Areas in blue are under a freeze watch tonight. Areas in turquoise are under a freeze warning. (National Weather Service)

Note: A freeze watch means freezing temperatures are *possible*, a warning means they are *likely*.

From Sunday afternoon: Just 48 hours ago it was in the low 80s, but in another 30 hours, temperatures may dip near or even below freezing in the metro region. The National Weather Service has issued a freeze watch late Monday night into early Tuesday morning everywhere in the greater Washington, D.C. metro region except for Calvert and St. Mary’s county - due to the moderating Bay waters.

Temperatures are likely to dip to about 31-34 inside the beltway and and east of town, but 27-32 west and north of the beltway.

Related link: Summer in spring? Head for the hoses...

In addition to spots along the Bay, normally warmer locations along the Potomac and downtown may also be spared freezing temperatures.

Because it has been so warm lately, the growing season is well underway - so gardeners may need to protect sensitive, tender vegetation. Temperatures so far this month have averaged 12 degrees above normal.

The culprit for the sudden freeze potential is a sharp cold front from the northwest that will plunge southeast during the day Monday. But this is going to be a quick-hitting cold snap with temperatures recovering into the 50s Tuesday afternoon, and perhaps up to 70 or so by Wednesday.

One factor that could lead to temperatures slightly warmer than forecast Monday night and a lesser freeze risk is the wind. Should winds persist late into the night, it might prevent temperatures from falling off as dramatically.

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 provides a useful tool for determining the risk of a freeze at a given zipcode by date.

We’ll have more detail on the freeze potential in Monday’s forecasts.