5:15 p.m. update: Except for southern Maryland and Stafford county, the storms have moved away. After highs in the low 90s, temperatures have fallen into the 70s behind the storms. Humidity levels remain high, but should gradually fall overnight. Standing water on roads from earlier rains remains in some areas of northern Virginia so allow extra time for the commute home.
Storm reports: Flash flooding, due to rainfall rates of 1-3” per hour, was the most common effect from this afternoon’s storms, primarily in northern Virginia (although one report of flash flooding came in from around Gaithersburg). Flooding was reported in Wolf Trap, Herndon, Vienna, Dunn Loring, Falls Church, Merrifield, and Tysons Corner. As much as 2” of rain fell in a very short time according to doppler radar (shown to the left). Frequent lightning associated with the storms caused up to 47,000 power (down to 33,000 at 4:55 p.m.) outages in Virginia according to Dr. Gridlock. Isolated wind damage reports came in from western Loudoun county (Philomont) and in Fairfax, Tysons corner and Vienna.
Reader photos and video:
Video of storm from Alexandria (by Joel Housman) | Flooding in Gaithersburg (by @Foreverfit4u) | Video shows cloud to ground lightning as storm approaches Chantilly (by @origamislayer) | Swollen Lake Accotink and washed away road in Springfield (by @spencerski)
Forecast overview from 2:30 p.m.: Another 90+ day down, but fortunately a break is coming. That break, in the way of a cold front, is now producing a line of showers and storms across the area, and they’ll continue to sag south the rest of the afternoon into the evening. Severe weather is possible, with some already ongoing. A few storms could potentially produce strong and damaging wind as the main threat, though large hail is also possible.
Through Tonight: Showers and storms, some severe with strong winds, heavy rain and lightning, should sag through the area by early evening, with clearing getting underway afterwards. Even though the watch is up ‘til 10 p.m., it should be over well before that in our area. Dew points fall from the 60s into the 50s by morning, meaning that humidity level will feel much more comfortable by then. Lows should range from the lower 60s in the coolest spots to around 70 downtown. A fresh north breeze keeps the air mixed.
Tomorrow (Thursday): Expect a high daily digit for tomorrow! After our 4th heat wave, we’re surely due a bit of relief. Expect mostly sunny skies and temperatures rising mainly into the mid-80s, perhaps a few lower 80s well north and west. Humidity should also mainly be a non factor. Not too much more you can ask for with lots of sun during the warmest time of the year.
Pollen update: Walter Reed reports that tree pollen is LOW, grasses are MODERATE, weeds are LOW, and mold is N/A.
Earlier storm updates
4:30 p.m. update: The storms and heavy rain have now moved south and east of Fairfax county. Charles county (especially west and central, around La Plata), where a severe thunderstorm warning remains in effect, is catching the worst of it. This storm will head into the southern part of the county and then St. Mary’s county through 5:15 p.m., when the warning expires. Weaker storms stretch through southern Prince William and Fauquier counties. This activity will move into Stafford (in Va.) county and then out of the area in the next hour.
4:00 p.m. update: Storms are gradually sagging south and storm risk has ended roughly north of I-66 and into Loudoun, Howard, and Montgomery county, where the severe thunderstorm watch has been canceled. South of 66, storms with torrential rain continue and flash flood warnings have been extended into much of Prince William county, southern Fairfax county, southwest Prince George’s county and northern Charles county until 6:45 p.m. The heaviest rain totals have occurred from Oakton and Vienna to Merrifield and Falls Church/Tysons where flooding has been reported. Fortunately, the rain is gradually moving south of those areas. Behind the storms, 20 degree temperature drops have been reported, with temperatures in the low 90s falling to near 70.
3:30 p.m. update: Severe thunderstorm warnings are in effect for the southern half of the area from Prince William county through Charles county (including southern Fairfax county). A Flash Flood Warning is in effect for much of northern Virginia inside the beltway extending west to eastern Loudoun county. Flash flooding has been reported in Vienna and Tysons Corner.