Flooding "Beyond Anything Experienced"

There is no historical analog for the impacts of Hurricane Harvey.  The precipitation numbers being pumped out by our forecast models a couple of days ago were jaw dropping and beyond comprehension.  Unfortunately, those forecasts are coming to fruition.  

The numbers on the map below are 24-hour precipitation totals from the Texas Mesonet that I believe are since 7 AM CDT yesterday.  A significant swath of the area from northeast of San Antonio through the Houston area received more than 6 inches of precipitation.  Multiple stations in the Houston area reported more than 10 inches of rain, with a maximum of 18.02".  

Source: Texas Mesonet

Major flooding is occurring along streams and rivers across the region.  

Source: NWS

The National Weather Service Houston/Galveston forecast office has a graphic showing points that are forecast to reach major or record flooding stages, emphasizing that the impacts are "unknown and beyond anything experienced." 

Source: NWS

Humans like analogs as they help us put things into context, but that's not possible with this storm.  This morning I thought of the California Megaflood of 1861 (see http://wasatchweatherweenies.blogspot.com/2017/02/california-megafloods.html) as I surveyed data from Texas, as it affected such a large swath of the Central Valley, however, the meteorology and hydrology of California are drastically different from Texas, as well as the type and intensity of development there in 1861 compared to Texas in 2017.  

Ultimately, we're left with the reality that we are hurtling into unknown territory, with millions affected.