A potentially record-breaking December snowstorm is expected to escalate to blizzard proportions in Southern Maryland today, including Anne Arundel, Prince George's, Calvert, Charles and St. Mary's counties.

UPDATE 9:30 a.m.: The Blizzard Warning (orange on map) has been expanded to include Harford, Howard, Baltimore, Montgomery counties and Baltimore City.

The National Weather Service issued Blizzard Warnings early this morning for that region, meaning that forecasters expect low temperatures, strong winds and blowing snow will combine to whiteout  conditions that will make travel "extremely dangerous":

"Do not travel. If you must travel, have a winter survival kit with you. If you get stranded, stay with your vehicle."

Some will have no choice. At BWI this morning, where they were reporting 6 inches on the ground:

The National Weather Service's definition of blizzard conditions includes sustained winds of 35 mph and visibilities of less than 500 feet in falling or blowing snow, all lasting for at least three hours. Temperatures aren't an official part of the definition, but when all the other criteria are met, temperatures are likely to be below freezing anyway. And it's enough to issue a warning. The decision to issue the warning reflects the strong winds near the bay, not heavier snow, forecasters said.

Snow accumulations had already topped 8 and even 10 inches by daybreak today in parts of Charles and Anne Arundel counties. here's a sampling:

Bryan's Road, Charles Co.:  10 inches

Annapolis, Anne Arundel:  8.8 inches

Garrison, Baltimore Co.:  6 inches

Tracey's Landing, Calvert:  7 inches.

You get the picture. We have over 5 inches now on the WeatherDeck in Cockeysville. And the forecast has the snow continuing overnight Saturday into Sunday. The heaviest snow rates are expected between  8 a.m. and 6 p.m. Saturday.

Accumulations across the region are forecast to reach 1 to 2 feet before it's all over in the Baltimore-Washington area. That would break all December records for both cities. The record snowstorm for Baltimore was a two-day snow that dropped 14.1 inches in 1960. The snowiest December in Baltimore was in 1966, when 20 inches fell.

Here's more from the weather service:

"HEAVIEST SNOWFALL AREA WILL MOVE FROM THE CENTRAL SHENANDOAH VALLEY UP TOWARDS DC/BALTIMORE...WHERE IT WILL CONTINUE TO SNOW HEAVILY THROUGHOUT THE DAY. TOTALS NEAR 2 FEET POSSIBLE WES OF CHARLOTTESVILLE, WHERE 15" WAS REPORTED AT 1 AM...AND BY THE END OF TONIGHT NEAR 20" IN THE I-95 CORRIDOR.

"BELIEVE SNOW WILL BECOME LIGHT TONIGHT IN THE SOUTHWEST...BUT EXPECTED TO CONTINUE AT A MODERATE PACE IN I-95 CORRIDOR DURING THE EVENING HOURS. TEMPS OVERNIGHT IN 20S ACROSS THE [FORECAST AREA] - WIND CHILLS IN THE TEENS."

1. Travel is not recommended on Saturday. Avoid traveling alone, take a survival kit and let someone know where you're going and the route you plan to follow.

2. If you get stranded, stay with your vehicle. Run the motor 10 minutes every hour for heat, but open the window for fresh air. make sure your exhaust pipe is clear of snow and ice.

3. If you use a portable generator, keep the area around it well-ventilated. Do NOT use it in the house or in an attached garage.

4. Do not try to shovel snow unless you are physically fit. Hydrate yourself often with water and take frequent breaks.

5. Make sure your pets and livestock are sheltered and have plenty to eat and drink.

6. Listen to NOAA Weather radio. Stay informed.

Here's a snow forecast map from WeatherBug.com:

(SUN PHOTO/Frank Roylance/WeatherDeck station)