Thrashing Thunderstorms, Thermal Thresholds and Tropical Troubles
June 20, 2012; 9:47 AM
Wednesday, 11:15 a.m.
It took a while to come up with an alliterative title such as the one above, and I had to make one final adjustment to really stretch and make it work, but the three separate points are the highlights, I believe, of the weather over the past couple of days and over the next few.
Let's start with the first phrase, the 'Thrashing Thunderstorms.' It's really more a case of training thunderstorms, or even tropical torrents, but work with me here! It refers to the inordinate amount of rain over the past couple of days across parts of the Dakotas into Minnesota and far northern Wisconsin. At last check, Two Harbors, Minn., was inundated by over 5.5 inches of rain. Through midnight, nearby Duluth had picked up 4.14 inches, and it looks as if at least another 2 inches has been dumped on them since then, bringing the total to over 6 inches in the past day and a half. This is leading to some catastrophic flooding in the region. The latest watches and warnings:
The dark green areas are the ones with ongoing flash flooding.
This has been triggered by a slow-moving cold front that's running into the very hot and pretty humid air mass in place from the central Plains into the Midwest. While some of these thunderstorms have been severe, the fact that one thunderstorm after another has raked across pretty much the same area overnight and this morning has led to all of the flooding.
If there's good news, it's that this front will move more steadily southeastward in the next 48 hours, reaching the New England and mid-Atlantic coasts by late Friday and early Friday night. Therefore, the chance of this same kind of activity will steadily diminish this afternoon and tonight as the front picks up some forward momentum. In fact, this could well become a broken line of more scattered thunderstorms tomorrow and tomorrow night into Friday morning as the front moves more steadily through the Great Lakes and Ohio Valley into the Northeast.
Meanwhile, the 'Thermal Thresholds' is a cute way of saying records are falling with this heat, and more are sure to go from the Mississippi Valley to the mid-Atlantic and New England this afternoon and again tomorrow. 850mb temperatures will surpass the 20C mark, which roughly correlates to the mid-90s within a few hundred feet of sea level. If there's an abundance of sunshine (and there is), a good wind (in some places, but not all) and a long enough period of dryness preceding this heat (ask the folks in the Midwest), then you can tack on a few more degrees in some locations, which is why it's already nearing 90 in portions of southern Hampshire and eastern Massachusetts. And it's already over 90 in parts of the mid-Atlantic.
Two days of the heat, then it fades pretty quickly. It'll certainly be gone by Friday from the Appalachians on west. It won't be as hot Friday east of the mountains as it will be the next two afternoons, but it will still be over 90 in a lot of places before the front arrives. Even there, though, the weekend promises to more like the latter third of June - middle to upper 80s and certainly less humid.
Finally, the 'Tropical Troubles.' I won't waste your time on Chris, more or less a waste of a name for a storm in the north central Atlantic. You can see it here on the infrared image, well east of Atlantic City, and south-southeast of Cape Race, Newfoundland:
Of far greater concern is the area of thunderstorms in the northern Caribbean, northwest of Jamaica, but still largely south of Cuba. The modeling has been all over the map with this over the past few days, but the broad consensus is that this area of unsettled weather drifts steadily north and northwestward in the coming days and enters the southeastern Gulf of Mexico. The water over the Gulf is warm enough to support tropical development, so by the time we get to the weekend, we could be talking about Debbie.
There is far less agreement on whether or not this system develops, as well as where it goes. The latest NAM would suggest it gradually bends more toward the northwest and slows with time, as the first trough coming through the Northeast Friday night into Saturday may not be deep enough to pick it up. A look at the Saturday afternoon NAM forecast:
The Canadian has a similar idea, only with a lower surface pressure, which would lead one to believe it could be named in time. To be fair, though, the GFS is not only weaker but splits this into two entities, with one holding its ground over the south-central Gulf and the other moving northeast through Florida and off the Southeast coast.
At the very least, much of Florida looks to get a good soaking whatever this becomes or doesn't become, some of that rain could get into the Florida Panhandle and perhaps back into Louisiana. It is something that will have to watched very carefully in the coming days. Stay tuned!
The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com