time 1”+ fell was 1924, when the recording station was downtown. Once north and west of the city, odds go up slowly, and generally according to elevation. Why the lack of snow? Warming temperatures, of course…

TEMPERATURES


April temperature averages at Washington, D.C. since records began. Red line is the 1971-2000 temperature average provided by the NWS. (See sources for data)
April’s average monthly temperature is 56.1 (as per NWS provided 1971-2000 norms**). The warmest April D.C. has seen since records have been kept was 62.1 (1981), and the coolest was 47.1 (1874). Highs in the 60s and 70s average 38% and 25% of April days respectively over the more recent 1981-2010 period. Lows are mainly in the 40s (about half of the time) and 50s. The coldest temperature ever in April was 15 on the 1st in 1923, and the hottest reading is 95 (4 times, most recently in 2002).

If not before April even begins, we fully say good-bye to freezing temperatures (none have happened at DCA past April) until the fall. D.C.’s last freeze is roughly April 11 according to the NWS. But, only 11 out of 30 years from 1981-2010 witnessed an April freeze. The latest freeze on record came on the 29th in 1874. The latest freeze at DCA occurred on the 21st in 1956.


Number of occurrences of a high temperature equalling 70 degrees or greater on each day in April during the 30-year period from 1981-2010. (See sources for data)
While the odds of freezing temperatures are a puny 6-7% for any day during the first third of the month, the chance of those glorious 70+ days quickly grow. Assuming a linear pattern on the return of warmth, D.C. runs about a 23% chance of seeing a high temperature at or above 70 degrees on any day in early April. By the end of the month, the odds are a little greater than 50%.

Thankfully, particularly for those who love the transitional months between temperature extremes, big heat often does not arrive in force in April. We do taste 80 or higher here and there, but before the vegetation fully kicks in, and with some cooler air masses around, it’s not often oppressive.

DATA

30-year (1981-2010) Averages / Overall (All history) Averages...

Highs 70 or above: 11.2 / 10.3
Highs below 60: 7.6 / 9.4
Highs 80 or above: 3.6 / 3.4
Highs 90 or above: 0.4 / 0.4
Lows 32 or below: 0.6 / 1.5
Lows below 40: 4.2 / 7.3
Days with a trace of rain: 15.2 / 15.3
Days with .1” of rain or more: 6.5 / 6.4
Days with .5” of rain or more: 2.2 / 2.2
Days with 1” of rain or more: 0.6 / 0.6

All-Time Records (High / Low)...

Highs 70 or above: 20 (1954) / 1 (1874, 1904)
Highs below 60: 19 (1901) / 1 (1994)
Highs 80 or above: 11 (1976) / 0 (10 years)
Highs 90 or above: 5 (1960, 1976) / 0 (111 years)
Lows 32 or below: 7 (1874, 1896, 1899, 1943) / 0 (61 years)
Lows below 40: 21 (1907) / 0 (7 years)
Days with a trace of rain: 22 (1937) / 6 (1976)
Days with .1” of rain or more: 12 (1874, 1920) / 0 (1985)
Days with .5” of rain or more: 6 (1895, 1937, 1983) / 0 (15 years)
Days with 1” of rain or more: 3 (1899, 1918) / 0 (71 years)

SOURCES

Daily climate records for National Airport (DCA), 1871-present
- See selected and additional statistics compiled for this post (Excel)

DCA April Daily Norms and Records

DCA Monthly Temperatures

DCA Monthly Precipitation

NWS Baltimore/Washington climate information

NOTES

*All averages, unless otherwise noted, refer to the 30-year period of 1981-2010.

**All instances of monthly temperature average, daily temperature average or daily precipitation average refer to the 1971-2000 climate normals as presented by the National Weather Service. NWS smooths some averages without daily data in a method described here. Monthly rainfall is a simple average and new 1981-2010 data is used here. NWS data on temperature averages should update shortly and will be reflected in these posts.

ABOUT THIS SERIES

While numerous local climatology statistics including daily, monthly, and seasonal normals and records are available from National Weather Service Baltimore/Washington, there are myriad other pieces of information which help frame the story. Rather than attempt to recreate what is already available, this series of posts will act as a companion to most information presented there.

This is the first installment of a series of living documents. Over the next year, each month will be broken down in a similar or evolving way. As input is taken from the community, some items may be added to or changed in older postings. These postings will be updated as necessary to reflect changes when needed. Other articles may also become part of this series.

Feel free to share thoughts or additional data you may be interested in seeing.

Article last updated: April 8, 2011.

By  |  10:45 AM ET, 04/08/2011

Categories:  Local Climate, Latest

 
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