Maryland Geography and Topography

Two majors influences on the weather is land near water and elevation.

Proximty to Water

Places near the water tend to be warmer in the winter and cooler in the summer.  Maryland has plenty of water. It’s a lot more than the border on the Atlantic Ocean.  If you include all the shoreline around the Chesapeak Bay, the total length is 3,190 miles. According to NOAA, that ranks 10th in the US.


A little more half of Maryland is realtively flat and near sea level in the coasrtal plain. I-95 is arond the deviding line of the Fall Line. West and north of this boundary is where the hills gradually get higher.

A general rule of weather on a dry day is that temperatures will be 5ºF cooler for every 1,000 feet in elevation.


Atlantic Coastal Plain: Generally flat, influenced by the Atlantic Ocean and Chesapeake Bay water keeping it warmer than freezing in most events.


Western Shore Uplands Region: Marked very close to I-95.

Some rolling hills, but still influenced by Chesapeake Bay warmer water.

Upland Section: Rolling hills, increase in elevation close to 1000 Ft above sea level. This includes the Hereford Zone in northern Baltimore County, but that ridge extends to northern Harford, much of Carroll, and western Howard Counties.  The higher elevation and distance away from the water can often be cool enough to allow more more snow to fall and stick.

Lowland Section: This is broad valley between Frederick and Mount Airy. Temperatures can be warmer at lower elevations and trap cold air near the surface in some winter storms while warmer air is pushed above mountains. This is a prime target for sleet and freezing rain = ice storms.

Blue Ridge Province= Catoctin Ridge. Mountains reach up to around 1,500 Ft.

Mountain Region:

Great Valley Section, Folded Appalachian, and Allegheny Mountain Section and Appalachian Plateau

This region has steep mountains and valleys. The elevation reaches above 3,000 Ft in far western Maryland- Garrett County. This can catch Lake Effect Snow from Lake Erie in addition to larger coastal storms.

Split NWS Weather Zones

Topgraphy and Geography have led The National Weather Service to split some counties into differnt zones for weather advisories (alerts, watches, and warnings) in all seasons.

These split county zones in the ‘north and west’ areas of Baltimore are based on the elevation factor and proximity to the Chesapeake Bay

Closer Look at Zones Around Metro Baltimore

Harford County

The cut off is north of Bel Air. Fallston and Forest Hill tend to be just high enough in elevation and far enough away from the Chesapeake Bay to stay colder and keep snow around longer.

Baltimore County

The cut off is north of the I-695 Beltway. This is just on the edge of Towson/Timonium, and Owings Mills. The elevation can rise over 400 feet to make for colder temperatures north and west. This keeps the chance of snow around longer.

Howard County

The cut off is around West Friendship. The elevation here more gradual than Baltimore County, but it is farther away from the warming effects of the Chesapeake Bay to remain colder longer. Thus, they can get more snow.

 Montgomery County

This is a little father south, so elevation and being even farther inland plays a role. The line around Germantown is often the dividing point of more and less snow, or even frozen and melting in many events. Clarksburg and Damascus get more snow than Rockville and Silver Spring in most cases.


National Weather Service Zones

The problem is that multiple NWS Offices cover our region. There appears to be very little coordination when they issue some weather alerts. Especially in the winter. I can’t knock them with short staffing and other obligations, but I do wish there would be more communication for people who live on the edge of these boundaries.

Some counties may be under a watch or advisory from their local office, but the next county over might be under the guidance of a different office that did not issue anything yet.

See the NWS office zone breakdown below

NWS Zones Coverage Counties:

Sterling VA (LWX): Most of central Maryland west of the Chesapeake Bay, to Cumberland and Frostburg; plus north central Virginia.

Mount Holly NJ: Cecil, Kent, Queen Annes, Talbot, and Caroline Counties in Maryland; plus all of Delaware.

Wakefield VA: Maryland’s Lower Eastern Shore. This is for Dorchester, Wicomico, Somerset, and Worcester Counties.

Pittsburgh PA: Garrett County in far western Maryland.

State College PA: Southern Pennsylvania including Adams, York, and Lancaster Counties.