Flash Flood Watches and Warnings issued, heavy rain threatens to soak DC region tonight

- After what can only be described as a pleasant middle of the week for the region, with lower humidity and temperatures for most in the lower 80s, more typical July humidity is back in the Washington, D.C. region. At the same time, a storm system dropping into the Midwest will begin its slow journey eastward towards the region. A Flash Flood Watch has already been issued for much of the region including D.C. beginning Friday afternoon until Saturday afternoon, when the heaviest rains are expected. A Flash Flood Warning was added around 10:30 a.m. Friday for some parts of Virginia. 

Quick 5 things to know:

- 2-5” of rain (locally higher) is possible between Friday and Sunday around the D.C. region

- Heaviest rains are expected Friday night and Saturday morning

- Storms could contain blinding downpours and be hazardous to travel. Flash flooding is a big concern on both Friday and Saturday

- Storms containing gusty winds and even an isolated tornado are also possible, with best chances south and east of Washington, D.C.

- Showers may continue through Sunday with a second, weaker storm developing off the coastline this weekend

Friday may start with a few showers, but should be generally dry for most around the region. The one exception would be west of I-81, where there could be more widespread rain showers during the morning hours. As the storm system approaches the region and begins to strengthen during the afternoon, heavy showers and storms should become more widespread across the area. A few storms may contain gusty winds, and due to the winds turning with the strengthening storm overhead, one or two weak tornadoes cannot be ruled out. The best chances for these stronger storms will be south and east of the storm center. This includes southern Maryland, the Delmarva, as well as central and eastern Virginia.

As the day turns into night and the system continues to strengthen, showers and storms will become more organized and bands of extremely heavy rain will likely develop across parts of the region. Rain in these bands can fall with such intensity that they could be blinding to those on the roads, so travelers should take exercise caution. An abundance of available atmospheric moisture means rainfall rates of 2-3” an hour are possible in some of the heaviest bands. Due to the slow moving nature of these storms, perhaps the biggest threat for Friday evening is going to be flash flooding. As the system will be slow to move out to the north and east, the flash flooding risk is expected to continue into the overnight hours of Friday night and through the first half of Saturday.

Speaking of Saturday, the biggest change to the forecast today was with the weekend, and unfortunately it was not a positive change. Even as the main storm exits the immediate area on Saturday afternoon, a piece of upper level energy will swing across the region into Saturday evening. This means clouds and showers are expected to linger into the nighttime hours of Saturday, although these should not be as heavy as those in the morning.

This energy may lead to the development of a new, much weaker storm system off the Delmarva coastline on Sunday which could once again throw a few showers back towards the D.C. region, particularly during the first half of the day. By the afternoon and early evening hours, the system should finally start to exit the region, and we may even end the weekend with a little bit of sun. One thing is for certain, the clouds and rain will help keep temperatures unusually cool, as temperatures are not expected to make it out of the 70s all weekend long. The District has not had a high temperature below 80° since the first full week of June.

When the rain finally stops, many across the region will likely have picked up 1-3” of rain between Friday afternoon and Sunday morning. Locations that see the heaviest rains could easily get over half a foot of rainfall, but these amounts should be more isolated. Needless to say, if you live in a flood zone you will want to pay special attention to watches and warnings over the next few days.

Remember, if you come across any flooded roadway while driving NEVER travel through it. Only 6” of fast moving water has enough force to carry away a vehicle. Turn around, don’t drown!

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