The storm system that spawned our spring snowfall Sunday and Monday has grown into monster, stretching the width of the Atlantic from Canada to Spain. The fall, winter and early spring have produced a series of large and powerful North Atlantic cyclones, starting with Superstorm Sandy in October.

A temporary relaxation of the unseasonably cold pattern is under way for Southwest Virginia, just in time for the Easter weekend. Any of the next 4 days could reach near or possibly top 60 in the Roanoke Valley and points south and east, which would bring us back to near normal for late March highs, and it should be in the 50s most sites to the west. Moisture will stream in for Sunday ahead of a new cold front, which could mean some showers during the day on Easter. So while it will be milder and at least a little more springlike for Easter, it might be a little wet too — though amounts do look to be fairly light. Don’t consider Sunday to necessarily be  a total washout, but an umbrella to guard against showers might be in order.

Arctic air will roar back by late Monday into Tuesday. There is some potential for a low-pressure system to throw moisture into that cold air Tuesday and/or Wednesday. Some early April snow will be possible if that occurs. I think there are some good reasons to think that winter might finally lose its firm chokehold on early spring about 7 to 10 days into April, but until that time, enjoy this weekend’s milder weather before unseasonable cold returns.

The “upslope-a-thon” that has kept persistent  snow squalls and snow showers going in most of the area west of the Roanoke Valley (and south along the crest of the Blue Ridge, too) may still have another day left in it. The northwest wind flow leading to the upslope snow squalls will slowly be diminishing, as will the moisture, over the next 24-36 hours, but a couple more disturbances caught in that flow will enhance the snow showers overnight and early Thursday. We’re still looking for a warming — or should  I say “milding” — trend through the weekend, with highs back in the 50s to some low 60s possible, but it now appears the price for that will be a chance of rain showers on Easter. Rain, not snow.

Another cold front is going to bring temperatures back down to below normal next week, and there may even be a storm system or two that may deliver cold rain or even wintry mix (thinking mainly higher elevations, if it happens at all). But looking at the bigger picture, there are some signs that this historic blocking pattern that has superimposed winter weather onto the early spring portion of our calendar is shifting just a bit. You’ve read the term “blocking pattern” on here several times, but here is what it looks like at left, as depicted on European model late last week.  The green areas circled on this 500-millibar chart represent high pressure areas over Greenland and the North Pole, the classic North Atlantic Oscillation-negative (NAO-) and Arctic Oscillation-negative (AO-) patterns. The blue regions over much of central/eastern North America and over Alaska/western Canada were “blocked” or trapped areas of unseasonably cold air. The blocking has already eased up substantially as of today, though much of the cold air remains, with no new pattern having yet developed to clear it out. Some rebuilding of the blocking is expected over the next few days, enough to renew colder than normal air over most of the central and eastern U.S. after this weekend’s relaxation, but rolling the European model ahead seven days, it doesn’t look quite the same as it did before. In this linked chart, note where I have drawn zig-zag lines over some dark blue colors. This would be lower pressure aloft and colder air at the surface recharging over the North Pole. You can still see some green over the North Atlantic, but it’s a little east of Greenland, more toward Iceland. Another center of higher pressure has shifted west of its previous location into the western Arctic Ocean. If this comes to fruition, it would still represent some level of AO- and NAO- ongoing, but the orientation of the blocking features would have shifted such that the coldest air relative to normal would be more to the north of us. It doesn’t represent so much a sudden break in the pattern as a gradual shifting that could allow for somewhat milder, though still not consistently warm, weather to take hold in Southwest Virginia after next week’s cold push. A large-scale shift in the pattern over the Northern Hemisphere, however, does not appear to be likely soon. March will end averaging much below normal in temperature locally, and the early odds tilt toward April being at least a little below normal.

Same old, same old today, with cold northwest winds and more snow showers, mostly west of Roanoke, caused by those winds blowing over the Appalachian slopes, lifting and squeezing out moisture. There will be a slow dwindling of low-level moisture that will very slowly decrease intensity and coverage of snow showers by Thursday, and they should finally end by Friday. A slow warming trend will be on tap this weekend, with some low 60s possible by Sunday and Monday, especially Roanoke south and east. The big question for the Easter weekend is when exactly showers might roll in. We’ll try to pinpoint that better as we get closer.

Today’s Weather Journal column, linked here, looks back at other large spring snows in the past several decades at Roanoke and Blacksburg. (Spring here is defined as astronomical spring, when the calendar says spring March 20 or shortly thereafter each year, not meteorological spring, which begins March 1 for statistical convenience. So the 1993 Superstorm, for instance, which happened March 12-13, doesn’t count as a “spring snow” as defined here.) Before researching this column, I knew nothing about the March 22-23, 1981, snowstorm that dumped 13 inches on Blacksburg and 9 inches on Roanoke, which appears to be the largest spring snow at both sites in the modern era of record-keeping (since 1947 at Roanoke, 1953 at Blacksburg). Some of the other spring snows, like the twin snowstorms of 1971, early April 1987, late March 2003 and late April 1978 we’ve discussed at varying levels on here previously. I went back and looked at weather maps for each of these events, and the one linking element is a coastal low-pressure system (except for 1987, when it is a little inland — and 2013, with the additional strong inland low). I’ve linked those weather maps below if you want to take a look.  All these maps are for 7 a.m. time periods, so they don’t capture the exact timing of the period of snow in Southwest Virginia in all cases, but they get across the idea of major weather features in play.

March 25, 1971

April 7, 1971

April 27, 1978

March 23, 1981

April 4, 1987

March 30, 2003

March 25, 2013

If somebody will give me some rabbit ears I will kindly drive up to Gobblers Knob and pin them on the groundhog. I think he needs a good disguise.

– National Weather Service-Blacksburg forecast discussion

Snow rabbit my son and I built on Monday.

The groundhog’s “early spring” forecast has certainly come under widespread derision, not just here, but in much of the U.S. Check out here a comparison in snow cover  between Monday and March 25 a year ago, when record warmth — and in many case, runaway record warmth — absorbed much of the country. (Thanks to Stu Ostro of the Weather Channel for putting these maps together.) Speaking of records, March appears likely to finish among the top five coldest since 1953 at Blacksburg (currently averaging 35.1 degrees) and has a shot  for a top 10 coldest finish since 1912  at Roanoke (currently averaging 41.5 degrees), but has no real shot at catching frigid and snowy March 1960 for the record coldest.

As the same forecast discussion quoted above notes, it will be more of a Bill Murray kind of groundhog on this Tuesday … and again Wednesday … with a repeat of cold northwest winds and periods of snow showers, especially west of Roanoke. Snow is continuing to pile up in West Virginia’s mountains and some of the higher elevations west of I-77 and along the Virginia-West Virginia border, the areas that get the most when northwest winds blowing over the Appalachians lift and squeeze out moisture. Highs in the 40s — well above freezing, but well below normal — and late March sunshine will continue to melt the snowpack from the Roanoke Valley eastward; it will erode a little more slowly to the west with more clouds and highs in the 30s. Ironically, that same snow-melting March sun may help trigger more afternoon snow showers, some briefly heavy, as warmer air near the surface bubbles some moisture upward into much colder air aloft. It’s a lot like how our summer pop-up storms form. If you get in one of these heavier snow showers, visibility may get cut to 1/4 to 1/2 mile for a short time as you are swallowed by a snow globe world, but the sun will quickly return afterward.  In the lower elevations around the Roanoke Valley and out in the Piedmont, these showers may even start with sprinkles of rain, but cold downdrafts will likely bring the snow to the surface not long after.

While the overall pattern of high-pressure blocking in the far northern latitudes leading to colder than normal weather in much of the central and eastern U.S. doesn’t look to break entirely anytime soon, it does appear there will be a break in the winterlike cold just in time for Easter. Highs may even reach the 60s — at least the mid to upper 50s — as southwesterly winds ahead of a low in the central U.S., perhaps assisted by a weak high off the Southeast coast, bring in milder air with sunshine. (Well, maybe, maybe not on the sunshine.) The relatively mild air won’t last long, as a new cold front approaches early next week, likely with a round of rain followed by more cold, northwest winds.

I’m not going to absolutely guarantee that we’ll be done with snow this week, but it looks like you won’t be hiding Easter eggs in snow.

The National Weather Service in Blacksburg has posted a winter storm warning overnight for  the potential of 3-5 inch snowfall amounts as a band of moisture pivots around a low to our west, and moving up the I-81 corridor. We discussed the expectation of this band moving through overnight in the previous post, and the weather service has upgraded the previous winter weather advisory based on some data suggesting amounts will be toward the high end of earlier projections. Such snowfall –  or even an inch or two, as we discussed before — would add to the problems created by 3-7 inches of snow that fell in and around the Roanoke and New River valleys earlier Sunday. It still appears that areas north of our region will have the best chance at large snowfall totals overnight and early Monday.

Will it happen? Honestly, I’m kinda still leaning to the old 1-2-inch idea, more toward I-64. But let’s see.

You can keep up with the progress of the overnight snow band on our Radar / Futurecast.

A few days ago, we talked about whether or not it would be the front side or the back side of this complex storm system — or rather, cluster of storm systems — that would deliver the most potential for snow in Southwest Virginia. I leaned to the front side then, and it has dumped widespread 3-7 inch snowfall amounts on the Roanoke and New River valleys and nearby areas today. Accumulating snow might not be over, though I think the majority of it is for our neck of the woods. The next piece of upper-level energy approaches from the west overnight. While we were having our Palm Sunday snow today, this system was triggering severe thunderstorms north of Nashville in much milder air. As it approaches overnight, and also interacts with a low along the East Coast, it may spread snow back into the area late tonight or early Monday morning.   Most forecast guidance suggests that the greatest emphasis of this storm will be north of Roanoke, more for the I-64 corridor and northward. But another inch or two of snow may be possible as it swings through. The one thing that gives me pause that it might be a little more is the heavy thunderstorms on the line today, and their remnants maybe bringing some heavier snow bursts. In any event, the area of snow is unlikely to be as large or as long in duration as today’s system was. Between now and the next wave, some scattered light snow, light drizzle or freezing drizzle will be possible.

It’s going to keep being wintry into midweek, with stiff northwest winds behind the tightening storm off the East Coast, upslope-driven snow showers, and perhaps even some Alberta clipper-like disturbances spreading yet more snow east of the mountains. Below normal temperatures will continue into next weekned. Beyond that, there maybe a few signs of the unseasonable cold breaking. Spring will win this battle eventually against this reluctant-to-start, yet reluctant-to-leave winter

Rain and sleet have changed to snow in most of the Roanoke and New River valleys and nearby areas as of late this Palm Sunday morning. How much snow will collect at any given location now is basically a matter of intense it can fall to overcome the early spring factors that fight accumulation. While there may be some slack periods and gaps, bands of snow are expected to continue to develop and move through the region much of the afternoon, as we are influenced both by a low forming on the Atlantic coast off the Carolinas and another to the west in the Tennessee Valley. After a possible lull period late this afternoon, an upper-level low may bring another round of snow overnight and early Monday. Total accumulations of 2-5 inches seem to be on tap for the Roanoke and New River valleys, varying some by elevation and where heavier bands set up. Expect more to the north and northwest and a little less south and east, though Southside has seen some periods of snow this morning. Some forecast models continue to spit out very large totals, but those will probably be mitigated by the lesser snow:liquid ratios than we typically see in midwinter, some melting with borderline temperatures, especially during gaps in the snowfall. It is not out of the realm of possibility, though, that some of the 6+ totals may be realized. We’ll just keep watching it through the afternoon and evening. Be aware that some roads may become slushy or even snow-covered where heavier snow falls, and any amounts over 3 inches will start to bring concerns about localized power outages with the heavy, wet nature of the snow.

Latest warnings/advisories/accumulation maps from National Weather Service-Blacksburg linked here

Latest Radar / Futurecast linked here

There will not be much more time to speculate about whether or not the evening forecast model runs showing widespread 6+inch snow amounts — some even 10+ inches — are correct. Precipitation early on this Sunday morning was rapidly spreading across central and eastern Tennessee and is likely to arrive in Southwest Virginia near or not long after sunrise, spreading across most of the region by mid-morning. It appears mid to upper-level temperatures will be supportive of snow or perhaps snow/sleet mix through the Roanoke and New River valleys northward, as well as along the Blue Ridge south of Roanoke. Questions arise as to how much rain will mix in farther southwest and southeast. It appears that whatever falls will come down hard and fast — locations that are all snow could easily overshoot official 1-3 inch forecasts in effect late Saturday night. Surface temperatures hovering a little above freezing, especially in urban areas like Roanoke city, could be a limiting factor in accumulations, as well as the much talked-about higher sun angle in late March, but the biggest question will be how hard it falls and how much sleet (or rain) mixes in. Additional snow may develop Sunday night and Monday, and there is even some potential for another system to affect the region Monday night and Tuesday with more snow. Winter, tired of being mocked, is mocking us now that it is spring.

WINTER WEATHER ADVISORY ISSUED SUNDAY MORNING THROUGH MONDAY MORNING, MOST OF ROANOKE AND NEW RIVER VALLEYS

Trends on forecast models today have been moving toward a colder and snowier direction for Sunday across  the Roanoke and New River valleys and much of Southwest Virginia. Even though high temperatures have been in the 40s and 50s today, much of the air above us is still unusually cold and dry for late March. As a feed of Gulf of Mexico moisture rams into that air early Sunday (beginning perhaps as early as 7 a.m. to 10 a.m.), it is expected to rapidly cool the atmosphere falling through the cold dry air, with a mix of rain, sleet and snow, possibly giving way to all snow in many locations. There are still a wide array of potential amounts, owing to variables with moisture and temperature, mixing of rain/sleet, and especially the marginal surface temperatures and ability of the ground to absorb solar warmth from a high sun angle even if it is cloudy. The National Weather Service in Blacksburg has put out a map showing 2-4 inches in most of the Roanoke and New River valleys, more to the northwest, less to the south and east. This is probably a good middle ground of the possibilities, which could range upward significantly if the moisture and temperature on some models is correct, but could range downward with more rain or sleet mix if more warm air streams in aloft. There will be potential for additional snow into Sunday night and early Monday as well with this complex spring storm system.

Stay tuned. It will become largely a “nowcasting” show soon.

A year ago this weekend. on Saturday, March 24, 2012, parts of Franklin County and the Smith Mountain Lake area gained a white coating up to 6 inches deep … but it wasn’t snow. An unusually well organized supercell thunderstorm for this region tracked from Patrick County — where baseball-sized hail was reported — northeast toward the Ferrum and Rocky Mount areas and then Smith Mountain Lake. You can click here for a reminder of the event as covered on the Weather Journal blog. Numerous tornado warnings were issued on the storm based on Doppler radar indications of tight circulation but there was no ground evidence of a tornado touchdown was ever found. Low-level wind shear was the only parameter that was missing for a tornado.

We’re not talking about tornadoes or severe thunderstorms locally on the same weekend this year — that’s staying near the Gulf Coast. Instead the warmest March weather on record setting us up for severe weather, a March with a legitimate shot at being one of Blacksburg’s five coldest since 1954 and Roanoke’s 10 coldest since 1912 has set us up for an early spring wintry precipitation event on Sunday. Like most of the wintry   events when it actually was winter, this one is a murky borderline event between snow, sleet and rain, as the boundary between warm-air advection aloft and cold-air wedging on the east side of the mountains is likely to fall right across our region. Generally, a slushy mix is expected in the Roanoke and New River valleys with minor accumulations (2 inches or less), with more snow and more accumulation the farther north you go, maximized in higher elevations, and less southward. There is some risk, though, that moisture will rush in more intensely than forecast in a slightly colder atmosphere, and, if that happens, snow could come down hard for a few hours and quickly pile up a few (2-4) to even several (4+) inches. A few forecast models have shown this, particularly the North American Model, which has depicted it for several runs. The Weather Prediction Center this morning has a moderate risk of 4+ inches of snow nudging Roanoke and Blacksburg, while also barely having a coin’s flip chance of getting just 1 inch. Spring snow events are known for being mercurial like this, often forecasting busts in either direction. Just a little warmer than modeled in the bottom mile of the atmosphere and it could easily be just cold rain with maybe some mixed sleet.

Most models show two waves of precipitation with the complex and somewhat loosely organized storm system featuring two low-pressure centers, one moving west of the Appalachians and the other developing in the western Atlantic.  One precipitation wave arrives during the mid-morning or so and the other on Sunday night into early Monday morning. The first wave has the best chance of being heavy snow, but also more chance of being rain or mix.  The second wave would probably be snow, but not as intense. Midday to afternoon snow rates often have to be quite heavy to accumulate much because of the higher sun angle leading to more absorption of solar radiation than in midwinter, even with cloud cover. It is possible some places will see some accumulation in the first wave, have it mostly melt off afterward, then get a little more Sunday night and early Monday.

Bottom line: Expect to see at least some snow in the Roanoke and New River valleys northward on Sunday. Major disruptions are not expected at this time, but do keep an eye on radar and forecasts for changes that could develop rapidly during the day Sunday. Roads can quickly become slushy even in spring, even at 33-34 degrees, if wet snow and/or sleet falls heavily enough. Because of the cold weather, we have not had nearly the same greening of trees we saw in 2003 before the March 30 snowstorm, and therefore would not expect the same level of tree damage if heavier snow occurs, but January 17 showed us that wet snow can still do quite a bit of tree damage and knock out power to thousands even without that. If we start getting above 3 or 4 inches, that would be a concern.