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Focusing in on the Stormy Weather

5/10/2011, 6:57:36 AM

Tuesday, 11:30 a.m.

For the first time this spring, my general neighborhood, and for argument's sake let's call that the greater mid-Atlantic region, is enjoying not one or two nice days in a row, but a whole string of them. A large part of it can be attributed to the massive storm well southeast of Cape Cod:

That's a potent system that is brushing Maine down through eastern Massachusetts and Rhode Island with plenty of clouds, a stiff wind out of the north and northeast gusting between 20 and 30 miles an hour (high at the coast and offshore, where gale warnings are flying), and some on-and-off rain showers. In short, it is just one ugly day from Eastport to Narragansett Bay!

West of there, a lot of dry air is being yanked out of high pressure in Quebec down through western New England and New York state into the mid-Atlantic, resulting in an abundance of sunshine. This is resulting in chilly nights with pleasant afternoons - no heat wave, mind you, but by the same token, no cold wave, either. It's about as good as it gets at this time of the year.

While the big ocean storm is far enough offshore so that most of the East is in good shape, there are other storms that are not playing so nice. They're best seen up upper-level charts, like the one here for this morning:

The feature over the Southwest is producing showers from portions of eastern Nevada into Utah, Wyoming, southern Idaho and Montana. The southwest flow around it is also bringing some disturbance out of Mexico, and that is helping seed thunderstorms in Texas, where the air mass is not only quite warm, but also very moist as well. In between the two, you can see all of the dry air over New Mexico up into Colorado and much of Kansas, and the contrast between the bone-dry air there and the high humidity in the southern Plains is striking. Dew point temperatures go from 60 and high from Wichita Falls and points east to the low 20s in the Texas Panhandle - your classic 'dry line.'

With this disturbance helping to highlight this discontinuity in the atmosphere, there will continue to be strong thunderstorms bubbling up across Texas into Oklahoma this afternoon into tonight. This activity, though, will be fairly scattered in nature, and not a lot of it will truly be considered severe.

However, that will likely change tomorrow as that upper-level low comes through the Four Corners area and turns northeastward, aiming for the central Plains. This will help to cool the air aloft, while it remains quite warm to downright hot and humid from central and eastern Texas up into Oklahoma and Kansas. It is this kind of mixture that should lead to more numerous strong thunderstorms, and a lot of those may will generate severe weather such as large hail, destructive winds and, yes, even a few tornadoes:

As you can see from the graphic, what begins down there is likely to expand northeastward with time to include portions of northern and western Missouri into Iowa. If you look pretty closely at some of the low-level winds, they will be carrying the very warm, humid air mass northward and northeastward over time, but as we head to Thursday and beyond, the normal west-to-east progression of weather systems sort of takes a break. Here's the most recent NAM 500mb forecast for Thursday morning:

Now compare that to the Friday evening forecast:

The upper-level low doesn't move an awful lot, but what movement there is of it is more toward the east, then southeast over time.

This is even slower than what we had speculated upon late last week, and it means the nice weather in the East may linger into, if not through, the day on Friday, and it will remain warmer than normal through Friday in the Ohio and Tennessee valleys as well. The latter will be more a result of clouds keeping temperatures much above normal at night, though there will be scattered showers and thunderstorms along and west of the Appalachians back to that upper-level low.

With a large high forecast to build into southern Canada late in the week, there will be a push of cooler air down the front range of the Rockies and across the Plains, and it could lead to some pockets of double-digit temperature anomalies in the central and northern Plains late this week into the start of the weekend, especially where it is cloudy with any kind of rain that would keep daytime highs way below normal. Those normals, by the way, are getting well up into the 60s in the northern tier of states, and climbing steadily, so it implies a few days where temperatures are unlikely to get out of the 50s.

This will not be the 'classic' stormy weather pattern, at least not like the one that spawned the deadly tornado outbreak of two weeks ago, but there will be some severe weather, including Thursday and Friday. Some of the rain will be heavy enough to contribute to flooding, though probably not in the same way that we have been witnessing flooding in recent weeks, up to an including the present time along the middle and lower Mississippi Valley. Still, any kind of stormy weather in these flood-ravaged and storm-weary areas will be unwelcome.

It should help to bring SOME much needed rain to portions of the Gulf Coast region, including at least northern Florida, and it's likely to bring a few days of cooler-than-normal weather along for the ride this weekend into early next week. Of course, as that is happening, the coastal mid-Atlantic into New England may actually go the opposite way! With the large ocean storm removed from the playing field, the onshore flow should weaken, and it might actually turn a bit warmer this weekend and especially next week!

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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