A couple of inches of snow before dawn was enough to slick the roads in most of the region, close most schools and snarl the morning commute. But the main event is still not scheduled to get underway until this afternoon.

Forecasters are predicting 4 to 8 inches north and west of the I-95 corridor, with only a bit less to the south and east, including the Upper Shore. Western Maryand  - Garrett, Allegany and Washington counties- could see 6 to 10 inches. Bel Air was already reporting 3.5 inches this morning on the CoCoRaHS Network. There was 2.8 inches on the WeatherDeck in Cockeysville at 8 a.m. What does your yardstick say?

The National Weather Service has posted Winter Storm Warnings for Frederick. Montgomery, Carroll, Baltimore (city and county), Harford, Cecil, the northern Shore and the western counties. The Warnings call for "moderate" snow to begin falling this afternoon after mixing with the morning's "light" snow and rain.

The snowfall is expected to become heavier late in the afternoon, and will be at its most intense between 4 p.m. and midnight. Commuters? Are you paying attention?

South of the Warning zone, Sterling has put Winter Weather Advisories in place. There, the morning snow will mix with more sleet and rain before switching back to all snow in the afternoon, holding projected accumulations to just 3 to 5 inches - below the Warning criteria of 5 inches.

All told, what we're looking at here is the most - the only - significant snowfall of the season so far for Central Maryland. The two-part event has begun with an inflow of relatively warm and wet air from the Gulf and the Atlantic as it is swept north by a Southern low in Georgia. It's encountering cold-enough air in place here to trigger the snow. Temperatures will rise above freezing as the morning wears on, creating a wetter mix, and rain, especially closer to the coast.

By late morning it may seem like the storm has worn itself out. But as the Southern low makes its way up the coast it's forecast to intensify. Heavier precipitation will move into the region from west to east, and by late afternoon, winds will shirt to the north northwest, temperatures will drop. The mixed precipitation will change over to snow and start to pile up quickly. Here's a bit from the NWS morning forecast discussion: 

"...A SOLID CHANGEOVER TO SNOW IS EXPECTED AND ACCUMULATION WOULD LIKELY BEGIN IN EARNEST. SIMILARLY INTO THE EARLY-MID AFTERNOON THE LEE OF THE BLUE RIDGE AND FOOTHILLS...AS WELL AS NORTHERN MD...WILL SEE THE CHANGEOVER TO ALL SNOW AND ACCUMULATIONS THEREAFTER. FOR THE PIEDMONT AND DC/BALT METRO AREAS...MID-LATE AFTERNOON W/ POSSIBLY A FEW MORE DEGREES TO OVERCOME IN TERMS OF GETTING BACK
BELOW FREEZING. FOR LOWER SOUTHERN MD AND AREAS SE OF THE METRO
AREAS...JUST IN THE LATE AFTERNOON/EARLY EVE."

Eric the Red is a little more aggressive than Sterling with total accumulations: "Considering what greeted me this morning, think it may be wise to up the totals a hair in the Piedmont... and go 6-12" across the colder locales north and west of Baltimore and DC.  The coastal low has produced more snow than I thought, altho the precip is falling as rain just east of I-95. ... 

"Once the heavy precip arrives early in the afternoon, the real fun should start.  Any precip that is not snow will change to snow, and it will be heavy.  Still foresee snowfall rates as high as 2" or more an hour hammering the afternoon rush. ...  I would strongly advise you plan to be home by 1 pm or be willing to drive in very heavy snow, because it will arrive quite suddenly. Totals... Along and east of I-95: 4-8" (I'm wondering if even in these locales this might be low) Colder burbs north and west (Piedmont): 6-12"

AccuWeather.com's Alex Sosnowski warns against taking the mid-day lull in the storm as an all-clear: "The rain and wintry mix in the Washington/Baltimore to Philadelphia/New York City slot [during the day...] will have many people think the storm is a bust. After a relatively small amount of snow and slush in these cities on south and east, it may seem like the storm has slipped by." But the storm will turn colder as it strengthens off the New England Coast, he said, allowing the majority of snow to accumulate in the major Northeast cities.

And, Foot's Forecast: "We do expect a change over to rain for areas around Baltimore, but areas N&W could stay all snow. If it stays all snow totals will be higher. We will see a break in the action after noon before the second round of precip comes in tonight with heavy snow for most of the area. We still are calling for a general 5-8" for the entire Central MD region (Ending Thursday-2am)."

(SUN PHOTO: Frank Roylance, Snow on the WeatherDeck this morning)