#vawx Storms Saturday are doubtful but Monday could be a chase day

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A Bermuda High parked off the East Coast is pumping heat and humidity into Virginia. A cold front approaching from the west and north would seem to be a good trigger for storms Saturday except for two things: the upper level support for the front is weak and the upper air temperatures are pretty warm.

Here’s the surface-based CAPE (instability) map for 5 pm Saturday per the 0Z Friday GFS run:sbcape.us_ma (1)

Forecast soundings yield monster CAPE values of well over 3000 j/kg but very little shear and LCL’s (cloud bases) >1000 meters. That would scream H-A-I-L given potential updraft strengths but not tornadoes. However…there’s the cap.

Surface convective inhibition is pretty robust with this air mass plus there’s a stout cap at the 800-700 mb level. IF this cap can be overcome by an updraft (perhaps along the slopes of the Blue Ridge) there could be an awesome storm or two, especially in northern VA closer to the front itself. I’m still withholding judgement on whether to chase Saturday afternoon as there’s a very large potential for a bust. Need more data!

Meanwhile another – stronger – cold front will approach from the west on Monday. There are concerns about a persistent overcast that would suppress CAPE but shear values will be better. Monday looks like a more promising chase setup and we’ll be talking about it on a Google Hangout Sunday evening at 8 pm (https://youtu.be/UeOF9mtx1ZA).

 

 

 

#vawx Don’t write Saturday off

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The title above is the motto for today’s chase. Up until this morning all the model runs I had checked showed a slowing cold front sagging south of the VA/NC state line early in the day. The timing left little room for convection north of the border. Then I woke this morning to this:day1probotlk_1200_torn

After alternately chuckling and groaning (obviously I hadn’t planned to chase today!) I readied the chase gear and checked the latest model runs. Sure enough the front’s southern progress had been slowed so I headed out to chase before noon.

Given that surface observations indicated the boundary to be already south of Lynchburg I motored south on US Route 220 to the Wirtz area where I set up shop to await the action.While sitting there I noticed this juxtaposition of cloud movement:E002D02C-A0DB-4DDF-AC4D-4FBE5AE0E4FA

The top photo looks due west and shows clouds moving south to north. The bottom photo looks due east and shows clouds moving north to south. Thus I was sitting literally under  the edge of the frontal boundary itself.

Storms fired along the Blue Ridge and rolled northward so when the rain neared I relocated a few miles north as well, stopping in Burnt Chimney to watch for a bit. Seeing nothing of note and with a few minutes to spare I decided to head south to Rocky Mount and grab a quick lunch. From there I pushed east on VA Rte 40 and dove north on Webster Road, scrambling around to find a vantage point that wasn’t someone’s driveway.

I settled for a commercial parking lot that had a limited sightline. I really wanted a place to check out what THIS radar view actually looked like.IMG_6762

Finally frustrated enough I conducted a rolling reconnaissance and promptly ignored my rule about not pulling into driveways when I saw this:Rocky Mount shelf again

Here’s another look as the rain engulfed Rocky Mount.

Rain engulfing Rocky Mount

When the precipitation got too close I pushed east on Rte 40. Stopping just east of Glade Hill I watched as the shelf cloud developed greenage, suggesting a very tall updraft behind it.greenage from Glade Hill

The shelf kept moving east and I retreated ahead of it, stopping several times before turning south at Penhook. Discrete cells were firing along the southern edge of the line and I wanted to intercept a few of them. I maneuvered my way along rural roads to Callands where I turned southwest on VA Route 57. When that route took me back into the rain I worked my way east to VA Route 41 and wound up catching a glimpse of a wall cloud just before it became rain-wrapped.

Wall cloud in Pittsylvania county

Wall cloud is the rain free base to the right of the growing rain shaft

This was the pattern to be for the remainder of the chase as cells would fire and almost immediately become rain-wrapped. I sat through one storm just north of Danville to try to gain position on the next one but the rain filled in quickly. Thus even though I saw this circulation on radar just to my southwest I never found a place where I could see any features.IMG_6794

I wandered along rural routes southward toward the US Route 58 corridor not seeing much of anything other than rain. When I finally got there I saw that one storm – probably the one with the circulation that I missed seeing – was now tornado warned but was already over the town of Halifax. I did a quick intercept vector and realized that I was at least an hour from catching up to the storm given available road directions and the storm speed. Given the copious amount of rain involved I wasn’t convinced I would see anything anyway so I punted.

There were, however, more cells going up over North Carolina and moving northeast so I drove south to the Semora NC area to check them out. After dithering about a bit I witnessed a wall cloud under a developing storm.

When I followed this feature to another vantage point only 5 minutes away the rain had completed filled in around the wall cloud, rendering it all but invisible. Also I noticed on the NWS Raleigh radar velocity view that the cold front was already south of this storm and moving further south into North Carolina. At that point I made the command decision to pull off the chase given the trajectories plus the very wet atmospheric environment.

Pretty busy chase for a day that I thought would be a quiet one at home!

#vawx Slightly better parameters but still not much to show

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Today’s instability and shear values were better than yesterday’s but obviously not enough to create a lot of strong convection. The SPC thus had most of Virginia under a Marginal Risk for good reasons:VA_swody1

Westerly surface winds were likely a factor in today’s lack of severe weather as they tend to suppress convection. Also the stronger upper level winds and better shear lay well to the north.

Even so I had to clench my teeth and ignore a nice looking complex scooting eastward along the NC/VA state line from the I-77 corridor. I deliberated whether to chase or ignore it before deciding to let it go. Good thing I did as the next time I dared check radar the section of that storm in Virginia had weakened while the southern tip had built further south into undesirable chase territory in NC.

I finally rolled down the driveway around 2:30 and headed into Bedford county via VA Route 24. Towers were already going up across the area with one raining itself out near Smith Mountain Lake before I could get to a spot to watch.first cell near SML

I sat at this vantage point just north of the Huddleston area until another robust cell built east of the Blue Ridge and headed toward me. I found a rural spot from which to stop and live stream which turned out to be directly in the path of this slow moving but picturesque storm.In the path of the storm

I kept an eye on the rain free base on the left (south) side of the updraft and saw at least one lowering that wasn’t obviously rotating.

When the rain from this cell impinged on my location I made a big loop south, east, north, and then back west again to miss most of the precipitation. Another storm trailing this one looked cool but had no distinguishing characteristics so I maneuvered around it and wound up at the intersection of Rte 24 and VA Route 122.

Dithering a bit on what to do next I finally headed south across Smith Mountain Lake to the VA Route 40 corridor to intercept what looked like the storm of the day as it crossed the Blue Ridge near Floyd. I wandered around the countryside a bit to find a vantage point and finally stopped just off U.S. Route 220 south of Rocky Mount. There I noticed another lowering under the southwestern edge of this complex as dusk approached.lowering under last storm near Ferrum

At this point all the convection was to my south and east with little chance for strengthening given the approach of sunset. Thus I called it a chase and motored to Rocky Mount for a late dinner. It was a decent day but it left me wanting more.

#vawx A local chase today but Friday & Saturday will be on the road again

When I looked at this morning’s model runs I made the command decision to stay home today – Thursday – given that the next two days look like out of town chasing. Plus the overall lack of shear meant today’s storms would be garden variety pulse stuff with absolutely no cap in place.

Sure enough that’s what transpired this afternoon. The leading cell approached the Roanoke valley from the west just after 1:30 pm so I unhurriedly drove to a local vantage point to watch. This was the radar and MK 1 eyeball view as it crossed the ridgeline to the west.

As it rumbled along I videoed it (but didn’t live stream) and wound up capturing a couple of CG’s. This is a frame grab of the best view:CG_2r

Eventually the cell intensified and developed a hail core. The indicated hailstone size was only half-inch so I decided to intercept it by repositioning a couple miles further north and east.  (I know, that’s not necessarily a bright thing to do but I did it anyway.)IMG_6698

The core washed over the chasemobile as I sat in a retail parking lot (a “static core punch”). I experienced several minutes of pea-sized and smaller hail along with what felt like 30+ knot wind gusts that rocked the car a bit. Rain came down fast and furious and resulted in localized street flooding in my general vicinity.

Shortly after the hail and rain ended the sun came back out. However I stayed put for a few more minutes to allow the water time to drain off the roads. I then headed for home which was less than 5 minutes away. Pretty cool stuff close to home!

#vawx Chasing likely Thursday and Friday but Sunday looks most interesting

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Model-watching is about all I can do on a grey showery day stuck under “Da Wedge” here in Virginia. What I see is that once that chasing nemesis retreats northward tomorrow – Thursday Apr 20 – enough instability will be in place to fire storms east of the Blue Ridge. However shear will be a scarce commodity so individual cells shown on these two model representations will not likely be long-lasting.

There could be a severe storm or two if any cells exhibit a strong enough gusting out phase but that’s about it. Target area and timing will be TBD until Thursday morning short range models come into play.

Meanwhile Friday a cold front will slide across the Old Dominion triggering storms along and ahead of the boundary. CAPE (instability) will once again be plentiful but with more shear in place. The latter parameter will still be on the low end for severity but it’s likely going to look good enough to entice me to head out.Fri 21Z 3 km NAM

Sunday looks very interesting with a surface low skirting eastward along the VA/NC border. At the moment the timing and location of the associated warm front doesn’t look favorable for me to go out but I’ll be watching that models closely as upper level winds could impart plenty of energy to this setup.

#vawx A non-severe chase of discrete cells

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Yes, I bit on today’s non-severe setup (not much shear but decent instability). The slow moving discrete storms exhibited on short term model solutions (HRRR and a WRF model or two) sufficiently tempted me that I rolled down the driveway at noon today. I drove south to Rocky Mount and then east on VA Route 40 keeping an eye on updrafts building on the edge of a high level overcast. The differential heating boundary between sunny and overcast areas proved to be near the U.S. Route 29 corridor so after a brief stop in Gretna to gain better situational awareness I dropped south to check out the first storm.

Noting that this cell had edged east of Rte 29 I turned in that direction on a rural road and wound up at the crossroads of Sheva with this radar view:IMG_6669

This was a rain-free base under that first cell (looking east):northern updraft from Sheva

Turning to the south this was the updraft looking over top the church there:Second storm near Sheva

With more storms building to the southwest I plunged southward from Sheva. Pausing a few miles further on this was my view of the first storm as it continued eastward with a hint of scud developing into a lowering under the rain-free base:Lowering under first storm

I chose to let this storm go in favor of pushing to get south of the next cell steaming in from the west. This was intensifying and looking more robust:IMG_6675

Unfortunately that first storm turned out to be the storm of the day. It was never severe-warned but its radar signature somewhat resembled a classic supercell with a split updraft by the time the base reached the town of Halifax.

I spend the next couple hours navigating through, in, and around a number of new cells and wound up east of Danville watching this weakening storm approach.

From here it was a simple decision to call it a chase and head home as the convection was continuing to weaken. Even though I saw nothing severe it had been a fun couple of hours!

#vawx Nothing severe but convection to soothe the chaser’s soul

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I was a bit optimistic that SPC would issue a Marginal Risk across parts of Virginia today. They didn’t, but a severe TS did rumble eastward across the Roanoke valley this afternoon. I wasn’t able to get into position on it given timing issues so I dropped south on U.S. Route 220 to Rocky Mount and then turned east on VA Route 40.

My plan was to check out the severe storm as it crossed the Blue Ridge mountains but I had no good road options with which to so so. (Smith Mountain Lake was in the way.) I wound up traveling all the way to Gretna to get ahead of the growing convective line. Along the way I stopped east of Penhook to watch this lowering to my west for a few minutes.Lowering from just E of Penhook

The most energetic part of the line looked like it was aiming at Altavista but by the time I reached Gretna that section had weakened. Not to worry, though, as several cells began firing out ahead of the line just west of town. Thus I found a spot a bit north of Gretna to watch and live stream a bit.

When the rain encroached on my location I rolled thru rural Pittsylvania county to reach Rte 40 east of Gretna. I sat at a road junction near Mt. Airy for a while hoping to conduct a “static core punch” as the storm slowly moved toward me.IMG_6654

Unfortunately that section of the line weakened before it reached me so I dropped south to intercept a newly intensified portion. That too fell apart so all I was left with was 25+ mph outflow winds and heavy rain.

However all was not done yet. I turned west on VA Route 57 toward Chatham and then noticed a section of the line to my south that had some interesting features.

That rain-free base seemed to be vacuuming up scud so I watched for a few minutes. Nothing else occurred before more heavy rain filled in so I called it a day and pointed the chasemobile toward home.

#vawx Easter Sunday looks clear but Saturday could bring storms over western VA

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It now appears that Virginia will be spared any rough weather Easter Sunday as an approaching cold front won’t be close enough to affect things (with little upper level support arriving until after midnight). However Saturday may feature some storms across the western half of the Old Dominion as a warm front retreats northward. The warm moist air mass behind this boundary coupled with low level convergence near the Blue Ridge mountains looks like a combination that’ll lead to convection.

Here’s the NAM NEST forecast dew point map at 18Z (2 pm) Saturday:NAMNSTMA_sfc_dewp_030

The general position of the warm front is pretty evident on this graphic. The Storm Prediction Center has much of the state under a general thunderstorm risk for Saturday but part of that area could be bumped up to a Marginal risk in the Day 1 outlook.

Meanwhile the next potential for severe weather looks to arrive Wednesday in the form of a 500 mb short wave. If that trend continues we’ll conduct another On Air Hangout Monday evening to discuss it. Stay tuned!

#vawx Oh c’mon now…Easter Sunday? Really??

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I’ve had my eye on this coming Sunday – Easter – and this morning’s 12Z GFS run has continued a trend for severe weather potential that afternoon. Here’s the 3 km EHI forecast graphic at 5 pm Sunday:GFSMA_con_3kmehi_105 (1)

Surface based CAPE values are over 2000 j/kg near Lynchburg VA with 0-6 km shear values over 30 knots. That’s enough to make a chaser sit up and take notice. What’s even more enticing is that forecast storm speeds are in the 30 knot range (i.e. chaseable) rather than recent setups that produced interstate-worthy speeds.

The GFS shows a surface front approaching Virginia during the wee hours Monday morning so that’s not the triggering mechanism for storms. There appears to be a weak shortwave moving across surface dew points in the low to mid-60s (F). That plus a pre-frontal trough just east of the mountains seems to be the storm triggering mechanism.

Regardless it’s worth keeping an eye on…and I may schedule another video Hangout to discuss the potential. However given the weekend that it is such a Hangout may not draw a lot of attention. We’ll see.

#vawx A recap of last week’s severe weather in Virginia

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As suspected Wednesday (4/5) and Thursday (4/6) featured a storm system that arrived at the wrong time on the clock for me to give chase. The Day 1 SPC convective outlook did hold promise of interesting things to come, especially with this tornado probability graphic in place:day1probotlk_1630_torn

The 2 and 5% tornado probability contours were close enough to entice me to keep track of the action and have my gear ready to go at short notice. Of course with forecast storm motions in the 50 knot range it would have been stop and watch as the cells flew by.

The approaching upper level trough and accompanying short waves / jet streaks combined to fire up thunderstorms across the western part of Virginia during the wee hours Thursday morning. I awoke at 2 a.m. to a couple of loud peals of thunder and heavy rain but after checking radar I wasn’t even tempted to step outside for a peek.

I got up just after 6 a.m. Thursday in case something fired close enough for me to check out during daylight hours. A Mesoscale Discussion was issued just about that same time for most of eastern Virginia with a Tornado Watch following an hour later:

Around 8 o’clock I moseyed to a local vantage point to check out a couple of cells that actually heralded the passage of the surface cold front. One developing complex just north of me looked interesting with hail indicated on radar but it was flying northward at a brisk pace. I chose to stay put and never saw anything else worth even photographing.

Meanwhile two separate regions of Virginia experienced severe weather as it developed later in the day. Both the Tidewater area east of I-95 and sections of Virginia north of I-64 bore the brunt of straight-line winds and several brief tornadoes. Tree and structure damage occurred across a wide swath  in both areas as a strong squall line (QLCS) marched through.

The severe potential over the southern part of the Old Dominion was effectively squashed by a cold pool of air and overcast skies left behind by a large area of rain across North Carolina on Wednesday. That created an in situ cold air damming wedge which held down dew points and suppressed instability in my usual chase area. So given little desire to travel 3+ hours one way to chase storms along a grungy fast-moving squall line I stayed home and missed all the action. (I’m not unhappy about that decision.)