The massive high pressure that darted by the Northeast yesterday left behind a puddle of cold, dense air in the low levels of the atmosphere. It hung around long enough ahead of an approaching storm off the Eastern Seaboard to bring some snow and ice to the interior mid-Atlantic and New England overnight and this morning, but the cold air is giving up the fight. Look at the late morning surface temperatures:
It's giving up now in the Susquehanna Valley, with temperatures approaching 40, and all of southeastern New England has charged up into the 40s with howling winds from the northeast. A teeming rain is soaking parts of New Jersey, southeastern New York and Long Island as well as Connecticut, and that is already triggering some flooding. More is likely this afternoon and early tonight in southern New England as this heavy rain band shifts on through with 1, 2, even 3 inches of rain falling in a short window.
As far as snow is concerned, thus far the storm would be considered an 'underachiever' by many, as there just hasn't been a lot of heavy snow. The warm air aloft is simply too impressive. Look at this evening's 850mb temperature forecast:
That doesn't mean the snow chances are done with the storm. As it reaches Connecticut early tonight, it will come to a grinding halt, with an upper-level low forming over the tri-state area late tonight and tomorrow. At this point, the storm will have reached its 'mature' phase, and it will no longer deepen. Instead, it will slowly start to unravel, and it will spin off bands of moisture to the west and southwest tomorrow into Thursday before the whole complex begins to lift out to the north-northeast slowly on Friday. Compare the 500mb forecast tomorrow afternoon to that of Friday evening:
It does not move much in two days plus! That means the entire Northeast and mid-Atlantic will remain in its clutches through Friday. Furthermore, as this unwinding takes place, and these bands of moisture rotate outward from the storm center, there will be some snow west and southwest of the storm. Most of it will be centered on upstate New York, though some of it will wander into Pennsylvania at times, too. From this some places will rack up more than 6 inches of wet snow, especially later tomorrow into Thursday.
Look back again at those two 500mb images for tomorrow afternoon and Friday evening. Notice that the upper-level low represents a pocket of cold air, surrounded by milder air. The main branch of the stream is well to the north and retreating with time. That takes the last of the low-level arctic air off the playing field, and it won't be back for a while.
Shifting our attention to the West, including western Canada, a series of storms will bring heavy rain and strong winds through the Northwest and into British Columbia. The first one rolls through today, followed quickly by another late tonight and tomorrow. A third one takes aim at the Northwest coast tomorrow night and Thursday and could bring several inches of rain coursing through northern California and southwestern Oregon in the process. A weaker storm may pull the rain farther south and east on Friday to get most of the state of California in on the rain.
What these storms will do is flood western Canada with mild air, and as that air climbs over the Rockies and descends into Alberta and Saskatchewan, it will become very, very mild. The same thing will happen in Montana, Wyoming and Colorado out into the western Plains. Once there, it will spread slowly to the East and lock out the arctic air for not just the second half of this week, but probably through all of next week, too. Thus, the last two weeks of autumn will be comparatively mild, and seemingly unlike the season to come.
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