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The radar is starting to fill in with precipitation just to the west and southwest of our region. The first waves are falling into very dry air, so it may be a while before we see anything at the ground. I suspect we may see sleet -- possibly even a flake or two of snow -- as it begins, but then go to rain or freezing rain not long after, depending on exactly where that surface temperature rests. The dew points remain extremely low at the surface, all of 4 whopping degrees at 10 p.m. in Roanoke (with a temperature of 39). So as this precipitation, whatever form it's in, starts falling into that dry air, we'll see the temperatures drop. Following standard expectations with that temperature and dew point, the temperature could fall into the upper 20s with evaportional cooling. MIlder air moving in aloft and eventually sinking to the surface with the rain may make 30-32 more feasible.

My best stab at it says we do end up as low as 31 for about 3 or 4 hours in Roanoke, enough for some ice on the trees. It could get quite slick in higher elevation and outlying areas, and on bridges, and I would not be surprised to see a few power outages as ice starts building on trees in many areas. This does have the potential to be a signficant ice storm across much of the area if the full extent of the evaporational cooling is realized and the cold air hangs in a few hours before the warmth modifies it.

Once again, we're skating on the razor's edge.

Latest Roanoke hourly conditions

Latest National Weather Service-Blacksburg radar

Weather service advisories and warnings

Check out the list of observations across Virginia and North Carolina. Note the numbers under "DP," or the dew point. Very, very low numbers in places away from the coast, single digits in many places. Roanoke's was 4 degrees at 3 p.m. A few are even below zero.

The difference in the temperature and the dew point reflects how dry the atmosphere is. With temperatures in the 30s and 40s and dew points scraping zero, precpitation falling into that dry air near the surface will evaporate, taking heat out of the atmosphere. This evaporational cooling is where forecasters expect to get much of the cooling that would be necessary to trigger an ice storm. That cooling will eventually be overcome by warmth moving in from the south, but that may be hours later.

It's another situation where a degree or two could make all the difference. Most of you will probably have some ice in the morning, even if it's just a little on car metal and trees, while a few of you may escape without any ice. I expect there to be about a 4-6 hour windown from 3 a.m. to about 7-9 a.m. where Roanoke may drop to 32 or even 30 or 31. I don't expect huge glaze ice issues on the roads in the immediate Roanoke Valley, but please do be careful driving, as even a small patch of ice can be treacherous. As you fan out from the Roanoke Valley in distance and elevation, conditions will be considerably worse.

Probably just a few showers of rain/freezing rain and maybe some sleet before midnight, with the heavier stuff moving in after midnight.You can follow its arrival on the national Doppler radar loop.

Latest advisories and warnings from the National Weather Service in Blacksburg.

A big chunk of Southwest Virginia is now under an ice storm warning late tonight through midday Friday, including Roanoke County and every adjacent county, plus the New River Valley and everything north and west. Click here for the latest on warnings and advisories from the National Weather Service in Blacksburg.

Everything about this storm system is more powerful than similar borderline ice situations we've had in the past year, particularly Feb. 13 and Dec. 16 of last year. The damming of cold, dry air ahead of the storm is stronger, which gives more opportunity for ice to develop, but so is the flow of warm, moist air aloft. That flow of warm air will eventually overcome the cold, but the longer it can keep from doing so, the more ice threat we will have. The weather service is thinking a quarter to a half inch of ice is quite possible over most of the area, hence the ice storm warning. That much ice would result in scattered power outages and some tree damage, locally very troublesome in areas that get the worst ice, but not an areawide paralyzing ice storm like many of you remember from 1994.

The Roanoke Valley is always the big question. I will reiterate my thinking that the potential for the floor of the Roanoke Valley, all the way to downtown, to get some ice out of this situation is greater than in the 33-degree escapes Roanoke city had twice last year. The opportunity for evaporational cooling on the front end -- initial precipitation evaporating in cold, dry air at the surface, thereby lowering the temperature -- is much greater. I wouldn't be surprised to see an hour or two of sleet mixed in at the front end, either, which could lay down a cold surface layer. Higher elevations and the fringe areas of the Roanoke Valley are highly likely to see ice, and quite possibly the quarter-inch required to verify the ice storm warning.

The trouble will come if the cold air holds in more stubbornly than expected on Friday. That is how this potentially significant ice storm could become a major one. For now, it looks like the falling rain itself will pull some warmer air toward the surface Friday morning, and an advancing warm front will get us above freezing before this can get extremely bad.

UPDATED AT 5:30 PM

The battle between the irresistible force -- warm, moist Gulf of Mexico air being pulled northward by a strong low pressure system to our west -- and the immovable object -- cold, dry air pushed southward by a high pressure system in southeast Canada -- will put Southwest Virginia in an atmospheric tussle that could lead to widespread freezing rain Thursday night and early Friday. As a result, the National Weather Service has issued a winter storm watch that includes the Roanoke and New River valleys and most counties along the Blue Ridge and points northwest.

The irresistible force will win, and temperatures will rise above freezing Friday to melt the ice. It all depends on how much rain falls before temperatures can get above freezing how big a deal this will be.

Latest HPC map puts moderate ice risk threat, in green, farther west than earlier maps

The Hydromemteorological Prediction Center had our area in a high risk of .25-inch ice or more earlier in the day. The latest map, inset at left, backs off a little on the ice threat, and shifts it slightly west. Click here for the latest winter weather threat maps from HPC (and note all that heavy snow potential out toward Illinois and Indiana).

The obvious question that arises for the immediate Roanoke area is whether the city can again pull out a 33-degree escape as we did on Dec. 16 and last Feb. 13.

It is certainly possible that will end up happening, but three factors argue against it: (1) a greater degree of evaporational cooling, with moisture moving into cold, dry air at the onset, (2) more well-established cold air damming against the eastern slopes of the mountains than in those previous episodes, and (3) the overnight arrival of the precipitation. We could well see some sleet or even very brief snow on the front edge of the precipitation, which would help cool things that much more.

It seems likely to me from here that we will see some ice even on the floor of the Roanoke Valley on Friday morning, but the low to the west will be so strong it will easily pull warm air northward to push things above freezing by mid-morning Friday. In an unusal twist ... the Roanoke Valley could actually end up being one of the last to warm significantly as milder air is pulled in at a higher elevation above the valley first. Would not be surprised if we struggled through the 30s during the day on Friday while some higher elevation areas to our south soared into the 50s.

As this radar grab from earlier this evening shows, a wide band of rain is headed our way with a cold front approaching from the west. It will probably weaken some overnight, as projected rain totals don't look like a whole lot. Overnight, we'll end up with wind and maybe a few snow flurries in the morning. A very similar storm system to this one, but slightly farther east, is expected to make its move northeastward into the Ohio Valley come Thursday. It is expected to bring a LOT more rain than this one to our region. The question is whether at the least first few hours of rain will catch up with freezing temperatures at the surface, presenting the possibility of ice. Government forecasters in Washington continue to place our area in at least a slight risk of significant ice for Thursday night, but the area of moderate risk has shifted slightly north. This seems like another very borderline situation that will warm quickly, but it only takes a little ice to make driving slick. Certainly something to monitor.

The long-term outlook is still warmer than normal.

At least we might get a little drought help the next 72 hours.

We will get a fair amount of rain and wind tonight as a new cold front pushes through, and maybe some snow showers in the morning. Wind advisories and a few high wind warnings are out for tonight.

The next big thing on the horizon is the ice storm potential on Thursday night and Friday. The Hydrometeorological Prediction Center already has us in slight to moderate risk of significant icing, defined as .25 inch or greater. This will be caused by a new low pressure system, quite a strong one, sweeping a lot of Gulf moisture up and over a cold air mass at the surface. Check out this map for forecasted precipitation totals -- yep, that's about an inch of liquid. Hopefully that won't all be ice for us.

If the linked maps above look a little different than I described, it could be that they have been updated by HPC. I'll get some fresh information up later this evening.

The earlier arrival of a cold front and rain on Tuesday may stymie the potential warmup this week ... so maybe not the 60s like I hinted at in today's Weather Journal column. Still, temperatures will be well above freezing so there will be no significant threat of wintry weather with the next system. The late week system is another matter ... it is possible that some moisture may make it into cold air, at least to start. No use getting too specific about that now. The picture will change many times before then.

Here are a couple of National Weather Service radar grabs this afternoon showing precipitation both near the Great Lakes and in the Gulf Coast states. Much of the precipitation to the north is snow, and even some of the precipitation to the south is freezing rain and sleet. But the likely outcome is that we miss both of these areas of disturbed weather as they scoot eastward. There could be a little snow or rain here and there Saturday, but it doesn't look like any kind of really organized, large-scale system. That kind of system may well form just off the East Coast late Saturday ... Tidewater could have a close brush with significant snow, with a better chance up toward New Jersey.

This split system will bring this round of winter to an end, as warmer air rushes in the next few days and a strong storm system takes aim on the Great Lakes for midweek, keeping us firmly in its warm sector and away from ice and snow. Neither a 70-degree day nor thunderstorms can be ruled out in the Monday through Wednesday timeframe. Late next week, a new storm system could follow the same track, or may aim for an East Coast track that would bring wintry precipitation back to our region. Lots of time to consider that as we bask the next few days.

We're in the typical snow flurry pattern this afternoon, as a new punch of Arctic air is bringing northwest winds that are carrying moisture up the western slopes of the Appalachians, where the lifted moisture condenses into low and mid level clouds and spits out snowflakes. While the western upslope regions near the Virginia-West Virginia border and points west get the most out of a setup like this -- a few inches may accumulate there -- some of the snow bleeds eastward over the mountains. In the Roanoke Valley, we have been seeing off-and-on snow flurries today. While you can never rule out a briefly whitened ground in a localized heavier snow shower, these usually don't amount to much for us on this side of the Appalachian spine, and that looks to be the case again today.

UPDATE 9PM: Just drove home to south Roanoke County for a while to find a dusting of snow from about the Tanglewood Mall area southward, including some on parking lots and even streets. A heavier snow squall must have blown through that area earlier this evening. If you were under one, you had quite a show for a few minutes. Elsewhere, such as back here in downtown Roanoke, just some flurries.

We have another shot of Arctic air coming in on Thursday that will settle in for most of the weekend, and there is at least some chance of snow showers on Thursday and mixed precipitation over the weekend, though neither of these chances look very impressive. Beyond the weekend, it appears more likely that the last few days of January will feature a sharp warmup as the jet stream pattern shifts slightly to allow southwest winds to take hold aloft. I would not be surprised to see some 60s return next week. The Hydrometeorological Prediction Center's 6-10-day temperature outlook puts us squarely in the red, or a heightened chance of above-normal temperatures. If that transpires, the month will likely conclude a couple of degrees above normal. Despite all the recent cold, Roanoke is averaging about 2 degrees above normal for the month thanks to those really balmy days, especially the 6th through the 9th. A few more cold days may shave us closer to normal before warmer-than-normal weather pokes the average up a bit next week. The HPC's 6-10-day prognosis is wetter than normal, which is a good thing considering that we're an inch and a quarter below normal precipitation for this month and have been at least half an inch below normal in 18 of the last 23 months. It's going to take a lot more than these dinky winter weather systems we've been getting to spring us out of our long-term drought.