Thursday, 11:30 a.m.
Much of the attention in the past month has been rightly focused on all of the storminess that has pounded the mid-Atlantic and Northeast, from Sandy, to a nor'easter, to the most recent snowfall a couple of days ago. There was a round of very wet weather in the days leading up to and through Thanksgiving in the Northwest, much as what has now commenced from central California on north.
What is not getting nearly as much attention is the utter lack of storminess in between and how dry it really, really is. That can be shown in many ways. First, let's start with the current snowcover analysis across the country:
There is, of course, some lingering snowcover from the storm earlier this week from Pennsylvania into southern New England, but in most cases, the snow depth is under 2 inches, and most of that will be gone by the end of the weekend. As you would expect, there's more off the east end of Lake Ontario and inland from Lake Erie, but it's not terribly deep, and the snowcover over the upper Great Lakes is much below what you would typically see at the end of November.
Meanwhile, across the Midwest, there's very little snowcover until you get into northernmost Wisconsin and northern Minnesota, but even there, we're only talking a few inches at best. And there are only a few places across extreme northwestern Nebraska into eastern Wyoming with some semblance of snow on the ground. Only when you get into northernmost North Dakota and northern Montana to you find a decent snow pack, that gradually increases the farther north you go into southern Canada. Elsewhere? Nada. Zip. Zero.
How about recent precipitation? Here's a look at the percentage of normal precipitation over the past 30 days:
Wow! That tells a very vivid story! In the VAST majority of the country from the central and southern Rockies to the East Coast, November has not just been dry, but exceptionally so, with most places at less than 50 percent of normal and many at less that 25 percent of normal. If you think it has overall been a boring weather pattern, there's the proof of it.
But what about the long term view of precipitation, or the Drought Monitor?
Suffice to say that most areas from the Mississippi Valley to the central and southern Rockies and the Desert Southwest are hurting for moisture, and the pattern we're in right now doesn't look promising to change that in any meaningful way.
The anchor point to the pattern we've been in, and look to remain in through at least the first third of December, is the vortex in the Gulf of Alaska. Here's the GFS ensemble view of things this morning:
We typically focus on blocking in the north Atlantic, but blocking can occur anywhere, and you can see how strong the upper-level ridge is upstream of that massive low, occupying a position from east of Greenland, over the North Pole and down to western Alaska and northeast Asia into the north-central Pacific. Locked underneath is that huge polar vortex that, no matter how hard the models have tried to dislodge it, has remained locked in place. And right now it's spitting a series of disturbances at the West Coast, particularly the northern half of California and Oregon.
You'd normally think the storms there would carry moisture to the Continental Divide, with some sort of storminess redeveloping farther downstream, but that's just not the case right now. Instead, the trough is far enough offshore that a mean ridge position is in place over the eastern Rockies and plains, and the southwest flow aloft in between the two is sending a lot of mild and dry air aloft through southern California into the central and southern Rockies. Any low-level return flow moisture off the Gulf of Mexico is just that - in the low levels, and only contributes to a moistening of systems as the last minute as the come across the South and head toward the mid-Atlantic. To the north and west, virtually nothing.
Unfortunately, the long-term prognosis isn't good. It really looks as if that particular area of the central and southern Rockies out into the central and much of the southern Plains will get little moisture for quite a while. In other words, the drought may well spread in the coming weeks, not shrink. At this time of the year when evaporation rates are usually quite low, you want to see these areas get moist, when that moisture has a much better chance of seeping into the ground. Right now, though, that's just not happening, nor will it any time soon.
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.
The strong upper-level ridge over the southern Plains will promote intense heat there, while it forces disturbances through the Midwest toward the Ohio Valley with severe thunderstorms to follow.
A strengthening upper-level ridge of high pressure over Texas and Oklahoma will dry out the Plains, but it will remain unsettled from the Dakotas to the central Appalachians, as the Northwest trends cooler.