Here comes the rain. (Robert Miller/The Washington Post)

(This post, originally published Friday morning, has been updated. Some of the latest model forecasts introduce more rainfall during the day Saturday.)

Washington hasn’t had a truly rainy weekend since at least mid-March. The rainiest days have tended to coincide with the workweek this spring. So we suppose we’re overdue for a gray, wet weekend.

Earlier forecasts had suggested rain may hold off until Saturday evening. However, new information suggests rain showers may arrive sooner – perhaps as early as the morning hours on Saturday. While this forecast is somewhat uncertain, we’d suggest anyone attending the March for Science plan for rainfall and bring along rain gear and/or umbrellas.

If there’s any good news, it’s that the amount of rain likely to fall on Sunday has decreased.

Timing

There’s a great deal of uncertainty on exactly when the rain will start on Saturday, but we’d say there’s a 40 percent chance of showers before noon, increasing to about a 60 percent chance by mid-afternoon – unfortunately, when the March for Science begins.


GFS rainfall forecast during the day Saturday.

This rainfall should generally be light.

Our confidence is highest in periods of steady rainfall Saturday evening and overnight.

On Sunday, rainfall may taper off some, especially in areas from the District north – which could be mostly dry. South of the District, rain may linger. The cutoff in the rain will be sharp, but exactly where it will occur is uncertain. So changes in the forecast and who will be wet versus dry on Sunday could still shift.

It also looks like Monday could be somewhat soggy, especially in areas southeast of the District as low pressure meanders offshore. But – again – confidence is low in exactly where the rain sets up. Damp weather could even linger into Tuesday over parts of the region.

Rainfall totals

Since this morning, models have come into better agreement in forecasting a good deal of rainfall across the region through Sunday evening. Light amounts of 0.1-0.2 inches of rain could fall during the day Saturday, with the bulk of the rain more likely falling Saturday evening and overnight.

The average model total rainfall forecast through Sunday is for about 0.75 inches in Washington, with lower amounts to the north and substantially more to the south (where more rain is likely to fall Sunday). This is reflected in the official forecast from the National Weather Service, below.


National Weather Service rainfall forecast. (WeatherBell.com)

Here’s a brief summary of predicted amounts through Sunday evening in Washington:

  • High-resolution Canadian model: 0.6 inches
  • High-resolution NAM model: 0.7 inches
  • GFS model: 0.7 inches
  • Canadian model: 1.0 inches
  • European model: 1.1 inches
  • NAM model: 1.5 inches

The above amounts are through Sunday evening. Additional rain could fall Sunday night through Tuesday, although it’s premature to project amounts.