#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.

#vawx Online Hangout to discuss 2016 season Monday night. Will 2017 season kick off this week?

Monday night’s Google Hangout to discuss the 2016 Virginia chase season is gearing up with 7 speakers! The fun begins at 8 pm tomorrow.

Meanwhile the 2017 season threatens to begin later this week as both Thursday and Friday look like decent setups for late February. Instability and shear are both on the table:

The big question is what would be the trigger for convection these two days? Neither day features a surface front close enough to create lift across most of Virginia, although Thursday does look like a lee trough east of the mountains could fire storms. We’ll have to watch the upper levels for jet streaks and short waves to see whether a chase is warranted.

Meanwhile back to focusing on Monday night’s Hangout…

 

#vawx February 20th Online Hangout discussion of 2016 Virginia storm chases

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Okay, here’s the scoop on Monday night’s (2/20) online Hangout discussing the 2016 Virginia storm chase season. The following are the planned participants – in no particular order – with their specific discussion topic:

Andrew Smith: 2/24/16 Waverly VA tornadic storm

Mark Overbeck: 6/23/16 Southside VA severe and tornado-warned storms

Peter Forister: 6/16/16 Orange County VA supercell

Dean Davison: 9/28/16 Vinton/Stewartsville VA severe storm

Patrick Gannon: TBD

Alex Thornton: 6/23/16 Southside VA storms

Me: 9/29/16 Southside VA hook echo supercells

I’ll work up the agenda and speaker order between now and Monday (and we’ll have Patrick’s storm and date by then as well). Each speaker will take 5-7 minutes to present their chase with photos, maps, videos, and whatever else they can fit into their time slot.

This looks to be a great discussion starting at 8 pm Monday and it’ll be viewable at this YouTube link.

See you there!!

#vawx Online Hangout to discuss 2016 Virginia Stormchases

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Since nothing convective is on the near horizon I’ve decided to create / attract some CAPE (instability) by hosting an online Hangout featuring several Virginia storm chasers. The event will go live at 8 pm Monday February 20th at this YouTube URL. I’ve invited each of the participants to present and discuss one of their chases during the very active 2016 season here in the Old Dominion.

Depending on availability there could be as many as 7 other chasers besides me so a number of different perspectives will be provided. I’ll be discussing my September 29th chase of two different hook echo supercells thru Patrick, Henry, and Franklin counties. It looks like the September 28th Vinton severe storm and perhaps the February 24th Waverly tornadic cell will also be topics. Once all the topics are submitted I’ll publish the list along with chaser names.

Hey, a chaser’s gotta do something to stave off the blahs this time of year!

#vawx Midnight “excitement” across the Southside?

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Given the well-after-dark convective development expected tonight this chaser won’t be out and about. (A forecast widespread area of rain doesn’t help matters either.) However it does look like things could interesting around Danville VA near midnight. Here’s an excerpt from the 14Z HRRR run showing updraft helicity at 05Z (midnight):05Z UD track.jpg

That track continues thru South Boston in later frames, eventually dissipating near the I-85 corridor. If true it’ll mean a significant mesocyclone crossing that area with perhaps large hail and the potential for a tornado. All this occurs on the east side of a developing surface low center along what appears to be a warm front.

If this were 6-8 hours earlier…

#vawx Chasing is a 4-dimensional activity

I’ve uttered the statement in the post title a number of times, usually to new chasers. It’s not enough to be in the right place to intercept a storm. One has to be there at the right time as well.

Wednesday’s setup is a prime example of this. First, here’s the SPC Day 2 convective outlook covering tomorrow:day2otlk_0700

Just the fact that the SPC forecasters have issued a Marginal Risk for Virginia in February is encouraging for local chasers. However after delving into the details the setup doesn’t look very promising.

First – per the this morning’s 12Z NAM – here’s the surface low progged to form along the cold front over eastern KY and TN:namma_sfc_temp_036

Note the time on the graphic: 0Z Thursday (or 7 pm Wednesday). That’s after dark so keep that in mind.

Now here’s the 700 mb (~10,000 ft) vertical velocity graphic for the same time:namma_700_vvel_036

The only convective lifting mechanism visible in this graphic is – you guessed it – the surface low that is forming courtesy of an upper level vorticity center scooting across the Midwest. Again, note the time: 7 pm Wednesday.

And one more graphic, this being the 12Z 4 km NAM graphic showing simulated radar returns at 10 pm Wednesday:nam4kmma_prec_radar_039

Precipitation is finally breaking out over the Virginia Piedmont ahead of the low and associated cold front…but this is well after dark tomorrow night. Following the model data out further in time the available instability and shear reach a (limited) maximum after midnight across the Piedmont.

Other models (GFS and several WRF models) support this timing. So given that night chasing is out of my bailiwick the conclusion is that I’m not going out tomorrow unless things change drastically in this evening’s model runs. Hence the blog post title.

NAM vs GFS = cheerleader vs. cautionary voice

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The NAM and GFS models differ on the potential for thunderstorms this upcoming week based on how each handles the magnitude and timing of events.

According to the NAM the best thunderstorm potential this week looks like Tuesday afternoon rather than Wednesday. This is the SPC Day 3 convective outlook for Tuesday:day3otlk_0830

As indicated by the shading the Piedmonts of NC and VA are delineated with at least general thunderstorm potential. This morning’s 12Z NAM output takes that potential to another level with this EHI outlook for 7 pm Tuesday (courtesy of Pivotal Weather):ehi03-us_ma

In conjunction with this surface map the NAM model sounding for Southside Virginia late Tuesday afternoon hints at enough instability and shear for severe weather to be somewhat likely. This is due to the NAM’s tendency to be very aggressive at pumping Gulf moisture northward, resulting in higher dewpoints further north than the GFS.

Meanwhile the GFS – with its more conservative moisture return – doesn’t show the same severe potential for Tuesday. But interestingly enough it has slowed down Wednesday’s cold front passage as an approaching shortwave trough spawns low pressure over the NC and VA Piedmonts late that afternoon:sfctd_b-us_ma Thus the GFS holds thunderstorm potential – albeit VERY slight – for Wednesday afternoon vs. Tuesday afternoon. The backing surface winds around such a low pressure center could providing interesting helicity values such that rotating updrafts could materialize…that is, if enough surface instability is present.

It’ll be interesting to see how the short range models (RAP, HRRR, and the WRF suite) handle this setup. Chasing potential in February is always something to take notice of as an antidote for rampant SDS (supercell deprivation syndrome).