#vawx A present presentation and a rainbow from the past

This morning’s “Severe Weather in Virginia” presentation at the Hotel Roanoke went better than expected, especially given the shaky quality of my voice (stupid cold!). This was a breakout session at the 2019 Virginia Association of Science Teachers Professional Development Institute. We wound up having 20-25 folks in our meeting room and had a good discussion of severe weather here in the Old Dominion. Hopefully the teachers in the audience took away some useful information to pass along to their students.

Meanwhile here’s a decent rainbow from 13 years ago today:OLYMPUS DIGITAL CAMERA

#vawx One last item on the 2019 checklist

It’s now Veterans Day, the demarcation date I use to officially declare that the Virginia chase season is over even though last year I had to extend that since I actually chased on December 21st. Thoughts now turn to wrapping up the 2019 season – perhaps via another live video update in January? – and preparing for 2020.

But even before that there’s one last item on this year’s agenda. This coming Saturday (11/16) I’ll be giving a presentation at the Virginia Association of Science Teachers annual Professional Development Institute being held at the Hotel Roanoke. My topic is summed up in the title slide:VAST presentation title slide

And this is the abstract I submitted:

“Severe weather occurs much more often across Virginia than is generally recognized. Large hail, strong straight line winds, tornadoes, lightning, and flooding all pose threats to life and property. This presentation will illustrate the factors involved in formation and prediction of severe weather, what such phenomena look like, and recommended actions to take in response to watches and warnings issued by the National Weather Service.”

It’ll be interesting to see how many folks actually sit in on this during the breakout session Saturday morning. I at least know I’ll be there!

#vawx A wild and woolly Halloween

If the Halloween cold front had arrived even a couple hours earlier I’d have headed east of the Blue Ridge to chase. As it was the convection that did happen was too near darkness – and moving at highway speeds – to convince me to do so. Thus my “chasing” was limited to observing from a couple of vantage points in the Roanoke valley.

This, of course, was the tempting part: an  unusual Enhanced Risk on the last day of October.VA_swody1

An upper trough, a strong surface low moving up the Ohio valley, and a sharp cold front all contributed to the severe parameters. CAPE (instability) was a bit limited but shear values were incredible. The main concern was a cap in the 850-700 mb range that looked to limit convection ahead of the front itself.

The first observation point afforded me a great view to the north and west. This look at fog on Fort Lewis mountain was impressive:Fog on Ft. Lewis Mtn
But what was even more impressive was the view a bit later of low level scud moving right to left (south) in an apparent eddy behind the mountain until the cloud tags rose high enough to get caught by the low level jet and start scooting left to right:evidence of shear

This was visual evidence of the available shear that pervaded the region.

As the squall line associated with the cold front approached from the west I decided to relocate to another vantage point that gave me a better view to the southwest. From here I watched a small lowering under a rain-free base cross the southern Roanoke valley.rain free base with lowering

Rain filled in and obscured visibility not long after this. Meanwhile just enough weak sunshine had eroded the cap enough just east of the Blue Ridge for this pre-frontal cell to go up and rotate.IMG_1921

A couple of chasers who did brave the timing and conditions witnessed a couple of supercells near Lynchburg. And despite a plethora of tornado watches that blanketed the Old Dominion so far the only confirmed Virginia tornado occurred after dark not far from my son’s house.

Still glad I decided to stick close to home.

#vawx Squall line on the way

Still thinking that today’s tornadic potential will only be realized along the cold front. Here’s a 06Z NAMNEST forecast sounding at Lynchburg for 21Z today with the cap circled:3 km NAM capping at 21Z LYH

Now, from the same model run at the same time and location here’s the MLCAPE and shear vector panel:21Z MLCAPE & shear 06Z 3km NAM

The two graphics indicate first that the front itself will be needed to break the cap, thus pre-frontal storms won’t be likely. Secondly, storms along the cold front / squall line will remain in a linear mode and won’t become discrete with the shear vector aligned pretty much parallel to the front. That being the case it looks like squall line (QLCS) tornadoes will be very possible.

It’ll be interesting to see how this works out. Any way one looks at it today will be a very vigorous weather day!

#vawx Thursday still looking like a squall line event

As an update to yesterday’s post about Halloween here’s the SPC Day 2 convective outlook:VA_swody2

 

And then here’s a NAM sounding at 6 p.m. Thursday for the Lynchburg area showing a cap between 850 and 700 mb:NAM sounding at LYH 31Oct

Hence my concern that the lift from the cold front itself will be necessary to fire storms. The potential for rotating pre-frontal (and daylight!) storms will be very low as long as this cap holds. Now, if for some reason the clouds part and sunshine appears over the Piedmont “Katie bar the door”!

Otherwise tomorrow’s potential still looks like a squall line (QLCS) event. Meanwhile I’m keeping an eye on the models.

#vawx A raucous Halloween lies ahead

Halloween certainly looks like an interesting setup even beyond the rain that trick-or-treaters may have to contend with. A strong surface low will move northeast up the Ohio valley, dragging a strong autumn cold front eastward. That combination will pull abundant low level moisture into the North Carolina / Virginia Piedmont ahead of the boundary.

The NAM is typically optimistic on how much moisture will reach Virginia, showing >70 degree dew points streaming into the U.S. Route 58 corridor in Southside. The GFS isn’t quite that enthusiastic but both models show a fierce amount of shear available. Thus this sounding near Halifax VA is eyebrow-raising:2019102918_GFS_054_36.76,-78.95_severe_ml

However….there are several factors that mitigate thoughts of chasing Thursday:

(1) It’s Halloween and lots of pedestrians will be out and about.

(2) The severe parameters don’t sharpen until after dark, with low LCL’s and LFC’s likely meaning low-topped updrafts and thus little or no lightning to illuminate storm bases.

(3) There are hints of a low level (~850 mb) cap on a couple of model soundings which would require lift from the cold front itself to overcome. That probably means no pre-frontal storms that would be good candidates to chase. (High potential for a squall line / QLCS).

(4) There appears to be little upper level support until the front arrives. 700 mb positive vertical velocities arrive coincident with the boundary.

So while I’ll be keeping a close eye on things I don’t plan to chase Thursday.

#vawx A late October chase chance

UPDATE SATURDAY OCT 26TH: As I slowly recuperate from a successful Mid-Atlantic ChaserCon 2019 I realize that I never wrapped up this potential chase. As it turned out this setup was much less ballistic than I originally thought. I punted the chase that morning and stayed home. The lack of Virginia storm reports on this SPC graphic validated my decision:191021_rpts

END UPDATE

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Tomorrow’s setup almost took me by surprise with its high shear / low CAPE (HSLC) characteristics.  The shear seems to be courtesy of a surface low predicted to form along an advancing cold front that will create southeasterly surface winds along and east of the U.S Route 29 corridor. Here’s this afternoon’s SPC Day 2 outlook:VA_swody2 (1)

The best instability – CAPE – will be near and south of the Virginia / North Carolina state line, corresponding to available moisture. Here’s the HRRR simulated radar view at 18Z (2 p.m. EDT):HRRRMA_prec_radar_025

Thus I’ll need to get a fairly early start to get east of this developing action. It’ll probably be tough to maintain visibility on a given storm for very long but, hey, it’s a chance at an autumn chase.

And this is only four days before Mid-Atlantic ChaserCon!