#vawx Watching and waiting

…radar and visible satellite, that is. With Flood Watches & Warnings plus a Tropical Storm Warning in place east of the Blue Ridge I’m not heading out anytime this Thursday morning.

However…there are indications on a couple of convective allowing models that once the center of Zeta clears out of SW Virginia the clouds just may thin and produce enough CAPE to make life interesting late this afternoon. A second surface low center looks likely to form over the same area Zeta is scooting across this morning. With it is a cold front that could trigger convection.

In fact a couple of CAMs are showing just that along and south of the U.S. Route 58 corridor. Unfortunately the timing is near sunset. If I do head out I’d would need to do so around 5:00 p.m. to get into position in time to see anything before darkness falls.

Thus I’m watching and waiting to see what happens.

#vawx Some head-scratching going on

The core of Zeta’s remnants look to cross southern Virginia early Thursday with some eye-opening wind gusts per a few models, with the HRRR solution at noon shown here:

Coupled with the large amounts of rain expected I’m not too excited about the prospects of chasing during the mid-day hours tomorrow.

However…check out the forecast surface map at 8 pm tomorrow:

WPC surface map at 0Z Friday

And then check this 23Z sounding near Martinsville VA:

Convective allowing models are indicating a convective line – perhaps the cold front? – in Southside VA late Thursday afternoon. THAT may be my target for tomorrow. I’ll be watching radar, surface obs, and satellite to see if that activity occurs and is worth chasing.

#vawx Will a Greek-named storm provide chasing?

Amidst the throes of preparing for another Mid-Atlantic ChaserCon livestream session this coming Saturday it appear that Zeta could provide a late October chase opportunity on Thursday. Here’s the current NHC track forecast:

If Zeta’s center were to track along the left edge of the cone the heavier rain would occur over the Appalachians with better chances of instability over the Piedmont Thursday afternoon. But I’m not holding my breath for that to happen…I expect the highest rain totals to occur between me and the potential severe weather area along and east of the U.S. Route 29 corridor in southern VA. Here’s the SPC Day 3 outlook:

Just for kicks I checked the GFS supercell composite parameter forecast for Thursday afternoon:

And then the significant tornado parameter parameter from the NAM:

Both seem to bear out the SPC Marginal Risk area with LOTS of available shear but not much CAPE (instability). Couple all those thoughts with the lowering sun angles and sunset before 6:30 EDT and the chances of seeing something are not great.

But I still might chase.

#vawx Nope. Delta didn’t produce severe weather in Virginia

Well, I was right that severe weather from Delta would be well to the east but I was wrong about anything happening in Virginia. Here are the storm reports from Sunday Oct 11th:

Delta wasn’t a chase-producer for my area but there were a couple of tornado videos from South Carolina.

My near-term focus is now the virtual Mid-Atlantic ChaserCon sessions which begin October 24th and continue each Saturday through November 14th. Meanwhile whether another chase opportunity will come along this year is TBD at the moment.

#vawx Could Delta do it?

The above title question refers to an October severe storm chase potential here in the Old Dominion. The short answer is: maybe, but it would likely be along and east of the I-85 corridor.

The forecast track of Delta’s center is obvious here in this WPC-generated five day total QPF graphic which runs through 12Z Tuesday (Oct 13th):

The counterclockwise circulation around the surface low center will foster easterly winds across the western half of Virginia. Given the moisture advected northward by this system that will mean hefty amounts of precipitation thanks to uplift along the eastern slopes of the Blue Ridge mountains.

Unfortunately (for storm chasers) this will also mean plenty of cloud cover and thus little instability in the area of higher rain totals despite the available shear. We’ve dealt with High Shear / Low CAPE (HSLC) setups many times during the colder months but this one doesn’t look promising except perhaps for areas along and east of the I-85 corridor. This GFS forecast graphic for Monday afternoon illustrates:

The potential for breaks in the clouds in southeastern Virginia Monday afternoon is much better than areas to the north and west. Thus the potential is there for at least some limited convection to tap into the available shear and moisture. Things could always change between now and then so I’ll be keeping an eye on this setup. But if it doesn’t change I’ll let this one go since that area is outside of my self-defined chase territory, especially during this COVID-19 complicated year.

#vawx The one and only September 2020 chase

I’d been eyeing the setup for Tuesday 9/29 for a few days as a strong cold trough and negatively-tilting trough looked to plough into a juicy airmass across the Piedmont. There was enough shear and moisture available that I thought there was the potential for an SPC Day 1 Slight Risk but they – wisely – kept a Marginal Risk over the region.

However, with the shear values in place there was enough concern to issue a wide area of 2% tornado risk.

Thus I kept an eye on radar and surface observations Tuesday morning and wound up heading out just after 1:00 pm mainly to avoid areas of heavy rain setting up between me and points east. Traveling south on U.S. Route 220 and then east on VA Route 40 I stopped in the Union Hall vicinity to take stock of the situation. While there I noticed that surface winds were gusting out of the northwest while the low clouds were still coming from the south. Surface FROPA had already occurred here and the chasemobile’s exterior thermometer registered in the mid-60s.

Continuing east on Rte 40 I crossed the Franklin/Pittsylvania county line and noticed the exterior temperature had jumped into the mid-70s and the surface winds were gusting out of the south. Now ahead of the cold front I diverted south toward the hamlet of Climax and stopped at a ridgeline vantage point. This was my view of what apparently was the leading edge of the cold front.

This was the radar reflectivity and velocity view at the time:

(I should note that at no time during this chase did I see lightning visually or on radar nor did I hear any thunder.)

Departing this location I rambled about the countryside a bit and found a vantage point from which I snapped a photo of the oncoming shelf cloud. The winds had already swapped around from the northwest and temperatures had begun to drop so this shelf cloud was actually behind the surface cold front. This was a recurring theme of the day as a surface layer of cold air zoomed out ahead of the convection, stabilizing the lower atmosphere and quelling the potential for severe weather. (Other than one confirmed tornado in Isle of Wight county there were no SPC storm reports in Virginia this day.)

This cell moved on to the northeast and I dithered about where to head next. I noticed another discrete cell ahead of an oncoming line and vectored back west to intercept but wound up getting drenched as the precipitation shield expanded. Finally escaping that mess on rural roads I dropped south at Chatham via U.S. Route 29 to fill up the chasemobile’s gas tank as more rain developed over Danville.

Via radar I noticed yet another seemingly discrete cell scooting northeast across Halifax county so I detoured east on VA Route 360 to take a look. It turned out this wasn’t really a discrete cell but an area of rain underneath the cloud layer that was following the surface cold front.

Parking alongside another rural route I watched as this action soared by to my east without anything exciting happening.

After this the most challenging part of the remainder of the chase was plotting a course which would avoid at least part of the drenching rainfall between me and home base.

Unless the 2020 Atlantic tropical season provides some reachable action this may well be it for the season…but I’ve been known to eat my words before!

#vawx Tuesday may well be on the chasing docket

The models have settled on a strong cold front pushing across Virginia Tuesday, bulldozing its way into a warm moist air mass. The trough accompanying the front will produce decent mixed layer shear, enough such that the SPC has already placed much of the Old Dominion under a Day 3 Marginal Risk:

There is a question as to how much CAPE (instability) will be available, a parameter which is typically hard to come by with the sun angle continuing to lower as October approaches. However the upper level trough will provide some uplift as 500 mb vorticity looks to be accompanied by winds at that level reaching 50 kts on Tuesday afternoon. Another factor of interest is a surface low progged to form along the cold front which would bump surface winds around from the southeast over the Piedmont, eliciting a “Hmmmm…”

Thus I’ve dusted off my chase gear, charging batteries and updating software in anticipation of at least one last 2020 chase. As Tuesday afternoon nears I’ll be perusing the convective allowing models for times and target location(s). And I wouldn’t be surprised to see at least part of Virginia upgraded to a Slight Risk in future SPC convective outlooks.