WEATHER JOURNAL column: Tornado season awakens (also includes a link to local assistance efforts for Oklahoma)

UPDATE 11 PM: While it doesn’t appear a well-organized cluster of storms will plow through Southwest Virginia tonight, some storms with heavy rain and gusty winds have been occurring primarily west of I-77 and north along the Virginia-West Virginia border. These storms may linger a while overnight, even drift north or east a little bit. We’ll have chances of storms Wednesday through Friday as a cold front approaches from the west and daily warmth and humidity continue. END UPDATE

Some counties in Southwest Virginia west of Interstate 77 are under a severe thunderstorm watch until 10 p.m. because of cluster of thunderstorms that has actually propagated eastward out of Monday’s tornado outbreak in Oklahoma. The line of storms now in central Tennessee and Kentucky is encountering more unstable, sun-heated air as it moves eastward and poses mainly a large hail/strong winds threat eastward. Though there are some reasons this line may diminish later crossing the Appalachians or running out of daylight, I would advise Roanoke/New River valley folks to keep at least an eye and an ear out for this (RADAR LINKED HERE) as it approaches this evening. Sometimes these “mesoscale convective systems” — MCS’s, in weather geek talk — sort of get a mind of their own about where and how fast they want to travel, as their updrafts and downdrafts actually change the weather conditions around them, defying forecast models. The cluster is moving east-northeast, so it’s pretty much on a beeline for all of Southwest Virginia, IF it were to maintain its strength and heading. Other scattered showers and storms may pop up this afternoon simply because of the heat and humidity.

Courtesy Hokie Storm Chasers Facebook page

At left is an image of a possible tornado photographed by the Hokie Storm Chasers on Monday somewhere near the Red River (southern Oklahoma or northern Texas). We say “possible” because it is unclear if the funnel is in contact with the ground behind the cluster of trees. As you know, Monday was a vicious severe weather event in the southern Plains, particularly because of the deadly tornado at Moore, Okla., in the Oklahoma City suburbs. That storm has recently been rated EF-5, the highest on the scale, based on some new findings by the National Weather Service office in Norman, Okla. The Hokie Storm Chasers are in Texas today on what is likely to be their last day of tagging severe storms before the first team returns home. A second team is headed out on Sunday or Monday for 10+ days — I will be on that trip as a co-leader, which I will be posting about on the Weather Journal blog. In the Weather Journal column also posted at top, I discuss the current upsurge in tornadoes as I prepare for this trip. 

The soupy air of the weekend will slowly become a little less so the next few days over Southwest Virginia, as the slowly weakening “obnoxious” upper-level low drifts eastward and weak high pressure takes its place. Coverage of showers and thunderstorms — some of which dumped flooding downpours on parts of far Southwest Virginia on Sunday (this map shows the spotty nature of radar estimates of rainfall from Friday through mid-evening Sunday) — will be less today than it was Sunday, and even less on Tuesday, though likely not zero. Where it does rain, it could do so hard for several minutes, and with some sunshine poking through to heat the air near the surface, a few stronger thunderstorms popping up are possible. By later in the week, about Thursday, a cold front  currently terrorizing the central U.S. with severe storms and tornadoes, will be approaching, and this will up the ante on showers and thunderstorms again. Though we certainly won’t have the atmospheric dynamics that led to Sunday’s killer tornado at Shawnee, Okla., the potential for severe storms is likely to be higher later this week when the front arrives than it has been all spring to date — though without a low to the south to pump in Gulf of Mexico and/or Atlantic moisture as we’ve seen the last couple of days, overall rainfall amounts probably won’t be that great across the area.

Hokie Storm Chasers look at a wall cloud on a supercell near Hays, Kansas, on Saturday. — Courtesy, Hokie Storm Chasers Facebook page

The Hokie Storm Chasers — who have had two days of  tagging big supercell thunderstorms but have yet to spot a tornado amid the Plains outbreak — will have another opportunity today with yet another moderate risk of severe storms. On Sunday, the team was on a storm that spawned a tornado in Wichita, but had to bail out for safety reasons just before it entered the metro area — we generally do not chase storms in metro areas. This first trip — also being covered by WDBJ Channel 7 in the field for the first time — will be wrapping up late this week, and I’ll be Plains-bound with the second group starting near Memorial Day, my ninth year to be on board, eight as a co-leader.

Speaking of Memorial Day — that weekend is looking really nice for Southwest Virginia at this point, with warm temperatures and likely dry weather.

UPDATE 7:40 AM, 5/19: Just roll this over again for today (Sunday): More periods of showery rain in Southwest Virgnia, more threat of high-end severe storms and tornadoes in the central U.S. where the first of two Virginia Tech teams of storm chasers are. END UPDATE

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.

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.

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.

There isn’t much time to blog or organize photographs when you’re driving late into the night dodging storms in the Plains states. So only in the past few days of dry, calm weather here in Southwest Virginia (expected to continue through the weekend) have I had much of a chance to look back at the two 2012 Virginia Tech storm chase trips. We were out 16 days — 7 on the first trip (May 15-21), 9 on the second trip (May 28-June 5) – and had 8 storm days — 2 on the first trip, 6 on the second. While a few days fell short of expectations and felt a little like “busts,” we did not fail to observe a severe storm on any day we chased. By far, our May 29 chase in Oklahoma was the most intense, as we followed 2 supercells starting at initiation, saw numerous wall clouds and other cloud structures signifying rotation, and spotted a tornado after dark. Late-afternoon/early evening storms became the signature feature of these trips, with six of the eight chase days featuring storms right at sunset and/or after dark. On both May 19 in Beatrice, Neb., and June 4 in Sikeston, Mo., (the famous Lambert’s Cafe, home of the ”throwed rolls”) our dinner stops had to be hurried as new storms fired close by. Lightning was often so intense with the supercells  –particularly on May 29 in Oklahoma, June 2 in the Oklahoma Panhandle and June 4 in southeast Missouri – that we could see almost as much cloud structure at night as we would have in the daytime.  The photo gallery below captures many of our best storm intercepts — plus tourist stops at Monument Rocks in Kansas and Palo Duro Canyon in Texas. (You can click on “Show info” on each photo for photographer and caption information.) Virginia Tech and Southwest Virginia can be proud of how these young people represented you, and Middle America can be proud of the generosity and appreciation with which we were received.

Monday was a legendary day for the Virginia Tech storm chasers. We drifted across southern Missouri knowing there would be some threat of severe weather, but our two main objectives were (1) seeing the damage path and rebuilding efforts at Joplin from the deadly May 22, 2011, tornado and (2) eating at Lambert’s Cafe in Sikeston, Mo., the home of the “throwed rolls” in the southeast part of the state. We entered the restaurant with a storm to the north — looked like it could be a decent storm, a little wind and heavy rain, nothing extreme. But in the time our dinner was served, it ramped up into an intense supercell, with extremely rapid and vivid lightning illuminating striations and wall clouds the equal of any storms we would see in the Great Plains. And we were perfectly positioned from the parking lot to observe it — for a little while.  Once it became clear that a second cell with large hail was moving directly toward us, and the original storm had been given a tornado warning, we hurriedly finished our meal, got some takeout boxes, and took to the road to position ourselves better to observe the storms. I hope to get up some of the video and/or video stills in days to come.

We stayed in my hometown of Jonesboro, Arkansas, overnight and plan to return to Virginia this evening. I hope to resume regular Weather Journal blog coverage by Thursday.

Three quick links for a cool early June Sunday morning in Southwest Virginia:

Spring 2012 — March, April, May on the meteorological calendar was the warmest on record at Roanoke (dating to 1912) and at Blacksburg (dating to 1952). While April and May averaged above normal in temperature, it was really the extreme March that was the key in the spring warmth record.

The National Weather Service at Blacksburg will be looking into whether or not a tornado touched down in Botetourt County on Friday, based on a photograph by Botetourt View reporter Cathy Benson.

And finally … the Virginia Tech storm chasers had a good day Saturday tagging intense thunderstorms in southeastern Colorado and the Oklahoma Panhandle. We’re expecting to leave Guymon, Oklahoma, where we’ve been four straight nights, for eastern Kansas and a possible heightened risk of supercells and perhaps a few tornadoes on Sunday. At this late hour … I’ll leave it to fellow chase trip co-leader Chris White to provide some words and pictures from our day.

There were three areas of severe weather in the country on Friday, as seen on the Storm Prediction Center torm reports map. One was the east, with numerous wind damage and hail reports and a few tornado reports, most prominently the one that moved through parts of Hampton in southeast Virginia. The second was in the Texas Panhandle, where the Virginia Tech storm chasers observed some supercell storm structures, though the sparse road network didn’t allow us to position ourselves as well as we would have liked. And then there was a third in South Dakota, considered a marginal chance Friday morning, but ending up producing a few tornadoes.

Cooler, drier weather is moving into Southwest Virginia for the weekend, as the jet stream takes a big dip in the Eastern U.S.

Meanwhile, we’ll take another stab at Plains supercells on Saturday, quite likely in the Texas Panhandle once again.

TORNADO WATCH UNTIL 9 PM FOR ALL OF WESTERN VIRGINIA

A cold front is pushing into warm, moist air ahead of it today, with some degree of shifting winds aloft. That is a recipe for a substantial severe weather threat over the state of Virginia. There are some uncertainties in that seemingly straightforward forecast. One is the current showers and cloudiness over much of Southwest Virginia that could limit warming and therefore destabilization of the lower layers of the atmosphere. Also, as the National Weather Service-Blacksburg points out in its morning discussion,  there may be a chance of the “Blue Ridge jump,” where a storm line forms far to the west and then re-forms east of the Blue Ridge, with the stronger storms skipping over some or all of the New River and Roanoke valleys. All that said, there is enough lift with the cold front and certainly enough moisture that strong to severe storms will be a significant possibility during the afternoon. Strong downburst/outflow winds will be the greatest severe risk for Southwest Virginia, as shown on the Storm Prediction Center’s morning map rating the chance as high as 30 percent of occurring within 25 miles of any given point. The tornado risk is greater mostly north and east of our region, owing to somewhat better atmospheric shear and greater instability with more daytime heating. There will probably be a few tornado reports in central/eastern Virginia later today, though a large tornado outbreak on the scale of those of April 2011 does not appear to be likely. The pattern is more that of a strong summer severe setup rather than a spring outbreak. The more the sun shines at your location and the farther east you are, the better your chance of high winds, large hail and isolated tornadoes in storms today.

Being in the field with the Virginia Tech storm chase in the Oklahoma/Texas panhandle region -- the only other slight risk of severe weather on the Storm Prediction Center’s map today, where coverage will be much less than Virginia but the potential for supercells  higher — I will be unable to provide ongoing updates today. You can follow radar and the latest watches and warnings on the Radar / Future Cast link in the right margin of this blog.