Friday, June 28, 2013

Mission #6: The MCV That Took Too Long!

The DREAMS Project mission for Thursday, June 27th was contingent upon hoping that convection developed out ahead of a larger-scale thunderstorm system called a mesoscale convective vortex or MCV. The actual MCV was forecast to move across Long Island close to midnight. Students and faculty agreed that the environment was good enough to warrant a trip to Jones Beach to try to catch some storms.

12Z (8 AM) OKX Sounding.
The forecast for Thursday showed plenty of moisture throughout most of the lower atmosphere, instability that became enhanced with the diurnal, or daily, high temperatures, and a possible lifting mechanism produced by an upper-level shortwave that was helping to maintain a mesoscale convective system. Most of the ingredients for strong to severe convection were there and the Storm Prediction Center (SPC) placed most of the Mid-Atlantic region under a slight risk for severe weather over a day in advance. The model data and atmospheric observations were assessed early in the morning before the decision to deploy the DOW to Jones Beach was made. The morning's 12Z (8 AM) sounding from Upton, NY (OKX) showed a very moist atmosphere up to nearly 600 mb or nearly 16,500 ft above the ground. Assuming that the surface temperature would warm up during the day, then there would be a fair amount of instability (as measured by CAPE) to allow for storms to develop and grow. The CAPE was forecast to be highest over Northwestern Long Island and most of New Jersey. The idea was that the DOW would be stationed at Jones Beach with a clear view of storms that may travel to the south and north, depending on where they formed. With that plan, Mission #6 was a go!

The DOW left Stony Brook University around 11:30 AM and made its way to Jones Beach. This wasn't an easy feat because at 13.5 feet tall, the DOW can't simply take the Google Maps-suggested route with the low bridges on the parkways. As soon as the DOW arrived at the West End of Jones Beach, there were already some developing cumuli right along the sea breeze boundary near the Queens/Nassau border. This is almost exactly what was observed and scanned with the DOW on Monday! Because there was a lot of instability and moisture, the cooler and denser air that was flowing from the ocean acted like a boost to the air near the surface that caused it to rise and form clouds. The DOW reflectivity data showed the small cells producing rain, but nothing more severe like hail. The DOW velocity data showed the cells moving away from our location, or off to the northeast over the Long Island Sound.

The developing cells that greeted the DOW at Jones Beach for Mission #6.

The Tornado Watch issued by SPC ahead of the MCV.
The students out in the field on this mission were excited to see the real-time data that the DOW was producing. The tough thing about the small cells was that they were moving away from us and weren't going to last forever. The MCV was still centered in Pennsylvania and was hours away from arriving near Long Island. By 2 PM, however, the SPC issued a tornado watch for most of New Jersey. They were concerned about all of the ingredients for severe storms being present out ahead of the MCV, just as we had noted. We decided to wait at Jones Beach to see if any storms developed over southern NJ and got caught up in the mean southerly flow. Although the DOW is a Doppler On Wheels, those wheels don't have legal permission to go anywhere so we do have to deal with some element of waiting for the storms to come to us. We kept an eye on the analysis of the environment according to near real-time model output and saw that CAPE values over NJ were really high (> 3000 J/kg) but not too many storms were developing. This was likely because there wasn't much of a lifting mechanism or a way to get the air to rise from the surface vigorously enough to form clouds and storms. We waited until almost 7 PM to wrap up the mission with nothing much but clutter being measured by the DOW. We did witness the low-level moisture flux from the ocean with the strong southerly winds bringing visible, thin low-level clouds over the land.

The MCV was still rotating and causing flooding over western NJ by the time some of the team and the DOW returned to Stony Brook University. There were no reported tornadoes by this time either. At around 9 PM the decision to not have a night mission to catch the MCV was made. This decision was based on the fact that, at that time, the thunderstorm cells associated with the MCV were weakening and the line that was expected to pivot across Long Island was actually thinning and breaking apart. The mesoscale models also provided some support for that decision. Unfortunately, although that line of storms did weaken immensely, they released to the east a lot of low-level cooler air caused by the evaporation of raindrops near the surface which is known as an outflow boundary. The outflow boundary acted to organize a fresh line of storms that did in fact cross Long Island from 10-11 PM. Oh well, the DOW needed to get some rest after about 7 hours of scanning! Mission #6 was still a valuable mission that collected data on convection along the Long Island Sea Breeze. We didn't get to measure the MCV simply because it took too long and we want to be awake and eager for our next mission, of course!

- For the exact definition of a mesoscale convective vortex, please visit this site:
- For the near real-time data that we use to make some decisions out in the field, please visit this site:

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