Overview: A Flash Flood Watch is in effect through this evening as a plume of heavy rain flows through the region from southwest to northeast. A general 2-3” of rain is possible with locally higher amounts. Flash flood warnings are in effect for selected areas as shown below. Remember flood safety: never drive through standing water on a road: turn around, don’t drown. Follow this post for the latest updates - every 15-30 minutes (refresh your page for latest).

4:15 p.m. update: Defying model predictions, a push of dry air from the southwest has shifted the axis of heavy rain east such that it may largely miss portions of the metro region, especially west of the District. In addition, the rain looks like it may taper off quite a bit after 6 p.m. or so from southwest to northeast. Heavy rainfall amounts exceeding 2” may be limited to areas the counties adjacent to the Bay up to around Baltimore. This is our last update with this live blog. Stay tuned for our PM Update around 4:45 p.m.

3:50 p.m. update: The area of heavy rain moving up from the south is now on our doorstep and should cover much of the metro region between 4 and 5 p.m. Southern Maryland and counties adjacent to the Bay up to around Baltimore are already experiencing a band of very heavy rain. But well to the southwest, we see a bit of dry slot developing which may cut off the rain from the District and especially points west between 7 and 10 p.m. tonight. The Nationals game may no longer be such a longshot, even if there’s a delayed onset.

3:30 p.m. update: Flash flood warnings have been extended until 7 p.m. for northern Anne Arundel and southern Baltimore counties where downpours continue, and discontinued for Howard and Frederick counties where rain has decreased. Big batch of heavy rain to the south has reached Fredericksburg and Stafford county and is lifting northeast towards the metro region.

3:15 p.m. update: The visible satellite loop shows convective heavy rains developing along and just west of I-95 in Virginia. Front edge of the heavy rain band is into Orange and southern Fauquier county on radar (see below).

2:50 p.m. update: As we await the very heavy slug of rain to the south and southwest, consider that we have already now had about 8” of rain this month at Reagan National. Only four Septembers since 1872 have passed the 10” mark, and we might do that by tomorrow. The 1934 record September rainfall of 17.45” seems safe.

2:20 p.m. update: What’s coming for rush hour? Take a look at the regional radar. It’s a BIG area of heavy rain that begins in central Virginia and extends southwestward into central North Carolina

1:55 p.m. update: Check this out: GFS 12 hour rain simulation through 11 p.m. tonight. Notice the narrow ribbon of 2” or more from D.C. and to the northeast into NE PA - covering the same areas hit so hard by flooding rain during Irene and Lee. Rush hour may be ugly.

1:30 p.m. update: Big swath of heavy rain in Stafford, eastern Prince William and western Charles county moving north and will envelop Fairfax county and the District in the next hour. NAM model simulates a generalized 1-1.5” of rain between 2 and 10 p.m. for much of metro region, but locally higher amounts are a given. Does NOT look good for Nats game tonight.

1:15 p.m. update: Meteorologist Justin Berk tweeted Baltimore needs only 3 more inches of rain to break the 1934 September record for wettest month.

1 p.m. update: Due to the inbound heavy rain, Fairfax County is especially concerned about street flooding in Huntington. It sent out the following statement: Residents in the Huntington area, especially those who live on Fenwick Drive and Arlington Terrace, are encouraged to immediately move their vehicles to higher ground. Residents should also move valuables from basements.

12:45 p.m. update:A Flash flood warning has been issued until 3:30 p.m. for eastern Howard, northern Anne Arundel, and southern Baltimore counties, including the city of Baltimore. An inch of rain has already fallen, and another 1”+ is possible in the next couple hours.