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Posted at 12:10 PM ET, 09/30/2010

Deluge not done yet, flood risk remains

By Dan Stillman

Generally 2-4" and counting; some reports near 7"

* 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 *
* When does it end? Full Forecast | Share photos | Dr. Gridlock *
* Flash Flood Watch thru today | Wind Advisory (eastern counties) *
* Outside now? Radar, temperatures & more: Weather Wall *

It's still raining buckets out there in some places, though letting up in others, with rain totals to the tune of at least 2-4" for most locations thus far. Locally higher amounts near and over 7" have been reported, especially along the western shore of the Chesapeake Bay, which has been pummeled by a seemingly endless stream of heavy rain and seen a few tornado warnings as well. The flooding rains have created plenty of traffic problems and trouble spots across the region today.

Below is a map of rain totals as of noon from National Weather Service mesonet stations:


24-hour rain totals as of noon Sept. 30. Credit: National Weather Service.

What's next? Heading into the afternoon, radar and model data suggest the precipiation, or at least the heaviest of it, may try to split away from D.C., with one part breaking off to the north and another part consolidating to the south closer to the original tropical low pressure center. But, even if there is a lull in the rain or its intensity, the metro area or just to the east could be pounded with another surge of heavy rain this evening and maybe even another heavy parting shot tomorrow morning (forecast confidence for both potential bursts of more heavy rain is low).

Bottom line: Some areas could still see another 1-3" with locally higher amounts before this storm is finished. Which means the Flash Flood Warning curently in effect until 4:30 p.m. could be extended or re-issued later on for parts or all of the area.

By Dan Stillman  | September 30, 2010; 12:10 PM ET
Categories:  Floods, Updates  
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Next: Rain takes a brief breather, flood risk continues

Comments

Thanks for posting the map graphic; colors are neat although I imagine some of the rainfall totals are hourly.

Posted by: JerryFloyd1 | September 30, 2010 12:17 PM | Report abuse

Tried to drive at 10:30 am Thurs to Baltimore from Bethesda -- big mistake. Washington beltway zero visibility, managed to get off at New Hampshire south -- University Blvd flooded, car abandoned, etc.

Posted by: BethesdaFan | September 30, 2010 12:18 PM | Report abuse

Now imagine if it were cold enough to snow.

Posted by: ennepe68 | September 30, 2010 12:32 PM | Report abuse

Several bursts of heavy rain in south Arlington--no lightning or thunder here so far.

Which gets me to thinking...how can they issue a "severe thunderstorm warning" without a real thunderstorm??? The definition I've seen cites "visible lightning and/or audible thunder", not cumulonimbus clouds [which can produce heavy showers without electric discharges!]hus far the only evidence I've seen for lightning is one Vaisala strike near the mouth of Chesapeake Bay and one or two faint bursts of sferics "static" early this morning on AM radio. Since sferics can propagate over a considerable distance, the strikes involved could have been located in the strong convective cells training over Chesapeake Bay and St. Mary's County earlier today. I'd be careful about calling a convective cell a thunderstorm unless I saw the lightning, heard the thunder, or have a record of the strike(s) on Vaisala, StrikeStar or WWLLN.

Posted by: Bombo47jea | September 30, 2010 12:40 PM | Report abuse

3.4" at DC-South West (near waterfront). Of this, 1.6" in downpours mid-morning.

Posted by: SteveT-CapitalWeatherGang | September 30, 2010 12:51 PM | Report abuse

2.80 in Poolesville.

Looks like its almost over for the western suburbs.

Posted by: MKadyman | September 30, 2010 12:53 PM | Report abuse

You lopped Lexington Park, MD off of your map. 24 hour total=7.3 inches.

Posted by: jenniej | September 30, 2010 12:58 PM | Report abuse

CT is dry/damp, NJ had a few showers, PA was awful. Worst part was diesel on rt 78, no traction. Stiff x-wind on TZ bridge, tail wind now.

Posted by: eric654 | September 30, 2010 12:59 PM | Report abuse

ennepe68: A lot of this would not have been snow in winter with the low track.. not to mention you would not get these types of precip totals in the cold season.

Posted by: Ian-CapitalWeatherGang | September 30, 2010 1:03 PM | Report abuse

Looking at the National and MidAtlantic maps, looks like a dry slot for DC in the next hour or so. Still a pretty awful looking tail to this down along the NC coast. What's the current thinking on whether that passes over DC, the Delmarva or out to sea?

Posted by: blackbear336 | September 30, 2010 1:19 PM | Report abuse

blackbear336 - most of the energy that rolls northward will pass to the east of the Bay, but this rain plume will continue into the evening. Radar is having a hard time depicting the precip properly. So don't completely believe what you see!

Posted by: Camden-CapitalWeatherGang | September 30, 2010 1:30 PM | Report abuse

It stopped raining for about 10 minutes here in the Gaithersburg Airpark area, then it started up again.

With winds.

Not raining very hard now though it's warm outside.

Posted by: wadejg | September 30, 2010 1:32 PM | Report abuse

@blackbear336

Your question is the focus of discussion in the post text above.

Posted by: CapitalWeatherGang | September 30, 2010 1:32 PM | Report abuse

Quite a bit of moisture gathering down in North Carolina that appears to be heading this way! http://www.accuweather.com/us/radar/sir/us_/radar.asp?play=true Is that part 2?

Posted by: snowedin85 | September 30, 2010 1:46 PM | Report abuse

I just compared the measured 24 hr. precipitation total reported by NWS Mesonet from measuring stations with the calculated NWS 24 hr. precipitation total shown on the NWS doppler radar return screen. The numbers for the region between Frederick and Mt. Airy MD surprisingly match at 2.5 inches total. Are doppler radar values calibrated with the Mesonet numbers so the match is to be expected is this a good example of two differing technologies both giving values that appear to be similar because the technology is mature.

Posted by: iseyij | September 30, 2010 1:56 PM | Report abuse

Baltimore County (among other) schools are having early dismissals today.

Posted by: megamuphen | September 30, 2010 1:59 PM | Report abuse

some stronger gusts in old town

Posted by: snowedin85 | September 30, 2010 2:01 PM | Report abuse

blackbear336 - most of the energy that rolls northward will pass to the east of the Bay, but this rain plume will continue into the evening. Radar is having a hard time depicting the precip properly. So don't completely believe what you see!

Yeah, map I like least is this one:

http://www.goes.noaa.gov/ECIR3.html

If I'm reading it right, that large red blob off the NC/SC coast looks a lot more intense than the storm we just had....

Posted by: blackbear336 | September 30, 2010 2:05 PM | Report abuse

"blackbear336 - most of the energy that rolls northward will pass to the east of the Bay, but this rain plume will continue into the evening. Radar is having a hard time depicting the precip properly. So don't completely believe what you see!"

Yeah, the map I like least is this one:

http://www.goes.noaa.gov/ECIR3.html

That large red blob off the NC/SC coast looks a lot more intense than the storm we just had....hate to see than come thru tonight....

Posted by: blackbear336 | September 30, 2010 2:07 PM | Report abuse

New post up

Posted by: snowedin85 | September 30, 2010 2:28 PM | Report abuse

The comments to this entry are closed.

 
 
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