Day 35: Mid-Atlantic Winter Storm
As I alluded to in last night’s post, the mid-Atlantic states are preparing for what could be their second major snow storm this winter. Back in mid-December, portions of the mid-Atlantic received upwards of 2 feet of snow from storm very similar to the one forecast to affect the area tomorrow into early Sunday. Tonight I thought I’d take a few minutes to jot down a few remarks about the ingredients coming together in the mid-troposphere to enable such a major winter storm. We’ll begin with my favorite piece of observational data – the water vapor satellite image. I’ve previously mentioned why water vapor imagery is so valuable to meteorologists, so I’ll spare you the repeat of information. Suffice it to say, if I could only look at one chart a day, this would be the one I would choose.
I’ve identified several shortwave troughs (upper-low) / vorticity* maximums in the above water vapor image via a yellow ‘X’. [As an aside, meteorologists are often interested in minimums (min) and maximums (max) in vorticity. To label these phenomena, meteorologists use a 'N' for the miNs and a 'X' for the maXs.] Looking at the above image, I’ve used two big ‘X’s and two small ‘x’s. The size of the ‘X’ is to help identify the stronger maximums in vorticity (shortwave troughs / upper-lows). We’ll ignore the strong shortwave trough off the west coast as it will have little, if any impact on the east coast snow storm.
There is a minor shortwave trough over central Texas that is heading northeast toward eastern Oklahoma. This shortwave trough will most likely be absorbed into the larger trough that is moving east-southeast out of eastern Colorado. There is also a minor shortwave trough over the central Gulf of Mexico that is lifting northeast toward Georgia. It is this shortwave trough that will begin to affect the east coast late tonight into Friday with the first bout of precipitation. I’ve also circled an area of the western Gulf of Mexico in yellow. I believe that there is another minor shortwave trough somewhere in the circled area, but it is not discernible from a single satellite image.
Over the next 48 hours, the shortwave tough(s) over the Gulf of Mexico will move toward Georgia and then off the mid-Atlantic coast. This trough will help to draw warm, moist air northward from the Gulf of Mexico into the mid-Atlantic region. This warm, moist air will encounter very cold air at the surface causing the warm, moist air to be lifted into the atmosphere. Widespread precipitation – in the form of snow in areas away from the coast – will begin to develop and spread northward overnight into tomorrow as a result of this. At the same time, the stronger trough over eastern Colorado will continue to track east-southeast toward eastern Tennessee. This stronger tough will continue to strengthen over the next 48 hours and help to draw even more warm, moist air northward into the storm. The interaction of the two troughs will help to generate a very strong low-pressure system at the surface that will further enhance the precipitation in the vicinity of the Delmarva Peninsula (general area of Washington D.C.). Just north and west of the eventual track of the surface low will receive a prolonged period of very heavy snow that will allow for accumulation of up to 24-30″ in some areas. Furthermore, as the two upper-level lows (shortwave troughs) continue to interact with each other, and the surface low moves over the warm waters of the gulf stream current, the low should continue to strengthen. As the low does this, very strong northeast winds will develop along the coast (hence where we get the name ‘Noreaster’) and blizzard like conditions will be possible. In fact, portions of New Jersey already have Blizzard Warnings in effect for this potential!
People in the Washington D.C. area are hopefully prepared for a winter storm that could potentially shut down the city through the weekend. Some good-natured citizen has created a “snowpocalypse” website for Washington D. C. residents to gain the latest information. So, as a public service for those who might be affected by the east coast winter storm, please visit http://snowpocalypsedc.com/for the latest information.
*Vorticity is a mathematical quantity used to quantify the potential for an air molecule to exhibit ’spin’. Over simplifying this complex phenomenon, where ’spin’ is being blow toward tends to experience rising motion and wherever the ’spin’ is blowing from tends to experience sinking motion.
