A deluge and wild temperature swings tonight in D.C.

The rain is here and, by tonight, it’s going to fall fast and furious.

Model simulations continue to suggest storm totals of 2 to 3 inches of rain (with locally higher totals possible).

Here’s the high-resolution NAM model forecast:

Total storm rainfall from high-resolution NAM model (WeatherBell.com)

Total storm rainfall from high-resolution NAM model (WeatherBell.com)

Here’s the GFS model forecast:

Total storm rainfall from GFS model (WeatherBell.com)

Total storm rainfall from GFS model (WeatherBell.com)

Here’s the European model forecast:

Total storm rainfall from Euro model (WeatherBell.com)

Total storm rainfall from Euro model (WeatherBell.com)

Finally, here’s the National Weather Service’s precipitation outlook, which we think is slightly overdone (showing widespread 3-4 inch totals):

National Weather Service precipitation forecast (National Weather Service)

National Weather Service precipitation forecast (National Weather Service)

The National Weather Service has decided not to post flood watches due to “dry antecedent conditions” but cautions some minor flooding of streams is possible.  If you have storm drains or gutters clogged with leaves, that could be an issue – so consider braving the miserable cold and clearing them, before you have a problem.

Rain won’t wind down until Wednesday afternoon, when it may change to snow and sleet for a brief time before ending Wednesday evening.  More on that in a forthcoming post.

The hefty rain totals are the result of an impressive plume of tropical moisture surging up the East Coast, right along I-95 – parallel to a strong cold front.

The (high resolution NAM) model simulation below shows the precipitable water – a measure of the depth of rain if all humidity in the air column were to condense – at 10 p.m. tonight.

Precipitable water simulation from high resolution NAM model at x tonight (WeatherBell.com)

Precipitable water simulation from high resolution NAM model at 10 p.m. tonight (WeatherBell.com)

Anything over 1.5 inches is extremely high for this time of year – and that’s what we see along and east of I-95.

The presence of the strong front over the region will help squeeze out most/all of the available moisture in the atmosphere.

The signature of the front is unmistakable on model simulations, which show incredible differences in temperature over short distances.  The animation below shows the evolution of temperatures from  this evening (as the front jogs west initially as low pressure approaches from the south) to early Wednesday morning (as the front pushes east and low pressure passes to the north).

Evolution of surface temperatures between 4 p.m. Tuesday and 4 a.m. Wednesday from the high-resolution NAM model (WeatherBell.com)

Evolution of surface temperatures between 8 p.m. Tuesday and 4 a.m. Wednesday from the high-resolution NAM model (WeatherBell.com)

Note that around midnight the front splits the region in half.  East of I-95, temperatures surge up into the 50s.  West of I-95, temperatures are around 40 or colder.  We may see temperature differences of 20 degrees in under 20 miles – the mark of an impressive, highly energetic storm system.

Also on Capital Weather Gang

D.C. area forecast: Spotty wintry mix to driving rain; clearing out on Thanksgiving