Winter Weather Advisory and Warning Sunday for some snowy and icy travel

Saturday evening, 14 December 2024

Strong high pressure that brought us clearing and a cold start to the weekend is going to play a different role as the next storm approaches: Cold Air Damming. This is when a layer of cold, dense air builds up in the valleys between the mountains and coastal areas of the Mid-Atlantic, while a storm brings warmer air and moisture into the air. The net result may be a longer period of winter 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 inner suburbs west of Baltimore and Washington to Frederick, Westminster and York PA: There may be some showers or light sleet, but it looks like a cold rain event developing early to mid-afternoon, more steady in the evening.

Winter weather alerts

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 flurry and a few inches of snow.

Advice on winter weather: The models have a longer flurry of snow than sleet and freezing rain. I would lean more into the icy voyage, just given a model boat. Along and west of I-81 Virginia and Maryland, then passing just north of Harrisburg, PA. If you travel that way towards the Poconos, the afternoon will be very slow.

Before looking at the forecast timeline…

Preliminary storm forecasts

This from the NAM 3Km which tends to be a bit more aggressive and is still low on snow and more focused on the freezing rain.

Snow potential

This is NOT the primary concern.

Potential for freezing rain

This IS the primary concern.

Set up Saturday

The high pressure was centered near Montreal in Quebec Canada. The pressure level of 30.95 in Hg is very strong, which will help establish the code air to last longer.

The low pressure/storm center was located near Kansas City and already had a band of ice and snow on its northern end. This storm will track east-northeast and arrive in our region from mid-morning to noon Sunday.

Noe: There will be a number of additional storms to follow with warmer temperatures and rain midweek.

Model forecast map

There is a bias or error that often causes winter weather to arrive a little sooner than shown here. While the models will lean toward noon for arrival, I would plan for mid to late morning.

We’ll start with the Mid Atlantic view and then take a closer look with the NAM 3 km model at high resolution and key timeframes.

Wider view: Sunday morning to Monday evening

ECMWF model

• Blue = snow
• Pink = freezing rain
• Green = Rain

Note that this will develop throughout the day and transition to all rain overnight ending Monday morning. The next road arrives Monday night with all the rain.

6 hours of model overviews

ECMWF model at 13.00 to 19.00

GFS Model 1pm to 7pm

Take a closer look at the NAM 3 Km model

7 AM Temperatures

Deep range of freezing temperatures with ample support to start the day.

7.00 to midnight

Rain/snow often comes and goes 1 to 2 hours earlier than shown.

Snapshots

Dinner radar

Midday temperatures

Mid afternoon

15.00 radar

3 PM Temperatures

Sunday evening

22:00 Radar

22:00 Temperatures

Road trip profile

It is between 8 a.m. and 6 p.m

Long range forecast

From this morning

Wednesday afternoon to Friday afternoon

This round of rain will be followed by colder air and mountain snow. The subtle instability is not showing, but there will be energy to produce showers east of the mountains.

LONGER RANGE VIEW

Focus on the Jet Stream because the surface storm plots are not reliable that far away…

After the rain and warming, a blast of very cold air will arrive at the end of next week. This will dominate the eastern US by the end of next weekend.

Sunday Morning

The coldest air is expected to end this weekend. Freezing temperatures may reach parts of Florida.

7 day weather forecast

Sunday will be the most complex day with ice and snow in the mountains and rain in the evening in the metro areas.

Warming with rain next week. It won’t be just rain, but rather a few impulses for a few days.

The colder end of the week may bring showers.

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