Projected rainfall by NOAA’s Hydrometeorological Prediction Center covering Saturday.

The image to the right shows the preliminary rainfall assessment from NOAA’s Hydrometeorological Prediction Center. Generally, 1-1.5 inches is the best bet right for this storm system (around 1” in the metro region to 1.5” toward the mountains)- which will tap both Atlantic and Gulf moisture.

The biggest wildcard right now is the exact timing of the rain. It could start as early as mid-morning or hold off until early to mid-afternoon. And it could end as early as between 7 and 10 p.m. or continue until past midnight. At this point, the heaviest rain seems most likely to fall between late afternoon and mid-evening, when there could be embedded thunderstorms.

The National Weather Service in Sterling is highlighting flood potential, writing in its latest discussion:

SATURDAY - WITH POSSIBLE RAINFALL AMOUNTS OF 1 TO 2 INCHES...LOCALLY HIGHER...AND MOIST ANTECEDENT CONDITIONS...FLASH FLOODING WILL BE POSSIBLE. LATEST GUIDANCE SUGGEST THAT HIGHEST [RAINFALL POTENTIAL] WILL BE ACROSS POTOMAC HIGHLANDS...

We’ll keep you posted on the rainy details and any changes to the forecast as the weekend draws closer.