Projected rain through Monday morning from the National Weather Service.

Precipitation has fallen disproportionately on Friday through Sunday so far in 2019, and will pile on this Mother’s Day weekend.

The rainy stretch begins with thunderstorms Friday afternoon and evening. After a pause Saturday, periods of rain are likely Saturday evening through Sunday night although rain may break again for a time on Mother’s Day. The chance of showers may not totally depart until sometime Tuesday.

All told, about two inches of rain could fall, and we cannot rule out pockets of flooding.

(Ian Livingston)

Storms expected Friday afternoon and evening, some heavy

A cold front sweeping through the region is likely to set off thunderstorms Friday afternoon and evening. Downpours, lightning and gusty winds are possible in storms that develop.

The National Weather Service’s Storm Prediction Center has placed areas west of Interstate 95 in its marginal risk zone for severe storms, meaning a few storms could unleash damaging wind gusts to about 60 mph.

For updates on Friday storms, see: PM Update: Showers and storms crossing the region into evening ahead of a wet weekend

Because of high levels of atmospheric moisture and anticipated slow movement of some storms, we also can’t rule out isolated pockets of flash flooding.

It’s possible storms come in two rounds: the first between 2 and 7 p.m.; and a second between roughly 7 p.m. and midnight.

Forecast radar from HRRR model from 2 p.m. to midnight.

Storm dashboard

(The Washington Post/The Washington Post)

Approximate arrival time for storms:

  • 2 to 5 p.m., western areas
  • 3:30 to 6:30 p.m., immediate area, including the District and Capital Beltway
  • 5 to 8 p.m., areas east of Interstate 95

(Note that a second round of scattered storms is possible between about 7 p.m. and midnight from west to east.)

Storm duration: 45 minutes or so

All clear: Around 1 a.m.

Chance of measurable rainfall in any location: 60 percent

Storm motion: Northwest to southeast

Likely storm effects: Heavy rain, lightning, gusty winds

Small chance of: Damaging wind gusts, flash flooding, small hail

Rainfall potential: Highly variable — averaging 0.5 inches, but locally up to 1 to 2 inches

Saturday: Mostly dry, but spotty light rain may develop in the afternoon

Rain is likely to taper off overnight Friday. Through noon Saturday, at least, it should remain dry. But then, the chance for light rain gradually increases from southwest to northeast as low pressure develops along a front stalled just to our south.

It may take until late Saturday afternoon or even the evening hours for steady rain to begin in the immediate Washington area, though you can expect gray skies and cool afternoon temperatures in the 60s.

Certainly, of the weekend days, Saturday is your better bet for outdoor plans.

Simulated radar from the NAM model on Saturday.

Saturday evening through Sunday night: Waves of rain, but a pause possible

Starting late Saturday, waves of low pressure will ride along the front stalled over area bringing periods of rain, which may be moderate to heavy at times.

It will not rain continuously, and some models suggest rain could ease or pause for a portion of the day Sunday. So Sunday won’t necessarily be a washout, but it will be damp and cool, with highs barely topping 60.

If there is a pause in the rain on Sunday, models generally forecast it to resume late in the day or at night. And even Monday could be unsettled with showers at times before the weather system finally departs on Tuesday.

Model rainfall forecasts for Washington range from 1.5 to 3 inches through Monday morning (including Friday’s storms). Here is their range of projections:

  • NAM: 2.8 inches
  • GFS: 1.3 inches
  • Canadian: 1.4 inches
  • European: 1.7 inches

If the high-end totals are correct, Washington will reach its average rainfall for all of May less than halfway through the month.