As promised, we have to go through a few more bouts of cold, icy weather before spring finally starts to settle into the country. This week will be an epic battle between cold and warm air, culminating in an ugly winter storm on Wednesday night and Thursday. It's like the weather has the flu: a sudden hot flash today and tomorrow, followed by miserable chills on Thursday and Friday.
A pretty decent warm front extends off of a weak low pressure system moving east towards the Great Lakes this afternoon. The warm front—bringing temperatures in the upper 50s and low 60s as far north as Kentucky—is forcing a large area of lift to its north, allowing for heavy rain/snow/ice to fall over a wide swath of real estate from the U.P. of Michigan east to the Atlantic Ocean.
Much of this precipitation is falling as regular ol' rain near and south of the warm front, while areas along and northeast of the front are seeing a sloppy wintry mix or just some plain heavy snow. This is just the beginning, or as weather dot com puts it in vaguely apocalyptic terms, "PREPARE NOW: THE MAIN EVENT HAS YET TO COME."
It won't be a blockbuster snowstorm by any means—a couple of inches in most spots—but snow will gradually change over to freezing rain as the night progresses, leaving a crust of ice on top on any exposed surfaces. Once precipitation changes over to freezing rain, it'll be a good idea to stay inside until surface temperatures warm above freezing and the ice has a chance to melt.
Now, this is where it's going to start getting weird.
Cold to Warm to Cold
It's cold and dreary across North Carolina and Virginia this afternoon due to a process known as cold air damming. Winds across the region are blowing from the northeast thanks to a weak high off the coast of New England, causing cold, dense air to pool up against the base of the Appalachian Mountains. The warm front is actually stalled out along the mountains right now, unable to erode this stubborn bubble of cold air at the surface.
The air is very humid behind that warm front—more humid than we've seen in a long time across the Mid-South. Just after midnight tonight, the GFS model predicts that the dew point will reach the upper 50s and low 60s in the Ohio Valley, affording the cold front plenty of moisture to produce heavy precipitation as it crashes into the warmer airmass.
Winds will shift around to the south and southeast during the day on Wednesday, eroding the cold air dam over North Carolina and Virginia, allowing temperatures to soar into the upper 60s and low 70s as far north as central Virginia for a period on Wednesday afternoon.
Given the abundant moisture available in the atmosphere—along with a weak area of low pressure expected to develop over the Carolinas on Wednesday—we will see a large slug of heavy precipitation extending from the Gulf of Mexico straight up into New England.
Usually when we see precipitation with a cold front, it stays all rain until the very end of the event when the rain can change over to a quick burst of snow as the front moves out of the area. With this system, however, the rain will change over to ice or snow, and it'll keep on icing and snowing.
Here's What'll (Probably) Happen
The atmospheric profile north of the Mason-Dixon line (PA/MD border) is less ambiguous, allowing a wintry mix or pure snow to fall for the majority of the event. However, for most people from around Baltimore down to the Gulf, here's what will happen on Wednesday night and into Thursday:
- From Richmond and to the south, it'll get pleasantly warm on Wednesday afternoon. Throw open your windows and air out your house.
- It will start raining (some thunder is possible in the southeast!) as the cold front approaches from your west-northwest on Wednesday evening/night.
- Once the cold front passes through, temperatures will drop like a rock. I'm not kidding—they could drop 30°F or more in an hour or two, and they'll keep dropping through the day on Thursday and into Thursday night. For many people, Thursday's high temperature will occur at 12:00 AM.
- Precipitation will quickly start to change over to snow and ice as the surface freezing line approaches and the mid-levels of the atmosphere cool below freezing. A significant ice storm could unfold over the southern United States on Wednesday night.
- Temperatures on Friday morning will bottom-out below zero around the Ohio Valley, with many major cities in the Midwest, Mid-Atlantic, and Northeast seeing lows in the single digits and teens. Temperatures will slowly start to warm up each day thereafter.
How much snow and ice are we talking about? Here's what the National Weather Service thinks will happen.
These are the forecast snowfall accumulations between this afternoon and Thursday night. This takes into account snow that's falling today and snow forecasters expect to fall in Wednesday night's storm. The big winners (or losers, depending) from this system live across the Ohio Valley and Long Island/southern New England, where snowfall totals could reach eight to ten inches under heavier bands.
It's extremely likely that this snowfall will push Boston's seasonal total over 107.6 inches and make 2014-15 the snowiest season ever recorded in the city.
Snow isn't the whole story—this storm will likely produce extreme ice accretion across parts of the southeastern United States, with the highest totals aiming for parts of southern Arkansas and western Mississippi.
The odds of the forecast busting—or not panning out—are a little less than 50% right now. We'll call it medium rare. The best case scenario in this kind of a situation is that there's less moisture available than the models are currently predicting, keeping much of the snow and ice from coming to fruition.
Here are your forecast low temperatures on Friday morning. Sorry.
It's going to get ugly for the next couple of days. Take it easy if you're expecting snow and ice, and watch the frozen hell unfold from the safety of your living room. It won't be long until this winter is a distant memory.