Forecasters say it's much too early to determine where and how much snow will fall Sunday. But here is the speculation so far.

Update 4:30 p.m. The National Weather Service forecast discussion: 

"SNOWFALL AMOUNT CONFIDENCE IS LOWER FOR THE WASHINGTON DC AND
BALTIMORE AREAS. GUIDANCE SHOWS THERE IS A GOOD CHANCE FOR SNOW TO
ACCUMULATE ON AREA ROADWAYS SUNDAY...BUT IT IS UNCERTAIN HOW MUCH
WILL FALL. THERE WILL BE A REAL TIGHT PRECIPITATION GRADIENT NORTH
OF THE FRONT. WE HAVE RAISED PRECIPITATION CHANCES TO CATEGORICAL
FOR THE METRO AREAS AND INDICATED PRECIPITATION WILL BE ALL SNOW.
WE WILL CONTINUE TO MONITOR THIS AS THE TRACK OF THE SURFACE LOW
BECOMES MORE CLEAR. PRECIPITATION MAY START OUT AS A MIX OF RAIN
AND SNOW IN SOUTHERN MARYLAND. SNOW WILL TAPER OFF TO SCATTERED
SNOW SHOWERS SUNDAY EVENING AND PRECIPITATION WILL END SUNDAY
NIGHT. ICY ROADS WILL LIKELY IMPACT THE REGION INTO EARLY MONDAY
MORNING."

Baltimore professional meteorologist Eric the Red is also feeling the uncertainty:

UPDATE 1 p.m.: 

"All the morning models have come in, and they have definitely gone lighter and farther south... except the Canadian, which has gone a bit wetter and a hair farther north.  So, ... 'Think low, Aim lower.'  I'll pull back my forecast amounts... and hope that I'm wrong.
 
North of MD - Nothing.
Northern MD - I'm thinking 1 to 3" may be generous, but I won't pull the plug entirely north of Baltimore.  I would not be at all surprised now if nrn MD ends up with nary a flake as well.  Man I hope I'm wrong.
Baltimore to DC - Here, 3-6" is my new take, and I'm afraid this also could be high.  Again, hope I'm wrong.
South of DC - 4 to 8"

Previous quote below:

"The first real winter storm of the season is coming, but with serious, serious caveats.  ... Despite taking a very favorable track out of the Gulf to the Carolina Coast, an incredibly tight south-to-north precipitation gradient will set up.  We're talking that within the span of 20 miles or so, you could conceivably go from 6-12" of heavy wet snow to nothing.  Where this sharp gradient sets up is anybody's guess - I sure don't know - but we've got some ideas.  It appears the gradient will set up... yup, right across central Maryland, with northern portions of the state ending up on the light side, while central and southern portions of the state get smacked pretty good. ... This one is tough, and I do not envy the NWS forecasters out at Sterling, Va. on this one who have to issue a forecast for the entire region.  Storm will impact the area Sunday into Sunday night."