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UPDATE 12:55 a.m. Friday Feb. 22: New precipitation is firing over Arkansas, Mississippi, Alabama and Tennessee as I write this. This could move into our area later this morning, though it's still doubtful that this will be much more than a minor ice/sleet event. But it will have to be monitored in case heavier precipitation moves in while it's still below freezing. If rain arrives much later today, it could well warm above freezing. It's a very disorganized winter storm, sort of symbolic of a strange winter.

As the great radar split continues on this poorly organized storm system -- rather, two upper-level storm systems, barely interacting with one another -- it's obvious at this point that widespread wintry precipitation will not be beginning before midnight. A few flakes, pellets or sprinkles maybe, but not much. There really is a big question whether it will do much of anything, but as better atmospheric lift arrives after midnight and into Friday, we may well eventually see some light precipitation. Temperatures are cold enough that any little bit can make things slick, but at this point it looks like the chances of a major or even significant winter storm are closer to none than to slim.

Following national radar has been interesting today, as one blob of precipitation has been staying north of us and another has been staying south. This split reflects two different disturbances, one in the northern branch of the jet stream, the other in the southern branch. If the jet stream pattern were a little different and these two disturbances could have joined forces, we would be looking at a monster storm somewhere in the eastern half of the U.S. now. (Not necessarily a snowstorm for us ... it could have well traveled west of us and made things even warmer with rain.) But as it is, they are imperfectly linked.

This split in precipitation we've been seeing was not entirely unexpected -- forecast models have been picking up on it for days. The question is whether or not overnight or on Friday a low moving east will drag more of the southern piece of moisture northward toward us. The two precipitation areas are connected now by a thin band near the Mississippi River -- we'll probably get that, if nothing else, and it will probably grow. But if we are going to get anything beyond an inch of snow/sleet and a thin glaze, the southern precipitation area will have to become more involved. Some of our moisture may well be getting eaten up by the thunderstorms along the Gulf of Mexico.

As of now, it still looks some wintry precipitation will move into our area late tonight, probably after 10 p.m., but it's looking like a rather light event at this point unless something changes in the next several hours.

With the expectation that most of the area will see enough of a mix that the freezing rain portion of the event will not collect more than 1/4 inch, the National Weather Service in Blacksburg has gone the route of issuing a winter weather advisory for most counties in Southwest Virginia, including the Roanoke and New River valleys. Floyd, Carroll and Patrick counties, and a few more in northwest North Carolina, are under a winter storm watch for the possibility of getting 1/4 inch or more of ice on top of whatever snow and sleet falls to begin tonight's winter weather event.

While it seems likely that wintry precipitation will occur across the area tonight, the amounts are the tricky part, especially weighing how much falls as snow/sleet and how much ends up as freezing rain, which all depends on how deep the cold air is being pushed from the north and how fast warm, moist air from the south can erode that colder air in the upper atmosphere.

The local forecasters in Blacksburg, as this map shows, believe that counties along the Blue Ridge south of Roanoke have the best chance at getting more ice, owing to some southeast winds banking moisture against the eastern slopes of the mountains. But national forecasters at the Hydrometeorological Prediction Center favor areas from Roanoke northward having a better chance of getting 1/4 inch of ice or more, as this map shows.

There is a question about the amount of moisture that will be available. This morning's radar shows the precipitation splitting up north and south, looking as if it might go on either side of us. I would expect that to fill in later today, as the split is primarily the result of separate pieces of energy in the northern and southern branches of the jet stream that will eventually become better aligned, though not perfectly. The moisture from the south is what is expected to spread northward, but thunderstorms down there could reduce the moisture flow. That's always an issue to watch when moisture is moving in from the Gulf. The flip side is that if fewer thunderstorms fire, we could see a surge in moisture that could push us into winter storm warning territory.

My early guess: About an inch of snow/sleet on the front end in Roanoke with a quarter-inch of ice, pretty similar in New River with maybe a little more snow/sleet accumulation, just enough to get us on the edge of significant ice storm potential. I'm skeptical of any forecast or computer model that warms us above freezing before late afternoon on Friday ... the wedge of cold air from the northeast should hold tight and ice/snow accumulation will keep the air chilled near the surface at least a few hours longer than projected.

Forecasters are facing a complicated storm system with a tricky forecast tonight and Friday. What seems very likely is that significant moisture will move over below-freezing air at the surface. Wintry precipitation is all but absolutely certain, and it could be quite troublesome -- at least a nuisance for travelers, but possibly a problem for trees and power lines if only a little more occurs than is forecast. That's not what we want to hear after the Feb. 10 windstorm and Feb. 1 ice storm power outages.

One of the hardest things in winter forecast is projecting ice accretion. It's not as simple as saying "we're going to get a quarter-inch of rain, therefore we'll get a quarter-inch of ice."

* The first complication is that much of the early precipitation may fall as snow or, especially, sleet. The more falls as snow and sleet, the less will fall as freezing rain, and therefore the less ice can accumulate.

* Secondly, more of the rain will freeze if temperatures are a few degrees below freezing than will if it's very near freezing. The same level of freezing rain at 25 degrees is much more of a problem than it is at 32.

* Temperatures aloft matter. If the air is very warm above the surface, the rain falling through it takes a longer to freeze at the surface than it would if it were falling through air just a few degrees above freezing.

* How hard the rain falls also matters. A heavy rain may run off more and not freeze on objects as readily, whereas a steady, light to moderate rain runs off less and therefore has more of a chance to freeze on trees and power lines.

Weighing all of those factors and many more as of late Wednesday night, forecasters were expecting up to two-tenths of an inch of ice on top of a layer of an inch or so of snow and sleet. That forecast could change many times today. If the National Weather Service believes there is a reasonable chance 1/4 inch or more of ice could accumulate, a winter storm watch or ice storm warning may go into effect.

Expectations could change many times as the storm takes shape today. For the latest, click on the National Weather Service-Blacksburg's "Current Event" page.

The National Weather Service in Blacksburg has, for the time being, declined to issue winter storm watches for the system headed our way Thursday night into Friday. It takes an expectation of 4 inches of snow or 1/4 inch of ice to trigger watches, and right now, the fast speed of the system may keep precipitation amounts light. Also, we may see so much mixing of snow, sleet and freezing rain that the ice won't get to 1/4 inch by itself (very little chance the snow would get to 4 inches under any circumstances -- an inch, maybe). So for now, it looks like a messy, mucky winter storm that could be a nuisance but not a particularly severe winter storm. New data could change expectations. Click here for the latest on advisories and warnings from the weather service office in Blacksburg.

Meanwhile, snow continuing to fall in parts of Alleghany and Bath counties could accumulate a few inches, hence the snow advisories. Cold, windy weather will spread across the area later tonight, and those winds could carry a few snowflakes, but significant snow is not expected in most places tonight.

Hopefully for watchers of the lunar eclipse, the clouds will at least become broken in the gusty winds by 10 p.m.

The low passing through our area has drawn enough warm air northward to push our temperature in Roanoke to 51 degrees at 2 p.m.... yet just 90 minutes drive northwest there is heavy snow and 28 degrees at Hot Springs. A snow advisory is out for Alleghany and Bath counties westward into West Virginia.

It's going to get weirder as cold air arrives across the area tonight and temperatures plunge across the area into the teens and low 20s This new Arctic air will set up the likelihood of a signficant winter weather event on Thursday night and Friday, with snow, sleet and ice all possible. I will be interested to see if the National Weather Service flies winter storm watches. We should know in the next couple of hours.

Some of you saw a few snow showers today with a passing disturbance, and a stronger one passing just north may bring some showers of snow and rain to the area on Wednesday.

The bigger issue, though, is the potential for a winter storm in the Thursday night-Friday timeframe as disturbances in both the northern and southern branches of the jet stream move near the area. The Hydrometeorological Prediction Center is already calling for a moderate risk of substantial ice for our area on Thursday night and Friday. It's unusual to be in a moderate risk still 3 days out. That signals a pretty high degree of confidence by forecasters that wintry weather will affect the area, but it also allows 3 days time for things to change. The current thinking is that precipitation will start as snow and then change to sleet and eventually freezing rain. It looks as if cold air will be pushed down into our area by high pressure to the north as the precipitation moves in.

Winter has not let go of its grip on the area just yet.

Before we can really begin to pick apart the series of disturbances from Wednesday to Saturday and what they could bring in terms of winter weather, a few stronger gusts of wind combined with dry conditions could easily spread fires today. As a result, the National Weather Service has posted a red flag warning for much of the area from Roanoke south and east. A red flag warning signifies an enhanced fire risk. This should not be a repeat of Feb. 10, as the lower atmospheric winds are not as powerful as they were that day. But we could see some gusts topping 40 mph during the day.

The first threat of snow comes Wednesday with an Alberta clipper diving southeast. If you've followed weather for a while around here, you know that most Alberta clippers do not produce accumulating snow for our area, but once in a while, one will. Additional disturbances pose a snow/ice risk through the weekend, with gradually warming temperatures. It remains a tricky forecast.

Though we've started out warm today, a cold front will soon be moving through, and over the next couple of days we will be sinking back to cold wintry temperatures. The tricky part of all this comes in the Wednesday to Saturday time frame when a series of disturbances will be moving through, as well as a warm front lifting northward. The timing and placement of each disturbance, the thickness of the cold air and the speed of the warm front moving north will all come into play into determining precipitation chances. On one extreme, there could be off and on snow and ice throughout that time period. On the other extreme, the cold air could suppress the storms so much that little precipitation can occur until the warm front moves north, when it would only be rain for the weekend. Something in between those scenarios is most likely. Stay tuned.

I think we're going to escape the freezing rain with Sunday's system. It's just not very cold and there's nothing to hold the cold air in place when the rain arrives, unlike last Tuesday night. As for rain amounts, looks like another decent but not especially soaking rain, as seen by the Hydrometeorological Prediction Center maps for the 24-hour period ending early Sunday evening and for the next 24 hours ending Monday evening. Add 'em up, and it might be half an inch. It will be helpful, but not a cure for the drought or even the lingering fires.

As for wintry precipitation, we are going to have to keep an eye on the late week period, Wednesday-Friday or so. We may well see high pressure in southeast Canada forcing cold air southward as a moist storm moves in from the west. We've got a few days to watch that as it develops.