From the ABC 7 Weather team

Flooding Rains: What happened

July 12, 2013 - 08:32 AM
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Heavy rain overnight caused flooding and road closures. What happened to our dry Friday forecast?

The D.C. area woke up to heavy rain and flooded roads this Friday morning.  As of 8:30 this morning, the rainfall totals ranged from 1-6"  Check out the official recordiing stations.  



24 hour Rainfall Totals

 
And here's a look at some of the highest totals we could find on our weather bug network. 



Weather Bug Rainfall Totals Since Thursday

 
While we did expect some wet weather, we didn't think it would exceed flash flood criteria.  So, why did we get so much rain?  The cold front that crossed our area yesterday was expected to keep pushing to the south and east of our area.  However, drier air to our west has been pushing up to the warm and moist air from the Atlantic and the two have been converging on top of us.  This is a water vapor image that I have added weather features on top of to help you understand what is happening in the atmosphere.  



Water Vapor Satellite


The brownish colors show dry air and the green colors are moisture.  They meet up right along the I-95 corridor.  The cooler, more dense dry air pushes underneath the warm and humid air creating lift on top of us.  This is what is causing all of the rain.  To further complicate matters, there is an area of low pressure in the upper atmosphere that is trying to dig in west of us.  The computer models are retrograding this low to the southwest.  If it continues to do that, it will allow some leftover moisture from Tropical Storm Chantal to try and sneak up here late weekend.  Here is where the remnants of Chantal's moisture is now near the Bahamas.  



NOAA Satellite


Even if that doesn't make it here, there should be enough instability and moisture Saturday to at least give us a 30% chance of showers to start the weekend.  We will have to continue to monitor closely.  In the meantime a flash flood watch is in effect through this evening. 

 



Flash Flood Watch through this Evening


After today, the Bermuda high off the Atlantic coast will hopefully push back and shift that convergence zone to our west and bring warmer and drier conditions in with 90+ temps next week.  Our forecast confidence for the weekend is a bit lower than average due to these tricky circumstances.

 

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