* Freeze watch Saturday night into Sunday morning for Howard, western Montgomery, western Loudoun, Frederick and Fauquier counties *

Behind a powerful cold front sweeping through the D.C. region today, the chilliest air of the season will spill into the D.C. region this weekend into early next week. Both Sunday and Monday mornings, temperatures will flirt with freezing in many parts of the area.

A freeze watch has been issued for D.C.’s far western suburbs Saturday night into Sunday morning (see map) and a frost advisory is likely to be issued for closer-in suburbs. On Sunday night into Monday morning, freezing conditions may expand over an even larger area.

These high resolution computer simulations, adapted from the European model, provide a reasonable forecast of morning lows both Sunday and Monday:

Sunday morning lows

Monday morning lows

On both mornings, temperatures should drop to near freezing outside the Beltway and away from the Chesapeake Bay.  In fact, some upper 20s  will be possible from western Fairfax County to central Montgomery County and to the northwest, particularly on Monday morning, ending the growing season.

Of the two mornings, Monday is likely to be slightly colder – by about two to four degrees, and even some of the colder locations inside the Beltway could see temperatures plummet to near freezing.

Sensitive plants in these areas should be brought inside as they will otherwise be damaged or killed.

Urban locations in Arlington, Alexandria, and the District will likely be near 40 Sunday morning and in the mid-to-upper 30s Monday morning – avoiding a freeze.

This first spell of freezing temperatures comes right on schedule for our colder suburbs, if not slightly on the early side. The map below shows average first freeze dates throughout the region:

Dulles and BWI Airports, whose average first freeze dates are Oct. 15 and Oct. 29 and earliest first freeze dates are Sept. 24 and Oct. 4, should both fall to freezing both mornings or at the very least on Monday morning.

Record lows on Sunday morning are 27 (1982) and 30 (1982) at Dulles and BWI, respectively, and should not be threatened. However, Monday’s record lows of 25 (1976) and 30 (1976) at the two respective airports might be in play, especially the BWI record.

Reagan National, whose average first freeze is on November 18 and earliest is Oct. 20 (since 1945), should remain several degrees above freezing both nights.

(This post, initially published at noon, was updated at 3 p.m.)