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Posted at 2:00 PM ET, 09/30/2010

Rain takes a brief breather, flood risk continues

By Jason Samenow

New wave tonight may bring more floods, especially east

* Flash Flood Warning 'til 4:30 p.m. ('til 6:15 p.m. far N & NE burbs) *
* Tornado watch for eastern counties until 7 p.m. (map) *
* Storm impact coverage: PostLocal | Live chat transcript *
* Flash Flood Watch thru tonight | Share photos | Dr. Gridlock *
* Outside now? Radar, temperatures & more: Weather Wall *
* Citizen observer rain totals: VA, MD | NWS Mesonet rain totals *

Rain is starting to diminish in coverage and intensity from south to north, after a general 2 to 4.5 inches since last night. The big exception is around the Chesapeake Bay - primarily counties on the west side - where totals have reached 5 to 8 inches.

Though rain is currently on the decrease in many locations, scattered showers remain likely through the afternoon. More importantly, a second wave -- positioned near the North Carolina/South Carolina coast -- is beginning to surge north. This wave, also rich in deep tropical moisture, may bring another round of torrential rain tonight - particularly along and east of I-95.

Significantly, locations in the eastern suburbs near the Bay, that have already received extreme rainfall totals, are likely in for a double whammy. A few spots near the Bay could end up with double digit rainfall totals (10+"). The immediate metro region will be on the western edge of this second wave and could receive either a lot (1 to 3 more inches) or a little (less than an inch) more. But rainfall potential decreases the further west in the suburbs you go. For example, Loudoun and Frederick counties may not see a lot more rain - but are not entirely out of the woods.

Stay tuned for additional updates this afternoon and evening.

By Jason Samenow  | September 30, 2010; 2:00 PM ET
Categories:  Floods, Updates  
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Next: Some gusty storms, then possible rain round 2

Comments

Manassas VA the sun tried briefly to make an appearance here. It's still raining off & on, and the sky is moving fast & looking crazy.
How much rain did DC get with storm Isabel? I wonder will this event beat that total.

Posted by: FIREDRAGON47 | September 30, 2010 2:13 PM | Report abuse

5 inches in the rain bucket in Oakton, VA, and skies have just signficantly brightened in the last few minutes, along with increasing winds.

Posted by: FH59312 | September 30, 2010 2:14 PM | Report abuse

About 1.25" in Sposty, I always seem 2 get at least 50% less than every1 else.
Rapp river is up from a trickle 2 an average flow, no danger of flooding.
Looks like most of the rain will track E of 95 thru 2night. Doubt I'll get more than a few showers the remainder of this storm.
Next 2 weeks look dry, so it's a good thing we got this rain or the drought cond. would have continued 4 most of the area.

Posted by: VaTechBob | September 30, 2010 2:17 PM | Report abuse

Drying out and windy in Old Town Alexandria. The creek in the park a couple blocks away from work, was pretty high - and looks like it had been about 4-6 inches higher.

I'm cracking up at all these "Think if it had been snow!" comments. We'll see, this winter... :)

Posted by: MKoehl | September 30, 2010 2:32 PM | Report abuse

I know folks have been asking about Isabel - but I was wondering how this storm compares with Tropical Storm Hanna of 2 years ago?

Posted by: MKoehl | September 30, 2010 2:36 PM | Report abuse

These "think if it had been snow" comments sent me under my desk twitching. I hear it's nice in Tucson during the winter...

Posted by: haggis | September 30, 2010 2:37 PM | Report abuse

4.21" here in Del Ray (old town) Alexandria. Winds are really ramping up now, gusting 30-40MPH+ here now, with some brief peeks of sunshine. There have been some gusts up around 50MPH. Some tree limbs are starting to come down, as are lots of leaves.

Not sure why no one is discussing these VERY STRONG WINDS. Every weather forecast I see says 10-15 or 10-20 MPH. This is ALOT STRONGER than that. Maybe the sustained winds are 10-20, but they are frequently gusting up to 40.

Posted by: KJ71 | September 30, 2010 2:45 PM | Report abuse

KJ71: i agree. working in old town and watching the wind pick up in the last hour or so.

Posted by: snowedin85 | September 30, 2010 2:49 PM | Report abuse

Is the Potomac river high around Old Town Alexandria yet? No one is saying anything about the Potomac.

Posted by: SusanMarie2 | September 30, 2010 2:52 PM | Report abuse

SusanMarie2: walked down to the Potomac on lunch break and it wasn't that high yet but we'll see what tonight's rain event does to it. A little bit of street flooding at the end of King St. but it hadn't reached the sidewalks yet.

Posted by: snowedin85 | September 30, 2010 2:55 PM | Report abuse

I just noticed that the rain chances for Friday on the CWG forecast box just increased from no chance to 50%.

I always interpreted the "---" in the forecast box as a 0% chance of rain, but how is a 0% forecast meaningful if it actually does rain on some of the days with such a forecast? Given such a forecast, it seems like the prior probability of rain on those days is not really 0%.

Posted by: stuckman | September 30, 2010 2:57 PM | Report abuse

Thanks Snowedin! I was thinking too that it may not happen till later when all this creek flooding flows into the Potomac from points all around the area...

Posted by: SusanMarie2 | September 30, 2010 3:00 PM | Report abuse

Snowedin85: I just lost some siding from the 2nd floor of my house. 2nd time this summer! (well now its fall but you know what I mean) First time was the severe storm / microburst that ripped apart Del Ray with 100+mph winds. These gusts are getting more and more frequent, and ALOT stronger. That last one had to be over 50MPH. The entire house shook and it sounded like a freight train going by with lots of small branches, debris, recycling bins going flying through the air.

Now TWC is saying winds are 20-30MPH. At least they upgraded their wind forecast.

RE: the Potomac River, the minor coastal flooding is only due to the strong south/southeasterly winds pushing the water up the tidal portion of the river. I would expect that the actual rise from the rains is continuing and it may not crest for another 12 hours or so.

Here we go again with another WILD wind gust!

Posted by: KJ71 | September 30, 2010 3:12 PM | Report abuse

@stuckman - That is probably due to the fact that it might rain very early in the morning from this storm.

Posted by: snowlover | September 30, 2010 3:12 PM | Report abuse

For those asking about Isabel, the region received 1-3" of rainfall according to this link: http://www.hpc.ncep.noaa.gov/tropical/rain/isabel2003.html

Posted by: jaydreb1 | September 30, 2010 3:19 PM | Report abuse

I miss the winter-style forecasts. For example, for DC tonight CWG is calling for a 50% chance of an inch or less of rain and a 50% chance of 1 to 3 inches (and just to be safe, probably an implicit 5% chance of over 3" inches) - did I get that right? Sounds spot-on to me.

Posted by: manatt | September 30, 2010 3:20 PM | Report abuse

@stuckman

The forecast box you refer to is fed by the National Weather Service. The change is likely the result of the increased chance from earlier today of some more rain into late tonight/early tomorrow. This is the potential rain we've been talking about in this and previous posts -- the rain that we're uncertain whether it will come through the metro area head on, or veer east and just graze the area.

Posted by: Dan-CapitalWeatherGang | September 30, 2010 3:21 PM | Report abuse

Stuckman: I think the reason you are seeing the rain %chance values go up for tomorrow is because we still have the remnant tropical low that was Nicole to move through. That low looks like it is going to track very similar to the strong tropical low pressure that just tracked to the West of Washington, that brought us the big rain fall totals, and now the very strong and gusty southerly winds. I would guess that the early thinking was that most, if not all of the energy from the remnants of Nicole would get sucked up into the newer low that moved just to our west today. That did not happen and what is left of Nicole is now a separate and very strong low pressure system lagging behind this first one. My guess is that it may track slightly east of where the one that just went through did, bringing much of the same areas the same types of rains over night tonight, along with more gusty winds. This airmass, and both low pressure systems are not actual tropical systems but are very tropical in nature, and are LOADED with very deep tropical moisture and energy which really allowed them to ramp up. Both of these systems really remind me of what happens when you have decaying tropical system moving through. Lots of torrential rains, some very strong winds, and lots of vertical wind sheer causing some spin up tornadoes. I know no tornadoes have been confirmed by I have family in both Smithfield VA, and Annapolis MD, and they both have reported to me some sigfigant wind damage including many large trees being uprooted or broken down. This stationary front, along with the strong trough of low pressure just to our west are really acting as a focusing mechanism allowing these low pressure systems to maintain or even increase their energy.

Posted by: KJ71 | September 30, 2010 3:23 PM | Report abuse

re: the wind

At least downtown, it's breezy -- probably 15-25 mph and I'm seeing quite a few stations are gusting between 35-40 mph. So yes-- we underestimated the wind a bit when we called for 10-20 with some higher gusts.

Posted by: Jason-CapitalWeatherGang | September 30, 2010 3:31 PM | Report abuse

Hannah had a lot more wind with her and the rain bullseye was further West. I ended up at around 7-8 inches in Southern Loudoun. Im guessing that ill get home in an hour or so and have closer to 3 inches. Hannah was much wetter and windy than Isabel was for most of Fairfax and points west. As for Nicole - I think that the folks in Anne Arundel and Calvert will have something different to say than us Western Burb folks, though.

Posted by: DullesARC | September 30, 2010 3:36 PM | Report abuse

New post up.

Posted by: snowedin85 | September 30, 2010 3:48 PM | Report abuse

I remember well going out to Calvert County right after Isabel. We were beachcombing for fossils; big trees were hanging off the clifftops & some had gone over down to the water's edge. Tons of debris from boats all over the beach. Somebody must have had a huge stash of candy bars in their boat because we picked about 100 of them for the trash bin. Tragic.
The rainfall during that storm seems comparable to what we had in Centreville last night & today. This is a big storm & it looks as if it's not quite done with us yet.

Posted by: FIREDRAGON47 | September 30, 2010 3:52 PM | Report abuse

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