Not Irene, but cold front inspired storms

The Storm Prediction Center (SPC) centered a slight risk for severe weather in my chase area and I took full advantage, leaving home around 2:00 p.m. to head for the Route 29 corridor near Culpeper in hopes of catching a discrete storm in the lee of the Blue Ridge mountains. Unfortunately the storms crossed the ridge as a line and continued on their way, but I did manage to choose the strongest cell to follow thanks to radar and GPS. I rambled through a bit of eastern Culpeper county to find a spot to watch and found this view of an oncoming shelf cloud:
Continuing eastward from here I found an even better vantage point from which to observe the severe-warned storm approach and watched for several minutes.

When the rain shaft approached I scooted northeastward toward the back side of the town of Lignum and wound up catching this view of a suspicious feature very near the rural route I was on:
It was suspicious not only in looks but also in that CG's were raining down in its vicinity plus a very large hailstone suddenly and without warning smacked the middle of my windshield. I couldn't tell how large it had been but the leftover slush pattern was about three inches in diameter. After that surprise I saw and heard several other hailstones but none seemed larger than quarter-sized. I stopped in Lignum to watch and video this lowering but never saw any rotation.

Then, somehow I came up with the not-so-bright idea to closely follow and even core punch this storm as it continued eastward. Thus I pulled out onto Virginia Route 3 and gave chase, noting the further east I traveled that the rain intensity increased, the wind speed picked up dramatically, and the smaller twigs and leaves that were showering the highway began to get larger and more numerous. When I reached the Lake of the Woods vicinity I was finally convinced that I needed to get off the road for safety's sake. By this time the rain was horizontal, branches were snapping off trees and landing in the roadway, and the continuous pea-sized hail sounded like shotgun pellets bouncing off the car's exterior.

When conditions improved significantly I eased back out onto the highway and moved east a few miles, stopping just behind the storm to call in a report to the NWS Sterling office. (I had tried to do so earlier but couldn't get a call through.) Watching for a while longer I finally headed home through the damage path of this severe storm, including a number of traffic signals that were non-functional due to widespread power outages. After playing "dodge 'em" cars at a few intersections I made it home to no electricity for a couple of hours. The upside? The sunset:
And this doesn't begin to do it justice...

Sunday afternoon line of storms

When the SPC listed Northern VA today as not only under a Slight Risk for severe weather but also with a 5% tornado probability I had my gear ready to go by lunchtime. Shear looked good, instability was excellent for the Mid-Atlantic, a prefrontal trough provided lift, and dewpoints had climbed to near 70 degrees F. Lacking a cap convection began firing east of the Blue Ridge much earlier than I'd expected from the short range models, so I headed to Bealeton at 1:30 pm in hopes of catching a solitary supercell (or two!). Unfortunately by the time I got into position the discrete cells with severe thunderstorm warnings had already begun the process of coalescing into a line so I was forced into an eastward cycle of retreat, watch, photograph, and retreat again.

Tiring of this I beat feet southeastward as quickly as I could along Fauquier and Stafford county rural routes until I reached the Stafford Regional Airport just off Interstate 95. There I was able to park, watch the line approach, and plan my next move. I saw plenty of scud and lowerings but nothing I could pin to a wall cloud. Meanwhile the storms' intensity diminished as they moved eastward.

Line approaching Stafford Airport

As the rain approached I scooted eastward into King George county east of Fredericksburg, stopping at a quarry just off Virginia Route 3 where I watched the line approach. Again, I saw features that seemed to indicate preliminary storm organization but nothing materialized by the time the rain washed over me. It was a good chase but somewhat disappointing in that the potential for some rotating storms seemed to vanish before my very eyes.

Translating weather terms into more common language

Given recent weather-related tragedies - one being the stage collapse at the Indiana State Fair - I have been more cognizant of people's tendency to either misinterpret or ignore official weather forecast terms. Pondering this and wondering what may be done to alleviate the situation has occupied my background thoughts for several months now since a late-night conversation between chase vans (via CB radio) brought similar issues to light during the May 2011 Hokie Stormchase trip. There are no simple answers to the problem of translating official weather "geekspeak" into a more common vocabulary that the wider public will relate to, but one factor that may shed some light recently dawned on me: Meteorologists tend by nature and education to be "numbers oriented" while the average person is not, leading to very different understandings between the two groups of what the numbers mean.

As an example today's National Weather Service (NWS) forecast for the Fredericksburg VA region indicates a 30% chance of thunderstorms. That is a summation of the forecast solution spit out by the numerical models used by meteorologists, thus the official forecast and accompanying graphics depict that solution. As I see it the problem is that the average person doesn't always relate to the numbers represented by the probabilities and instead focuses on the thunderstorm portion of the forecast, either basing their weather-related concerns on the fact that there WILL be storms at their location or ignoring the forecast because they don't understand what the numbers mean. In point of fact here is the official definition of probability of precipitation lifted from the NWS glossary:
"The probability that precipitation will be reported at a certain location during a specified period of time." How helpful is that definition to a non-numbers person? Not very.

Possibly an even grimmer misinterpretation lies with the probabilities given along with official NWS severe weather forecasts. Here is today's tornado probability map from the Storm Prediction Center (SPC):
Note that a 5% tornado probability exists for northern Nebraska and southern South Dakota. What does that mean? Here's the explanation copied from the SPC graphic: "Probability of a tornado within 25 miles of a point."

Numerically that can also be interpreted that there is a 95% chance of NO tornadoes within 25 miles of a given point in those states, and if the average person seizes on that interpretation the odds are that they will ignore the potential threat. However context is crucial here in that a 5% probability is significant enough for storm chasers to pay attention to that area as a place to bag a tornado sighting. Even more importantly, a 5% tornado probability forecast for the Mid-Atlantic is a very significant number given that (a) tornadoes don't happen here as often as they do in Nebraska or South Dakota and (b) the population density is much greater, providing a higher probability of damage and injury if a tornado does occur here. Thus the value of providing a numerical probability without an accompanying translation into locally understood terms means the populace could very easily misinterpret or even ignore the forecast when they don't think in terms of numbers the way that meteorologists do.

Does this explain away the aforementioned tragedies? Of course not...but maybe it does behoove the forecasters - and even us amateur weather geeks - to provide the general public with a more broadly understood interpretation of the numbers spit out by the forecast models.

August 14 driveway "chase"

After a weekend away we arrived home an hour before storms hit the Fredericksburg area. I decided to give "chase" from my driveway as (a) I was done with driving for the day, (b) the storms were in a line that would have necessitated a continuing eastward retreat to stay out of the rain, and (c) evening was upon us with full dark fast approaching. So I set up my monopod with video on top of a car and attempted both digital stills and handheld video with the other camera. Unfortunately it was almost too dark for stills and the autofocus on the handheld so the fixed video became the key player, but here's one touched-up still photo:

Overall the storms were rainy, a bit noisy, and only somewhat windy, but they were storms!

August 3: The Fizzle

Today was supposed to be the best chasing conditions in several weeks, given a surface low crossing Virginia and plenty of wind shear, moisture, and a frontal approach. So what happened? Overcast from an earlier mesoscale convective system (MCS) blotted out the sun and eliminated enough instability to prevent severe weather.
Ever the optimist I began watching the radar picture around lunchtime, finally convincing myself that a cell on the leading edge of a large rain area was worth chasing. I rolled down the driveway at 2:45 pm toward Bowling Green to intercept this storm but never made it to my original target. I motored down Virginia Route 2 keeping one eye on the radar and noticed the leading edge cell was developing northward as well as eastward, so to intercept the better convection I made a U-turn just north of Bowling Green and headed northward.
After a couple of fits and starts I realized that I wasn't going to see much in the enveloping gray mush so I continued northward in an attempt to catch a solitary cell developing ahead of the main area. Approaching Corbin this updraft to the north caught my eye:
There was no visible lightning or rotation but it did look like it could develop into something interesting, so I continued northward to New Post in order to dart southeastward on U.S. Route 17.
By that time the cell had become rain-wrapped and invisible but I spied another updraft to the northeast and gave chase south of the Rappahannock River on Rte. 17. This storm had an interesting base with all kinds of funky scud underneath:
Just to the left of this scud was another rain-wrapped feature that I was really interested in but couldn't see very well. None of my photos or videos caught any detail either, and by the time I finally crossed the Rappahannock northward on the U.S. Route 301 bridge several cells had coalesced over King George county and the bases were no longer visible in the heavy rain. No warnings, no rotation, and only a little lightning and thunder...but it was a chase!

August 1 chase

The SPC had our area listed under a 5% chance of severe weather Monday August 1st with high winds the main threat. When storms began firing and moving southeast I took notice of a complex northwest of Culpeper and ignored a juicier set of cells traversing the DC suburbs (to my later chagrin). Thus my target was Culpeper and I left the driveway just before 4:00 pm to motor in that direction.
The original line that was visible as I drove west - complete with discrete bases and rain shafts - collapsed before I could get to it but another cell built behind it just east of the mountains. As this storm grew and others fired near and around it I videoed, photoed, and then hop-skotched east and south ahead of it to keep an eye on it. I stopped on a ridge top just off U.S. Route 522 to catch this view.
Lightning was flashing from several cells, and the rain foot evident in the right hand storm in the photo was an indication of strong outflow winds.
I kept moving south along Route 522, stopping several times to watch the cells - several with radar-indicated hail markers - coalesce into a line while marching toward me. At one vantage point I noticed a feature that acted and looked suspiciously like a very small wall cloud, with abundant CG's raining down from and around it.

I finally chose to let the line catch me near Ware's Crossroads so I could head back toward home on Virginia Route 208 through the Lake Anna area. As I did so I adjusted the scale on my radar view and noticed two very nice severe-warned cells pounding King George county about 20 minutes from my home. Yep, those were an outgrowth of the previous storm complex that had traversed the DC suburbs before diving south and east. If I had waited a couple more hours I could have chased in my back yard...