Friday, 11:55 a.m.
Time has been hacked today, so I'll be brief and get right to the point. A major ice storm is in progress from parts of Texas northeastward across Arkansas and into portions of Kentucky and Tennessee. It is mercifully over in the Dallas-Forth Worth Metroplex, but only after more than an inch of sleet and freezing rain. About a quarter of a million people are in the cold because of the ice storm there, and power outages are only going to be strung out along the way across Arkansas and Tennessee into Kentucky.
Farther north, it's been snowing and snowing pretty hard. Parts of southern Missouri are already close to a foot of snow, as deeper moisture combined with better precipitation rates have led to a more prolific snow than had been anticipated. This 'max' of precipitation is going to streak northeastward this afternoon from southern Missouri and Arkansas through southernmost Illinois and southern Indiana toward southern Ohio and southern Pennsylvania, largely as snow, but also with some ice for a time. Farther south, an ice storm, with an inch of precipitation through portions of Kentucky and northwestern Tennessee all the way to parts of West Virginia. Even in these places, the rain and ice will turn to snow before ending.
East of the Appalachians, it will be mostly a rain event, that may end as a little wet snow north and west of Washington, D.C., Baltimore, Philadelphia and New York, and there the cold air will have trouble getting in deep enough until the storm is completely gone.
Here's the 12z Dec. 6 NAM forecast of total precipitation for 24 hours, starting this morning at 12z:
As hard as it will come down in whatever form at the height of the storm this afternoon into tonight, it is a fast-moving system, owing to the positive tilt to the trough. That will keep it from being a worse ice storm or heavier snowfall. By tomorrow morning, most all of the precipitation is simply done, the wave of low pressure racing offshore. Then the cold air will follow to the coast, and the sun will return in many areas to dry things out.
That's wave number one. By the end of the day tomorrow, wave number two will be rolling out of the southern Rockies, and some light rain will start to fall along the upper Texas and Louisiana coasts. The trailing piece of upper-level support will come out of the central Rockies and cause snow to expand across the central Plains into the Midwest tomorrow night, but the snow won't be terribly heavy owing to a general lack of moisture. Still, up to a few inches of powder will fall in the Midwest late Saturday night and Sunday and into the Great Lakes late Sunday and Sunday night.
Meanwhile, farther east, with the primary low sneaking up into the eastern Ohio Valley late Sunday and early Sunday night, warm air will be pushed up and over the low-level arctic air, changing an initial period of snow over to sleet and freezing rain. My fear is that a cold wedge will form and buttress itself up against the mountains Sunday and hold its ground Sunday night as a secondary area of low pressure begins to develop along the triple point along the mid-Atlantic coast. That's seen here by the Monday morning NAM surface forecast:
Basically what that means is that the low levels will remain cold Sunday night, leading to a prolonged period of ice in the Shenandoah Valley and on up into central Pennsylvania, while it very easily transitions to rain along the coastal plain. This could lead to a damaging ice accumulation in some areas in and just east of the spine of the Appalachians, where the precipitation will be relatively heavy.
Then the arctic hounds come a calling again, send most places east of the Mississippi deep into the ice box for most of the rest of the week. More tomorrow.
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