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‘Exceptionally cold’ weather for May arrives tonight with near-freezing temperatures and bitter wind chills

Records are likely to fall in D.C., and there’s a ‘non-zero’ chance of snowflakes.

Some of the coldest May weather the Washington region has experienced in modern times plunges into the area tonight and persists into the start of Mother’s Day. Freeze watches and warnings are in effect both tonight and Saturday night for many locations west of the District. On Saturday, February-like wind chills in the 20s start the day areawide.

The cold is courtesy of a lobe of the polar vortex, crashing south into the eastern United States from the Arctic. Scores of record low temperatures are forecast from Texas to Maine on Saturday.

Polar vortex blast surges toward eastern U.S. with historic May cold and even some snow

The National Weather Service office serving the Washington region described an “exceptionally cold air mass for May standards” in recent forecast discussions, noting that temperatures at several different levels of the atmosphere are likely to challenge the lowest levels on record for May and are “more typical of mid winter.”

The average high temperature in Washington on Saturday is 74 degrees, whereas the actual high may struggle to exceed the low 50s, some 20 to 25 degrees below normal. Saturday is almost certain to be the coldest May day in Washington since at least 2008. Add in winds gusting over 30 mph and it will feel 10 degrees or so colder.

While computer models have backed off earlier predictions for some wet snow in the region, there is still an outside chance a few flakes could mix with rain in our colder areas either late Friday or in any passing showers on Saturday. Snow this late in the spring has happened only two times in weather records dating back to the late 1800s in Washington.

Frost and freeze advisories for Friday and Saturday nights

After rising into the 60s Friday, temperatures throughout the region are predicted to drop into the 30s Friday night. The biggest drop in temperature is expected between 8 p.m. and 2 a.m. in the wake of the Arctic front. That’s also when a few snowflakes could mix in with rain, mainly toward the Interstate 81 corridor and into the mountains. By the predawn hours, most spots along and west of Interstate 95 should be in the 30s.

The best chance of freezing temperatures Friday night into Saturday morning is close to and west of the Interstate 81 corridor, where a freeze warning is in effect. In this zone, the Weather Service predicts temperatures as low as 29 degrees. This zone includes Hagerstown and Winchester.

Temperatures may come close to freezing early Saturday in areas just to the east of Interstate 81 corridor, including some of Washington’s far western and northern suburbs, which are also under a freeze warning. This zone includes northern Montgomery, western Howard and Frederick counties in Maryland (including Germantown and Frederick), as well as Loudoun and northern Fauquier counties (including Warrenton, Ashburn and Leesburg) in Virginia. Here the Weather Service says lows could drop to 31 degrees.

On Saturday night, the freezing weather may expand farther east. A freeze watch covers all of the areas under a freeze warning Friday night, but also extends into Washington’s close-in western and northern suburbs, including central and southern Montgomery, southern Howard, Fairfax, Prince William and Stafford counties.

“Frost and freeze conditions could kill crops, other sensitive vegetation and possibly damage unprotected outdoor plumbing,” the various freeze alerts state.

They further advise: “Take steps now to protect tender plants from the cold. To prevent freezing and possible bursting of outdoor water pipes they should be wrapped, drained, or allowed to drip slowly. Those that have in-ground sprinkler systems should drain them and cover above-ground pipes to protect them from freezing.”

While Dulles International Airport could see freezing temperatures on both Saturday and Sunday mornings, cold of this magnitude so late in the season is not unprecedented there.

Dulles’s latest freeze on record occurred on May 22, 2002, and, as recently as in 2013, it occurred 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 — with this year a case in point. Dulles’s average last freeze is around April 20.

Locations around downtown Washington and near the Potomac River and Chesapeake Bay should only see lows in the mid-30s to near 40, where freeze concerns are low.

The weekend weather could make history

The cold is likely to establish or at least challenge numerous low-temperature records and milestones for the region considering the time of year.

The National Weather Service put together a useful summary of all the records that could be challenged this weekend at Washington and Baltimore’s three airport locations, not just for temperature but also for snow, considering a “non-zero” chance of flakes:

The most likely records to be beaten include Baltimore-Washington International (BWI) Marshall Airport’s record low of 36 on Saturday, the record cold high temperatures on Saturday at all three airports, and Dulles Airport’s record low of 33 on Sunday.

In addition to these records, consider the other possible temperature milestones that could occur:

  • If the high in Washington remains below 55 Saturday, it will be the first such instance during May since 2008. As recently as 2003, however, it happened twice during the month.
  • In the unlikely event temperatures stay below 50 in Washington on Saturday, it would be the first instance since 1946 in May. Highs in the 40s have happened only three times in the modern record dating back to 1871.
  • At Reagan National Airport, where Washington’s weather records have been kept since 1945, Saturday’s high could challenge the coldest mark so late in the season, set in 2008, when the high was 52.
  • While it is unlikely temperatures will fall this far at National, if they drop to 34 either Saturday or Sunday, it would match the lowest so late in the season, set in 1947.
  • If the temperature drops below 40 in Washington either Saturday or Sunday morning, it would be almost a month later than normal. The average last date with a low in the 30s in Washington is April 11.
  • If temperatures at National drop into the 30s, it would be only the eighth time this late or later in the season, and the first instance of 30s in May since 2005, when the thermometer dipped to 38 on May 3.

When it will turn warm?

Temperatures will remain cooler-than-normal through the middle of next week, but all signs point to a rather sudden pattern change and arrival of warm weather in roughly seven days.