#vawx A 10 year anniversary of a mid-November chase

I missed this date yesterday while dealing with the snow/ice/rain/flooding yuck that was happening. Ten years ago yesterday (11/15/08) my son and I intercepted this wall cloud in King George county VA (east of Fredericksburg):Nov152008 wallcloud_2 copy

We had chased storms all the way from central Culpeper county eastward through Fredericksburg and into King George county, witnessing shelf clouds and multiple lowerings under the cloud bases.

The area was under a Slight Risk issued by the SPC. The storms that day were decent for November with enough updraft helicity to create visible rotation (note the flag indicating surface winds blowing toward the wall cloud, i.e. inflow). A non-chaser friend who lives further west in King George county mentioned that even he’d noticed rotation in the base of a storm that crossed over his neighborhood.

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#vawx Nope. Not today.

Just a quick note that underscores yesterday’s doubts about a possible chase today. Nothing has really changed in this morning’s model solutions which are still showing LOTS of shear oriented parallel to a weakening squall line crossing the Appalachians. In addition there is very little instability (CAPE) to create sustained updrafts that could tap into the strong upper level wind field until the squall line is well east of the mountains. Thus the SPC has pared back its convective outlook for today to this:VA_swody1

The Slight Risk area has been pushed further east while the tornado probabilities have been dropped from yesterday’s 5% to today’s 2%. Both the Marginal Risk and the general thunderstorm areas have been edged completely east of the Blue Ridge crest.

A peek at the forecast for updraft helicities (i.e. potential for rotating storms) shows little evidence of such until this afternoon east of the I-95 corridor, about where any rotating storms looked to appear per yesterday’s model runs. So no chasing for me today!

#vawx Tuesday looking less favorable for a chase

So now we’re within 24 hours of the “event” and I’m much less optimistic about the potential for something worth chasing tomorrow (Tuesday). Since last night’s runs several convective allowing models have been consistently projecting an anemic convective line crossing the Blue Ridge Mountains during the late morning tomorrow.

Instability looks very weak west of the U.S. Route 501 corridor, a reflection of which is shown in today’s mid-day SPC Day 2 outlook. The Slight Risk area has been pushed essentially two counties east from this morning’s graphic:VA_swody2 (1)

In addition the shear vectors are aligned parallel to the cold front which is a pretty strong indication of a squall line, something that’s rarely fun to chase (or be chased by!). The convection looks to be low-topped, i.e. containing little or no lightning, and if any updraft does rotate it’ll be embedded in the line over the western part of the Slight Risk. Individual cell motions will also be problematic, screaming northeast at 50+ mph across rural areas with few high speed routes on which to keep up.

East of the I-85/I-95 corridor things could get interesting in mid-afternoon for folks in southeastern Virginia. That may well be where some pre-frontal discrete storms go up and begin rotating. However I’ll leave those for folks in that part of the Old Dominion.

So whether I chase tomorrow or not will wind up being a last minute decision Tuesday morning. I’ll check out the radar view and surface observations and consult with the local TV station before making a decision. But if I had to decide right now I’d call it off as a high potential for a bust.

#vawx The 2018 chase season just won’t give up yet

So then there’s Tuesday (11/6). Here’s the GFS 500 mb view at 1 pm Tuesday afternoon:GFSUS_500_avort_078

I added the blue line to indicate the negative tilt of the trough.

Now for the SPC Day 4 convective outlook. It’s especially unusual for them to show a 15% risk out at Day 4 in November:day 4 probs

So Election Day is on the chase calendar now given the tremendous shear (but limited instability). Hopefully the activity will be more visible and earlier in the day than yesterday’s setup.

#vawx An early November bust

I went. I saw nothing. I came home. That about sums up today’s “chase” amid a typical HSLC (High Shear / Low CAPE) setup. Several of the short range model solutions indicated an updraft helicity maximum – indicative of storm rotation – would roll through the Danville VA area between 5 and 6 pm so that’s where I headed while plowing through heavy rain across Franklin county.

My son had time to chase today so he met me at a fast food restaurant north of the city where we hung out for a couple of hours talking and watching radar. Several convective line segments rolled northeastward out of North Carolina with some indication (on radar) of rotation at their southern end but that didn’t last. Neither did we see any indication of lightning given that the updrafts topped out well under 30,000 ft.

This was the Mesoscale Discussion issued by the SPC for our area just before 4 pm. It only mentioned a 20% chance of a watch being issued (and it didn’t happen):mcd1616

I did switch on the livestream for a few minutes near 6:30 pm (now almost dark) but other than rapidly moving low clouds with no rotation there wasn’t much to see.

Wait ’til Tuesday…

#vawx Waffling model solutions aren’t waffling any more about today

All right, blast it! I’m chasing today!!

The models now seem to agree that the short wave mentioned in earlier blogposts will actually swing thru the area today and force a surface low to form over southern Virginia. That feature, in turn, will back the surface winds which will contribute to the already hefty low level shear values.

Here’s the forecast sounding from the 12Z RAP near Danville VA:21Z RAP forecast sounding nr Danville

In accordance with this here’s the 21Z significant tornado parameter (STP) from that same model run:RAPMA_con_stp_009

Thus it is a foregone conclusion that I’m heading out this afternoon.

Oh, and wait ’til this coming Tuesday…the 2018 chase season is not over yet.

#vawx Friday? Maybe not.

Friday isn’t looking as promising for chasing as it did a couple of days ago. The 500 mb isobar “kink” that was reflected in a small surface low pressure center over Southside Virginia is now almost non-existent in the GFS portrayal. Thus the cold front won’t be delayed much in its forward progress across the state. The NAM does show the kink and surface low but the feature is further east and late in the day.

This combination of factors is probably why the Storm Prediction Center shifted the Marginal risk area a bit eastward in its convective outlook. Here is a side-by-side comparison of the Day 3 and Day 2 outlooks for Friday showing that eastward shift:

Looking at simulated radar reflectivities on the WRF models the main action will occur over the I-85 / I-95 corridors. This has always looked like a squall line setup with the potential for a couple of discrete cells ahead of the line. I’d have to motor 3+ hours to the South Hill / Emporia VA vicinity by mid-afternoon for a small chance at glimpsing a possible discrete storm as it zoomed northeastward at an estimated 50 mph, quickly followed by a shelf cloud on the leading edge of a rapidly moving squall line as darkness approached. No, thank you.

I’ll keep an eye on successive model runs but at the moment I’m not inclined to head that far for this setup.

#vawx So you’re saying there’s a chance on Friday?

OK, I’m beginning to come around to admitting that I may have been hasty in my earlier declaration of the end of the 2018 chase season. Earlier runs of the GFS (and to some extent the Euro) insisted that a cold front would be pushing across eastern Virginia this coming Friday morning (11/2). According to today’s 06Z and 12Z runs of the GFS that boundary will be slowed by a wrinkle in the 500 mb flow that is reflected in the 700 mb upward velocity at 21Z (5:00 pm):

In response a surface low pressure center is forecast to form along the cold front over southwestern Virginia and slow the eastward progression of said boundary:GFSMA_sfc_temp_081

The forecast sounding at 21Z over Bedford county VA thus looks like this:21Z forecast sounding Bedford county

This is the epitome of a high shear (67 knots 0-6 km) / low CAPE (~600 j/kg) setup in this part of the country. Storm motions are forecast to be out of the southwest approaching 40 mph so keeping up with individual cells will be a challenge. And it should be noted that the NAM generally agrees with the GFS and the Euro at this point.

So I just might have to re-equip the chasemobile with chasing gear before this Friday…not that I’m complaining about that!

#vawx End of the 2018 season and Mid-Atlantic ChaserCon

In past years I’ve waited until Veterans’ Day (November 11th) to declare the end of the annual storm chase season. This year it may still be a bit early but after a peek at the long range pattern I’m calling it now. My only hope for staving off SDS (supercell deprivation syndrome) for a while longer is the advent of the inaugural Mid-Atlantic ChaserCon in Richmond VA this weekend (Oct 27th).

My hope for this event – beyond keeping SDS at bay! – is to pull together severe weather enthusiasts in the Eastern U.S. to foster a sense of regional community. Not everyone has ready access to the awesome storms over the Great Plains but there is enough severe activity in this part of the nation to warrant paying attention. The array of speakers on the agenda this year reflect both a geographic and professional spectrum of severe weather interests.

So as the first nor’easter of the autumn roils the Mid-Atlantic atmosphere this weekend we’ll be ensconced in a meeting room at the Science Museum of Virginia talking storms and storm chasing.

IMG_0714

Science Museum of Virginia

I’m very much looking forward to viewing other peoples’ photos and videos and listening to their accounts of storms they’ve encountered!

#vawx Rain, flooding, but no tornadoes for today’s chase

After reviewing the medium range and then the short range models I decided I wasn’t going to chase today’s setup from Michael. Too much rain was on the way which would lead to yet more flooded roads. Then this happened:mcd1565

Followed by this (yellow shade is a Tornado Watch):rnk warnings

The watch area covered an area much further west than I’d anticipated.

Agonizing for at least two minutes I decided I couldn’t let this pass. All the model runs had been consistent with a couple of rain bands pushing through Southside Virginia toward Lynchburg out ahead of Michael’s core circulation. The window of opportunity for potentially discrete cells in this western section of the tornado watch was narrow, beginning about 11 am and ending by 2 pm. That was when the heavier and steadier rain closer to the core was forecast to slide northeast across Southside.

Based on that and the real-time radar depiction I motored first to Bedford. The rain was heavy and visibility was very restricted until I got east of the Blue Ridge where conditions improved slightly. During a stop at Bedford to gas up the chasemobile the rain was steady but light and ceilings were a bit higher than in Roanoke. From there I pushed further east and stopped just off U.S. Route 29 south of Lynchburg. I had decided I wasn’t venturing any further east than this given the narrow timeframe available.

I sat there for quite a while watching radar and straining to see details in the clouds. During one break in the rain I could make out some low level structure but everything was fuzzy and hard to keep track of. After wandering around the countryside a bit I called it and headed home as the steadier precipitation around Michael’s core approached. Water ponding on the roads became more prevalent as I neared Roanoke and while multiple alerts sounded for Flood Warnings and even Flood Emergencies.

This was the scene just down the street from our house:IMG_0850

That’s normally a very well-behaved creek that runs through the trees well away from the road.

In hindsight I should have stayed home today. But I chased in a tornado watch (which I would have regretted missing) and I was home well before dark. That’s not something that happens often here in the Old Dominion.