UPDATE, 4:30 p.m.: The National Weather Service has upgraded the freeze watch to a freeze warning for the District, Alexandria, Falls Church, Arlington and counties east of town. The only area not under a freeze watch or warning is Calvert and St. Mary’s county in Southern Maryland.
From 2:54 p.m.: Despite an abundance of late March sunshine, cold winds blowing in from the northwest have held afternoon temperatures in the upper 50s - setting the stage for freezing temperatures in many areas tonight.
Officially a freeze warning is in effect from 3 a.m. to 9 a.m. Tuesday morning for north and west of Washington, D.C. including Fairfax and Montgomery counties. A freeze warning means sub-freezing conditions are *imminent or highly likely*.
The District, Alexandria, Arlington, Falls Church and counties to the east are excluded, but remain under a Freeze Watch. A freeze watch means sub-freezing temperatures are *possible*. Note: the freeze watch has been extended from earlier updates to now cover Calvert and St. Mary’s county.
Unseasonably cold air is already pouring into the Northeast. Temperatures have fallen back into the 40s in much of Pennsylvania and 30s in New York State. Locations in northern Maine that were around 80 last Thursday are now only in the 20s! Check out some of the forecast lows in the Northeast tonight:
Philadelphia: 29, New York City: 30, Albany: 20, Boston: 26, Burlington: 17, Caribou: 13
Although freezing temperatures are a good bet tonight north and west of the District from Fairfax to Rockville and to the west and north, it’s not as clear if it will reach freezing in urbanized locations inside the beltway, as well locations near bodies of water (either the Potomac or the Chesapeake Bay). The National Weather Service writes in its afternoon discussion:
THE AREA FROM THE DISTRICT EAST AND SOUTH ALL THE WAY TO KING GEORGE...ST.MARYS AND CALVERT ARE STILL MORE UNCERTAIN AS WINDS STAY UP A BIT LONGER AND GROUND CONDITIONS REMAIN WARM. NOT AN IDEAL COOLING SCENARIO BUT NONETHELESS...BUFKIT [A MODEL TOOL] DOES SHOW SURFACE TEMPERATURES APPROACHING FREEZING AT DCA. THE POTENTIAL IS STILL THERE BUT NOT ENOUGH TO PULL THE TRIGGER ON THE WARNING.
Here’s my best bet for morning lows at the three airports:
Reagan National: 35 (chance of dropping to 32, 30%)
Dulles: 31 (chance of dropping to 32, 75%)
BWI: 31 (chance of dropping to 32, 60%)
For locations in the freeze warning, the National Weather Service cautions:
UNPROTECTED VEGETATION THAT ARE SENSITIVE TO A FREEZE WILL BE AT RISK FOR DAMAGE. MORE SIGNIFICANT DAMAGE TO VEGETATION WILL OCCUR IN LOCATIONS WHERE TEMPERATURES DROP BELOW 28 DEGREES FOR 3 OR MORE HOURS
Fortunately, most spots in the D.C. metro area should not experience temperature below 28 for 3 or more hours...
Here is some additional information you may find useful from my earlier blog post:
The average date of the last freeze in Washington D.C. (at Reagan National Airport and its predecessor location at 24th and M St.) is from around this time to early April. The earliest last freeze to occur was February 27, 2010. The latest last freeze was April 29, 1874 (though this was prior to considerable urbanization, any greenhouse warming and at 24th and M, rather than Reagan National).
As you go west and northwest of the District and the beltway (e.g. towards Rockville, Leesburg, and Frederick), the average date of the last freeze extends into mid-and-late April.
The website Davesgarden.com provides a useful tool for determining the risk of a freeze at a given zipcode by date.