Sea-Breeze Convection-July 19, 2013

 A large area of ridging aloft along the eastern U.S. slowly retrograded westward and weakened as it moved into to middle of the U.S for the greater part of the last week.

As a result of this ridging, 500 mb heights climbed to near 5910 gpm with 850 mb temperatures topping a toasty 20 degrees celsius at KOKX at 12Z on July 19, 2013. Given mostly clear to partly cloudy skies associated with subsidence aloft, surface temperatures climbed into the low to mid 90's.  In addition to the oppressive heat, a subtropical air mass was situated over the entire northeast U.S. allowing dewpoints to reach into the mid 70's.

On the morning of July 19, the KOKX sounding revealed a relatively shallow unstable layer extending from 950 mb to 750 mb with a strong surface based inversion and little to no wind shear.

Given strong surface based heating associated with mostly clear skies, the forecasted sounding for the KOKX region showed that by 18Z the surface based inversion was largely dissipated and showed a well-mixed layer extending from the surface up to around 850 mb.  While surface based CAPE values were rather low, MU CAPE values topped 3000 J/kg in the Long Island region given the heat and moisture content of the air. 

A sea breeze boundary was rapdily  advected to the north-shore of Long Island through the morning hours due to a southerly flow. The boundary was difficult to identify in base reflectivity loops, but can be seen in surface based observations around noon EST between Port Jefferson and Wantagh through the convergence of the wind field. 

The convective cells appear to be initiated over the same general region near Sunken Meadow State Park (appox. 10-15 miles west of Stony Brook Campus) and train westward along the ill-defined boundary as evident in this loop from 16UTC (1 EST) to 18UTC (3 PM EST).  One hypothesis for the initiation of convection over this region could be that the Sunken Meadow region had the greatest low-level convergence.  This would agree with the mesonet observations around mid-day (not shown) which  showed defined low-level convergence on the north shore of the Middle of the Island near Sunken Meadow State Park.

These cells were  short-lived given weak wind shear profiles and a shallow unstable layer, however, one cell did muster the strength to produce 1" inch diameter hail in Mt. Sinai, New York and penny sized hail on the SOMAS campus. The reports of hail in Mt. Sinai were enough to verify a Severe Thunderstorm warning issued by KOKX moments in advance. 

All in all, the intensity of thunderstorms triggered by a weak sea-breeze boundary was an uncommon occurrence and would have made for a very useful field day if the DOW had been around...

Final Mission: The Long Island Sea Breeze Front

The final mission of the DREAMS Project, Mission #12 if you are keeping track, took place on Monday, July 8th. The goal of the mission was to target the Long Island sea breeze front and any possible pop-up convection in the area. The forecast was very supportive of a robust sea breeze forming around noon so the decision was made to travel to Calverton Airport (EPCAL) to capture it.

The forecast for July 8 called for westerly winds which meant that, unlike the previous sea breeze missions with a southerly wind, the sea breeze front wouldn't be pushed towards the Sound so quickly. If any clouds formed, they should move to the east in a noticeable line. The DOW left Stony Brook University at 10:15 AM and was set up and ready to scan by 11:00 AM. By noon, large cumulus clouds had formed indicating that there were converging winds along the sea breeze front that allowed for near-surface moist air to ascend and form clouds. As the forecast suggested, most of the clouds moved east.

 

The DOW under clouds formed along the sea breeze front in Calverton.

The reflectivity and velocity data both showed a convergent wind boundary indicative of the sea breeze front for most of the afternoon. The pod was deployed which took surface air measurements before the sea breeze front moved to our north and then shifted back to our south. The changes in the surface air characteristics aren't expected to be that apparent because of the characteristics of the surface near the pod, mainly that it was surrounded by sun-soaked concrete.

The DOW under the clouds along the sea breeze convergence boundary. (Photo credit: Matt Sienkiewicz)

A sounding was launched from the New York City office of the National Weather Service in Upton at around 2:00 PM. From that vertical profile of the environmental temperature and dew point, the boundary layer (air near the surface extending up a few thousand feet) showed a temperature profile and wind shift when compared to the air above it that provided further evidence of the sea breeze front. Additionally, the sounding showed that there was only a little bit of instability, one of the main ingredients for convection so the chance for storms looked very small.

The sea breeze front evaporated to scattered cumulus clouds by 3:00 PM and the lack of convection in the area allowed for the final mission of the DREAMS Project to officially wrap up. While the field work is over, the more tedious data analysis begins! However, students understand that hours of staring at a computer screen will be eased by the thought that the data was collected by them personally. With the DOW's visit over, a huge thank you goes out to Rachel H. for being there for us through sea breezes, stratiform rain, and a broken down DOW. Another huge thank you goes out to all the folks at the Center for Severe Weather Research (CSWR) for making the DREAMS Project come true. And lastly, a huge thank you is due to the lead investigators and organizers, Drs. Brian Colle and Kelly Lombardo and NWS liason Jeff Tongue! And, of course, this project would have been nothing without the eager and excited participation of the students, especially those of Stony Brook University.

The posts found on this blog may be updated with more information about the data that was collected once it is analyzed, so feel free to check back. Thank you so much for reading and for following the DREAMS Project!

Mission #10: DOW 6 is Sick and Mission #11: 4th of July Fireworks

Mission #10 of the DREAMS Project at Stony Brook University was originally scheduled to take place on Tuesday, July 2nd but was cancelled because of a lack of activity. The atmospheric pattern was generally stable which inhibits convection so any precipitation in the area was falling pretty lightly which would have made for a boring mission! Mission #10 was then rescheduled for Wednesday, July 3rd. The target was very weak convection (hey, at least it's something!) that was forming in the most atmospherically unstable regions of New Jersey (relative to the region) and moving northeast with the wind around the largely weather-preventing Bermuda High that had taken up shop just off the coast of the Mid-Atlantic.

What's the deal with the Bermuda High? As you probably know, high pressure is known for clear skies and nice weather. This is because with a high pressure at the surface there is actually sinking motion throughout the atmosphere in the vertical direction. The sinking motion causes air to warm and clouds are mostly inhibited because the air dries as it warms and most clouds form from the rising motion of water vapor condensing. While beach-goers were probably happy with the weather, members of the DREAMS Project weren't as happy. Another interesting fact about high pressure is that the air around it moves in a general clockwise, or anticyclonic in the Northern Hemisphere, pattern. Because Long Island was near the western edge of the Bermuda High, the wind was generally from the south-southwest. Any storms that fired up over the southern portions of New Jersey would then tend to move north towards Yonkers and into Connecticut. Therefore, for Mission #10 any chance of catching something would be by pointing the DOW south and hoping a cell or two moved out over the water into our sight. The site chosen for the mission was Jones Beach.

Besides the uncooperative weather, an interesting note about field campaigns like the DREAMS Project is that the success depends solely on the instrument being used. In this case, without the DOW there would be no project. En route to Jones Beach the A/C stopped working in the cab of the DOW and the engine overheated. From a mess of engine coolant, the driver and technician (and saint!) Rachel discerned that this was a big problem. She jumped into action and called her colleagues back at the Center for Severe Weather Research in Boulder, CO and the decision was made that the DOW had to get towed. Thus, Mission #10 was cancelled again, this time due to bad luck!

The DOW being towed away for repair on July 3rd on Montauk Highway.

The DREAMS Project was likely going to see an early end, but thankfully the DOW returned from the great shop in Brooklyn that worked on the 4th of July so that we would have it by our next mission, Mission #11 on Saturday, July 6th. It was decided to scrap the name of "Mission #10" even though there technically wasn't one because it just seemed unlucky after two failed attempts!

Mission #11 was based on an interesting idea from Mission #7's late night at Cedar Beach. During that mission, there happened to be some fireworks going off in CT that students claimed to have seen evident on the reflectivity data from the DOW. The idea to use the DOW to scan a fireworks display had been floating around for some time, so thanks to the students' involvement and the DOW's recovery, a fireworks display was selected and a site determined and Mission #11 was a go! The Peconic Bay Medical Center Family Fun Festival in Wading River was chosen due to its proximity to Calverton Airport (EPCAL), a site we were already pre-approved to use. The DOW set up at 8:30 PM and although after 9:00 PM there were some scattered or more distant fireworks displays, they were not showing up clearly in the reflectivity or velocity data. We kept up hope, though, and at 10:15 our target fireworks display occurred and the smoke from the festive explosions were reportedly visible on the reflectivity data. We weren't show going into that mission whether or not it would work, but we got to enjoy a great show and gather some data for science!

The DOW waiting for the sun to set to scan fireworks in Calverton on July 6th.

After Mission #11 ended at 11:00 PM, that meant there was only one more mission left with the DOW before it left Stony Brook and traveled back to Colorado. It might have been more appropriate to conclude the DREAMS Project with Mission #11 just to go out with a "bang" but we had something more exciting in store (to us at least)-- a sea breeze!

- For more information on the Bermuda/Azores High, please visit this site: http://www.springerreference.com/docs/html/chapterdbid/3926.html

Mission #9: Surprise Strong Storms Strike Early!

The DREAMS Project started off the month of July with a mission. Mission #9 took place on July 1st and a lot earlier in the day then the organizers had anticipated. Strong-to-severe thunderstorms developed early in the morning and propagated northeastward over Long Island and Connecticut. Thanks to the quick action of the DOW team (especially Rachel Humphrey who's been driving the DOW and teaching us how to operate it) the radar was set up in time for the action at Cedar Beach in Mount Sinai. A strong cell passed just to our north and some strong showers developed and moved overhead. After everything cleared up we were in a parking lot with a few inches of water to navigate around!

Weather Prediction Center's 12Z (8 AM) surface analysis.

The forecast for Monday, July 1st was very similar to the previous day's forecast. Most of the ingredients for strong storms were there such as tons of moisture as evident by dew point temperatures in the 70's F and some instability that would increase if there was solar heating during the day. Another ingredient that hasn't been mentioned is called wind shear. A thunderstorm develops from rising air that grows depending on the available moisture, instability, and lifting mechanism. That rising air is concentrated into a narrow swath called an updraft. Wind shear is defined as the change in wind speed or wind direction with height. If there is no wind shear than the updraft is perfectly vertical and when the air rises and condenses its water vapor to form clouds that rain, the rain can actually "choke" the updraft by flooding it with cold, descending air. Wind shear is important to tilt the updraft so that it isn't vertical so that the storm can persist for a longer period of time before dissipating. For Monday, the lifting mechanism was predominantly a stationary front that was situated just east of the Appalachians for most of the day. The forecast was for thunderstorms to develop later in the afternoon when the daytime heating of the surface from the sun would be at a maximum and therefore the amount of instability (CAPE) would also be at a maximum. However, what actually happened was strong thunderstorms got going during the overnight hours and because of the strong wind shear (strong winds from the south near the surface and stronger winds from the southwest higher up) and the added forcing of the stationary front, they organized into a strong line of storms. The original plan for Mission #9 was to catch some late afternoon thunderstorms, but after the National Weather Service issued a tornado warning for Union County in New Jersey around 9 AM (1300 UTC), the DOW team sprang into action.

DOW scanning to our northwest.

Pod in front of approaching storms.

The DOW left Stony Brook University around 10:30 AM and headed to our favorite location on the North Shore- Cedar Beach in Mount Sinai. The plan was that if the line of storms held together as it swept across Long Island, then we'd have the perfect view to our north over the Long Island Sound. We started scanning the skies by 11:30 and watched the line approach our location from the west-northwest. We deployed the pod to measure conditions near the surface throughout our deployment. An interesting feature that we measured with the radar was a possible updraft core. We took vertical slices through the cells as they approached us and saw a narrow area extending up into the storm of velocity values that were opposite of the storm motion. By 1:00 PM a shelf cloud was visible just to our north associated with a strong cell. A shelf cloud forms when there is air rising just ahead of the cooler air gusting outward from a thunderstorm.
 

Shelf cloud over the Long Island Sound (photo by David Stark).

After the strong storm passed to our north and east, we noticed there were a few smaller cells developing to our southwest. We positioned the DOW to take vertical slices of them as they grew and organized into a flash-flood inducing line of storms that passed overhead between 1:15 PM and 3:00 PM. The photo on the right is of the reflectivity data (top screen) and velocity data (bottom screen) that is showing a vertical slice through the second line of heavy rain. The yellows in the reflectivity data show a core of high value of dBZ (the unit of reflectivity) just about to approach the DOW. The velocity data shows mostly blues and purples which meant that all of those rain and cloud drops were moving towards the DOW (i.e. inbound). The students in the DOW had front row seats for the downpours that occurred and could see them approaching using the radar. Despite a leaky roof in the DOW, most of the participants in today's mission were able to keep dry! After the mission wrapped up at around 3:00 PM, water had pooled in the Cedar Beach parking lot to a depth of over four inches in spots! Dr. Kelly Lombardo's car is pictured below sitting in one such puddle. The DOW had to be backed out of a puddle to allow for its occupants to jump down to dry land.

Dr. Kelly Lombardo's car and the DOW sit in a few inches of post-storm water.

Despite having planned on an afternoon/evening mission, the DREAMS Project participants made a great effort to get the DOW out and into position to sample the surprise convection that maintained itself across the Tri-State area. Although we could not have measured the confirmed tornado (with any sites that we have legal permits for), that particular storm jump-started our day. We used that storm to decide that the convection was strong and would hold together as it traveled eastward closer to Stony Brook University. We recorded some great data of the passing convection before it cleared up for the rest of the evening. Therefore, Mission #9 was a success!

- For more information on shelf clouds, please visit this site: http://eo.ucar.edu/webweather/cloudpic1.html
- For more information on thunderstorm ingredients, please visit this site: http://spotterguides.us/advanced/advanced03.htm

Mission #8: A Quick Trip to the South Shore

The DREAMS Project celebrated the end of the month of June by having Mission #8 on Sunday, June 30th. The forecast was for scattered thunderstorms and the impromptu decision was made Sunday morning to try our luck at Smith Point beach in Mastic Beach. The students spent a couple hours with the DOW before wrapping up the quick mission. During that time they were able to scan two areas of weak, scattered storms. Something is better than nothing according to our optimistic sides!

The DOW left Stony Brook University around 2:00 PM and was set up to start scanning by 3:00 PM. There had been some fog at Smith Point but it had lifted a bit upon our arrival. The students were first able to sample some showers and thunderstorms to our northwest. After identifying the area of higher reflectivity with the horizontal scan, they chose to do vertical slices to see the semi-3D structure of the cells.

The DOW at Smith Point ready to start sampling nearby showers and thunderstorms.

Have you noticed that most posted photos of the DOW have the truck on what appear to be stilts? The DOW6 is equipped with 5 hydraulic feet that can have varying heights to make the DOW level on uneven surfaces. Why is this important? With a radar beam of energy coming and going from one point and moving in a circle and even up and down, there's a lot of math involved (especially trig)! To simplify the calculations, the DOW is leveled in reference to the ground that it is sitting on. This also ensures that the radar beam isn't being transmitted at really odd angles and completely missing storms. For the quality of the data, it makes sense to have it level if the DOW is going to be in one place. However, the data is perfectly fine if the radar is operated while the DOW is in motion. We haven't had much storm activity to actually need to operate the radar while in motion, unfortunately!

The level DOW using its hydraulic feet at Smith Point.

By around 4:00 PM an interesting single cell had fired up over the open ocean and was moving north-northeast. The students' attention thus focused onto this cell and they changed the orientation of the radar to take vertical slices of the cell instead of the activity to the northwest. Over the course of a couple hours, the cell grew and became more stratiform (i.e. a broader area of lighter rain versus convective which is heavier showers over a smaller area) before going out of range of the DOW. Interestingly enough, a group of very small-scale cells developed to the southwest of the original cell likely due to the fact that the original cell may have produced some outflow of cooler, denser air that forced air to rise above it. That may be how the cells were activated. At around 6:00 PM the mist began to thicken and cover anything exposed with water droplets. The students luckily all fit inside the DOW and paid attention to the developing fine-scale cells before wrapping up the mission at 7:30 PM. Despite being a quick mission, the students were able to become more comfortable operating the radar and with making decisions about where to selectively perform RHI, or vertical, scans through a particular area of higher reflectivity.

- For an inside look at how the different components of the DOW, please see this operations manual: http://somas.stonybrook.edu/downloads/DOW6OperationsManual.pdf
- For a near real-time update on where we'll be next, please see the DREAMS Project website: http://dreamsproject.weebly.com/schedule.html