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April 2011

Mid-Atlantic Discussion – Apr 20, 2011

SPC has been playing up what I consider to be a more marginal event in the Mid-Atlantic today. The main threat is for individual cells or small lines of damaging winds from storms that are expected to develop along the cold front as it passes through this afternoon/evening. Storms should be isolated, but those that do form have good mid-level lapse rates to gain momentum off of. Somewhat dry low-levels and downsloping WSW-erly surface winds will inhibit these storms to a degree, with high-level clouds and high LCLs also working against storm development.

Any storms that do form should die off quickly once the instability fades around sunset. There won’t be any chasing today, but there’s still a chance that some storms could develop locally to video and photograph. It certainly doesn’t look like a widespread event, and I don’t expect much beyond some spotty reports to come out of today’s storms.


16 April 2011 Storm Chase (Pt. 3 of 3) – Chase Log

Jason Foster and I left Gaithersburg, MD a few minutes after 8am to make the trek down to North Carolina for what turned out to be one of the biggest East Coast tornado outbreaks in history. The plan was to be near Wilson, NC around 12:30-1:00pm to eat and begin our chase. However, being the first day of Spring Break for many, I-95 southbound was clogged with traffic, sometimes coming to a complete stop all the way from Washington, D.C. down through northern NC. At one point we even resorted to using back roads to help make up for the time lost in transit. We finally arrived at our target destination over an hour later than planned after 2:00pm when discrete supercells were just starting to get organized to our south and west. Having no time to stop and eat, Jason and I quickly fueled the car, grabbed some snacks and headed towards the cell that was tracking towards Raleigh.

We headed towards the Raleigh cell as the Raleigh metro area was getting tornado warned. Being a bit behind the cell, we had to play catch-up. Visuals weren’t spectacular as the circulation was rain-wrapped as it pushed through the southern suburbs. The cell showed signs of cycling, so Jason and I continued with it into eastern Raleigh, where we spotted a funnel cloud and possible tornado. Since trees were in the way, we could not see whether or not the circulation had reached the surface while we were observing it. Shortly after this circulation became rain-wrapped as well, so we headed back south to catch the nearest of several storms that had active tornado warnings.

After dropping south to come in through the western edge of the core, Jason and I turned back onto I-95 to get to the second storm’s circulation, which had also become rain-wrapped. The cell weakened substantially and didn’t look like it was going to cycle, so we dove back to the southeast to get behind another storm.

The third storm had produced a tornado over Snow Hill not too long before we had arrived in the outskirts of the town. A couple miles NW of town we came upon 3″ hail, took some quick photos and measurements and headed SE. We were stopped just short of town where many emergency vehicles were already on scene. A small community and a couple of commercial buildings had taken heavy damage by a small, concentrated tornado. Some of the homes had very little damage, but two homes in the direct path of the tornado had been completely ripped off of their foundations. One of these houses was still relatively intact within the property lines, but another house was pretty much gone.

Jason and I spent some time documenting the damage before hearing of another storm entering the area. This storm passed us to the east, and we headed off to try to catch the cell as it traveled NE at ~50 mph, which was actually one of the slower storm motions we had seen from the many warnings that had been issued in NC that day. Alas, the road network was not favorable for an intercept, so after a short chase with the daylight fading we started to trek back towards I-95 to get back home.

16 April 2011 Storm Chase (Pt. 1 of 3) – Pictures

A full chase log will be coming later today, and when Jason has his chase log up I’ll post a link to that as well. I’m having FTP issues with the site at the moment, so images are hosted on Photobucket for now.

These pictures were taken at Snow Hill, NC. The hail was about 2 miles NW of the tornado path on Fort Run Rd. near the intersection with Peanut Rd.

The approximate visual tornado path based on the damage. Not to be used for scientific purposes (click to enlarge):

Chasing a Possible Tornado Outbreak in NC today

Jason and I will be heading out to North Carolina around 8:00 this morning, and our target area that was picked 2-3 days ago is in the heart of the Moderate Risk area today, which includes a strong risk for tornadoes. A full chase log will be posted later today or tomorrow. It’s potentially going to be pretty epic.

Putting things into perspective, as of now there has been 6 deaths and 23 injuries from the tornado outbreak that occurred yesterday in the Southeast, and the threat for severe weather will be almost/just as significant today from central Virginia through Georgia. For those living in the risk area, please pay very close attention to the weather today, as these storms could form quickly and with very little warning, so do your best to avoid becoming another statistic in today’s severe weather.


Mid-Atlantic Discussion – Apr 11-12, 2011

A wall of precip. to our west will be slowly pushing eastward today as a secondary low develops over the TN valley. Timing the line will be rather difficult as the secondary low slows the progression of the front, and the threat for severe storms could extend into early afternoon tomorrow in the far eastern parts of the region.

The main concern with this system will be damaging winds along and just ahead of the cold front. The northern end of the line, which has a more E-W tilt than the bottom part of the line, will drape itself across the northern parts of the region. The northern part of the line down to the change in the orientation of the line could be an enhanced tornado risk, though the risk is still on the low side. This area is expected to be in WV, SoPA, NoVA, and NoMD as we head into the late afternoon through the overnight hours. The main tornado threat should stay north and west of most of the region, but we’ll see what happens.

Tentative chase area is SW PA or S-Cent. PA.

Mid-Atlantic Discussion – Apr 4-5, 2011

This may be my only update for the week as I have quite a busy schedule which includes moving.

The severe threat looks to be pretty marginal overall for the region Monday afternoon into Tuesday morning, with the key issue being timing as the cold front works with limited/no instability. West Virginia has the greatest risk for severe as a few pre-frontal storms and a QLCS (quasi-linear convective system) move into the westernmost parts of the region the late afternoon and evening hours. The line of storms will weaken and push east during the overnight hours, moving off of the coast by late morning or early afternoon. These storms are currently modeled to hit the DC/BWI region around morning rush hour, depending on the overall speed of the line. During the overnight hours, these storms are expected to be rather weak and/or elevated, but a loose line should be able to make its way through the coastal areas.

A positively-tilted upper-level trough will become neutral as an UL vort. lifts N+E through the region. At the same time, an UL jet will intensify just W of the cold front, putting the Mid-Atlantic in the right-exit region of the jet. The dynamics that we need for severe weather are there because of these UL features along with the surface front, but without any thermal instability that potential could be lost for most of the region as the storms skirt by. Directional shear isn’t terribly impressive for most of the region, with largely unidirectional winds out of the SW. The biggest threat will be from wind as a LL jet with a speed max of 70-80 kts around 900mb orients itself over the region. It would take minimal surface-based convection to bring severe-level gusts of 50+ kts to the surface, but getting surface-based convection will prove to be difficult once the late evening hits. Dry air out ahead of the front will also hurt instability as the column tries to saturate just ahead of the front. The risk for hail and tornadoes is minimal threat for most of the region, with an isolated risk for those in the western parts of WV.

18z NAM and GFS showing somewhat better potential for strong/severe winds tomorrow night into Tuesday morning compared to previous runs with weak instability in the mid-levels… will continue to monitor possible nocturnal instability as just a small amount is needed for the severe winds to occur.

Jason and I are thinking about heading to SW PA to intercept storms just ahead and along the cold front during the late afternoon and early evening as instability fades. Directional shear should be decent enough there for isolated tornadoes if the storms can tap into enough instability.

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