Turning the blog over this evening and Tuesday to two weather stories from Monday:

* Destructive and deadly tornado in Moore, Oklahoma — same place leveled in 1999 F-5 tornado.

* Flooding  from a localized but very heavy downpour in Roanoke.

The Hokie Storm Chasers were on storms south of Oklahoma City and were not near the Moore, Okla., tornado.

In Southwest Virginia: Expect a warm, sticky day on Tuesday (after some locally thick morning fog) with highs in the 80s and some scattered afternoon showers and thunderstorms — fewer than on Monday, but a few spots could some locally heavy rain, as occurred in downtown Roanoke on Monday.

There may be a few more snow showers today as some direct impact from the departing complex storm system that delivered our region’s biggest widespread spring snow in 10 years lingers. We will slowly be shifting into a weather regime more dominated by upslope northwesterly flow over the mountains  and periodic upper-air disturbances caught in that flow through at least Wednesday. That will translate into lots of snow squalls in the typical snow belt areas — eastern West Virginia’s montains especially, west of Interstate 77 in Virginia, and the ridges along the Virginia-West Virginia border farther north — with snow showers periodically blowing into the New River and Roanoke valleys.  Some high-elevation areas in West Virginia may pile up a foot or more in the lingering upslope event.  High temperatures through Wednesday are going to remain 15-25 degrees below normal, in the 30s to maybe some low-mid 40s in the Roanoke Valley and locations south and east. There will start being some periodic sunshine, maybe this afternoon but more so Tuesday and Wednesday, which will do its number on the snowpack, but still at a slower rater than we would typically expect for a late March snowfall.

A gradual warming — uh, let’s say “moderating” — trend late in the week may grudgingly nudge temperatures back toward normals, with highs in the upper half of the 50s and lows in the 30s. But the blocking pattern of high pressure in the far northern latitudes that has brought us the unusual early spring is only slowly going to lose its grip, and there may yet be reinforcements of the cold air that continue into early April.

A reminder that this is Tornado Preparedness Day in Virginia.

Today’s weather will get windy behind a cold front, but not necessarily all that cold, depending on how much warming your location gets from winds blowing down the Appalachian slopes and in-and-out sunshine. Most places look to warm into at least the 50s, and some low 60s won’t be out of the question south and east of Roanoke. But the reality of the cold front hits overnight and Wednesday, with lows in the 20s and 30s areawide, and even some snow showers, both from upslope flow over the western side of the mountains and some weak disturbancs moving through. Highs may not top 40 west of Roanoke on Wednesday and likely will be 40s to at best some low 50s areawide on Thursday.

Looking ahead, it appears we will be on something of a roller-coaster ride, though not as steep as some we’ve seen earlier this year. High temperatures will bounce back into the 50s to low 60s by Friday and Saturday, before another cold front slides through. Late in the weekend and early next week, there may be some moisture overrunning the colder air at the surface, and then perhaps a stronger low pressure system to deal with. At this time, it appears the major threat of any frozen precipitation with the overrunning moisture will be mostly north of our region, and guidance is beginning to gather more for a Ohio Valley-Great Lakes track for the stronger low rather than up the East Coast (though the inland low may transfer energy to a coastal low north of our latitude, as implied by Weather Prediction Center best-guess weather map for next Tuesday at left). All subject to change, of course, but it is looking doubtful there will be a large-scale winter storm in our region early next week. In any event, it appears there’s a good chance that the arrival of astronomical spring will be greeted with a push of Arctic chill mid to late next week.

Friday’s weather will continue to be breezy with highs a little warmer than Thursday, upper 40s and low 50s. Low 60s still look to be a pretty good bet one or both days weekend, at least from Roanoke south and east, with rain likely early in the coming week, and cooler temperatures again beyond that. More on the  next week’s weather this weekend.

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There’s a lot of buzz in the D.C. area about how the snowstorm forecast was a huge bust there — minimal amounts in the central city when various forecasts by experienced meteorologists ranged from 3-6 inches on the low end to 8-14 inches on the upper end.  Of course, snow accumulation picked up a bit in D.C.’s western suburbs, and the overall forecast for a major winter storm affecting the Mid-Atlantic region was generally accurate, as the area expected to be most heavily affected — the Shenandoah Valley and Blue Ridge region generally along and north of I-64 — was indeed hammered by 6-24 inches of heavy, wet snow.

Southwest Virginia area forecasts from various sources generally settled toward the correct idea that the heaviest snow would be to the north near I-64 with lighter snow amounts south to near the U.S. 460 corridor and little or nothing to the south.  But ahead of the game on that shift in thinking on the winter storm as early as the previous weekend (as shown on the map he posted at left) was Zach Robinson, a Virginia Tech geography student from Fancy Gap who puts some of his thoughts on his “Blue Ridge Weather Blog,”  and often posts comments and links on Weather Journal. (And I will get the link to his blog added to regional weather blogs on the right margin of this page).

Zach had an interesting online discussion with famous meteorologist Larry Cosgrove, who pointed out that the “blocking” pattern in place was far from perfect. Cosgrove pointed out to Zach that blocking high pressure over Greenland had shifted somewhat eastward and been replaced by a low-pressure shortwave, and that high pressure was not showing signs of recovering over Greenland and eastern Canada behind the shortwave. The result was that it was not a true Greenland block that we expect to see during the more persistent cold outbreaks and large winter storm threats for our latitude. The “50-50″ low near Newfoundland, a common feature in many Southwest Virginia winter storms acting as a “traffic cop” to guide a storm system farther south, also drifted somewhat eastward as a result. The butterfly’s wings were flapping, and it fluttered a couple of factors just a little out of place for the potential large scale winter storm hammering all of our region.

Zach said his conversation with Cosgrove took place after he had already started to back off the big snow threat, but it expanded his knowledge and confirmed some of his thinking, which is summarized by Zach himself below:

“Why was I so adamant on this being a relatively minor event for most of our region, and what did I see early on that others didn’t?  Very early on, a few weeks ago I was very skeptical on my blog and Facebook page (Blue Ridge Weather), that a cold pattern would actually setup.  My argument was the pattern over the Pacific was simply too strong and too fast to allow any major blocking to setup. … So going into last week, I had my doubts that a true cold pattern would take shape and hold. …. Using this belief, I had a sneaking suspicion of two things.  One: The energy diving south out of Canada would enter further EAST than originally forecast.   Consequently, the energy would have to take a steeper angle to get to our latitude, and given the lack of significant blocking I didn’t see that happening.  I thought the models would adjust North some.  The amount of amplification in the Jet Stream to get the energy to dive into Georgia/South Carolina was just simply not there.  2) From this, I believed that the initial surface low would also ride a bit further west into the Ohio Valley, because I believed (again due to the lack of a real block) that the 50/50 low would escape to the East, allowing the initial energy to ride into the Ohio Valley.  Using basically these two criteria, I thought that the energy would not develop far enough South to hit our area with a widespread crippling storm. 

Backing me was my knowledge and history of storms of these types.  To get to the point to have the storm re-develop far enough to the South, we would have to be in a very high amplitude pattern, and we simply were not.  A bit of it too, was my gut.  I’m not going to lie it was a very difficult call to make, because the models we’re screaming something different, but I just had this feeling that they would adjust.  The driving reason behind that I would attribute more to my knowledge and history of patterns in this area, rather than to my understanding of the blocking pattern of the Northern Hemisphere.  I had seen storms growing up do this exact same thing.  The pattern to me screamed Shenandoah Snowstorm, and not Southwest Virginia Snowstorm.  9/10 snowstorms for us seem to not involve some sort of energy transfer. “

So there you have it from a young weather forecaster who ended up looking pretty good in how it all played out.

Channel 13 (WSET) meteorologist Sean Sublette in Lynchburg posted an interesting post-mortem look at the snow expectations with a more local emphasis.

* WINTER STORM WARNING TONIGHT/WEDNESDAY FOR BOTETOURT, ALLEGHANY, ROCKBRIDGE, AMHERST COUNTIES AND NORTHWARD

* WINTER WEATHER ADVISORIES ROANOKE/NEW RIVER VALLEYS AND SOUTHWESTWARD

* Some icy spots possible this morning from overnight periods of freezing rain, sleet and snow that moved across much of Southwest Virginia.

* Additional rain begins later today — possibly wintry mix to start — and continues overnight as milder air aloft overrides cold air at surface ahead of a low-pressure system moving into the Ohio Valley. More than 1 inch of rain possible.

* Rain expected to change to snow from west to east in the pre-dawn hours as cold air is pulled toward new developing low in North Carolina.

* An area of heavy snow develops on northwest side of low-pressure system on Wednesday. Where exactly it sets up difficult to pinpoint. General thinking based on forecast model output is that the edge of it extends southward to just north of the U.S. 460 corridor (Blacksburg-Roanoke-Lynchburg).

* Projected snowfall amounts generally 4+ inches in winter storm warning area north of Roanoke; 2-4 inches in winter weather advisory, Roanoke-New River Valley and southward.

* Snowfall amounts will shift upward if (1) cold air to support snow develops or remains in place much farther south than expected this evening; (2) cold air moves in faster in the pre-dawn hours; (3) the snow area on Wednesday extends farther south than modeled. A slight shift southward in the low’s projected track near Virginia-North Carolina border could result in more/wider snow coverage in Southwest Virginia on Wednesday.

* Snowfall amounts will shift downward if precipitation moves out faster than cold air can arrive in early morning and edge of snow area behind low is farther north than expected. A slight shift northward in the low’s projected track, moving further into southeastern Virginia, could result in lesser snowfal coverage/amounts for our region.

* Upslope snow showers on northwest winds develop  mainly west of Blue Ridge Wednesday afternoon  into Thursday monring, possibly adding to snow amounts in locations that usually receive snow squalls, especially west of I-77 and near Virginia-West Virginia border.

* Strong wind gusts exceeding 50 mph possible behind departing low late Wednesdsay/early Thursday.

* Warming trend with highs possibly topping 60 by weekend.

Clipper No. 3 in the series (though you could have called the Saturday-Sunday system a series of about 4 different clipper-like disturbances) dives our way late Monday into Tuesday. There are many complications that will lead to a trickier forecast. First off, the Arctic air mass is starting to moderate, so that the critical freezing line at the surface and up to a mile high will wander northward into or very near our region. Secondly, the main center of the next clipper appears likely to move north of our region, which means we could be on the “warm” side of the system, enhancing the pull of slightly milder air northward. Thirdly, there may be a low near the Gulf Coast that becomes at least partly involved and supplies a bit more moisture. Most forecast models do not show the northern and southern lows teaming up very effectively, so it’s possible this low stays to the south and is not a major player (other than perhaps consolidating the moisture flow to the south and drying up the air in between the two lows.) In all of that, it appears unlikely, as of late Sunday, that we are headed to a widespread snowfall, even a light one, late Monday and early Tuesday. But there could be a light mix of precipitation, with the best chance of snow north and west of Roanoke. The Hydrometeorological Prediction Center focuses the core likelihood of 1+  inch of snow in West Virginia (no surprise) with high chances west of Interstate 77 in Virginia, and lesser chances edging eastward into the western New River Valley.   There will likely be some more upslope snowfall — northwest winds squeezing out moisture crossing the mountains — once this storm system passes.

We are heading for a steadily milder pattern through the week as highs push back into the 40s and 50s rather than recent 20s and 30s. A storm system late in the week will spread moisture again over our area by Friday and Saturday. From this distance, it looks to be a mostly rain situation, but ice/snow on the front end with lingering or wedged cold air and some upslope snow showers on the back end with colder air on the back side of the storm are at least possible. It appears we may be headed for another rainy storm in the days before Valentine’s Day. Long-range guidance has been conflicting on whether the mid to latter part of February turns warm or cold, but I’ll just pitch in that rumors of winter’s soon demise have been greatly exaggerated.

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Snow meter
2/4-2/10

Chance of 1 inch of snow, rated from 0 to 10 snowflakes.

Roanoke:  *** 3 snowflakes out of 10
Blacksburg: ***** 5 snowflakes out of 10

Outlook: Another Alberta clipper – a fast southeast-moving low-pressure system — like the ones that affected our area early Friday and again late Saturday into Sunday is headed down for late Monday night and Tuesday.  Temperatures will be more marginal for frozen precipitation with it than the previous clippers, but it may connect with a southern low and tap a bit more moisture. Given marginal temperatures and the typical elevation/topography issues, I don’t expect Roanoke to get an inch of snow out of this. Blacksburg, again, could much more easily squeeze out an inch, though it’s a close call. I’m going with an even-odds chance for Blacksburg and two flakes less for Roanoke. There is a late-week storm that looks to be much milder than the first one. It’s not out of the realm of possibility for this to encounter a little cold air on its front side or to swing some cold air behind Friday or Saturday. It doesn’t change my thinking on the probabilities for the week too much, though.

Looking back: I didn’t catch onto the parade of Alberta clippers until after the snow meter had published. If I had, I would have gone much higher than three snowflakes for Blacksburg. Instead, 2.9 inches of snow fell there Friday through Sunday, which busted the snow meter (more than an inch of snow with less than 5 snowflakes) and gives me a loss. Roanoke only got 0.4 inch, officially, so I get a win for going three snowflakes and less than an inch falling.

Current records: 7-2 for Roanoke, 5-4 for Blacksburg.

When warm southwesterly winds begin to take control from an Arctic air mass, a common result is a period of freezing rain. That is what Southwest Virginia may be facing late Sunday and Monday, as Gulf of Mexico moisture, pulled northeast by a passing upper-level disturbance and increasing southwesterly wind flow above the surface, overrides cold air at the surface banked against the Appalachians. A period of freezing rain will be possible late Sunday and early Monday, as temperatures at the surface may be in the upper 20s and low 30s in most or all of the region while layers aloft warm above freezing. This will allow precipitation to fall all the way to the surface as rain (maybe a period of sleet to begin) and then freeze on objects near ground level. Because we have been cold for many  days and there have been two snowfalls  (I’ve had snow cover on my yard for 9 consecutive days now, just a few hundred feet above and a couple miles south of Roanoke), the ground will be cold enough that the potential for icy streets and sidewalks will be high if the freezing rain develops. As of Saturday evening, large enough amounts for widespread power outages are not expected. The Hydrometeorological Prediction Center is, as of Saturday evening, giving mid-range (near 50 percent) chances of at least .01 of ice developing. You can link here for the latest ice forecasts from the HPC (potentially major ice storm in the Upper Midwest) and here for latest updates and possible advisories from the National Weather Service in Blacksburg.

As for the week ahead … this is going to be a truly volatile week of weather nationally, with a large-scale warmup (60s locally on Tuesday) followed by a strong Arctic cold front. Severe thunderstorms and tornadoes will be a good bet in the Mississippi and Tennessee river valleys. Our region may be headed for an inch or more of rainfall with the midweek frontal passage. There may be a few-days window as February begins that would support development of a winter storm in the South and East, though there are no obvious indications yet that this will occur. As I’ve said before, those who want the weather to get cold and stay that way and those who want it to get warm and stay that way are all out of luck, as it appears we’re headed into a roller-coaster pattern for at least the next couple of weeks with up and down shifts in temperature and potential large-scale storms that will deliver severe storms, heavy rain, ice, snow and wind to large sections of the nation.

WINTER WEATHER ADVISORY EXPANDED EASTWARD … now includes Franklin, Bedford, Henry and Pittsylvania counties … continues for all localities to the west.

UPDATE 1:15 PM: It appears the heaviest snow is likely to end in the Roanoke and New River valleys by 3 p.m., with some flurries or patchy freezing drizzle continuing into the evening. Snow amounts of 1/2 to 2 inches are being reported so far, so the 1-3 inch expectations appear to be well on track. END UPDATE

UPDATE 11:45 AM: It appears that a heavier patch of snow is moving through much of the New River Valley and will spread into the Roanoke Valley during the lunch hour. The snow rate will pick up such that any roads not already covered may become white fairly quickly. Accumulations totaling 1-3 inches with some heavier amounts are still expected. END UPDATE

UPDATE 10:15 AM: Snow is now rapidly overspreading the New River Valley, and appears likely to begin in the Roanoke area by 11 a.m., roughly an hour ahead of the moved-up times I listed below. Expect roads to deteriorate rapidly. Some sleet may occur at the outset of the snow in some locations. END UPDATE

UPDATE 8:30 AM: Moved up start times of snow by 1 hour. Snow by 11 a.m. in New River Valley and by noon in Roanoke Valley. That is “by” not “at” so possibly a little earlier. END UPDATE

Radar is picking up echoes, some heavy, in central/eastern Tennessee and Kentucky, even edging into far southwest Virginia, as of just before 7 a.m. That’s not what you’re seeing at left — the inset image is what the NAM forecast model “thinks” the radar will look like about 1 p.m. today. Everything appears to be on track for a quick burst of snow — 3 hours or so of moderate, even heavy for a brief spell — that will likely accumulate 1-3 inches widely (not necessarily every single point) across Southwest Virginia and perhaps more in some heavier bands. The  showery looking echoes in Tennessee and Kentucky are expected to become more solid in coverage, but there may still be some “mesoscale banding” or regions of more intense snow that, in some cases, may align west/east and move over the same location for an hour or two. That’s what could boost some local snow totals above forecasts. The moisture will be hitting very dry Arctic air as it heads eastward, so you may see an hour or two of radar echoes over your head before you see snowflakes, especially at lower elevations.

Approximate start time is spreading over the region west of Interstate 77 by 10 a.m. (already has begun in far southwest corner of the state), as far east as the New River Valley (Blacksburg/Chrsitiansburg/Radford/Pulaski) by 11 a.m. and into the Roanoke Valley by noon   (I say “by” not “at” because it’s more likely to be a bit earlier rather than much later.) With the consistently cold weather we’ve had the last several days, snow will accumulate on untreated roads very quickly, and so slick conditions will develop rapidly even with minor amounts of snow. As we’ve noted, it will be a fluffy snow that is unlikely to cause large-scale power outages, as the Jan. 17 heavy wet snow did.

From here, it’s a radar-watching and waiting game.

WINTER STORM WARNING NOON TO MIDNIGHT

UPDATE 11:30 AM: A short update to say, well, not much has changed. NWS-Blacksburg is estimating 3 p.m. for rain to snow changeover in the Blacksburg area and 4 p.m. for Roanoke. That could vary an hour or two either way.  Some wintry mix and snow reports are occurring on the northwest fringe of the moisture shield in West Virginia into the far southwest corner of  Virginia. The Radar / Future Cast link at right on this blog will give you an approximate idea where the mix (pink) and snow (blue) are being reported. END UPDATE

Summary: All indications are that the region is on track for 4+ inches of wet snow beginning early to mid-afternoon and continuing into the evening. Snow will be heavy at times with reduced visibilities and rapid collection of slushy accumulation on some road surfaces near rush hour. It should be over by 10 p.m.

It’s snowing this morning – in Jackson, Mississippi. And so begins a slow, sloshing trudge from a not-all-that-cold rain this morning in Southwest Virginia (temperatures in the 40s, mostly) to a potential heavy, wet snow event by late afternoon and early evening. The cold pocket aloft with the upper-level low spinning over Mississippi will slide northeastward, and a surface low forming just east of Atlanta will begin pulling cold air southward as the day progresses. We’ll likely see the rain/snow line begin to slip southeastward through West Virginia by mid to late morning as snow reports also begin to increase in central/eastern Tennessee and into some of Kentucky and eventually far southwest Virginia with the advancing upper low. During the afternoon, say between 1 and 4 p.m., temperatures are expected to be cooled in the low and mid levels of the atmosphere enough over Southwest Virginia east of I-77 (may happen before then to the west) that snow will begin reaching the ridgetops first, then progressively lower, with air temperatures also decreasing to near or barely above the freezing mark. If you’re anxiously waiting on snow this morning, this process will be like watching paint dry. Snowfall amounts by all available guidance appear to be on track for widespread 4+ inches across the region, with some amounts up to 12 inches, or maybe a little more, especially in higher elevations along the I-81 corridor southwest of Roanoke and westward. The snow won’t last long, probably no more than 5 to 8 hours at any location, but will likely come down fast and furiously at times, with some low visibilities developing near rush hour. It’s that intensity that is expected to overcome a relatively mild, moist ground, collecting on grass and exposed objects first, then forming a slushy layer on the ground once the rate of snowfall exceeds the melt rate. Once the thin layer of slush develops, snow can collect on top rapidly. In the heaviest periods of snow, roads may become slushy and even ice/snow covered — I-81 southwest of Roanoke is a particular concern, with its steep hills and curves, and considering the trouble that ensued there from heavy snowfall rates in December 2009. Due to the heavy, wet nature of the snowfall, especially in its early stages, there may be some tree and power line damage, similar to what we saw last Feb. 19. This snow will probably be moving east of us by 10 p.m., and a cold night with lows in the upper teens and 20s will ensue that will freeze slush and water on streets.

Another dense fog advisory has been issued overnight/early Sunday for a similar portion of the region as last night. Fog probably won’t be as widespread as late Friday and early Saturday, but could be dense and hamper travel in some locations.

There is so much going on with the weather pattern, short term and long term, that it’ s hard to boil all of it down. Perhaps this is a format I can replicate in the future. Here are the “Big 5″ weather points, based on impact and likelihood, for Southwest Virginia looking forward from Sunday.

(1) Record highs likely again on Sunday. Roanoke’s 73 and Blacksburg’s 71 on Saturday set new standards for Jan. 12, eclipsing previous marks from 2005. Roanoke’s high made for the hottest January day in 8 years, while Blacksburg’s appears to be the second-warmest January day in its entire period of record, dating to 1952, beaten only by a 73-degree day on Jan. 30, 1975. The same southwesterly winds at the surface and aloft, plus in-and-0ut  sunshine, will continue the springlike weather for another day, with many temperatures topping 70. Roanoke’s record high for Jan. 13 is 73, set in 1932; Blacksburg’s record is 64, set in 2005. It appears Blacksburg’s record is very likely to fall and Roanoke’s has a good chance. Sunday will be the end of the record warmth, and quite likely the last truly springlike day we’ll see for weeks — maybe even until spring itself.

(2) Good chance of soaking rain Monday-Wednesday. As the leading edge of much colder air that has invaded the western half of the U.S. grinds against high pressure off the Southeast coast that has helped bring us record warmth, the cold front will stall, and only sluggishly advance eastward through the early to middle part of the coming. Waves of low pressure moving along the slowing front will bring abundant moisture from the Gulf of Mexico, leading to periods of rain, especially on Monday and Tuesday, maybe leaking into Wednesday too. The Hydrometeorological Prediction Center is expecting 2-plus-inch amounts to be common this week, mostly falling during the 72 hours ending Tuesday evening (which really means the 48 hours beforehand, since no rain is expected through Sunday evening). Rainfall will be enhanced some by southeasterly winds blowing up the slope of the Blue Ridge as low-pressure centers move up the front. Roanoke has not topped 2 inches in a single rainfall event since Sept. 17-18. Much of the region continues in moderate drought, so though it will be messy outside, the rainfall is needed.

(3) Much colder period ahead for late January. This will become a huge weather story, not just locally, but nationally, if what many long-range forecast models show comes to reality. Extremely cold air, displaced southward by a “sudden stratospheric warming” event over the North Pole that began about3 weeks ago, is expected to move southward through central and eastern North American over the next 1-2 weeks. While the first chunk of this cold, in a greatly modified fashion, will bring our temperatures back down from intensely warm this weekend to near-normal January cold by late week, it is the subsequent pushes of cold air afterward that will have the potential to bring unusually cold weather to much of the central and eastern U.S., including Southwest Virginia, generally in the Jan. 20-30 timeframe. It’s hard to tell exactly how cold it will get, but it would be a good time to review what to do about your water pipes and make sure heating systems are in top-notch working order just in case the most extreme cold scenarios comes to fruition.

(4) Some ice/snow risk as cold penetrates back side of precipitation shield Tuesday. The cold air will only be grudgingly moving eastward, but enough of it may move in by Tuesday that some ice or snow may be possible, primarily in the highest elevations (3,000+ feet) and along/north of the I-64 corridor. The Hydrometoerological Prediction Center has highlighted a few higher spots around the region on its map for a slight risk of heavy ice (.25 inch or more ) mostly on Tuesday. The HPC also has posted maps showing a low-end risk of 1 or more inches of snow generally along and north of the I-64 corridor for the 24 hours ending at 7 p.m. Tuesday, and also a slight risk for light icing farther south in the same time frame.  This is an iffy situation and will most likely be spotty, if it develops at all.

(5) Late-week snow chance not entirely out of the question just yet.  The forecast models have been bouncing around on some upper-level energy moving across the South on or near next Friday. This just remains something to keep one eye on, as there is at least some potential for snow (or mixed precipitation, or cold rain) if a sizable low were to throw moisture over marginally cold air late in the week.