Forecasters are expecting 6-10 inches of snow across most of the Baltimore area, with chances that sleet and rain could mix in along Interstate 95 and keep accumulations at the lower end of that range.
The National Weather Service is forecasting 6-8 inches across areas along I-95 and closer to the Chesapeake Bay, with 8-10 inches on the northwest side of I-95. Further northwest, snow totals could top a foot in parts of Carroll and Frederick counties.
With recent forecasting model runs suggesting more warm air mixing sleet and rain with snow, accumulation predictions from some sources have dropped. The weather service forecasts at least 75 percent chances of 4 inches of accumulation or more across the region, with 40-50 percent chances of 8 inches or more across Baltimore.
Still, Gov. Martin O'Malley issued a state of emergency ahead of the storm and emergency officials urged state residents to prepare for travel difficulties.
Uncertainty in the forecast depends on minor shifts in the storm's track, as well as how the storm develops. A frigid system moving across the country from British Columbia is expected to merge with a moist system expected to bring ice across the Southeast, but it's unclear whether that merging will occur before or after the storm passes Maryland.
If the systems meet and intensify quickly, heavy snow can be expected across the region. But if that occurs later, a weaker storm will pass by, bringing some "significant snowfall accumulations" but not as much as might otherwise be expected, weather service meteorologists wrote in a forecast discussion.
Foot's Forecast meteorologists are predicting 5-9 inches along I-95, with 8 inches to a foot northwest of that, according to an update posted Tuesday evening.
AccuWeather.com is calling for 6-12 inches of snow across most of the Baltimore area, with up to a foot and a half of snow across parts of Carroll and Frederick counties.
Local meteorologist "Eric the Red" said he is expecting "our first big, regional winter storm in years", with 8-16 inches across Central Maryland, with a chance of that prediction being conservative in isolated spots. However, snowfall could be limited if the storm tracks too far off the coast, keeping much of the moisture out to sea, or if it tracks too far inland, drawing in warm air and causing more mixing with sleet or rain.
Clear, sunny skies were expected Tuesday, with 10-15 mph winds. Lows early Tuesday and Wednesday mornings were forecast in the mid-teens, with temperatures again struggling to climb out of the upper 20s Wednesday afternoon.
Snow was forecast to move in by Wednesday night, with winds picking up as a coastal storm moving up from the Carolinas intensifies. Winds could reach 20 mph with gusts upward of 30 mph.
A winter storm watch was in effect across most of Maryland, with the snow expected to fall between Wednesday and Thursday evenings.
After the storm passes, temperatures could reach 40 degrees Friday with partly cloudy skies.
Baltimore Sun reporter Carrie Wells contributed to this report.