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.

UPDATE 4 PM: The flood watch has been lifted for Southwest Virginia. Some flood warnings remain in effect for local rivers, such as James River at Buchanan in Botetourt County. END UPDATE

FLOOD WATCH RE-ISSUED FOR MOST OF WESTERN VIRGINIA THROUGH THIS EVENING

A large area of moderate to locally heavy rain is moving southeast from West Virginia into Southwest Virginia. That’s right, I said southeast — after two days of odd east to west/southeast to northwest motion on rain and storms we’ve returned to a “regular” direction of movement, because we’re now behind the low, centered just north of us. This will add to rain totals and may exacerbate flooding or at least slow runoff in some areas still suffering it. (Latest information on rivers/creeks linked here.) Rain will obviously be more widespread in Southwest Virginia than earlier thought and likely with heavier amounts than previously anticipated (more than a half inch for most, an inch plus for some.) The system is continuing to slowly unwind and drift northeast, though, and will probably be (mostly) out of our hair by tomorrow.   Check out local radar for the latest. 

TODAY’S WEATHER JOURNAL COLUMN: Cold, snow dip far south in May

WEATHER JOURNAL COLUMN: Cold, snow penetrate deep to the south this May.

UPDATE: 9 AM, 5/8: A large area of moderate to locally heavy rain is moving southeast from West Virginia into Southwest Virginia. That’s right, I said southeast — after two days of odd east to west/southeast to northwest motion on rain and storms we’ve returned to a “regular” direction of movement, because we’re now behind the low, now centered just north of us. This will add to rain totals and may exacerbate flooding or at least slow runoff in some areas still suffering it. Rain will obviously be more widespread in Southwest Virginia than earlier thought and likely with heavier amounts (more than a half inch), at least for some. The system is continuing to slowly unwind and drift northeast, though, and will probably be out of our hair by tomorrow.   Check out local radar for the latest. END UPDATE

Cut-off upper lows die slowly. Each day, this one is becoming just a little less organized, and rainfall is becoming more sporadic and diurnal — or connected more and more to daytime heating rather than remaining organized through the night. That doesn’t mean it can’t rain at night — some showers will be ongoing at almost all hours — and it certainly doesn’t mean there won’t be some heavy rain, though it’s getting more and more localized. But just as Tuesday’s rainfall spinning around the upper low tended to be more patchy than Monday’s, Wednesday’s will likely be even a little more sporadic. The North American Model simulated radar for Wednesday afternoon at left shows a fair amount of showers, storms and rain bands blowing up with daytime heating (you can see the swirl of the upper low, expected to be centered over Virginia, sliding a bit northeast from its North Carolina position much of today.) The Weather Prediction Center projects most of the area to get a quarter to a half inch in the 24 hours through Wednesday evening – more likely, this will be an averaged-out amount rather than evenly brushed, with some spots getting more (a couple of inches would not be out of the question in a localized downour) and many getting less. The cut-off low had a cold enough center on Tuesday for some snow to reach the surface above 6,000 feet in the western North Carolina mountains, and for hail to develop in storms that typically wouldn’t be tall enough to support hail this time of year. Because of the presence of this cold air aloft, hail will be a possibility in some of the stronger storms on Wednesday.

By Thursday, the cut-off low will finally become not so cut off, pulled north and east away from us. That day could easily end up being sunny and quite warm (70s) with only minimal chances of showers and storms with some residual moisture and influence from the departing storm. A weekend cold front will bring the next organized chance of showers and thunderstorms Friday and Saturday — the kind that will move west to east, not this weird east to west we’ve been watching on radar the last couple of days. Early next week there may be a couple of frosty mornings — keep that in mind for outdoor vegetation.

SEVERAL FLOOD WARNINGS ISSUED AS STREAMS/RIVERS RISE FROM RUNOFF OF MONDAY’S RAINFALL; PARTS OF NEW AND ROANOKE RIVERS WILL REACH OR EXCEED FLOOD STAGE; FLOOD WATCH CONTINUES THROUGH TUESDAY NIGHT.

We are not done with rain yet from the cutoff upper-low that continues to spin in place roughly over Chattanooga, Tennessee. I do think most locations in Southwest Virginia have seen at least two-thirds of the total rainfall they’ll get through Wednesday, when the low finally wiggles eastward or northeastward and then gets tugged northward away from our region. But the upper-low will continue to spin some spokes of energy around, and tug in additional moisture off the Atlantic, for a few more rain bands and maybe even a few thunderstorms that could add to rain totals that have generally run 1 to 3 inches with some locally heavier amounts. Overnight and early Tuesday, showers and storms in North Carolina, some of which have been severe with some large hail, may connect and drift northward for rain in at least some of our region. Additional bands of rain and a few thunderstorms may recharge during the day Tuesday — the Weather Prediction Center shows much of the area getting at least a quarter to half inch of rain (dark green color in map at left) with a few spots of more (dark blue)  in the 6 hours from 8 a.m. to 2 p.m. on Tuesday. The concern overnight will be continued runoff from rain that has already occurred, plus any additional rain, raising creeks and rivers to near bank full or in some cases slightly over their banks. Barring an additional infusion of much heavier rain than expected, this does not appear as if it will be a major flooding episode, but beware that some lower elevations near creeks and rivers may become covered in water. As the National Weather Service regularly tells drivers who face water covering the road: “Turn around, don’t drown. “

UPDATE 9PM: SEVERAL FLOOD WARNINGS OUT AS STREAMS/CREEKS/RIVERS RISE FROM RUNOFF OF MONDAY’S RAIN; FLOOD WATCH CONTINUES THROUGH TUESDAY NIGHT 

Bullseye, Southwest Virginia. That’s what the Weather Prediction Center is showing for rainfall over the next 3 days, with the red colors indicating 3+ inches of rain with some localized spots of 4+. This will be the result of a slow-moving upper-level low, now making its way through northern Alabama and Georgia. The cold core of the upper low is no longer supporting snowfall as it did, unprecedented for May,  in the Ozarks of Arkansas and Missouri on Friday and Saturday morning, but has been supporting some hail in storm cells that wouldn’t typically be hail producers, as the freezing levels are unusually low over the Deep South. The counterclockwise flow of this low has already begun pulling thick moisture into our region off the western Atlantic — that was the curtain of low clouds and drizzle that moved in during the afternoon after a morning that had some sunshine. As this Atlantic moisture continues to be pulled in by the slow-moving low tracking south of us, the moist flow up the higher terrain and periodic disturbances rotating around the low will cause bands of rain to develop and move through. Some locations in northwest North Carolina have already topped 2 inches from periodic rain band through the day on Sunday. Rain looks to be showery on this Sunday evening with mostly light amounts in most of Southwest Virginia, but some heavier bands are likely to develop Monday and Tuesday, before the low moves to our southeast and eventually turns northeastward away from us. Rainfall amounts of 2+ inches will be capable of causing some streams and rivers to overflow, and 4+ inches may cause more serious flooding for some. It will just be a matter of monitoring how the bands develop and move the next couple of days to determine just how bad the flooding threat will be and where it will be the worst.

Temperatures will continue to be unseasonably cool. Roanoke and Blacksburg were 16 and 19 degrees cooler than normal with highs of 57 and 50, respectively, Sunday.  With rain and easterly wind flow around the low, temperatures will remain similar overnight and through the day Monday, and likely much of Tuesday too. That will mean some extraordinarily chilly 40s in many higher elevations (the blue colors on the NOAA map at left; some of the other numbers may be a bit generous). When the upper-level low pulls out by late week, there is no cold air mass behind it, so we may see a few days of seasonably warm (or even slightly warmer than normal) temperatures before another cold front moves through during the weekend or early next week.