A change is on the way for Maryland starting during the afternoon on Sunday. A powerful arctic front will plow through the state delivering a one-two punch of cold air across the entire eastern seaboard. The air up until now has been mild with batches of cold air mixed in from time to time. Key blocking over the west coast will allow for the first "cross polar flow" to develop dropping Maryland temperatures some 10-20 degrees below their seasonable averages. Daytime highs will struggle to get to 30 (N & W of Baltimore the middle 20s) while nighttime temperatures will feature single digit to lower teens.
The Cross Polar Flow theory is strong blocking over the pacific dragging air that has originated over the north pole southward. As the arctic jet stream drops south it will throw on the breaks essentially over Maryland.
You can see the beginning stages of the cold blasts migrating out of Churchill Canada which dropped to an impressive 40 below zero Wednesday night.
As the pacific pattern develops a strong ridge (versus the flat trough it had most of the winter) it will send little vort maxes or areas of low pressure down the front side of it. Climatology tells us that is a favorable storm track to bring storms into Maryland. Given the cold air in place next week into the end of January our potential for more snow increases.