Friday, 11:30 a.m.
There has been plenty of cold air this month, and there will be more to finish it out and ring in the new year. However, for the next 72 hours, the cold is in retreat across the East. It will lead to a storm moving from the Gulf of Mexico to the mid-Atlantic coast, then the Gulf of Maine this weekend that will have a lot more rain than snow with it, oddly enough.
Let's start with the 850 mb temperatures this morning:
Compare that to the forecast for tomorrow evening:
In the space of 36 hours, the cold air beats a hasty retreat across the Northeast, and temperatures tomorrow afternoon from the Ohio Valley to the mid-Atlantic states and into southern New England will at least reach the 40s, and many places will be in the 50s, especially where there is no snow on the ground.
You may also note between those two images that difference in temperatures over eastern Montana and the Dakotas from this morning to tomorrow evening. That's the arrival of another arctic air mass on the playing field, one that will sweep all the way to the East Coast by late Monday. But that's getting a little ahead of ourselves.
What you don't see in those images is the upper-level low over the Rio Grande Valley right now, a feature that has brought a good soaking to South Texas over the past day or so. As this feature rolls slowly eastward and begins to open up this afternoon and tonight into tomorrow morning, it will continue to pull moisture from the eastern Pacific and across the Gulf of Mexico. There are already a lot of clouds across the Gulf and into the Deep South as well as Florida, and more and more showers will develop over the course of time.
By the time we get to tomorrow night, low pressure will be forming over the north-central Gulf, spreading even steadier and heavier rains across Alabama and Georgia into the Carolinas. Look at the Sunday morning surface map forecast from the 12z Dec. 27 NAM model:
There will be a distinct separation between the southern stream storm and all of its rain, and the low moving into the Great Lakes, and the cold front advancing across the mid-Mississippi Valley and across the Red River Valley. And with the arctic air absent, most of the precipitation associated with the storm through the daylight hours of Sunday will be in the form of rain.
Late Sunday and Sunday night as the storm moves off the mid-Atlantic coast and across southeastern New England, colder air will be pulled into the storms' circulation, and that will lead to rain changing to wet snow in some areas, especially in the high ground from the Poconos northeastward. It could lead to 6 to 12 inches of snow over the Green and White mountains, with lesser amounts farther southwest. Still, for the heavily populated I-95 corridor, it'll be all rain, not snow.
Once the storm charges into Eastern Canada by Monday morning, it will pull the arctic front over the Appalachians and into the East. With some sunshine and a relatively mild start to the day Monday, and a downsloping wind out of the west and northwest, Monday will be comparatively mild along the I-95 corridor, but the day will end fairly cold and it will get much colder Monday night and Tuesday.
The computer forecasts diverge after that as we ring out the old and ring in the new year, but there's likely to be even more cold to start off 2014. In other words, enjoy the respite from the cold. It won't be around long in the Ohio Valley and Great Lakes into the mid-Atlantic and New England.
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