Friday, 11:55 A.M.
One of the coldest air masses to invade the country since the 1980s is finally in full retreat. What remains of it is offering up token resistance to the advance of warmer air in the Northeast, resulting in snow and some freezing rain that has triggered hazardous driving conditions and scores of accidents from Pennsylvania into southern New England so far today. In the end, what snow that did manage to fall in these areas will be utterly demolished by a dramatic warm up over the next 24 hours or so in advance of the next cold front.
What eats snow in the dead of winter isn't warm air per se. Oh, if if warms to 60 degrees, the snow will melt! If there's sunshine and it's 35 to 40, there will be some melting, too. But the sun angle in the middle of January is too low to do much effective melting, so it and/or dry, mild air will only be able to melt so much snow. Instead, high dew points are the real key in seeing snow disappear. Once they climb above freezing, the snow just doesn't stand a chance.
And lo and behold, those dew points that were below zero in much of the east just three days ago are suddenly charging into the 40s! Look at the latest dew points:
Once that high dew point air reaches the snow-covered fields from the Ohio Valley to the mid-Atlantic states and New England over the next 24 hours, fog will become much more widespread, and you'll be able to watch the snow disappear before your very eyes! Here's what that snow cover looks like right now:
Much of the snow cover will be erased in southern New England, as will be the case in the mid-Atlantic and the Ohio Valley. Maybe not all of it, but a lot of it. Just how far above normal will temperatures be tomorrow? Here's the 6z January 10 GFS ensembles forecasts for tomorrow:
Adding to the melt down of the snow will be some pretty hefty rains, too. Many places (shaded in pink/purple) will likely pick up more than an inch of rain from this storm:
There is some concern for flooding in the Ohio Valley from the combination of rain and melting snow, but once you're out to northern and western Ohio into Illinois, I believe the existing snow pack will be able to absorb much of the rain. The heaviest rains will be along the I-95 corridor, and flooding is more likely from Eastern Pennsylvania and New Jersey into southern New England.
By Sunday, the front is off the East Coast, the rain is gone, and the warmth of tomorrow fades. That said, it won't be cold, at least not compared to the brutal cold of a few days ago! Indeed, temperatures in most places from the Plains to the East Coast will still be warmer than average. Colder air will be returning to the pattern with time next week, but with the pattern remaining progressive, with the source regions no where near as cold as they have been, and with less snow on the ground, it's hard to see it getting remotely close to as cold as it has been so far this winter, nor should it stay cold for more than 2 to 3 days at a time over the next week to two weeks.
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