Ramblings of a Graduate Student

Today marks the end of what is often referred to as “meteorological winter”.  Typically seasons begin and end on the solstices and equinoxes, but meteorologists tend to break our seasons based on calendar months.  Below are the months contained in each “meteorological season”.

• Winter: December, January, and February
• Spring: March, April, and May
• Summer: June, July, and August
• Autumn: September, October, and November

The United States will end a very active meteorological winter that saw numerous blizzards, at least one ice storm (in Oklahoma), and snow in all 50 states.  Two mid-level lows (shortwave troughs) are moving through the southern plains (yellow x’s) as well as a strong mid-to-upper-level jet stream (cyan color to the southwest of the southernmost x).  Also, the strong nor’easter that has affected New England for the past few days is slowly moving east, out to sea.

These mid-level lows are aiding in the development of precipitation in the central plains and western Texas as indicated by the radar images below.  There is a chance that portions of western and central Oklahoma will see some snow mix in with the rain, but little-to-no accumulation is expected.

Above is the precipitation forecast for the next 5 days from the National Weather Service’s Hydrometeorological Prediction Center.  Several areas of the United States will experience a wet 5 days.

1. The northeast will experience a very strong storm system during the next 5 days.  A strong cyclone will park itself over New England and continue to draw in warm, moist air into a cold airmass at the surface.  Although along the coast will see a lot of rain, a lot of snow will fall farther inland.  This could be the first real big snow for upstate New York this winter.
2. Central Texas and areas along the Gulf Coast will experience several mid-level shortwave troughs moving through the area.  Each of these troughs will result in a new round of precipitation – some of it falling as snow tomorrow!
3. Oklahoma and Arkansas will experience precipitation late week as more mid-level shortwave troughs move through the southern branch of the jet stream.  It is too early to tell, but this may fall as snow across the northern portions of the states.
4. The west coast will continue to be battered by numerous storms over the next five days.  Each one will bring more precipitation to central and northern California.

With all of this, my attention will be focused on the northeast for the next few days.  The storm that is forecast in this area could be one for the record books.  The potential exists for a lot of snow in the inland areas, a lot of coastal rain, and beach erosion along the coast of Maine.

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.