Wednesday, 11:10 a.m.
Low pressure has steadily continued to advance northward off the East Coast early today, and it is throwing precipitation back into New Jersey and onto parts of Long Island at this hour. This is a storm that will produce pretty much what has been expected of it all along - wind, rain, coastal flooding and some snow. There may be a little more of the snow when all is said and done than what I was thinking 24 hours ago, and closer to the coast than I had been thinking, but as nor'easters go, we are likely to see stronger ones with more far-reaching impacts in the end than this one.
The biggest problem in getting the precipitation deep into the interior mid-Atlantic is the lack of an overrunning surface. The latest surface pressure analysis shows high pressure over Quebec and low pressure off the coast. Period. This has greatly reduced the upward motion potential of this storm across the interior, one of the things I questioned last week at this time when I first thought the storm would form but would mainly impact New England and the coastal mid-Atlantic. As it turns out, that assessment from a week away is going to turn out better than most of my fumblings every day since!
Still, I don't want to play down the impacts of the storm on the mid-Atlantic and southern New England. The storm will be strong enough, and close enough to the coast, with enough of a surface pressure gradient to generate gale-force winds along the coast from Virginia to Long Island this afternoon into tonight before the storm begins to weaken. That will cause some downed trees in areas where they managed to survive Sandy's strong winds, and/or bring down some power lines that may have been restrung in the wake of Sandy.
There will also be some coastal flooding, too, with a surge of 2 to 3 feet expected. Thankfully, it shouldn't be much more, and it's not associated with a full moon or a new moon. However, as we have been harping on, without the normal protection afforded many coastal communities by sand dunes, the flooding along the coast is likely to be a little worse with this storm that it otherwise would be.
The rainfall will be hard along the mid-Atlantic coast and up into portions of southern and eastern New England, but probably not enough to cause widespread flooding. The exception may be pockets of central and southern New Jersey, but even there it will be fairly isolated in nature.
Snowfall could be a bit problematic. Here's the latest update on projected snow fall totals from the storm:
This represents a bit of a pull back over the eastern half of Pennsylvania. Truth be told, I can see the 1-inch line ending up even farther east. Note, however, that the highest amounts are projected for the higher terrain north of Philadelphia into the Poconos and western New Jersey into parts of the Catskills, with a secondary area of similar snow projections for parts of the Berkshires and into parts of Vermont and New Hampshire.
As the storm begins to weaken late tonight and tomorrow, it will slowly drift away from the mid-Atlantic coast. Gusty northwest winds will help dry things out behind the storm across the mid-Atlantic. That said, it will still be cooler than normal tomorrow throughout this region despite any return to sunshine that occurs. In some areas, that will be delayed until Friday.
After that, the action shifts to the West. In fact, there will be a series of storms, disturbances, fronts - whatever you want to call them - that will completely turnaround the record of heat of recent days and replace it with a dramatically colder period into the start if the weekend.
The first of these features will dart eastward across the northern Rockies this afternoon, pulling a cold front through the Northwest and dramatically lowering snow levels. Then a second disturbance will dig down the West coast tonight and tomorrow, pulling even colder air southward with it, and causing some rain and mountain snow to break out from northern California northward. Here's the 500mb chart for tomorrow afternoon:
Low pressure will eventually emerge later Friday over the eastern Rockies, helping to draw more cold air southward out of Canada into the northern Rockies. The combination of snow, wind and falling temperatures will likely lead to blizzard conditions in parts of Montana later Friday and Friday night, spreading into parts of North Dakota on Saturday. That's initially where the bulk of the snow will go, but it's looking more and more likely that still another storm will come out of the central Rockies later Saturday and Saturday night, drawing the arctic air farther south, and perhaps bringing snow into metro Denver late in the day and at night.
That very same storm will head for the Midwest Sunday and Sunday night. With all of the warmth building or amassing ahead of the storm and its attendant cold front, it's a recipe for severe weather, and that's clearly implied by the Sunday afternoon GFS surface forecast with precipitation:
This same front will march across the Great Lakes and Ohio and Tennessee valleys Monday and Monday night with more strong to severe thunderstorms likely. I don't know about the tornado risk yet, but it looks to be a very volatile system as it tracks across the country. Fortunately, the upper-level disturbance supporting the front will lift northeastward Monday into Tuesday, which means the front itself will weaken. Therefore, the threat of severe weather will be much reduced coming into the East on Tuesday.
After that, it appears as if the blocking pattern that has directly contributed to all of the storminess in the East will finally break down. That blocking led to Sandy getting captured and mushrooming in size and scope last Monday, and today's nor'easter not being able to easily escape out to sea. With the blocking gone, any cold air coming eastward will be modified in nature and probably not last for terribly long, either. That's good news in the mid-Atlantic and southern New England as clean-up efforts continue in the wake of Sandy.
A building upper-level ridge of high pressure in the West will promote hot, dry weather in the Northwest, while a downstream trough brings cooling through the Midwest into the Great Lakes and Ohio Valley.
A pattern more typical of late July and early August is shaping up around the country, one with heat and humidity, but with fewer incidents of severe thunderstorms and flooding.
There will be plenty of heat and humidity from the southern Plains to the East Coast this week while much cooler air prevails for a time over the Northwest to the northern Plains.
Severe thunderstorms raked across the Midwest and Ohio Valley in the past 24 hours, with more on the way this afternoon. The pattern will repeat itself over the next week.