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So far this winter, we have gone through a four-week period of Arctic air from mid November to mid December and now one of more than two weeks without once mixing a large amount of moisture with the cold air. Our only winter weather events in Southwest Virginia so far have been (1) upslope-snow showers, moisture squeezed out by northwest winds being lifted over the mountains; (2) weak disturbances triggering light precipitation out of limited moisture, with only a few local areas getting more than an inch or two of snow; and (3) in one case, some significant icing in very localized areas while most places got rain with above-freezing temperatures. We have not had anything even close to an areawide winter storm yet, ice or snow.

The face of the 2008-09 winter is about to change this week. Probably.

Abundant Gulf of Mexico and Pacific moisture will be hurled over an Arctic air mass at the surface as a series of disturbances move eastward on a newly resurgent southern branch of the jet stream. A mix of freezing rain, sleet and snow will likely spread across Southwest Virginia Tuesday, Tuesday night into Wednesday.

This storm will probably not satisfy those of you dreaming of a pile of fluffy white snow. It's possible there could be a considerable period of time when mainly snow falls, maybe several hours, and possibly multiple inches, though 1 or 2 would be more likely.: The Hydrometeorological Prediction Center is extending its Day 3 potential for 4-plus inches of snow into our area, and keep in mind this map cuts off early Tuesday evening before the bulk of the moisture will likely arrive. But, almost inevitably, whatever falls this week as warm, moist air fills the atmosphere above a  cold dome at the surface will eventually become freezing rain and sleet (and later this week, plain ol' rain). The same HPC maps for ice show a big area to our southwest through Tuesday evening ... more moisture that will arrive after this forecast period ends.

A muck storm appears likely. It's too early to assign amounts, or even narrow down what type of precipitation falls at what time. Several things could still change the forecast. Deeper cold air holding on a little longer could lead to more snow; more shallow colder air could lead to a brief period of ice changing to rain. Judging by the position of the jet stream and the Arctic air, it's would be very hard to completely miss the precipitation this week, though the amounts are very much in question. Some models favor light amounts, others point to heavy amounts.

And even if we knew the amounts exactly right now, what type of precipitation falls will vary the impact a lot. A half-inch of liquid as a couple of inches of snow, an inch of sleet and some light glazing would be a nuisance, but not a major problem. The same amount entirely as freezing rain would bring trees and power lines down and could make roads extremely treacherous.

Many details remain to be ironed out. Though nothing can ever be said to be certain about any weather event still 2-3 days out, this is the first time this entire season when the odds favor a significant, widespread winter storm for our region rather than lean against them.

Roanoke's high of 64 today was the warmest so far in January and only the second time it has topped 60 -- a high of 62 on Jan. 5 was the last.  The last four Januarys have had anywhere from 5 to 9 days above 60, and most have had days above 70 as well. This January may not have another 60-degree day, though it's not outside the realm of possibility very late next week, depending on how much warm, moist air floods in with the upcoming pattern change.

Roanoke's low today was 35, the first day with an above-freezing low temperature since Jan. 11.  After a low of 19, Blacksburg recovered to a high of 57, its warmest day so far in January.

This winter respite is over on Saturday, though, as a new Arctic front pushes through the area. Temperatures will probably not get out of the 40s on Saturday, and may even fall back into the 30s during the afternoon, with teens and low 20s by Sunday morning. This cold air mass is setting the stage for the very dicey weather situation developing in the Tuesday-Thursday period next week. We'll be talking about that some more in the days ahead.

A week ago Friday, the morning started at 8 degrees in Roanoke and 1 degree in Blacksburg. This Friday, it could well hit 60 in Roanoke and may get close in Blacksburg. Mild air will be briefly surging before the cold air is renewed over the weekend ... though it doesn't look to be nearly as cold as last week's Arctic surge. A noticable southern branch of the jet stream, carrying moisture and energy, is expected to develop next week, and it will just be a matter of its timing and placement relative to the cold air mass regarding how much, if any, wintry precipitation we get.

David Sobotta, who alternates between living on a mountain overlooking the Roanoke Valley and living on the Outer Banks of North Carolina (check out his blog "View From the Mountain"), sent in this photo of a white beach at Emerald Isle, N.C. ... not white sand, but snow. He said he got less than an inch where he was, but 3-7 inches was common inland, as this map shows. The main reason North Carolina got the bigger snow, rather than Southwest Virginia, was because the "trough axis", the center line of the jet stream dip that brought the frigid air, was a little too far east. Disturbances diving through the jet stream bunch together near the base of the trough, where upper-level winds swing from northwesterly to westerly and then more southwesterly, allowing them to interact and become a larger storm. The southwesterly flow aloft just east of the trough axis also allows for moisture to be swept in aloft over the cold surface. The result was that just enough of a storm system wound up near the Carolina coast for a fairly large snow event to occur over central and eastern North Carolina. Some areas of Southwest Virginia to the southwest and west of Roanoke caught a few inches of snow as one of the disturbances dived through Sunday night and early Monday, and the upslope effect enhanced amounts as well in mountainous areas. It was just a case where the elements were just a little off for a widespread winter storm across Southwest Virginia. We really haven't had one of those yet this season as we enter the final 10 days of January.

It will slowly get milder this week, and we might even push into the 50s by Friday. But then, a reinforcing shot of Arctic air will arrive, not as severe as last week's, but enough to chill us back to sub-freezing weather for a few days. Late in the weekend or early next week, there is significant threat of an "overrunning" scenario developing, with moisture from the Gulf of Mexico overtopping cold air at the surface as a new storm system -- an actual "southern stream" system, the bread-and-butter of winter precipitation but rare the past couple of years -- approaches. The depth of that cold air will determine if it's snow, sleet, freezing rain, a cold rain, or some crazy mix of all that. But that's way too far out to be getting into details, or even to say it will definitely happen. Beyond some light snow in Southside today on the back side of eastern North Caorlina's winter storm, and some snow showers and flurries coming over the mountains on upslope flow, this disorganized round of winter precipitation is winding down.

You may wake up to at least a dusting of snow in the Roanoke Valley; you may wake up to more than that if you are south or east of the valley. The back edge of an area of snow scraped the Roanoke Valley shortly after 1 a.m., wih heavier snow to the south and east. I captured a series of radar grabs below to illustrate the progress of the area of precipitation representing the back edge of the winter storm affecting the Carolinas.

11:45 p.m.

12:20 a.m.

1:20 a.m.

Snow is expected over most of North Carolina tonight and Tuesday as the last disturbances in the series tango together enough for a moderately strong low pressure system to form. Much of central and eastern North Carolina is under a winter storm warning for the threat of several inches of snow, likely in the 3-5 inch range, mostly. Virginia's Hampton Roads area may get in the action, too. Folks closer to the Virginia-North Carolina border south of Roanoke who got some snow overnight and today will probably get a little more tonight and early Tuesday.

I know, this is a bitter pill to swallow for Roanoke Valley snow fans, and others in Southwest Virginia who mostly missed last night's light to moderate snow and have been missing throughout the winter. Missing a storm that goes north is one thing ... it's supposed to snow more to the north. Missing one of the south is harder to take. For those who hate snow ... you're living well so far this winter.

Unless ... unless ... the snow shield around the developing low manages to push farther north overnight. There is something of a northward component to radar echoes in northwestern North Carolina presently, and at least one recent model run does push the northern edge of the snow shield roughly to the Blacksburg-Roanoke-Lynchburg corridor of U.S. 460.  Such a scenario that would expand the snow shield farther north, while unlikely, is not ridiculous, and that's why the weather service is still holding a 40 percent chance of snow overnight.  It's a long shot we could get anything more than an inch, but this is a weird storm in a weird winter, so who knows.

Latest National Weather Service-Blacksburg radar

It's a disorganized storm system, to be sure, but a lot of those disorganized pieces appear to be taking aim on Southwest Virginia. This radar shot from a little after midnight shows areas of snow strung out from our backyard all the way across Kentucky into Illinois. So, in fits and starts overnight and into Monday, as these patches of snow move over, I would not be surprised if almost everybody got a white ground out of this, and probably 1-2 inches for many, with even more in the favored areas of the mountains to the west that will get upslope enhancement. A series of weak disturbances are moving through, but these disturbances are squeezing out enough moisture for patches of snow -- light to moderate, mostly, with a few heavier bursts. So it's not the major winter storm it could have been if all this had come together and been more organized, but it could be at least be a notable enough snow to prove that it still can snow decently in Southwest Virginia.

UPDATE 1:30 AM: Just in case you missed the little snow squall that turned things white in much of the Roanoke Valley between 1 and 1:30 a.m. here's a radar grab from about 1:20 a.m. showing the compact but vigorous cell over Roanoke. END UPDATE

Latest National Weather Service radar

Latest warnings and advisories from National Weather Service-Blacksburg

The next disturbance in the series may trigger a weak surface low pressure system near us on Monday. As a result, there will be a heightened chance of light snow in the area ... the weather service is even going so far as to say snow is likely on Monday, even in Roanoke, though light with no more than an inch. Meanwhile, overnight light snow to our west, mainly from upslope effect, is enough to warrant a winter weather advisory for almost all counties from Giles and Wythe county westward. Another disturbance will approach the reason Tuesday, which may enhance the light snow a bit once again.

Click here for the latest from the National Weather Service in Blacksburg

So, the little pieces of atmospheric energy are still not getting together for a bigger storm system, but each individual one may be enough to make things a little wintry, just like this morning's made things icy in the New River Valley and points west.

Moisture returning on south winds has warmed the air aloft on top of the cold layer at the surface. As a result, spotty freezing rain and drizzle have broken out, and with road surfaces extremely cold from the frigid weather we've had, even a small amount of liquid could freeze into ice very quickly. So a freezing rain advisory is out to the west of Roanoke, including the New River Valley, until noon. Be extremely careful if you are traveling in these areas, and anywhere else if you note precipitation falling.