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Due to some weather data issues and other problems, I've scrapped what was on this blog entry altogether and recapped July on a later entry that can be found by clicking here.

A strong disturbance spinning through the southern states triggered an unusual out-of-season outbreak of tornadoes and damaging winds near Memphis today (tornadoes are more common in January in that region than in late July).  That disturbance will be swinging northeastward overnight and into Friday, with a cold front also dragging through during the day. Showers and thunderstorms are likely to develop Friday morning, and there may be enough wind support this time for some supercells and possibly isolated tornadoes in parts of Virginia ... primarily east of the Blue Ridge, where instability will be stronger and daytime heating will have a better chance to take hold. It's just close enough that it bears some watching in our neck of the woods for a few severe storms, particularly in the late morning to mid afternoon period. A warm, sticky pattern with occasional bouts of storminess in our area is projected to continue through next week.

If you wonder where the summer heat is ... try somewhere you wouldn't expect, Seattle, which shattered its all time record high temperature by 3 degrees on Wednesday hitting 103. Meanwhile, it's still a strangely cold summer around the Great Lakes.  The two are related, as the jet stream is pushing far north into Canada above strong high pressure in the West, then diving southward bringing cool air into the East.

Here in Southwest Virginia, Thursday should be about normal, with highs in Roanoke in the mid to upper 80s after morning lows in the upper 60s. There could be scattered afternoon thunderstorms as daytime heating bubbles moisture upward.

I wrote in today's Weather Journal column about how training effects -- heavy showers and storms moving over the same area repeatedly -- have focused heavy rainfall totals in narrow corridors while leaving others out several times this month. That's actually happening right now (click here for 1:15 p.m. radar shot), as a heavy band of rain takes aim on the Roanoke Valley, especially the southern half of it, and neighboring areas to the south and east. This band is aligned southwest to northeast and is moving northeast, so regions under the yellow color on radar stand to get an several minutes to an hour or more of moderate to heavy rainfall.

Latest National Weather Service-Blacksburg radar

The last couple of weeks, we've had an interesting phenomenon where it seems the heavier rains often develop at night. Don't be surprised if that repeats itself overnight into the wee hours of Wednesday morning. A strong upper-level disturbance to our west, the one throwing all these wads of moisture across the South as depicted in radar image to the left, will be moving northeastward toward the Ohio Valley. We'll be on the east side, perfect for southerly winds to bring in Gulf of Mexico moisture. With an impulse or two circling the upper-leve low, the potential for bands of rain and storms will increase overnight and continue during the day Wednesday, which might be one of those summer days when rain and clouds hold temperatures below 80. There is a big wad of rain in northeast Tennessee that might move our way this evening. Part of eastern Kentucky is under a flood watch for the threat of heavy rain with this system.

Latest National Weather Service-Blacksburg radar

Latest national and regional radar

I wrote in a Weather Journal column earlier this week about how temperatures are extremely cool for July in much of the northern and eastern states, while they are blazing in Texas. Here are some articles from The Associated Press detailing the effects of the unusually cool summer weather from the Northern Plains and Upper Midwest to the East Coast and the extreme heat and drought in Texas.

Locally, we'll be between the temperature extremes this week. The core of the coolest air will drift westward slightly, so we won't have temperatures way below normal, but the hottest air to the southwest will also be kept at bay, so don't expect stifling heat, either. Normal this time of year for Roanoke is highs in the upper 80s and lows in the upper 60s, and temperatures this week will likely be in the mid 80s most days with upper 60s at night, so very near or slightly above below normal. Expect moisture to build through the week with stalling fronts and weak disturbances providing a chance of showers and storms each day. The chances of heavier and more concentrated rain may grow later in the week as thicker sub-tropical moisture builds into the region.

A squall line has formed in West Virginia and is approaching the Virginia state line. We'll see how much juice this line, which has prompted several severe thunderstorm warnings, has to get over the mountains into the Roanoke and New River valleys soon, but at least some places in Western Virginia should see some gusty winds, heavy rain and dangerous cloud-to-ground lightning with this line in the next hour or two. This is the kickoff of several days worth of scattered showers and storms, as frontal systems stall and disturbances move through a more humid air mass. Temperatures will hold near normal in the 80s for highs and 60s for lows this week.

Latest National Weather Service-Blacksburg radar

I wrote in Weather Journal today about the unusually cool summer across much of the eastern and northern U.S.  That's what could make Saturday a rare event this July: It has a chance to be Roanoke's second 90-degree day of 2009 (provided today doesn't shoot well above the projected high in the mid 80s). Ironically, the approach of a cold front may be part of the reason Saturday could be so hot, as winds turn southwest ahead of the front and sweep in hotter air, warmed a little more by downslope effects crossing the mountains. The front's arrival just to our west on Sunday could trigger a round of thunderstorms, some of which may be severe.

Overall, the next week looks to be a bit warmer than we've gotten used to, but even at that most days will be right at or a little below the normal high/low of 88/66 for the Star City. It will probably be warm enough to keep July 2009 from being the coolest on record, but not enough to pull it away from being among the 10 or so coolest Julys, going back to 1912.

Some locations ... especially in eastern parts of Roanoke city and Roanoke County ... got a quick 2-plus inches of rain from overnight storms (see rainfall list in extended entry below), while other areas got much less. The presence of a cold front, upper-level disturbance and abundant moisture will offer the potential for additional storms to develop today, some of which could produce similarly heavy rain and possibly localized severe weather.

Latest National Weather Service-Blacksburg radar

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UPDATE 12:30 PM: Flash flood warning for City of Roanoke, Salem, parts of Roanoke County and northwestern Franklin County as heavy storms continue to move over the same areas repeatedly.  Torrential rain occuring now. Very reminiscent of Monday morning. END UPDATE

There were a few showers and storms to our west through the afternoon, but they have started developing along the Blue Ridge this evening in response to an upper-level disturbance to our west. Showers and storms will also be possible Thursday as a weak cold front approaches, a few of which could be strong or even severe.

Latest National Weather Service-Blacksburg radar

Roanoke area rain totals