#vawx No chasing foreseen today but next week looks potentially busy

Nope. Nothing worth a chase today. There will be a diffuse cold air damming type wedge front along the U.S. Route 501 corridor but that’s it. Surface winds on both sides of the boundary look very weak and there isn’t any apparent upper level support for convection. Thus none of the short range convective allowing models are showing anything interesting. In fact vertical velocities at 500 mb are forecast to be negative this afternoon across that region.

However next week appears to hold several chances for severe weather across the Old Dominion. Originally Sunday looked to be juicy but last night’s 0Z GFS backed off on that potential. (That’s good since I have another weather-related commitment Sunday afternoon!) But several days next week could well provide chasing action so I’ll be monitoring those setups.

So, on to this morning’s tornado drill.

#vawx A wedge front for a Tuesday chase?

In an effort to NOT be caught unaware of the next chasing opportunity I glanced at the SPC convective outlook for Tuesday 3/21 and then checked out several models. Interestingly enough there is sufficient instability and shear showing up Tuesday afternoon to catch my attention. However a peek at forecast soundings puzzled me as the winds are northwesterly at pretty much all levels at the locations I checked. What could be a lifting mechanism?

Then I checked the NAM suite of models and found this at 21Z Tuesday. It’s a surface wedge front aligned roughly with U.S. Route 501 from South Boston to Lynchburg VA. (I added the white dotted line to delineate it.)

wedge front 06z NAM 21Z Tues

Courtesy Pivotal Weather

The GFS also shows a wedge boundary near this location but it sets up a few hours later after dark Tuesday evening. Oh, and none of last night’s 0Z WRF runs show much convection in Virginia tomorrow afternoon.

So it looks like I’ll be inspecting the models both today and tomorrow morning to determine whether a chase ventured would be worthwhile. The irony? Tomorrow at 9:45 a.m. is the statewide Virginia Tornado Drill.

 

 

#vawx Today’s chase sneaked up on me

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I had no expectation of a chase today (Saturday 3/18), only four days after the snow/sleet bust here in Virginia. However when I noticed SPC had a chunk of the Old Dominion under a General Thunderstorm risk I checked the short term models. ALL of them (HRRR, RAP, 3 and 4 km NAM, and three different WRF models) showed storms firing over the Piedmont this afternoon. A couple of cells even showed decent updraft helicity.

Checking the surface observations revealed Td’s in the 40s, pretty low for storms to form. Thus CAPE was only a few hundred j/kg but both low-level and bulk shear were robust. A short wave – Alberta Clipper – was forecast to provide uplift and when I checked 700 mb temperatures I knew why. Coupled with the available surface based CAPE those upper level temperatures of -7 to -9 screamed of early spring storms that would produce small hail. Just after I’d decided to go chasing the SPC upgraded much of Virginia’s Piedmont to a Marginal Risk. (It was nice to know the pros agreed with what I was seeing!)

I motored to Gretna ahead of the first line of showers and wound up slipping just east of town to watch it approach. As it did I experienced the rush of lightning/thunder couplets that I’d been missing all winter. In addition some pea-sized hail (1/4″) rattled off the chasemobile which I promptly reported to the NWS.view from E of Gretna

When the rain set in I moved east along VA Route 40 and then dropped southeast via the Cody Road. I stopped a few times amid the steadily developing rain to watch the system approach. This was a neat shot of the leading edge at one stop:leading edge approach

As the complex continued to grow the northern end took aim at Brookneal and intensified. Instead of plowing thru steadily worsening rain (and hail) I turned south on U.S. Route 501 to head toward the end of the line. I stopped and waited just north of Halifax and had more small hail rattle off the vehicle before continuing south thru town where a third round of stones made its presence known.

I had noticed on radar a trailing cell heading east across the Danville area so I turned southwest on VA Route 360 to catch a glimpse. When I did find an open vantage point I noticed a very likely – and visible – hail shaft coming out of that cell:hailshaft E of Danville

At this point I decided to let the action continue east without me but I did stop a bit later  to catch this structure shot of that “Tail End Charlie” storm:backside structure shot

And after I grabbed some dinner near Blairs I motored toward home, stopping along the way to snap this sunset photo:sunset

Overall it was a pretty decent surprise chase today. I hadn’t seen an early spring hailfall for a few years so this filled that need.

#vawx A look back at a Pi Day 2016 chase

A year ago today SDS (supercell deprivation syndrome) was strong enough that I bit on a setup across Southside Virginia. The southern edge of a cold air damming wedge was hovering near the NC/VA state line, prompting the SPC to issue a Slight Risk for that area. Thus I moseyed down to the U.S. Route 58 to await the action.

This was the best view I had of convective towers that day, looking south from Martinsville. The chase territory in that part of North Carolina is not good but I did drop south to the Eden vicinity and noted that these towers were still well south of me. Towers S of Martinsville

I headed back north to Martinsville again to await more action. Unfortunately the wedge surged southward as evening approached and created a ground fog that reduced surface visibility to a couple hundred yards. Discrete storms did fire but I couldn’t see anything and wound up dodging a couple of hail cores amid the atrocious visibility.

As for Pi Day 2017? The snow/sleet/ice storm just departed the area for New England not long ago.

#vawx A March 1st B-U-S-T

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It sucked.

Yes, that’s crass, borderline vulgar, and its use hints at a narrow vocabulary. But “sucked” characterizes today’s chase perfectly.

Just in case folks might forget this was today’s SPC Day 1 convective outlook this morning:va_swody1-march-1

The threat was upped from a Day 2 Slight Risk to an Enhanced Risk for a good chunk of Virginia. Adding fuel to the fire was a Severe Thunderstorm watch issued for much of western VA just after 10:30 am followed closely by multiple Severe TS warnings in my chase area.

After perusing the short term models this morning I determined my initial chase target to be Bedford. A squall line was to blast across the mountains and enter the Piedmont during the early afternoon, possibly firing discrete cells out ahead of it that would take advantage of a juicy environment to rapidly intensify. Knowing full well that storm motions near 60 mph meant I needed to get out early I planned to leave home at noon.

However after watching the radar for a while the storms seemed to be ahead of schedule, the first indication of a potential problem with the morning model solutions. Thus I departed a little after 11:30 and based on the storm motions and timing that should have given me 30-45 minutes of lead time once I got to Bedford. Alas, that was a pipe dream. The squall line was perhaps 10 minutes behind me when I arrived in Bedford. Given a stop for gas and a potty break much of that 10 minutes was squandered.

The next couple of hours involved rapid decision making and maneuvering across rural Bedford county with the rain and wind nipping at my heels. I did stop – very briefly – in a western section of the county to snap a few photos and live stream for literally a couple of minutes as the line approached.shelf-cloud-over-western-bedford-countyWhen it inevitably drew too close I retreated south and east to Altavista where I picked up U.S. Route 29 and dove south to Gretna. There I stopped just as the line arrived with a burst of wind, a spit of rain, and then…nothing. No mesocyclones, no hail, no wall clouds, and not even any lightning.

Instead of a juicy environment forecast by the models that could be energized by this massive outflow boundary the Piedmont was stable and capped. Rather than surface dewpoints in the 60s per forecasts most stations were showing 50s before the line and 40s behind it. And every time I checked the surface-based CAPE values on the SPC mesoscale analysis page it showed the entire region under significant convective inhibition, e.g. capped. (The shear WAS awesome.)

Thus I glumly sat in Gretna for quite a while watching radar as the line petered out and overcast cold clouds blocked the sun. Another stormchaser – Alex Thornton – joined me there for a bit and we monitored radar as a broad area of rain built over far southwest Virginia. This, too, hadn’t shown on the model solutions I remembered perusing.

I finally bade Alex farewell and motored west to a vantage point near Climax for this very unconvective western view:western-view-from-climax-rd

Chastened, I rolled west toward Rocky Mount only to hear to my utter disbelief that another Severe Thunderstorm Watch had been issued that included Pittsylvania and Halifax counties. Those counties had been capped previously and were now under dense cloud cover with dewpoints in the mid-40s. I didn’t buy into that Watch and therefore ignored it, heading back home to ponder if the White family Moderate Risk curse had been extended to Enhanced Risks.

A very disappointing “chase” if I say so myself.

#vawx Another round of early season convection in Virginia

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Oh why not start meteorological spring off with a convective bang?! Wednesday – March 1st – looks to be a rumbly kind of afternoon across much of the Mid-Atlantic. SPC has almost all of Virginia in a Day 3 Slight Risk:va_swody3-copy

Today’s 12Z 4 km NAM is hinting at discrete cells ahead of an approaching line during the late afternoon:nam4kmma_prec_radar_057

The 4 km NAM forecast CAPE is >1000 J/kg and 0-6 km shear values are over 70 kts at the time of this graphic. Cell motions are well over 50 kts to the ENE!! (The 12Z GFS is less ballistic but it does show a classic high shear / low CAPE setup.)

This obviously bears watching as a Day 3 SPC Slight Risk is nothing to sneeze at. Whether it will result in a squall line (can we say shelf clouds and strong straight-line winds?) or discrete storms is still TBD. But with those predicted storm velocities the location where I choose to start the chase will be critical. These things will be zooming along at better than highway speeds.

#vawx A successful unsuccessful February chase

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At the last minute I decided to chase today, albeit with a self-imposed eastern limit of the U.S. Route 501 corridor due to other priorities. Based on several convective allowing models – HRRR and several WRF models – I motored south to the Danville area. The models consistently showed a couple of large cells firing in that vicinity with significant updraft helicities (i.e. rotating cells).

I left home a bit earlier than I’d planned to get ahead of a rain shower. Thus I moseyed to Rocky Mount and then to Gretna, stopping along the way to watch a line crossing the Blue Ridge. While motoring east on VA Route 40 I could see convection bubbling up to the south so I turned south at Gretna, stopping just south of Tightsqueeze. After watching towers grow there for a while I decided to work my way further south and east. I wound up northeast of Danville with this southern view:waiting-for-things-to-take-off

About this time some towers I could see further south were beginning to show radar returns so I maneuvered along rural roads to get to this vantage point just east of Danville.this-was-the-one-i-waited-for

This cell went up at the time and place predicted by the models so this was IT. I retreated east ahead of it on U.S. Route 58, stopping to watch a couple of times. Unfortunately the storm’s motion took it across the back country toward South Boston faster than I could keep up with it even using highway speeds. Thus it escaped and went on to become – I think – this classic supercell well to my east:img_6360

Frustrated, I pushed north through South Boston  and watched more cells build. I found a rural spot southwest of Halifax to observe this storm as it came right at me:

I actually let it wash over me to check if it contained hail but all that fell was rain. But before I left this location I noticed an interesting feature under the right (north) side of this cell. I photographed it from here and then moved a couple miles north and west and snapped it again from another angle:

It certainly appeared to exhibit shear but that’s about the most notable thing associated with this storm.

So I was in the right spot at the right time when the storm-of-the-day fired. That’s a success. But I didn’t see anything resembling a severe feature. In fact the storm bases all looked pretty bland. That’s an unsuccessful chase.

#vawx Could Saturday bring a reprise of the February 2016 severe weather outbreak?

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Today is the 1 year anniversary of the very unusual February 2016 tornado outbreak here in Virginia. Ironically with temperatures in the 70s today and a cold front on the way another round of February severe weather could be on the horizon. Here’s the SPC Day 2 convective outlook covering Saturday 2/25:va_swody2

This is “only” a Marginal risk vs last year’s Moderate risk. The forecast shear vectors are closely aligned to storm motions, hinting at a squall line (sorry, QLCS for the weather terminology sticklers). However this model graphic shows some robust updraft helicities near Richmond and northeast of DC tomorrow afternoon:uh25_001h-us_ma

Thus there’s a potential for rotating supercells along and east of the I-95 corridor tomorrow afternoon that could feature large hail and perhaps a tornado or two.

Unfortunately that’s too far east and not robust enough for me to consider chasing. Moreover I have a local commitment Saturday afternoon which prevents me from straying too far. I will, however, keep an eye on radar here in Roanoke and may venture out to a local vantage point in the morning to watch the line go thru. I don’t expect to see much but why totally pass up a wintertime chase opportunity?

#vawx Talking about chasing increases the desire for the 2017 season to begin

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I gave a storm chasing presentation in a Survey of Meteorology class at Virginia Tech this afternoon, concentrating on the 2016 chase season here in Virginia. Talking about those experiences made me look back at the YouTube clips from last year and I realized I hadn’t watched this particular video for a while.

It’s from April 28th near Chatham VA, looking west at the second storm I observed that day. A ground-scraping wall cloud formed before the overall storm weakened.Storm_2 wall cloud

The wall cloud then morphed into a roll cloud separated from the parent updraft and that’s what the video clip shows. Speeding up the video 8x reveals the horizontal rotary motion of the roll cloud as it moves away from the storm.

Meanwhile I’m still keeping an eye on tomorrow’s potential for thunderstorms along the I-81 corridor in southwest Virginia. Parameters look borderline for severe weather but if something fires up close enough I could be tempted to venture out for a looksee. I’m not planning to chase Saturday’s setup due to other commitments so Thursday is my only chance this week. (Indiana on Friday is tempting but…no.)

 

#vawx Thunder on Thursday? Perhaps

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Last night’s online Hangout discussing the 2016 Virginia storm season was a rousing success. Can that translate into Old Dominion thunder this week?

A cold air damming wedge has set up across much of Virginia today and will be reinforced by showers on Wednesday. Thus neither the NWS Blacksburg forecast discussion nor the SPC outlook for Thursday has any mention of thunder. However…

The last several runs of the GFS model have seized on the concept of a wedge boundary setting up across the Piedmont Thursday. By late afternoon the eastern edge of the wedge seems to align with the U.S. Route 29 corridor. The resulting dewpoint map looks like this at 21Z (4 pm EST) Thursday:21Z Thursday dewpoints.jpg

Checking the forecast sounding at 21Z near Altavista VA yields a CAPE of >1000 j/kg with relatively weak bulk shear, although the directional shear turns nicely from southerly surface flow to westerly winds at 500 mb.

Is this worth getting the chasing juices stirred up about? Maybe not, but if this GFS trend holds and some of the shorter range models pick up on it a trip over to Rte 29 Thursday afternoon might be justified. That’s about as far as I’m willing to travel this early in the chase season.