#vawx A look at the rotation tracks for the 3 storm intercepts on Good Friday

For grins and giggles I looked up rotation tracks associated with the storms I chased yesterday. Here’s what I found.

For storm #1 (the one that dropped the tornado in Franklin county) here’s the low level rotation view at about the time of the tornado:1432Z rotation tracks storm #1

Now here’s the 1 hour rotation track ending just before I snapped photos of the storm:1444Z 1 hr rotation track storm #1

And here’s the rotation view (left) about the time I took the picture looking west on the right:

Obviously I was paralleling a weakening mesocyclone. It never regained the strength that it had when it produced the tornado.

Now for storm #2 which my son and I intercepted east of Rocky Mount parked just off VA Route 40 looking southwest. Here’s the 1 hour rotation view (left) with our location at the blue star and a photo of the updraft (right). Even though the radar reflectivity signature resembled a hook echo the rotation was weak and didn’t tighten up.

Next is storm #3. First, here’s a 30 minute rotation track (left)  that ends about 8 minutes after we pulled away from our vantage point at the blue star west of Chatham (photo on the right):

Now for “Tail-End Charlie” on the southern end of that line. Here are two rotation images at 4:26 pm (left) and 4:30 (right) p.m. Again, our location is at the blue star next to U.S. Route 29:

And just for reminders here is an image taken at 4:30 p.m. looking directly west at the southern circulation.view of rotation part of storm #3

It was obvious at this point that this area of rotation had weakened while the northern part had intensified so we gave chase via Rte 29. However we never caught back up with the storm as it zoomed northeastward. This was our final view from just southeast of the hamlet of Hurt:Final view of storm #3

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#vawx It was a very busy Good Friday

I have a confession to make: I don’t look forward to chase days like today. Low ceilings, lots of rain, rapid storm speeds (50+ mph), and messy line segments that morph into “rainy blobs” all translate into spending lots of time zooming around in the chasemobile and not much time outside ,watching convection. Throw in our family’s “Moderate Risk curse” (we’ve had very little luck under the big “M”) and today had all the ingredients of a trying and difficult chase.VA_swody1

Having said all that I did obtain a measure of enjoyment today DESPITE the early start. Given the dynamics and timing derived from short range models I was prepared to head down the driveway before noon…but then I peeked at the radar at 9:45ish this morning. A cell southwest of Martinsville was already exhibiting a strong rotation couplet and tracking northward so I hurriedly finished my chase preps and departed.

After plowing through heavy rain I finally reached an almost dry location near Burnt Chimney to stop and regain situational awareness. That storm (#1 of my day) had gone tornado-warned and looked as if it was tracking toward my position:IMG_1487

With both the storm motion and the polygon “leaning” to the east I decided that I needed to retreat in that direction. Unfortunately the lack of a helpful road network in that part of Franklin county coupled with the forward speed of the storm put me too far away when it screamed past my latitude. I quickly doubled back west on VA Route 40 to Glade Hill where I turned north on a rural road in an attempt to catch back up.

This was the best view of storm #1 that I was afforded during a very quick stop on that country route:First storm_r1

During that stop the inflow winds were ferocious, pushing me around while I snapped the picture. This was my location on the radar with respect to the storm:IMG_1492 I wound up traveling north of the Smith Mountain Lake area in a vain attempt to (a) find a vantage point to watch from and (b) catch back up with the business end. I finally called off the pursuit and reversed course to intercept more storms that were pressing northward.

By this time my son was out chasing and joined me at Glade Hill where we temporarily dropped a vehicle to chase together for a bit. Storm #2 was moving in our direction so we stopped to watch as this storm, showing broad rotation and a hook-like feature on radar, took aim at Rocky Mount.IMG_1500

We thought the rotation would tighten up but it never did and we didn’t see anything remarkable under this updraft nor did it receive any kind of warning:storm #2 nearing Rocky Mount

Given a break in the action we rolled onward to Rocky Mount for lunch where we listened to the locals talk about the tornado that had ravaged areas not far south of town. Photos and videos were all over social media so I had to chalk up another missed opportunity.

After our fast food “feast” we spent some extra time catching up on life before driving back to Glade Hill. There we picked up his vehicle and convoyed southwest to Callands in Pittsylvania county. We found ourselves in a dry slot between several discrete cells that had gone tornado-warned east of us and a severe-warned line of storms to our west. Given how fast things were happening we decided to split the difference with an eye toward intercepting the “Tail-End Charlie” cell on the line. It was showing interesting structure on radar:IMG_1512

We rolled east on VA Route 57 to find a spot from which to watch the line approach. This was the pleasant rural view we had for 20 minutes or so from the site we chose:Watching the line approach

When the line built east a bit we retreated in that direction to stay out of the rain. Just before we pulled away from this section of the squall line we had a good view of some nascent “greenage” that I tried – mostly unsuccessfully – to capture in a photo:bit of greenage under severe TS line

After struggling to find a spot from which to check out this action again we punted and drove through Chatham to U.S. Route 29 where we headed south at highway speeds. “Tail-End Charlie” had gone tornado-warned by this time so we stopped at a favorite vantage point just off Rte 29 south of Tightsqueeze to watch. This was our view of the updraft:storm #3 updraft

Per radar the circulation passed less than 3 miles west of us but we never saw anything notable visually:

Jumping back onto Rte 29 northward we diverted onto back roads east of Chatham to try and gain position on this accelerating storm. Falling further behind it we wound up pulling back onto Rte 29 to use the highway speeds to try to catch back up. We didn’t have much success. Thus at our final stop in rural Pittsylvania county near the village of Hurt we waved bye-bye to this storm as zoomed away.

Overall today was a decent chase day despite my misgivings. I can’t complain about that!

#vawx Could this be February 2016 deja vu all over again?

The “Big Event” is tomorrow, Friday April 19th, and the dynamics still look impressive. The SPC’s Day 2 convective update has pulled the Enhanced Risk area further north and west than earlier today:VA_swody2 (1)

Per the GFS cloud cover will limit instability although the NAM is still insisting the Virginia piedmont will see some sunshine. Regardless here’s the NCEP SREF plume viewer for MLCAPE in Danville VA:MLCAPE at KDAN

The median value peaks near 750 j/kg at 18Z which is somewhat low but not anything to sneeze at, especially given the bulk shear values over 50 knots:

0-6 km shear at KDAN

Having pored over a couple different runs of several models the overall consensus is that early showers and possibly strong storms across the I-85/I-95 corridor could put a damper on afternoon destabilization in that region. Meanwhile the area west of the I-85 corridor will see scattered convection during early afternoon that could tap into the available shear and provide some discrete rotating updrafts. These cells will be zooming north-northeast at 45-50 mph so “chasing” may be limited to “watch them scream by”.

Then a strong and wet squall line looks to intensify along a boundary and charge northeast. Timing of this activity varies a bit between models but it looks like a mid- to late afternoon event for the western piedmont with storms reaching the I-95 corridor just before sunset. Strong straight line winds accompanied by embedded supercells will very likely foster wind damage and localized flooding. A few tornadoes are certainly possible especially along breaks in the line.

This looks a bit like the February 2016 severe weather outbreak in which the NAM was more accurate with its “look at me, look at me!!” outlook than other models. Thus, after hunting for discrete cells ahead of the squall line my chase philosophy will be similar to that 2016 event: pick a west-to-east route and stay ahead of the line while watching individual cells zoom along it. My initial target is still up in the air (pun intended) but I usually don’t nail that down until the morning of…e.g. tomorrow.

 

#vawx Another Friday, another potential chase

The next chase opportunity looks like April 19th – Good Friday – with the SPC showing a 15% probability of severe storms in its Day 4 outlook:day4prob

Checking the two models available to me at that time the NAM is more bullish than the GFS (no surprise there!). Here are supercell composite parameter maps at 18Z Friday from both models courtesy of Pivotal Weather:

The limiting factor – again – is the amount of instability that’ll be available, with both models showing mostly cloudy to overcast skies all day Friday. Still, even the GFS at 18Z Friday has decent vertical velocity at 700 mb east of the Blue Ridge mountains:700hvv.us_ma

The GFS has a low level inversion across that area possibly due to earlier rain that would tamp down the instability. The shear looks robust enough but there may not be enough directional shear for mesocyclone development.

We’ll see. More to follow in Wednesday evening’s online Hangout at 8 pm. Join us!

#vawx A brief Palm Sunday stormchase

As it turned out I was able to squeeze in a short limited range chase today. After all how could I let a Palm Sunday setup go unchased given all the past outbreaks on this particular Sunday?

I hurriedly threw my gear in the chasemobile and rolled down the driveway just before 1:30 pm to intercept the “Tail-End Charlie” cell of a rapidly moving line segment headed northeastward through Franklin county. It had been tornado-warned for well over an hour by the time I got on the road. I planned my intercept to be near Bedford on U.S. Route 460 as this storm zoomed in that direction.

Dodging through Sunday afternoon traffic I kept an eye on the forward progress of the cell via radar as ceilings were fairly low which limited MK 1 eyeball visibility. I basically core-punched it as I scooted east on Rte 460 around the town of Bedford after I determined the risk of encountering hail or a tornadic circulation was basically nil. Driving through heavy rain I pushed east of town onto dry roads as the storm rushed northeast.

I turned north on a county road, stopping briefly to gather my bearings. While there I snapped this photo of the business end of “Tail-End Charlie” which had already passed by and was north of me:Storm NE of Bedford

Trying to keep up with it I twisted and turned along Bedford county back roads, finally winding up at the edge of a field just off VA Route 221 northwest of Forest. This was the radar view at the time:IMG_1468

And this was my view of the storm from that vantage point:cell N of Forest VA

Slow rotation was visually evident at the eastern edge of what looks like an RFD cut in this photo and a sped up video clip corroborates that rotation.

With this cell pushing into mountainous – i.e. unchaseable – territory I bade farewell to it and motored back toward Bedford. A line of showers and storms had formed along and atop the Blue Ridge mountains with yet another tornado warning on the southern end of a line segment coming out of North Carolina. (This was to be the pattern for the afternoon and evening hours, pointing to a probable warm front perched along the eastern slopes of the Blue Ridge.) I repositioned south of Bedford at a rural vantage point in hopes of more storms firing ahead of the line but such was not to be.

I finally pulled up stakes and dropped south past the Smith Mountain Lake vicinity and onward to Rocky Mount. All I encountered was more heavy rain so, running out of time, I called it a chase and rolled homeward. It was more than I’d expected to be able to accomplish today with respect to chasing so I was satisfied.

#vawx Can’t chase tomorrow but the window may be limited anyway

Even though I can’t chase tomorrow (Sunday, 4/14) I couldn’t let that setup go by without commenting on this setup. Here’s the SPC Day 2 outlook:VA_swody2 (1)

With an Enhanced Risk in place across southwestern VA and a Slight Risk covering the remainder of the state one would think this is an ideal setup for chasing. But timing is everything. For instance here’s the significant tornado parameter (STP) forecast map from the WRF ARW model:stp.us_ma

Those values are very high for the Mid-Atlantic. The only problem is the time, which for this map is 02Z or 10 p.m. EDT. Chasing rotating storms after dark here in Virginia is NOT something I will voluntarily do nor would I recommend it to others.

Here are two reflectivity forecast maps from the same model. The left panel is at 0Z (8 p.m.) while the right one is at 02Z (10 p.m. again):

 

Even though two separate areas of convection look to cross Virginia things just don’t look like they’ll go ballistic here until dark. Several other short range models seem to agree with this timing. Thus even though I can’t chase tomorrow the window for chaseable storms (by my definition) may be very limited. We’ll have to see.

But meanwhile take a gander at the Day 7 SPC convective outlook for Friday 4/19:day7prob

It’s very unusual to see any forecast probability of severe weather here in Virginia this far ahead of time. Thus the end of next week may well feature (a) another Hangout to discuss the details and (b) another chance to chase a volatile April setup. Stay tuned!

#vawx Lots of weekend action but chasing is off the menu

It’s the most convective weekend of the spring so far and it looks like (a) the timing and location of storms won’t be ideal for me to chase and (b) I have other plans/responsibilities this weekend. Of course.

Here are the SPC convective outlooks for today and Saturday:

Northwestern Virginia, including the Shenandoah valley, presents an interesting setup for this evening. CAPE values, shear vectors, moisture indices, and an approaching front all point to a strong squall line (sorry, QLCS) that will be approaching the WV/VA state border near sunset. Several short range models are showing shear vectors to be at an acute angle to the QLCS axis at that time and location, meaning breaks in the line are likely. Those breaks are prime spots for brief spinup tornadoes. Unfortunately such action looks like it’ll occur near or after dark meaning that chasing would be dicey and that local residents need to be on their toes listening for weather warnings.

Meanwhile Saturday’s setup across eastern Virginia and northeastern NC is associated with the stalling cold front. I’d bet a couple of cells along the I-85/I-95 corridor will be worth checking out. However my chasing availability both today and tomorrow will be very limited.

And then there’s Sunday. How about a Day 3 SPC Enhanced Risk to garner attention?VA_swody3

The most ballistic action looks to take place across and west of the Appalachians but sufficient energy is available to make life interesting even over the Piedmont of Virginia. Unfortunately, I won’t be available to chase Sunday. All I’ll be able to do is to check out any local storms via a spot/chase near the home front.

However, there’s always next Friday…

#vawx Chasing outlook Friday-Sunday

April 2019 is turning out very active as strong low pressure systems scoot across the nation. Two of those systems will affect Virginia tomorrow throughout the weekend. The powerful storm that is currently bringing amazing mid-April quantities of snow to the northern Plains will continue to track northeast across the upper Midwest into Canada Friday night. The trajectory of that almost vertically stacked system will keep the main dynamics well north and west of Virginia. That, in turn, is leading to both a general slowing of the eastward progression and a weakening of the associated cold front. Thus a lack of forcing will lower the likelihood of severe weather east of the mountains Friday. The SPC’s convective Day 2 outlook bears out that conclusion:VA_swody2

As a result almost all of the short range models indicate a general weakening of storms as they cross the Appalachians. That Marginal Risk may(?) be extended eastward into northern Virginia on Friday but that remains to be seen.

That same cold front will then stall across Virginia on Saturday, providing a focus for both convection and heavy rain. There may be some strong to severe storms across southeastern parts of the Old Dominion (i.e. south of the stalled boundary) due to differential heating and possible sea breeze forcing but at best I’d expect an SPC-generated Marginal Risk covering that part of the state.

A second storm system will then affect the region Sunday with its upper level dynamics tracking across the Mid-Atlantic. Here’s the Weather Prediction Center forecast graphic for 12Z (8:00 a.m.) that day:Forecast sfc map 12Z Sunday

Given the amount of moisture both already on the ground and in the atmosphere by that time flooding may become a concern. The NWS Blacksburg forecast discussion for Sunday includes a mention of yet another high shear / low CAPE (HSLC) situation which is typically tough to chase due to low ceilings and reduced overall visibility. Flooded rural roads may also be an issue. The discussion does mention the potential for low-topped rotating storms – a characteristic of HSLC setups – with the expectation of either a Marginal or Slight Risk to be issued by the SPC by Sunday.

I doubt I’ll be chasing any of these three days due to schedule conflicts. If the setup looked promising enough Friday or Saturday I could rearrange things but that doesn’t look likely. Sunday is a definite no-go for leaving town to give chase. The best I could do would be a local spotting opportunity.

Hopefully this progressive pattern will lead to more April chasing opportunities that don’t conflict with personal schedules!

 

#vawx A look back at Monday’s chase

A post-mortem of yesterday’s chase revealed that, yes indeed, I made exactly the wrong choice during yesterday’s chase. Here are 3 radar reflectivity images plus the initial photograph of the splitting storm we first observed at ~ 1745Z (1:45 EDT) yesterday over Cahas Mountain:

 

Cahas Mtn cell 1840Z

1840Z

Cahas Mtn cell 1850Z

1850Z

Note that the core that passes over Bedford is a right-split of the original cell.

Now, take a look at the rotation tracks for a better illustration of the split:Cahas Mtn cell rotation trackThe right split wound up being a fairly discrete cell with great (and visible!) structure. Of course this is what I’d hoped we would see further south with updrafts going up ahead of the intersection of frontal convection with that from a southern impulse near the NC/VA state line. Such was not to be as the front seemed to stall further north than originally expected. And even the discrete cell we observed while we zoomed around Danville was very quickly swallowed by the vast precipitation shield of the “blob”.

Storm chasing becomes kinda like a multiple choice test once convection fires. Which cell to chase? Most of the time it seems wise to stick with the first choice…and I didn’t yesterday. Oops!

 

 

#vawx Foiled by the big grey blob

First the good stuff. In our YouTube forecast session Sunday night Andrew Smith and I postulated that with a cold front pressing southeast into Virginia running into convection from a short wave “wrinkle” crossing NC that the SPC may consider going higher than a Slight Risk for today. Sure enough:day1otlk_20190408_1630_prt

So I felt pretty good about the decision to bail on some northern convection as represented by this updraft over Cahas Mtn near Boones Mill:Storm over Cahas Mtn

After all, most forecast models were pointing to the main activity happening along the U.S. Route 58 corridor with the morning AFD from NWS Blacksburg basically saying the same thing. So we bade goodbye to that cell and motored south to the Blue Ridge airport west of Martinsville. At this point I was a little concerned about the size of the amorphous mass of convection heading northeast across the NC piedmont but I still felt that discrete cells would fire ahead of it. When the rain approached without any clear signs of storm details we left for parts eastward.

Even after we retreated to a point near Axton I still felt that discrete (i.e. chaseable) storms were possible ahead of the “blob” but I was beginning to have my doubts:IMG_1422

Especially when this is all we could see of the oncoming mess:The grey blob south of Axton VA

When the rain approached too close for comfort we retreated further east with the thought of stopping at the NC Visitors’ Center just south of Danville VA to check out the eastern edge of the convection. However as we drove along I saw nothing of interest on the eastern side. Meanwhile the blob’s precipitation shield began expanding quickly enough that it became obvious we weren’t going to reach the Visitors’ Center before the rain did.

At this juncture I decided to bail on this action and zoom north on U.S. Route 29 to (a) let the growing blob (MCS by now?) pass by to our south and (b) escape into some relatively undisturbed air north of Chatham. As we drove around the south side of Danville a discrete storm did fire:discrete storm over Danville

However this cell was quickly swallowed by the giant amoeba that was now inside a very large severe thunderstorm warning polygon.

We continued northward to Gretna and diverted onto a rural side road in an attempt to catch a glimpse of the remnants of the earlier northern activity evident on radar:IMG_1436

Finally parking alongside the road near Hurt VA we found a vantage point from which to view the back side of a cell to our east. the local TV station used our livestream feed of this storm during their five o’clock newscast;cell east of Altavista

And that was it. The convection was moving directly away from us at 30+ mph and the available road system wasn’t conducive to keeping up with it. Chasers who’d stuck with the northern convection caught a nice discrete cell near Bedford VA that may have been the downstream version of what we’d pulled away from near Cahas Mtn. Oh well…