|Radar reflectivity for 11:14 p.m. CDT August 9 (left) and 1:18 a.m. August 10 showing storms approaching|
Kearney, NE (inside white circle)
The rain caused flash flooding as you might expect as the amount of water exceeded the capacity of storm sewers to drain it away. You probably have seen this video - it's making the rounds on the Internet, but just in case you haven't I've included it here. A security camera at Good Samaritan Hospital in Kearney captured flood waters bursting through windows on the lower level of the hospital flooding the cafeteria and other areas.
|Surface weather map for 8:00 EDT on Monday, August 11, 2014|
Then, Tuesday through early Wednesday morning very heavy to extreme rainfall occurred from the mid-Atlantic into southern New England. This rain resulted from the same system that affected Michigan on Monday. The cold front extended along the Appalachians Tuesday evening, with warm, very moist air feeding into it from the Atlantic and the surface low moving east through northern Virginia.
|Surface map for 2:00 a.m. EDT, August 13, 2014|
|Water vapor satellite image. Green arrows indicate the wind flow. The divergent wind flow from the mid-Atlantic up through New England helped produce the strong lift needed to generate the heavy rain.|
Here is the 500 millibar chart for about the same time;
|500 millibar chart for 2:00 a.m. EDT August 13, 2014|
In the Baltimore-Washington area flash flooding snarled traffic and caused numerous other problems. Rainfall amounts were in the 3 to 5 inch range around Washington DC, but in Maryland amounts were higher. Several Maryland CoCoRaHS observers reported more the 7 inches of rain,and the highest amount reported was 10.32 inches near Greenhaven in Anne Arundel County.
The band of heavy rain extended from Baltimore-Washington northeast across southern New Jersey and across western Long Island. For more information on the rain in New Jersey, see this special report by the New Jersey State Climate Office. The band was quite narrow, and amounts rapidly fell off as you went north and west from the rain band.
|Radar estimated precipitation from the radar at Upton, NY from about midnight on August 12 to noon EDT on August 13.|
|Long Island showing location of Islip|
and CoCoRaHS precip reports
On Wednesday the heavy rain shifted further northeast into southeast Maine, where upwards of 6 inches of rain accumulated by this morning.
|CoCoRaHS map for Cumberland County, Maine for August 14, 2014.|
If you would like some quick summary information on flooding and its causes and costs,Weather Underground has a nice "poster type" web page on floods.