Saturday Evening Dec 14 2024
Strong High Pressure that brought us clearing and a cold start to the weekend is going to play another role as the next storm approaches: Cold Air Damming. This is when a layer of cold and dense air banks up in the valleys between the mountains and coastal areas in the Mid-Atlantic as a storm brings in warmer air and moisture aloft. The net result can be an extended period of wintry weather, mostly in the form of ice.
This is what is expected between the high mountains along the spine of the Appalachians and near I-81 across Virginia, Maryland, and into Central Pennsylvania.
The inland suburbs west of Baltimore and Washington to Frederick, Westminster, and York, PA: There may be some flurries or light sleet, but this looks like a cold rain event developing early to mid-afternoon, steadier in the evening.
Winter Storm Warning in the higher mountains. I see more of an ice storm, but the National Weather Service has identified the potential for a snow burst with a few inches of snow.
Winter Weather Advisory: The models have a longer burst of snow, then sleet and freezing rain. I would lean more toward icy travel along and west of I-81 Virginia and Maryland, then passing just north of Harrisburg in PA. If you travel that road towards the Poconos, it will be slow-moving in the afternoon.
Before looking at the forecast timeline…
This is from the NAM 3Km, which tends to be a little more aggressive. It is still low on snow and more focused on the freezing rain.
This is NOT the primary concern.
This IS the primary concern.
The High Pressure was centered near Montreal, Quebec, Canada. The pressure level of 30.95 in Hg is very strong, which will help establish the cold air and hold it longer.
The Low-Pressure/storm center was located near Kansas City and already had a band of ice and snow on the north end. This storm will track East-Northeast and arrive in our region mid-morning to noon Sunday.
Note: There will be a series of additional storms to follow, with warmer temps and rain into the middle of the week.
There is a bias or error that often leads winter weather events to arrive a little faster than shown here. While the models will lean towards noon for the arrival, I would plan for mid to late morning.
We will start with the Mid-Atlantic view and then take a closer look at the High-Resolution NAM 3Km Model and key timeframes.
Note that this will develop during the day and transition to all rain overnight, ending Monday morning. The next wave will arrive by Monday night with all rain.
Deep reach of freezing temps with ample support to start the day.
Rain/Snow often arrives and departs 1 to 2 hours earlier than shown.
This is between 8 AM and 6 PM
From this morning
This round of rain will be followed by colder air and mountain snow. The subtle instability does not show, but there will be energy to produce flurries east of the mountains.
Focus on the Jet Stream because the surface storm plots are not reliable this far away…
After the rain and warm-up, a shot of very cold air arrives by the end of next week. This will dominate the Eastern US by the end of next weekend.
The coldest air is expected to end the weekend. Freezing temps may reach parts of Florida.
Sunday will be the most complex day, with ice and snow in the mountains and rain by evening in the metro areas.
Warming with rain next week. It will not be all rain but rather a few impulses for a few days.
The colder end of the week may come with flurries.
Severe Weather: Storm Smart October and next spring
Winter Weather FITF (Faith in the Flakes): November To March
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