"
Gather huge amounts of snow from Moscow, ship it here, and dump it on the streets of DC.
"
Yes, very simple clima(c)tic weapon :))

Or just spray that substance, iodic silver or how it is called, in the skies so that all dispersed water condenses and falls.
This is routinely used around Moscow in days of important events to unload clouds before they reach the city.

I think that such areas are just not prepared for snow, you do not have winter tyres and some local roads are too steep (at least in Seattle) and cannot be used when it's slippery.

Poor Cathy, someone can call her and ask for assistance in making the weather better...