In the Washington region, the final freeze typically spreads from low elevations in the south and east to high elevations in the north and west between late March and late April.
Low-lying areas around the District have already reached the time of year when they usually have their last freeze. But in the colder areas that surround the District, we’ve still got a few weeks to go until folks might start to feel safe getting the garden going; for close-in suburbs, probably at least two weeks; and another month or so farther out.
Where we stand
D.C. (as measured at Reagan National Airport)
D.C. last registered a freeze on March 21, the day it snowed 4.1 inches. The low that day was 32. If the District doesn’t witness another freeze, the March 21 date would be among the earliest in the past two decades, and the earliest since March 6, 2012.
However, as recently as 2016, D.C. had a freeze as late as April 10. In addition, much-colder-than-normal weather is predicted this weekend into early next week, when freezing temperatures cannot be ruled out.
So, even if you live near downtown Washington at a low elevation, we would wait another week before planting.
Over at Dulles, which has a climate more representative of Washington’s colder suburbs, freezing temperatures were the norm through much of March. In a normal March, Dulles might expect to see 15 lows of 32 or colder. This March, it experienced freezing temperatures on 24 days, tied for second-most on record with 1981, behind only 1969 with 25. Between March 8 and March 27, it dropped to freezing on 20 straight days, a record for the month.
It’s almost certain that Dulles and surrounding areas will see additional freezes in the coming days and, quite possibly, weeks.
Since 2000, the latest freeze at Dulles occurred on May 22, 2002, and, as recently as in 2013, it fell on May 14. This is why, if you live well north and west of the Beltway, it’s normally not safe to put in sensitive plants until around Mother’s Day.
Is the end normally near?
In the District, the average final freeze is March 27, according to the 1981-to-2010 climate averages. In that time frame, D.C. had its last freeze as early as Feb. 27 in 2010 and as late as April 13 in 1990. In other words, even if D.C. hasn’t already seen its last freeze, it is probably right around the corner.
We should note that, in the entire region, D.C. typically experiences its last freeze close to the earliest because National Airport, where measurements are taken, sits near sea level along the Potomac River and is near the city. So, it’s not a good location to use as an indicator for planting outside D.C.’s urban core.
At Dulles, the average final freeze is around April 20, with the latest (in the past 30 years) of May 22 in 2002.
Baltimore has an average final freeze of April 10, falling between the District and Dulles. Its temperatures are measured at Baltimore-Washington International Marshall Airport and are fairly representative of many of Washington’s suburban locations. Its latest freeze in the last 30 years occurred April 26, 2001.
It’s important to note that the average final freeze date is not the one you should use as an indicator of when to safely plant, because year-to-year freezes necessarily occur earlier and later. To be safer, it’s best to wait at least two to three weeks after that average date.
Is the freeze date changing?
Like most climate indicators locally, the last freeze data reveal a warming signal over time. Around 1900, D.C.’s 30-year average for the last freeze was roughly April 4 or April 5. Today, it is around March 27. This is a loss of about 10 days.
If we look at the top five earliest last freezes, three have happened since 2008. In 2010, after D.C.’s snowiest stretch on record, the last freeze on Feb. 27 was the earliest on record.
In addition, D.C. has seen a notable trend toward later first freezes in the fall.
The delay in the first fall freeze and trend toward an earlier last spring freeze is expanding the region’s growing season, overall. However, in recent years, we have run into the problem of warm Februarys jump-starting plant life only to later face freezing conditions as cold makes a resurgence in March.
Capital Weather Gang’s Jason Samenow contributed to this report.