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One location near Wytheville reported 1 1/2 inches of snow Wednesday morning, but spotty amounts elsewhere were generally less than 1 inch. Even at that, the system may have maximized its snow potential for Southwest Virginia, as it arrived early enough in the day so that temperatures had not already climbed well above freezing. So with a good amount of evaporational cooling occuring as the snow fell into drier air, it cooled the atmosphere enough that flakes even reached the surface in much of the Roanoke Valley, and accumulated in grass and on exposed objects at several locations around Southwest Virginia. A little more than we were anticipating, but still very little in an almost non-existent winter.

We have one punch of Arctic air pushing in tonight, and that will take us to near normal temperatures (40s highs, 20s lows) for Thursday. As has been the case all winter, we quickly rebound back into the 50s by Friday afternoon, only to see a much stronger punch of Arctic air push into the region Friday night and Saturday, as shown by all these blue and purple colors pouring out of Canada on today’s European model. A round of light snow is possible in much of Southwest Virginia late Friday night and early Saturday as a upper-level disturbance pushes through. There may even be a touch of overruning moisture drawn up into the system from the western Gulf of Mexico. Some light accumulations will again be possible, the depth and extent of which should become at least a little more apparent by Friday. The big story this weekend will be the cold, with widespread low sin the teens by Sunday morning and highs in the 20s and 30s both Saturday and Sunday.

True to form, things quickly warm up next week, as there is  no strong high downstream in the north Atlantic  to hold in the cold air, and   a storm system is expected to take a path to our west, drawing up milder air from the Gulf of Mexico. Another heartbreaker for snow fans on the week of Valentine’s Day, another heartwarming tale in the winter of 2011-12 for snow dislikers.

UPDATE 8:15 AM: A band of mixed rain and snow showers has entered the region and may move across the New River Valley and possibly into the Roanoke Valley in the next couple of hours, though it may dry up some headed easward. (Latest radar linked here.) Additional precipitation is also possible later today with another band currently in Kentucky. Little accumulation is expected with daytime temperatures moving above freezing, but heavier bands could leave a brief dusting, especially this morning when it is close to freezing. An inch or two is possible along and north of the I-64 corridor later today, and perhaps in some other areas above 3,000 feet. END UPDATE

There may actually be some snowflakes in the air in some parts of Southwest Virginia by Wednesday afternoon and evening as a weak area of low-pressure zips eastward. Air temperatures near the surface are marginal, ground temperatures are unusually warm for February, there’s not much moisture to work with and the best atmospheric dynamics for heavier precipitation are passing to the north, so don’t expect much in the way of accumulation, especially south of Interstate 64. With temperatures rising into the 40s before any showers arrive, precipitation is likely to start as rain, and may stay as rain in lower elevations from Roanoke south and east. But the air aloft is cold enough to support snow, and if it can overcome the warmer “boundary layer,” or temperatures in the lower part of the atmosphere, snow will start reaching the surface, starting in the higher elevations and working down.  If moderate to locally heavy snow can sustain for several minutes to an hour in any location, it’s possible that a slushy coating on grass could occur, but the best chance of seeing accumulating snow (an inch or two) lies in the higher elevations of eastern West Virginia (possibly edging into the highest ridges of western Virginia) and through the northern half of Virginia. Even in those locations it may be spotty. Be aware of some slushy spots on roads if traveling north on I-81 Wednesday afternoon and evening.

Behind the low and cold front, temperatures will drop about 5-10 degrees for Thursday, then rebound again into the upper 40s-mid 50s for highs Friday before another stronger cold front pushes through for the weekend.

With highs in the mid to upper 50s for Roanoke and points south and east, possibly touching 60 in a  few spots, Tuesday may well be the warmest day we’ll see in the next week, perhaps 10 days or more. By Wednesday, we do have a weak area of low pressure that will be advancing eastward along with the leading edge of a cold front. This low pressure will trigger some showers on Wednesday — some of those showers could even be snow showers, especially in the higher elevations along the Virginia-West Virginia border. The mountains of West Virginia may get a couple of inches of snow, perhaps some light accumulations even in the higher elevations of the Alleghany Highlands of Virginia (think west of I-81 and north of I-64). While some snowflakes may eventually work into the New River Valley by late Wednesday, surface temperatures will likely preclude much accumulation.

Wednesday’s cold front will knock temperatures back 5-10 degrees for Thursday. It is a precursor to a much stronger Arctic front due to arrive by the weekend, when temperatures may not climb out of the 30s west of Roanoke.

There are still indications a storm system may form in the central or eastern Gulf of Mexico late in the week, though at this time, it appears likely to track over Florida and then northeast into the open Atlantic. There is still some chance  that will change, and it is also possible weaker disturbances or overrunning moisture could provide some chance of wintry precipitation during the weekend and early next week. On the whole, though, the Arctic air mass settling in looks to be a mostly dry one, as these kind of air masses often are. It will feel much more like winter by Sunday, though.

Temperatures are likely to be below freezing on Monday morning with some fog developing, and that could lead to patchy ice as fog freezes on some roadways, particularly bridges and overpasses. Be aware of this traveling in the morning. Highs will rebound into upper 40s to low 50s — close to where they’ll likely be any day this coming work week that has sufficient sunshine, maybe a bit higher on Tuesday.

The Hydrometeorological Prediction Center, in looking at the Wednesday to Saturday period this week, issued this analysis (one brief explainer by me, in parentheses) in its Extended Forecast Discussion that certainly rings true this winter:

CANADA IS COOLED TREMENDOUSLY VIA THE CROSS-POLAR FLOW INTO THE COUNTRY…BUT THE ARCTIC AIR HAS NO MECHANISM BY WHICH TO INFILTRATE THE UNITED STATES TO ANY APPRECIABLE DEGREE.  THE FLOW IS ALSO NOT CONDUCIVE TO SIGNIFICANT CYCLOGENESIS (i.e. low-pressure development)…SO EXPECT NO SPRAWLING AREAS OF ORGANIZED PRECIPITATION

True to form,  most current forecast modeling has rather weak low-pressure crossing the Gulf of Mexico and staying south of our region, crossing Florida and heading out to sea. It does have cold fronts originating from a polar vortex over Hudson Bay moving through intermittently through the week, with perhaps the strongest toward the weekend. Still, without a large, powerful low moving up the East Coast or high pressure forming over Greenland, as the HPC says, there is no mechanism to move a large amount of that Arctic air south. We will likely gradually stair-step down to near normal cold — 40s highs, 20s lows — by the weekend and early next week. It may even end up being colder than that for 2 or 3 days.

As for snow chances — there is still some chance the low in the Gulf will end up farther north. There is also a period of time when southwesterly flow aloft may develop atop colder air moving southward, and upper-level energy hanging back in Mexico may kick out a few disturbances in that flow. All of this is nickel-and-dime kinda stuff compared to the phasing of jet stream energy we discussed as a possibility Sunday that looks even less likely now. It’s certainly not a surprise this winter.

We’ll continue to monitor this week’s system and the north Atlantic for a change there, and also watch to see if any disturbances moving in from the west will be timed right and tap enough moisure to intersect cold air shots.

Sunday will start damp and gray, again, but we may see some sun by afternoon, though it’s likely to be chilly with highs in the 40s. There is a weak disturbance moving through Sunday night and early Monday that has some chance to trigger a few rain or snow showers, but it seems to be a minor deal, for now. The week ahead will be another fairly mild and dry week, with highs in the 40s and 50s, lows mostly in the 30s, some up-and-downing as a few fronts pass through.

Let’s set the stage for what is likely to become the big weather talker for this week. For the first time this winter, there are some pieces on the board that, if they connect in the right timing, might — MIGHT — supply a setup for a potential winter storm over the eastern U.S. by the weekend. I’ve pulled out an image from a Global Forecast System model run today depicting the pattern as it’s expected to look on Thursday, linked here. Circled are some areas of strong atmospheric energy riding two different branches of the jet stream. This is a fairly common development in most winters — we typically end up watching maybe half a dozen similar setups in most winters, most of which DO NOT produce large winter storms for us – but it hasn’t happened at all this winter. If the energy in Canada and that over Mexico’s Baja California — many models stall it there for days– can “phase” or combine forces somewhere near the Gulf Coast, a powerful low-pressure system could develop and ride up the East Coast, throwing moisture inland as it also pulls cold air southward. If they can’t, a variety of lesser situations could happen, including a weakened low scooting almost due east across the Gulf and missing us to the south, zooming out to sea. Whether this develops depends on a lot of factors across the northern Hemisphere. The position of a polar vortex — marked “PV” on the map, essentially a giant swirl of extremely cold air — over Hudson Bay is very favorable for such a storm to develop (if its location is in fact projected correctly), and if nothing else, this polar vortex will likely supply at least a brief shot of some cold to very cold air. One huge question mark in this situation is the North Atlantic Oscillation, which has been in its positive phase for weeks. There are some signals that it may make a quick shift to negative, which would supply a blocking high over Greenland, increasing the probability of some legitimately wintry cold air arriving and even sticking around a bit for mid to late month, plus tilting the odds a little more in favor of this or possibly subsequent winter storms developing.

There are so many things that can happen that will NOT result in a winter storm in our region that skepticism remains warranted. But it is something for us to monitor this week to see how it develops. One thing to keep in mind now: Often, folks like to post temperature forecasts from various weather sites for days in advance and say something to effect that “XYZ says it will be in the 50s, so there can’t be a winter storm.” If this storm system develops as it might, or if the pattern changes significantly this week, ALL of that will be in flux, possibly even for just 3-5 days out. If this winter storm doesn’t develop for us and there’s little evidence of a change in the North Atlantic by mid-month, it’s very possible that we’ll only get a quick, modified shot of cold and continue on our merry way with this mild and nearly snowless winter.

Are snow lovers due to catch lightning in a bottle after so many weeks of non-winter, or is this simply a winter for those who love the warmth and hate snow to continue to enjoy? It could all be decided in the next 7-10 days.

UPDATE 8:40 AM, 2/4: As National Weather Service radar (linked here) shows, showers are already moving into parts of Southwest Virginia this morning. Area that get showers today may be held well below projected highs in the upper 40s and low 50s, so chilly dampness may set in early for many. END UPDATE

UPDATE MIDNIGHT 2/3: No major changes in the below. It does appear the frozen precipitation is likely to stay north of I-64 — likely well north of I-64 — with any minor chance of snowflakes or freezing drizzle coming Sunday as the precipitation is ending. No big wintry deal from this one — par for the course this winter. END UPDATE

I could wake a lot of folks out of a mid-winter slumber with this headline: “PLAINS BLIZZARD HEADED FOR SOUTHWEST VIRGINIA.” And it would be accurate …  sort of. The strong upper-air disturbance responsible for the blizzard burying Denver and points east is headed our general direction this weekend, but alas, it will not be as potent or as moist when it arrives here, nor will it be entering the deep cold air it is ingesting in the Plains states. But that said — this system will encounter some cold air building southward this weekend. A disturbance diving out of the Great Lakes will pull some cold air down behind it, and a weak wedge or cold-air damming effect will bank that cold air against the mountains as it spreads southward. It may become cold enough for some freezing drizzle, sleet or even snow for a time Saturday night and early Sunday over much of the northern half of Virginia (I-64 and north in western Virginia), with some chance it works a little farther south than that into our region (the NAM model for Sunday morning, inset at left, shows the freezing line at roughly a mile up splitting our region). It’s  reminscent of the setup two weeks ago that led to patchy ice over a weekend of chilly dampness. Moisture will likely be limited, though, as the Great Lakes disturbance works to weaken the system coming out of the Plains. At the least, it’s going to make for a raw weekend, with off and on showers, some fog and low clouds, and temperatures hanging in the 30s and 40s.

Friday will be another relatively mild day, with highs well into the 50s (wouldn’t be surprised to see a few readings in the 60s for Roanoke south and east) and even Saturday during the daytime won’t be that cold, possibly some 50s again before the rain arrives and the wedge of colder air sets in late in the day.

UPDATE 8:40 AM: Punxsutawney Phil saw his shadow this morning — meaning six more weeks of colder weather always being two more weeks away. END UPDATE

It looks like we may squeeze out another afternoon in the 60s on Thursday. A cold front will pass in the morning, but the air mass behind it is of Pacific origin, not Arctic, so it will only be a little cooler, and even that won’t be felt til night. Because it is pushing through in the morning, it will help clear the skies, allowing plentiful sunshine by afternoon for temperatures to push upward. The front’s effects will be Friday will be to knock us back a little, with highs in the 50s and lows in the upper 20s to mid 30s — still above-normal for early February. A weekend storm system may bring wintry precipitation as close as the Pennsylvania-Maryland line or so, but looks to be on a trajectory too far north, with little or no cold-air damming, to allow any colder air farther south. So likely more well-above-freezing rain showers in our neck of the woods, like tonight.

Looking out at the big picture — two of three major climate indexes we typically look at for signs of a colder pattern have switched solidly in that direction. The Arctic Oscillation is in a negative phase (note the blue “icicles” hanging below the 0 line) — cold air being allowed to push out from the North Pole, rather than being held in tight — and the Pacific-North America pattern is moving into a strongly positive phase (note the bars above the 0 line), which will bank high pressure into the western half of North America, rather than hanging it over the East as has happened much of this winter. That will allow cold air masses to slide more easily southward from Canada into the East. The third index, however, remains stuck in a non-wintry mode. The North Atlantic Oscillation doesn’t yet show signs of budging from its positive phase, which prevents high pressure from forming over Greenland to block the jet stream and lock it in a southerly-dipping mode that favors prolonged Arctic air masses and potential winter storm tracks in the East. Research has shown that about 80 percent of the time, the Arctic Oscillation and North Atlantic Oscillation end up going into a negative phase concurrently, so it may yet happen that the NAO follows the AO. If it does, depending somewhat on the exact placement of the blocking high in the northern Atlantic, we might get a really cold period with significant snow potential in the next few weeks. As it stands now, we are likely to have colder weather than we’ve seen lately — emphasizing the “er” part, colder than we’ve seen recently, not necessarily very cold — and a somewhat heightened chance of possible wintry precipitation episodes in the next couple of weeks. But without the blocking high over Greenland that comes with a negative phase of the NAO, the cold air surges won’t lock in, and the pattern as a whole will probably return to above normal temperatures later in the month.

It’s not too much hyperbole to say that the game is on the line for winter 2011-12 between now and Valentine’s Day or so. The way the pattern sets up during this period will likely determine if winter has a chance to make a late run of cold and snow, or whether it will probably fizzle out with barely a whimper. Even with a milder pattern a fluke wet snow is always possible into March or even April, but I think by Valentine’s Day we’ll pretty well know whether this has a strong chance to be the least snowy winter in history for Roanoke or if there is a fourth-quarter rally for snow fans.

For now, expect gradually cooling temperatures over the weekend and early next week before a sharp Arctic front arrives late Tuesday or early Wednesday with significantly colder air.

UPDATE 11 PM, 1/31: Short update tonight. Wednesday will be a similarly mild day to Tuesday, with more clouds and showers toward the afternoon. This is the beginning of the storm system that will bring a Pacific front through by Thursday morning that will knock a few degrees off the temperatures. After Roanoke tied its Jan. 31 record high of 68 on Tuesday, record Feb. 1 highs of 74 for Roanoke (1989) and 73 for Blacksburg (2002) will not be challenged. More showers with a stronger low and front for the weekend, with the storm system likely taking too far of a northerly track and not enough cold-air damming being present for a wintry weather risk this weekend. Signals still point to a gradual step-down to near-normal February temperatures, and perhaps a somewhat greater  risk of wintry precipitation with a possible storm system near Feb. 10 — still too far out for many details. END UPDATE

UPDATE 11 AM: CORRECTION to information below: Blacksburg’s record high for Jan. 31 is 73 set in 2002 — not 63 as I reported below. Some discrepancy between databases on this, but I checked the NWS-Blacksburg  report of 73 against that month’s records and it is accurate. We’ll go with that. Blacksburg will NOT tie or set a record today. END UPDATE

It’s the last day of January, and there are red colors on a map of Virginia illustrating temperatures. That’s not the way it’s supposed to be. The inset map at left is from the map of projected temperatures for 4 p.m. today from the National Weather Service, as of late Monday night. As the legend at the top tells, the orange and red colors depict highs in the 60s. (You can find those maps linked here if you want to check to see if anything has changed.) There is a solid chance that Roanoke’s Jan. 31 record high of 68 — set in 1974 and 1916 — and Blacksburg’s Jan. 31 record high of 63 set in 2011 will be challenged today. My early guess is that Roanoke comes in just a bit short while Blacksburg ties its record — just a guess. Temperatures may actually be a little higher on Wednesday, but the bars for record highs are much higher for Feb. 1 — 74 for Roanoke (1989) and 73 for Blacksburg (2002) — and probably won’t be challenged.

Increasing showers and the passage of a Pacific cold front — cool front, really, not cold — will curtail the warmth in the latter half of the week. 50s for highs will be common.

Whether cold-air damming will be strong enough over the weekend and early next week for a storm system to bring ice, snow or mix instead of just rain is  doubtful, but still possible. Next week looks to mark a rather gradual shift from the mild to warm weather pattern we’ve experienced for weeks to something colder. We’ll keep an eye on the horizon for possible snow chances — some indication the Feb. 10-11 period may have a shot, but that’s just too far out to take too seriously yet.

UPDATE 8:45 PM, 1/29: No big changes to what I have below. Just three quick points. (1) 70 degrees may not be out of the question for Roanoke and points south and east on Tuesday and Wednesday. 60s look likely just about everywhere on one or both of those days below 3,000 feet in elevation.  (2) Note Sunday night’s 8-14-day Climate Prediction Center temperature map (linked here) and a return to blue colors, indication an enhanced chance of BELOW normal temperatures during that timeframe (Feb. 6-12).  (3) Yes, there is some potential for moisture and cold air to mingle by late in the weekend and early next week. There are way too many details in flux to say much more than that now. Let’s see how this looks at midweek before getting into any kind of “potential winter storm” mindset. For now, let’s just say colder weather looks very likely to set in after this week’s warmup, and that fact by itself increases snow potential looking down the road. END UPDATE

After a brief cold front-induced break Sunday and Monday (and not a huge on at that — Roanoke may not get below 30 and see highs in the low 50s, while 40s highs/20s lows will be about the coldest it gets anywhere in Southwest Virginia) — the mild winter weather will return in full force for Tuesday and Wednesday, with highs in the 60s possible in much of the region. Some showers and a new cold front will interrupt the warmup once again by late week. so again, we will likely be held short of the 70-degree mark. Beyond this week, the core of the warm air underneath high pressure appears likely to shift to the western United States. This is significant for us because, being east of the warm high and its clockwise circulation, we will be more in line for some deeper shots of cold air. This is referred to as the positive phase of the Pacific-North American pattern, when high pressure dominates near the West Coast and the jet stream dips southward in the East. Combined with a shift in the Arctic Oscillation from a strongly positive pattern to somewhat negative, which will allow more cold air to migrate southward away from the North Pole, the potential will be there for some pretty stiff bouts of cold air perhaps as early as next weekend. Whether any of this cold air interacts with moisture remains to be seen. Some forecast models show high pressure in the Northeast nosing cold air southward along the eastern slopes of the Appalachians next weekend just as mositure arrives, a familiar “cold-air damming” setup that could yield ice or snow if it comes to fruition. Whether it will or not is doubtful from this range, but it does reflect the growing possibility that cold air will be able to slide father south into the East than we’ve seen most of this winter. The North Atlantic Oscillation, however, remains in its positive phase, reflecting the lack of high pressure near Greenland to obstruct the jet stream, and that means these cold air shots will not get locked in for weeks, but will move out rather quickly. They may get more quickly replaced, however,  because of the high pressure building in the West.

This does not reflect a really dramatic pattern change to a winter wonderland that so many snow fans have sought, but more of a gradual drift toward something looking more “normal” for winter as we move into February.

Last weekend looked like it would be mild a few days before, but ended up cold and a little icy. This weekend looked like it would be cold a few days ago, but will end up mild — at least on Saturday afternoon. Despite the windy cold front that blew through early Friday, 60 is possible for Saturday in Roanoke. High temperaures in the 50s to low 60s will be widespread across our region, as downsloping westerly to southwesterly winds and sunshine combine to boost temperatures ahead of a reinforcing cold front that will arrive Saturday evening. Yet another reinforcing shot of cold air from Canada will arrive late Sunday after a not-so-cold day in the mid 40s to low 50s. We will finally have seasonably cold weather for Monday — highs in the 40s, lows in the 20s — before the temperature warms back up again for Tuesday and Wednesday, possibly again reaching the 60-degree mark.

You may see some discussion about a possible winter storm for late next week, but if that happens, it’s probably going to be somewhere to our northwest or northeast depending on the track of a likely-to-develop low-pressure system. That low will bring another cold front through that will lead to another shot of cold air and possibly some mountain snow showers. A lot of details remain to be worked out about the late-week storm, which could yet be a soaker for our region, or just splatter us with a few showers. Long-term, it does appear the core of warmest air will move westward into the western U.S., and that may allow a little bit more cold air to take hold beyond next weekend. I’m thinking seasonal kind of stuff, 40s highs/20s lows, not a big chill.