Storm bringing Rain, Wind, and Cold Leading Into Christmas

No White Christmas this year, at least not the one you've been dreaming of. Instead, in the days leading up to Christmas expect plenty of rain and wind, followed by plummeting temperatures.

Here is a quick look at the storm from Thursday morning to Friday Night

THE METEOROLOGY

Temperature drives all storms - It can determine its path, strength and progression because storm systems or low pressure like to form in areas of great temperature difference or frontal boundaries. Then, as this low pressure progresses and impresses its circulation, it can alter the shape of these temperature boundaries effectively moving temperature. Due to the counter clockwise circulation, cold air is advected southward behind the storm and warm air is advected northward ahead of the storm. Most of the snow we get from winter storms is from being north of the storm, right in between warm and cold air advection. Being in this area, along with preexisting cold air that is present at times, brings snow.

For this event however, we are going to be east of the storm, (warm sector) for most of our precipitation. Then as the storm tracks to our north we will encounter the cold front, howling winds, and perhaps a quick thump of backside snow.

Here is a graphic to show the evolving temperatures of our storm. At times along this boundary there is an extreme temperature differences of 40 degrees over a distance of 50 miles, going from 40 degrees to below zero over this distance. This extreme cold air barreling down from Canada forces a storm to circulate which forces an equal and opposite warm air mass on the east side of this low pressure center to flow northward ahead of the storm. It is this intense temperature difference, bringing about strong circulations around a low pressure that brings us warm air and plenty of rain out ahead of the storm. In the graphic below, be sure to pay attention to the changing orientation of the boundary between warm and cold air

In theory if we wanted the storm to ride up the coast, and bring us snow, we would need a weaker cold air mass to reduce the temperature gradient and weaken the circulation and intensity of the warm air being moved in Maryland's direction. This would keep us colder, and the storms energy would move into the stronger temperature gradient set up along the coast of Virginia and Maryland, where are low pressure already has formed yet diminishes in the real model runs because of the insane and stronger frontal boundary across the center of the country.

IMPACTS AND TIMING

Thursday Morning - Brief Snow to Rain - As temperature warms from below freezing, precipitation moves into the area. This may start as snow which will quickly transition to rain.

Thursday Day - Rain - Temperatures continue to warm into the high forties as rain continues to fall

Thursday Night - Warm and Rain/Wind - Temperatures continue to rise into the low fifties awaiting a cold front passage on Friday Morning

Friday Morning - Rain/Warm/Wind - Temperatures reach their peak in the low fifties as winds begin to pick up, rain continues

Friday Day - Rain to Snow/Peak winds - Cold front passes through, windy conditions, chance for rain to switch to snow, gusts up to 50 mph. Conditions get dangerous with potential for downed trees, and freezing surfaces

Friday Night - Frigid temps/Snow showers/Freeze - Winds persists, temperatures drop into the tens, or single digits freezing everything that is wet. Scattered snow showers overnight.

Christmas Eve and Christmas - COLD and WINDY

We are 3 days away from the onset of this event, things can still change, however with this storm being dominated by such a large air mass and not something minute and fine, I do not expect any large scale changes to my forecast. Things that could change include whether or not this event begins and ends with snow, and how much if any snow falls on the tail end of this thing. What I do know for certain is that there will be extremely cold temperatures with wind moving in Friday afternoon leading to a deep freeze and potentially dangerous conditions Friday and into the weekend from ice.