Major storm to strike the Nation and a look at cold air damming.

As December snuck in quietly, it will turn it's sneakiness around rapidly this week for much of the nation. A major storm system will affect a large amount of the United States through the work week. The storm will bring many extremes of nearly every variety strung out over hundreds and thousands of miles along with the nations first big winter storm event. Within this brief write-up, I will take a quick look at the variety of weather that will affect travel in every corner of the states, a brief explanation to the synoptic and some mesoscale reasoning for the weather, and finally just what this means for the great state of Ohio. I will quickly break down the entire nation and the main features of this system. A low pressure system that has been putting feet of snow atop of the mountains of Arizona, California, Utah, Colorado, New Mexico along with flooding in the valleys, and very strong winds (up to 100+ mph in some places!) will eject over the mountains and into the Southern Plains overnight Monday/early Tuesday. This system will gain strength from Gulf moisture and overspread a wide swath of heavy snowfall over the Central Plains and Midwest. With strong winds, blizzard conditions are expected across Colorado, Iowa, Minnesota, and Wisconsin. Heavy rain will develop over the Lower Mississippi Valley and spread northward into the Ohio Valley and eastern parts of the Midwest. Ice can be expected in the Appalachian Mountains of West Virginia, Virginia and parts of Pennsylvania. Into Wednesday evening/overnight as the low moves over the Great Lakes and into Canada, rain will continue to spread northward along with snow through New England. Here is a 48 hour graphic for the next two days depicting the storms path hand associated weather over the United States:
usa

A vast amount of snowfall is expected in the Plains and the Midwest. This is a accumulated snowfall map for the strom from the GFS model. Notice the max of 14-18" of snow that is predicted in the central Plains.



The developing storm can already been seen at 3z (9pm) Monday evening:


One region that deserves attention is the Appalachian Mountains. This region will experience ice in the form of freezing rain in the next 24/36 hours. The surrounding region lowland's of Ohio, Kentucky, and other parts of Virginia, Pennsylvania, etc will all experience widespread rain and no ice. Why is this? At first, this can seem quite complicated, but eventually it all boils down to a phenomenon called cold air damming. This occurs when cold air gets trapped against the mountains, and warm, moist air overruns the cold air. In this event, cold air is still being pushed south against the east/northeast slopes of the mountains thanks to a retreating high pressure system over New England. Warm, moist air with precipitation associated with the strong storm system will come over the mountains from the south/southwest. Precipitation that starts out as rain from the upper atmosphere falls into the colder air near the surface, creating supercooled droplets that freeze on contact-freezing rain.

Here is a close up and overview of the mesoscale conditions causing the icing (circled areas represent the focus areas for freezing rain):


And a close up of the circled region with arrows representing the cold air movement and warm air movement:


The thin lines on the left image represent the heights in the atmosphere. Since the 900(red), 0(purple), and 850(yellow) are all farther south than the others, they represent cold air's intrusion. The other level's lines being farther north represent the warm air in the upper atmosphere still pushing north despite the cold air at the surface. Here is a sounding that helps give a vertical look at this phenomenon:


So with all the events going on in the nation, what is in store for the Athens area? Luckily for many, the snowfall and ice will steer clear of the region. Rainfall, some heavy at times can be expected from Tuesday afternoon through Wednesday afternoon. The big story is the winds. With such a strong low pressure system, wrap around winds pulling artic air from Canada will blow in with the fronts passing. High wind watches are currenly posted for Kentucky and western Ohio. There is a good chance for these to be extended eastward to the Southeast Ohio area for Wednesday. Gusts up to 50 mph maybe possible with sustained winds around 25 mph not out of the question. Even colder air than last weekend will take hold of the region making highs in the 30s seem balmy and lows in the teens be the norm for several days.



The warning map is highlighted just like a christmas tree! Tis the season even for the weather! High wind watches are in dark brown. Red represents blizzard warnings. Pink are winter storm warnings, purple are winter weather advisories and freezing rain advisories, blue are winter storm watches, and light brown are high wind warnings. As you can see from the vast amount of warnings, this storm will affect most of the nation and it's indirect effects will also be felt through flight delays, etc. So in the meantime. Tie your lawn furniture down, bring the umbrella, and be ready for a extra cold blast with a fresh pile of wood to throw in the burner!



Christopher Redmond

cr898005@ohio.edu