Possible Ice, Then Buckets of Rain

We are monitoring the potential for some sleet or freezing rain accumulation north and west of the Beltway late Thursday night into early Friday morning, which could produce some hazardous conditions (see Josh's full forecast). But the majority of the precipitation in the region is expected to be plain ol' rain during the day Friday, and there could be a whole lot of it and even some isolated flooding. The National Weather Service indicates:

[PRECIPITATION AMOUNTS] LOOK VERY HIGH W/ AN INCREDIBLE GULF MOISTURE TAP FROM THE BEGINNINGS OF THE STORM SYSTEM AS IT DEVELOPS ACROSS THE DEEP SOUTH.

How much rain are we talking about?

Two of the major U.S. weather models -- the Global Forecast System (GFS) and the North American Mesoscale Model (NAM) -- are predicting (see graphic below) a substantial accumulation of rain over the area in the 24-hour period ending 7 p.m. Friday. The GFS (left) predicts at least an inch of water will fall, with the NAM (right) coming in at a minimum of about 1.25 inches. The pinkish color indicates areas of 1.5 inches or more. In both models, areas south and east of the Beltway are predicted to receive greater amounts than to the north and west.

Model graphics courtesy the National Centers for Environmental Prediction.

Where is all this moisture coming from? The Gulf of Mexico. You'll notice that both models show a colorful plume of moisture stretching from the Gulf to New England. As low pressure tracks northeastward from the Gulf Coast, winds from the south out in front of the low (winds circulate counterclockwise around low pressure) will draw up moisture from the Gulf. It's these winds that will also pump warmer air northward, eventually pushing out of the way the cold air that will be responsible for precipitation starting out as ice in parts of the metro area.

Bottom line: Get ready to be soaked.