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UPDATED 12:20 P.M.: Several counties west of the Roanoke Valley are under a frost advisory for Thursday morning.  END UPDATE

You might need a jacket this morning with temperatures in the 40s to low 50s, but autumn chill will settle in big-time by Thursday morning. Some valleys could see lows a few degrees above freezing, with frost possible, with most everybody in Southwest Virginia no warmer than the low 40s. Temperatures will moderate some by the weekend, but it does appear that rather mild fall weather is with us for several days.

A thin line of showers marks the arrival of the next cold front that will breezy conditions by afternoon and even cooler weather by tonight. Don't be surprised to see a brief shot of rain during the day, but most of it probalby won't make it over the mountains because of the downsloping nature of the westerly winds.  Behind the front, we will have two or three days of highs in the 60s and lows in the 40s, perhaps even a few readings in the 30s in some elevated valleys and very high elevations. It could indeed be sweater weather the next few mornings.

The rain is moving out. After several dry weeks, this was needed. After possibly a few more showers overnight and early Sunday, many days of cooler, drier weather are expected. By midweek, highs in the 60s and lows in the 40s will be common.

The last two weeks of humid dreariness is colliding with an advance of cool, autumnlike air from Canada, and the result will be some pretty robust rains over the next 36 hours or so. So far today we've mostly seen light rain and drizzle in Southwest Virginia, and that is likely to continue off and on overnight and into Saturday. By later Saturday and into Saturday night, the cold front may be able to force the moisture upward into some more vigorous showers and thunderstorms, which could have heavy rain. The 2-day rainfall map from the Hydrometeorological Prediction Center is projecting widespread 1.5 to 2-inch rain fall amounts across most of Western Virginia through Sunday, with even heavier amounts just to the west in eastern Kentucky and West Virginia. Giles and Bland County, plus most counties west into the coalfields of far Southwest Virginia and southern West Virginia, are under a flash flood watch for this threat of heavy rain.

The path to some cool, clear, dry, autumnlike days next week leads right through this soggy mess. Be sure and take the rain gear and something a little warm if you're going to the Virginia Tech-Miami game on Saturday, as temperatures may hang in the 50s in Blacksburg during what could at times be a downpour.

In Weather Journal on Friday, I am writing about some more fall-like weather pushing out the stagnant stickiness of recent days. That is still very much expected, but the Climate Prediction Center is forecasting warmer-than-normal temperatures to rebound by late next week, as this 6-to-10-day temperature forecast map shows. If this comes to fruition, cool temperatures will pool in the West to start October, though there are signals that may march eastward early in the month.

Between now and any of that, we're likely to have a pretty rainy weekend, which won't be a bad thing at all for lots of folks who have been a little dry the past few weeks. Might be sloppy for high school football games Friday night and for the Tech-Miami showdown in Blacksburg on Saturday.

I'm not about to say today will be the last 80-plus day of 2009 ... we're usually good for a few of those in October or even into November. But it may be the last sultry summerlike day for quite a while, with highs in the 80s and enough humidity for showers and storms to be a threat in the afternoon. A backdoor cold front from the north will cool things down considerably for Friday, then rain will do the same for Saturday before a stronger cold front from the northwest arrives to introduce a much cooler, drier air mass. So, yes, a taste of summer today will be giving way to more fall-like weather by next week.

Well, I see didn't miss much being out for four days. I actually got in the middle of the most intense thunderstorms I've seen all year waiting for my mother to finish shopping at Wal-Mart in Jonesboro, Arkansas, on Monday. There was gusty winds, extremely heavy downpours, hail and lots of close cloud-to-ground lightning. My drive back was almost totally dry except for the last 30 miles, where I started hitting the drippy, drizzly stuff at Christiansburg, this dreary upslope stuff that's going to be hard to shake the next couple of days.

I didn't miss much locally, that is. Georgia got caught in some incredible training downpours that caused deadly flooding and the Colorado mountains got their first substantial snow of the season, a kind of kickoff for autumn in the U.S.

The most important large-scale development is that we're finally going to see substantial jet stream dynamics moving over our region by the weekend, breaking us out of this stagnant soupy pattern into something a little more fall-like. A major frosty leaf-changing cold snap, it is not likely to be, but next week looks to at least start drier and cooler than this.

Thanks for the foliage discussion while I was away. I'll get back on that subject soon.

Largely because of weak upper-level steering winds, the slow-moving low in the south-central U.S. simply hasn't delivered on its rain potential for our region the last two days. Some sunshine is likely on what will likely be a very nice Saturday for outdoor activities. But by Sunday, the meandering low will finally be kicked out by another low digging in from the north. This will restore the southeast winds, the low clouds, and an increasing chance of showers. Next week could follow a very similar pattern as this week, with the new low likely to also stall and meander in the south-central U.S. before finally being kicked out late in the week. 

More days than not over the next 7-10 or so will be dreary, so enjoy Saturday's sunshine.

See the swirl back over Oklahoma and Arkansas. (Click here for bigger version of early evening satellite photo) That and a high pressure system over New England are your weather makers for the next several days. Currently, the easterly breeze developing between the two is beginning to stream Atlantic moisture up against the Appalachians. The low to the west will slowly move east-northeast, while the high to the north will build southward east of the Appalachians. The result will be a prolonged cloudy, damp, mild but not really cool period. A lot of days through about Tuesday won't see much difference between the low and high temperatures, mostly in the 60s. Rainfall expectations have continued to diminish, with the heaviest rain being held to the south. (Map courtesy of the Hydrometeorological Prediction Center) Still, much of Southwest Virginia might have a gradual push toward an inch through the next 5 days, more if the heavier rain manages to shift north (or an unexpected break of sunshine introduces some instability to squeeze out heavier downpours).  But this pattern probably will neither satisfy the folks who want copious rain to break recent dryness, nor those who want dry weather for outdoor activities (like the Salem Red Sox baseball playoff game on Thursday, high school football on Friday, Virginia Tech-Nebraska on Saturday, etc.)

For those (many of you) eagerly awaiting a taste of fall or even early winter, here's a sign: A push of Arctic air may make a run for the Northern Plains late next week. It probably won't get here this time, but it's the first real sign of autumn weather taking hold in the continental U.S., just about right on time for the start of astronomical autumn.

Forecasts are backing off the rain a little bit for Wednesday night and Thursday. The general setup, with an easterly fetch of moisture between low pressure to the southwest and high pressure to the northeast, is still the same, but it looks like there will be more dry air to overcome than earlier projected. So rainfall forecasts for Southwest Virginia over the next 3 days have been cut back to around 3/4 to 1 inch as opposed to the 1-plus previously. The heavier rain is expected to be farther southwest over the Tennessee and Mississippi river valleys, where some heavy rain fell today.

The cloudy, damp, showery, mild weather that develops over the next couple of days will likely, after a brief weekend break, repeat itself with a very similar scenario early next week.