The Hokie Storm Chasers are positioning for what could be an intense severe weather day in the central/southern Plains, likely somewhere in Kansas. This new tracking map shows their position, with the ability to zoom in (so the chase van isn’t 100 miles long) and add radar, warning boxes, and weather station observations. In a couple of weeks, you can follow my position on this map. Also, eventually, a webcam sending back pictures every several seconds from the front windshield of one of the vans will be operational. Here is a look back at their Wednesday chase in north Texas.

Southwest Virginia’s weather will also be unsettled this weekend, though not in the same way as the Plains states. The same upper-level low that spawned Wednesday’s deadly tornadoes in Texas is moving across the South, and will most directly influence our weather later today and Sunday. This will mean lots of Gulf of Mexico moisture (and eventually some draw off the Atlantic, too) being pulled around against our higher terrain. The coverage of rain and thunderstorms will be greater this afternoon and evening than it was Friday, with just about everyone in the region getting wet, and some getting heavy rain. The Weather Prediction Center is showing the potential for an inch or more over much of the area through Sunday morning … again, this map may be a little more smoothed out than what actually occurs, with more patchy/streaky amounts based on terrain and where individual bands of rain and heavy storms set up. The best bet for outdoor activities today is the earlier, the better, but keep an eye on radar and be prepared to go inside. Sunday is also likely to be a wet day, maybe not constantly, but frequently.

A RATHER OBNOXIOUS PATTERN SETTING UP THROUGH THE FORECAST PERIOD. — National Weather Service-Blacksburg forecast discussion

What makes it obnoxious? For the next 4 or 5 days, we’ll be dealing with a diffuse frontal boundary drifting around somewhere near us. Meanwhile, the same upper-level-low that sparked the tornadoes in Texas will be wobbling our direction, spreading out and circulating Gulf of Mexico moisture and periodic disturbances across us. The combination of a difficult-to-define front and troublesome-to-time disturbances means that there will be a middling to low likely (40-70 percent) chance of showers and storms throughout the weekend. Timing exactly when it may rain or storm in any given location is an exercise in futility — obnoxiously frustrating with graduations and sports and other spring events on tap across Southwest Virginia –  though afternoons and early evenings, when daytime heating (70s-low 80s) will be in play to destabilize the atmosphere, will tend to have higher chances of showers and storms. Late Saturday may be the peak of rain potential in our region, as the upper-level low comes into play most directly by streaming moisture and some upper-level wind energy. The Weather Prediction Center is highlighting our region for 1.5 inch or more of rain through Sunday evening, but I really doubt the pattern of heaviest rain will be the neat little smoothed out purple egg shape shown on the map. It will probably be more splotchy and patchy, with every location seeing some rain, but some seeing multiple inches while others get tenths. Some strong to locally severe storms will be possible, especially in the afternoons, but the tendency for more pervasive showers/clouds in the day and the much weaker upper-level winds than what Texas experienced will ensure no repeat of what happened there.

Meanwhile, deepening low pressure and an associated cold front in the Plains states will be setting that region up for what may be its longest and most extensive severe storms outbreak so far in 2013 — that’s where the Hokie Storm Chasers will be figuring out where to place themselves on the ongoing first of two trips. Eventually that system will help clear out the obnoxious pattern, but when and how exactly that will happen next week is a little fuzzy.

For Southwest Virginia, if you have outdoor plans Friday through Sunday, pay attention to the radar. It won’t rain anywhere constantly , but everywhere it will rain sometimes.

It appears tornado season has awakened from its yearlong national slumber with reports of massive damage, scores of injuries and some fatalities in the counties west and southwest of Dallas-Fort Worth. This was a situation that looked to be fairly marginal for severe weather, but some shear and instability ingredients came together just right along the Interstate 35 corridor for a small but intense outbreak of violent tornadoes. The Hokie Storm Chasers were on storms north of Dallas and observed intense rotation in some of the supercells. In time we’ll see more of what they came up with, as well as some of the horrible scenes of devastation morning is likely to reveal.

We don’t have the kind of ingredients the Dallas area did, but there will be a stationary front draped just north of us for a few days. This will be close enough that some waves moving along the front could trigger some scattered showers and storms in or near our area in the warmth and some humidity that has built. A repeat of Wednesday’s not-quite-record high temperatures (91 at Roanoke, 85 at Blacksburg) probably will not occur with more clouds and a bit thicker humidity, but highs in the 80s are likely, and that will be enough to help cook up some showers and storms. It appears we have several days of the spotty/chancy kind of showers and storms ahead, with periodic weak impulses and this front drifting around. By next week, we’ll finally get a push from a cold front to the west to clear this out a bit, with possibly a stronger, more organized round of showers and storms as it pushes through. There are some indications of another cut-off or at least slow-moving low developing over the eastern U.S. next week that could spin in a few days of cooler-than-normal temperatures. We haven’t entirely shaken the “blocky” weather pattern of slow-moving features and south-displaced cool air masses just because it got suddenly hot on Wednesday.

My latest Weather Journal column looks at instances of “temperature whiplash” we’ve had in the last several months.

And that’s what we’re about to experience, again. After Tuesday morning’s scattered frost, temperatures are likely to be 15-20 degrees warmer to start Wednesday … and then shoot up into the 80s by Wednesday afternoon. It wouldn’t be totally out of the question for Roanoke to record its second 90-degree high of 2013 on Wednesday, though the forecast high is just a tad cooler. After a record-breaking low of 35 at Roanoke and record-tying low of 31 in Blacksburg on Tuesday morning, May 15 record highs of 92 at Roanoke (1962) and 88 at Blacksburg (1985) will probably be just a wee bit out of reach — but not inconceivable. Westerly winds blowing down the slopes of the Appalachians will enhance the effects of the strong warm air advection rolling in from the west to produce the high temperatures 10-15 degrees above normal for mid-May. We’re not the only part of the country experiencing temperature whiplash, or even the part experiencing it most severely — some parts of Nebraska, South Dakota and Iowa soared past 100 on Tuesday, just a couple of days after sub-freezing lows and less than 2 weeks after abnormally late and in some cases record-large snow for May. Omaha, Neb., for instance, has recorded its earliest 100-degree temperature and its heaviest May snow just 11 days apart.

Some hard-to-time disturbances and ill-defined fronts will begin to affect our weather by Thursday continuing well into next week. That’s why you see forecasts with chances of showers and thunderstorms stretching out for days. In time, those forecasts may become a little more focused on particular periods with higher chances of showers and storms.

The Hokie Storm Chasers, who left chilly Blacksburg on Tuesday morning, may see some severe storm action Wednesday afternoon/evening in north-central Texas, or somewhere reasonably nearby. Targets sometimes easily shift 100+ miles as new data develops on these trips. We’ll see if they come up with any memorable storm photos on the second day of this first trip.

RECORD LOWS THIS MORNING: Roanoke 35 (previous May 14 record of 37 in 1996), Blacksburg 31 (tied record of 31, also set in 1996).

The first group of Hokie Storm Chasers head out Tuesday morning for 8-12 days or so in the central U.S. Looks like they’ll get a rather potent set-up for the weekend in a season that hasn’t had much severe weather. While preparing for my own journey with them on the 2nd trip starting near Memorial Day, I’ll be following this first trip closely from home base. We have a few new tracking features that I’ll share on here as they become operational.

The storm chasers may have to scrape a little frost off the windshield leaving home base.  However, you may have noticed a somewhat odd configuration of frost and freeze alerts for Tuesday morning from the National Weather Servie in Blacksburg, with the freeze warning primarily along and north of I-64, and the frost advisory primarily east of the Blue Ridge, leaving most of the Roanoke and New River valleys west and southwestward out of them. This configuration is a result of the expectation that light southwesterly winds and possibly mid to high level clouds will stymie the radiational cooling slightly in the areas from the Roanoke and New River valleys south and west. Still, with many lows in the 30s, there is likely to be at least patchy frost, especially in any valleys protected from any developing breezes. The record May 14 low of 37 at Roanoke could be challenged tonight, nonetheless, and the record of 31 at Blacksburg (both records date were set in 1996) definitely isn’t entirely safe if the weather service is even just a little wrong on the timing of the southwest winds and possible clouds. Roanoke’s latest freeze of May 11, 1966, will very likely stand, but I wouldn’t rule out a few 32-degree lows in the some of the areas rimming the Roanoke Valley. In any event, it does not appear a fruit harvest disaster is afoot for the region (per Lindsey Nair’s report on roanoke.com today), but it would be wise to protect any tender outdoor plants especially in areas away from Roanoke’s urban valley floor.

The southwest winds expected to start overnight west of Roanoke are the start of a warm surge that will overtake our region through Thursday, with highs returning to the upper 70s to mid 80s in most areas on both Wednesday and Thursday afternoons.

UPDATE 9:30 AM, 5/13: Some scattered frost reported in higher elevations and locations west of Roanoke this morning with lows in the 30s common — official low of 40 at Roanoke. A new freeze watch is already posted north of Roanoke for Tuesday morning, with more widespread frost advisories likely to be issued later. A few sprinkles are possible today with a quick-passing disturbance, but no major rain expected. This will be a week of winter-to-summer extremes, with some 80s temperatures later in the week. Full update this evening. END UPDATE

HAPPY MOTHER’S DAY! Expect a sunny day with temperatures rising into the 60s most places in Southwest Virginia. It will be a bit breezy and cool, but dry.

As on Friday, a smattering of severe weather reports occurred Saturday in Virginia (including trees blown down near Thaxton in Bedford County) with storms that at time looked quite impressive at times but were marginal on shear, instability and available moisture. My storm chasing friend and Roanoke resident Chris White of Roanoke photographed some formations with obvious rotation in central Virginia. I stayed closer to home and got a shot of a lowering with a rain shaft (sortakinda looks like a tornado, but it’s not) crossing the Roanoke Valley (was actually with my mother when I shot this, appropriate for the weekend, I suppose).  Here’s a nice approaching storm shot from the Valley View area tweeted to me by @Hokie_94.  Storm chasing and photography will be very much in our discussions the next few weeks — the first Virginia Tech storm chase trip leaves Blacksburg Tuesday (with Chris White as a co-leader) and the second leaves around Memorial Day (with me as a co-leader)! I think the first-trip group will get some central U.S. severe weather action next weekend.

The cold front that caused the storms has pushed through and a cooler, drier air mass is settling in for the next 3 days or so. We’ve talked a few days about the potential for freezing temperatures and/or frost both Monday morning and Tuesday morning in at least part of our region. The National Weather Service in Blacksburg has issued a freeze watch for Monday morning some counties along the West Virginia border (Craig, Giles, Bland) and along and west of the I-77 corridor (Tazewell, Smyth, Grayson) as well as mountainous counties in its forecast area in West Virginia and North Carolina. I would not be surprised to see freeze watches or warnings eventually issued a little farther east — especially on Tuesday morning — and frost advisories expanded to include most of our region, even into Southside and Piedmont counties, over the next couple of days. Temperatures near or below freezing are likely in most of the area west of Roanoke on Monday and Tuesday mornings, plus some outlying areas and sheltered valleys elsewhere. On Tuesday, the May 14 record lows of 31 at Blacksburg and 37 at Roanoke (both set in 1996) could be in jeopardy. Maximum radiational cooling conditions — clear skies and calm winds for several hours — could also challenge Roanoke’s latest freeze date, which, dating to 1912, was May 11, 1966. Short summary: It would be wide to protect tender outdoor vegetation on Monday and Tuesday mornings, even in the urban areas of Roanoke city.

We’ll shoot back into the 80s by Thursday. As we challenge May records for cold on Tuesday, temperatures may push toward 90 in what has been a very cold Upper Midwest this spring, places like Chicago and Minneapolis. The topsy-turvy, sometimes upside-down spring continues.

Just enough warmth and moisture combined with an upper-air impulse moving just to our northwest triggered a few strong to locally severe storms Friday evening with a smattering of high-wind reports — primarily 2 reports of downed trees in both Montgomery and Botetourt counties. There will be some threat of showers and storms until a cold front pushes through Saturday afternoon, though we’ve probably used up most of the instability for stronger storms on Friday evening, and likely won’t recover it before the front moves through. The main threat of severe weather will shift into central and eastern Virginia, where the front may arrive at just the right time to bite into greater daytime heating and more humidity. The weather map at left from the Weather Prediction Center depicts two cold fronts, and second that will arrive late Sunday — an otherwise pleasant  Mother’s Day with sunny skies and temperatures rising into the 60s, maybe even scraping 70.  It’s behind the second cold front that unseasonably cool, dry air will arrive for a couple of days. That’s where our concern for frost/freeze conditions lies for Monday and Tuesday mornings. The key will be whether the sky clears sufficiently of clouds and the winds die down enough for maximum radiational cooling conditions to develop one or both mornings. If those conditions are realized, Roanoke’s all-time latest freeze date of May 11 could be broken (better chance on Tuesday, May 14), and many locations to the west could land in the mid-upper 20s. Right now, it appears a disturbance moving through Monday might stir up just enough wind and clouds on Monday evening to quell the cooling a little and keep us more in the 30s to near 40 range. A close call on that, and either way, it would be wise to take care of tender outdoor vegetation for each of those mornings.  There will almost certainly be some scattered frost, at least.

PHOTO OF STORM MOVING OVER DOWNTOWN ROANOKE — ESTIMATED 45 MPH WIND GUSTS

LATEST VIEW OF SOUTHWEST VIRGINIA RADAR

While the greatest threat for severe weather and greatest risk for widespread heavy rain will pass well northwest of our region, a cluster of showers and storms with some heavy rain has developed along the I-77 and I-81 corridors in Southwest Virginia and is moving northeast through the New River Valley this evening. The heaviest activity is likely to be primarily west of I-81, but some of it may slip eastward into the areas along the Blue Ridge and into the Roanoke Valley as well. This is being caused by an upper-level impulse slipping northeastward through West Virginia. We’re catching the southern fringe of its influence, but that could be enough for some localized flooding with heavier downpours this evening. A localized severe wind gust can’t be ruled out entirely, either. There could be additional rounds of showers and storms overnight and into Saturday before a cold front clears the region by evening. Sunday still looks to be somewhat cool (60s highs, 40s lows) but mostly clear day for Mother’s Day, and we could be dealing with some frost and possibly freezing temperatures, especially  west of Roanoke, by Monday and Tuesday mornings. And then it could be 80 again by Wednesday afternoon. Jump on the spring roller-coaster, with a few rumbles and some splashes along the track this evening.

Roanoke recorded its first 80-degree high of May on Thursday. 2009 is the only other time in the last decade it took 9 days in May to reach 80 degrees. We may see another 80 in Roanoke, and 70s to the west (it was 74 Thursday in Blacksburg) on Friday. A cold front is approaching from the west, and will arrive by late Saturday (at left). There could be some showers and storms by Friday evening, more likely during the day on Saturday. It looks like neither a widespread heavy rain event or a ballistic severe weather episode, though some locally heavy rain and severe storms (58+ mph wind gusts, 1-inch or larger hail) are possible with warmth and some moisture streaming ahead of the front. Fronts from the west not supported by low-pressure systems moving from near the Gulf to provide more moisture and southeasterly upslope wind flow often leave us with weaker showers and storms, because of the  mountains’ effects of shortening updrafts and drying downslope wind flow. But the odds at this point do favor us getting wet on Saturday, with some rumbles of thunder. It should pass quickly, though, and leave behind a gorgeous Sunday for Mother’s Day, with lots of sunshine and mild temperatures rising into the mid 60s to lower 70s.

We will see two cold mornings on Monday and Tuesday, with some range in guidance about just how cold. The upper end would suggest mid 30s to low 40s lows; some of the lower guidance would lead to the latest freeze on record at Roanoke with widespread mid 20s to low 30s. We’ll take a closer look at the frost/freeze potential over the weekend as we move closer in time. The middle to latter part of next week could see quite the opposite, with some highs in the 80s possible.

We’ve been talking about this cut-off low since before I took my 3-day absence a week ago, so I’m quite ready to move on — and after 3 days of cool rainy days I’m sure most of you are too. Looks like we get to do that on Thursday, as it finally pushes northeastward away from us. The remaining residual effect may be some scattered afternoon showers and storms as highs push above 70, boiling up some of the moisture, plus any weak disturbances or boundaries that can rotate around the backside of the low. The Weather Prediction Center is showing very minimal amounts of rain for the next 24 hours. We likely get three consecutive days of highs in the 70s after six days in a row when it has failed to reach 70. A cold front pushes in Saturday, but it looks likes more like our typical spring cold front from the northwest, with a quick shot of showers and storms Friday night and/or Saturday rather than anything like the marathon rain we just experienced.

I’m going to go ahead and post this graphic — Tuesday morning’s projected lows on the 12Z GFS (courtesy Allan Huffman’s RaleighWx forecast models page) — even though it’s still a bit far out to get specific about this. The GFS has been consistent in showing lows dipping below freezing west of Roanoke and very near freezing to the east on Tuesday morning (and almost as cold on Monday morning). Behind this weekend’s cold front, high pressure may eventually settle right on top of us, which could lead to a clear, calm night or two in which radiational cooling will be maximized. The 32 on the graphic is very close to Roanoke’s position — a freezing temperature on May 14 would set a record for latest freeze if it occurred, the standing record being May 11, 1966 (nearly happened May 22, 2003, when it dropped to 33).  A freeze occurred as late as June 11 in 1972 at Blacksburg, but the record low for May 14 is only 31, set in 1996. Next week will bring drier weather, so temperatures may shoot up from these cold morning lows well into the 60s and 70s in the afternoon. While it may not end up quite as cold as this model is showing, it’s important for us to keep this potential freeze/frost situation in mind because of its potential disruptive impact on gardening and agriculture throughout the region.