Giving Thanks: The Turkey Day Storm Will Likely Arrive Early

For the past several days, the various weather models (NAM, GFS, Euro, etc.) have shown the possibility of a coastal storm impacting the East Coast, especially NYC and Long Island, around a very important holiday for the city, Thanksgiving. If a storm came up the coast with gusty winds and driving rains, would the Macy's Thanksgiving Day Parade be cancelled? Thankfully, the storm looks to impact the East Coast from Tuesday-Wednesday with conditions drying out by Thanksgiving. The trade-off is that travelers will likely face poor travel conditions on Tuesday and Wednesday.

The atmospheric players responsible for this coastal storm are a cut-off low that has been aimlessly spinning around in the Southwest US for a few days that is likely to finally get a move on its eastward trek and meet up with a broader trough digging down from Canada. As discussed in previous posts, mid-latitude cyclones (i.e. non-tropical storms) get most of their strength from air above the surface. The surface low and the wind pattern around the system provide a feedback mechanism that allows the storm to get stronger, as long as the upper-level energy is still there. The weather models had (and still have as of Sunday morning) some discrepancies of when and where the two key players will be and if there will be a significant storm.

The Stony Brook University Weather Research and Forecasting (SBU-WRF) model run, while only one possible solution of what may happen, is used here to discuss the event. Looking above the surface at 500 mb or about 2 miles up, the image below shows the two key players, a vorticity maximum associated with a cutoff low moving eastward in the South (A) and the vorticity maximum associated with a trough digging southward from Canada (B). Vorticity is a measure of the spin or rotation of the air. If air at upper-levels acquires a spin it can have the effect on air below it of drawing it upwards if the spin is positive (i.e. cyclonic or counterclockwise in the Northern Hemisphere). If the two features meet near the coast then a stronger coastal low may form than would have formed  from the systems independently.

500 mb height and vorticity from the SBU-WRF for two times (8 AM EST on Tuesday on the left and 5 AM EST on Wednesday on the right). The phasing of the two vorticity maxima (A & B) will provide the energy for a strong coastal low to develop.

Simulated Reflectivity for 5 AM EST on Wednesday.

Let's focus our attention closer to the surface. What can we expect from this coastal system? According to our SBU-WRF simulation, there should be periods of heavy rains Tuesday-Wednesday. The image on the right shows simulated reflectivity, or what you'd expect to see if you looked at a radar image around that time. The pockets of heavier showers are indicated by the yellows, oranges, and reds. The snapshot provided is for 5 AM EST on Wednesday meaning that that broader area of precipitation north and east of LI will have already moved through on Tuesday.

925 mb Temperatures for 5 AM EST on Wednesday.

A warranted question for this event is whether that precipitation should fall as rain or snow. If we look at 925 mb temperatures, which is a little bit above the surface, LI and other coastal regions remain well above freezing for the majority of the heaviest precipitation. As the system moves to the northeast, there may be some snow showers when that colder air that is to the west moves in.

One final issue with this storm is the presence of high winds. The 925 mb image shows wind barbs at this level which indicate wind speed. The triangles symbolize 50 kts (~ 58 mph) and the longer straight line is 10 kts (~12 mph). Just south of Long Island is a wind barb showing 3 long lines, so 30 kts which is roughly 37 mph. Those winds could reach the surface if the precipitation is heavy enough, but it is likely that the strongest winds will remain off the coast of Montauk for the majority of the event. As the system intensifies, there is a chance that windy conditions can persist throughout Thanksgiving Day but at least the precipitation should have moved through by Wednesday night.






We looked at one model run of one single model to deduce this forecast. However, models are run generally about 4 times a day and there are over 5 main weather models. Each model run at each time has its own solution. For a predictable event, there isn't much difference between each time a single model is run or between different models. However, this event had started out pretty unpredictable and thus there were widely varying solutions, such as the storm occurring on Thanksgiving and LI receiving a lot of snow. To illustrate the variability, forecasters look at "spaghetti plots" which show a solution from different models for a certain atmospheric parameter. The image below shows 500 mb heights, so the green lines would show the position of that Canadian trough, or "B" in the above images. Notice how there seems to be some variability in how deep that trough is (how far it stretches southward) and even its position farther east or west.

GEFS Ensemble Solutions for 500 mb heights at 1 PM EST on Wednesday. (Source: Kyle MacRitchie)

 As time gets closer to the event and the initial atmospheric conditions that are input into the model are actually observed then the models all continue to converge on a solution. The NAM, GFS and Euro models are the main models looked at by forecasters and they are all starting to converge on a solution of a wet and windy Tuesday-Wednesday but a cool and dry Thanksgiving. Safe travels and Happy Thanksgiving!

Useful Links
- For more information about synoptic meteorology please visit The NWS Jetstream Site.
- For the latest in-house model run please visit the SBU-WRF site.
- For more spaghetti please visit Kyle MacRitchie's site.

Watching Disaster from a Distance: Typhoons and Tornadoes

The weather on Long Island has been typical for Fall; one day you need a winter coat and the next day you are tempted to throw on shorts. This is due to the steady eastward progression of storm systems from the clashing of air masses across the country. This active pattern shows that the atmosphere has a lot of energy to dispel. Recently, attention has been focused to where the weather systems have been a lot more destructive and impacted so many unfortunate people that were caught in their paths.

Super Typhoon Haiyan: A Meteorological Perspective

Super Typhoon Haiyan before landfall. (Source: UW-CIMMS)

Super Typhoon Haiyan, or Yolanda as it was locally known, wreaked havoc in the Philippines before tracking towards extreme northern Vietnam and Southern China. Tropical systems form from a preexisting disturbance, or cluster of thunderstorms. Unlike the low pressure systems that we are used to during this time of year that get their energy from the air at upper-levels, tropical systems grow from the bottom-up. The heat and moisture from a warm ocean surface is what allows for tropical systems to grow to the highly-organized devastating systems that they can be. The heat from the ocean is brought towards the center which causes the center to be warmer than the outside environment. Therefore there is lower surface pressure in the center because warmer air is less dense or less heavy than colder air. Once a surface low pressure center is acquired, the storms can rapidly intensify and acquire much more of a spin as winds travel cyclonically towards the center (which is counter-clockwise in the Northern Hemisphere). Another difference between the non-tropical cyclones that we are used to in the fall season and tropical systems is that non-tropical cyclones need to have their low pressure center titling sideways with height otherwise air can fill it in and essentially kill it. The reverse is true for tropical cyclones that require a completely vertical core to survive. Think of a chimney, for example. If you close the flue then all of that smokey air comes right into your home instead of exiting and that smokey air is not healthy for survival, just like cold and dry air is not healthy for a tropical system's survival. In the atmosphere, the wind speed and direction varying with height is called wind shear, or just shear. In order for a tropical cyclone to remain upright there needs to be very little shear.

The three greatest risks to life and property associated with tropical cyclones are high winds, a lot of rain and storm surge. Long Islanders are no stranger to storm surge from last year's Hurricane Sandy impacts. Storm surge occurs when a storm travels over open water and as you've seen when you blow on the surface of your cup of coffee, water piles up downwind. When a storm is moving in a certain direction, the water piles up in the quadrant that lines up with the way the winds are blowing. In the case of Haiyan, that was its northwest quadrant (or upper-left). The geography of the Philippines made the storm surge even more impactful because water was channeled between islands of the archipelago and the relatively flat terrain allowed the water to reach far inland.  

Typhoon Haiyan formed from a small cluster of thunderstorms and fed themselves the energy from the warm waters of the West Pacific Ocean. The system acquired rotation and was able to intensify to the highest possible classification of typhoon (Super Typhoon is similar to our Category 5 Hurricane in the Atlantic Ocean Basin). The typhoon formed over waters near or exceeding 30 C (86 F) around November 6th and tracked westward in an environment with very low shear (< 10 m/s) which allowed it to form a nearly perfectly symmetrical eye and central dense overcast (CDO) region of clouds around the time of its estimated peak intensity before its first landfall. This landfall devastated the city of Tacloban on November 8th with high winds, driving rain and a sudden and powerful storm surge estimated at greater than 15 feet with 30-foot waves estimated from satellite measurements. The landfall and associated precipitation can be seen from this radar loop.  Lightning was found to be very prominent in the eyewall of Super Typhoon Haiyan which provides some insight into the ferocity with which winds were rising and taking a variety of raindrops and even ice very high above the storm that had a different electric charge what was within the nearby clouds.

Typhoon Haiyan left the Philippines and then made a northwestward move to extreme northern Vietnam. This was due to the steering flow in place, or the fact that a broad region of high pressure around which winds flow anticyclonically (clockwise in the Northern Hemisphere) so that once Haiyan got on its western edge, it was steered more towards the north (from 6 to 10 o'clock, for example). Although it weakened a little bit, it maintained typhoon status because the waters of the South China Sea were a very warm 26-29 C (78-85 F) and there was still very weak wind shear allowing it to keep its vertical structure in the moist environment of the region.

Super Typhoon Haiyan: A Historical Perspective

The Philippines unfortunately, like most Caribbean nations, lie right in a prominent tropical storm track. It's not unusual for them to make landfall and fortunately the strongest super typhoons do tend to stay out to sea and only affect mariners.

Source: Wikipedia

Prior to Haiyan's formation, several tropical cyclones had already crossed the Philippines this year with the more recent storm's associated rainfall causing the soil to be saturated and mudslides imminent.

Source: Brian McNoldy (UM/RSMS)

Dvorak Intensity Scale of Haiyan (Source: UW-CIMMS)

There was some discussion among the media that falsely claimed that this storm was the strongest tropical cyclone in history which isn't true. As of now there are no ground-based observations of wind speed to provide any information about the storm's actual intensity. In the Atlantic, we rely on aircraft observations of wind speed for official observational purposes that also help make the computer models of the storms more accurate. Unfortunately, there aren't usually aircraft flown into typhoons in that region of the Northwest Pacific so all of the wind speeds had been estimated from satellite imagery with what is known as the Dvorak technique. The Dvorak technique uses satellite imagery of structure, cloud top temperature and other quantities to estimate the strength of a tropical system where there is no actual observational data within the storm. Super Typhoon Haiyan did reach the highest level of 8 on the Dvorak Intensity Scale, but a lack of ground-based measurements will mean that it is unlikely that the strongest winds produced by Haiyan were measured and reported.

The rainfall from Super Typhoon Haiyan wasn't anomalously high for tropical systems traversing the Philippines, but unfortunately many tropical systems were tracking right across the archipelago in recent weeks. A tropical storm had just crossed a few days prior to Haiyan making landfall which caused a combined accumulation of about two feet of rain in ten days. Haiyan had slightly stronger rainfall rates as compared to that tropical storm, but only by about a half of an inch per hour. All rainfall measurements were derived from the TRMM satellite again due to the lack of ground-based measurements. (Source: NASA) 

This storm was incredibly powerful and our thoughts are with all of those affected. If you haven't already please consider donating to the relief efforts via organizations such as the Red Cross.

For more information about tropical cyclones please visit: Tropical Cyclone Introduction (NOAA/NWS) 
For more information about Typhoon Haiyan please visit the following sites:
- University of Wisconsin-Madison CIMMS Satellite Blog
- NASA's Haiyan Blog Entry

Closer to Home: Tornado Outbreak of November 17, 2013

Switching gears to a discussion about a much more recent event and one that struck a lot closer to home, today there was a fatal tornado outbreak in the Ohio Valley. A strong continental cyclone with a surface pressure at the center below 990 mb after 00 UTC on November 17th or after 7 PM local time moved from the Midwest towards the east throughout the day on Saturday and Sunday. Out ahead of its cold front, warm moist air moved northward and filled the Great Plains with that air mass that is very conducive for fueling thunderstorms.

Weather Prediction Center Surface Analysis for 00Z November 17 (7 PM EST).

As previous posts have discussed, for severe and especially tornadic storms the following ingredients are needed: moisture, instability and lift. The moisture is necessary because if dry air is lifted, clouds will not form. Instability is needed because the air being lifted needs to be able to lift itself very quickly which usually means it's warmer than the air surrounding it (think of a hot air balloon). The lifting mechanism can be the cold, dense air of an approaching cold front or if there is enough moisture and instability, a slight push from the cooler air from a neighboring thunderstorm may be enough to send the air rising violently. Another important ingredient is shear (just like as discussed regarding larger systems above). A thunderstorm that forms in an environment with a large amount of directional shear can actually have air horizontally rotating near the surface that is then bent upright by the storm's updraft that can then exhibit the same rotation and spawn tornadoes.

The models had predicted the environmental conditions conducive for a widespread severe weather outbreak in the Ohio Valley for Sunday, November 17th. The conditions verified by looking at the surface observations that morning as well as the weather balloon observations that showed plenty of moisture, sufficient low-level directional wind shear (winds from the south at the surface but trending to be more from the west with height), and the potential for instability as the sun warmed the surface throughout the mid-morning hours. The Storm Prediction Center issued a spine-tingling "Particularly Dangerous Situation" statement which they reserve for tacking onto watches that are highly probable and likely to be highly destructive to life and property. Two such PDS watches were issued today (#1 and #2). The SPC can't issue warnings as that is up to the local National Weather Service Weather Forecast Office.

Storm Reports as of 11 PM EST from NOAA/SPC.

As of 11 PM EST there have been reports of 81 tornadoes as well as over 400 reports of damage due to high winds estimated to be greater than 73 mph (65 kt). The news outlets are reporting 5 fatalities attributed to the outbreak. Hopefully that number won't increase and is likely a lot lower than it could have been without the skilled forecasting expertise exhibited with this weather event.

A question I have heard some people raise is whether or not this is normal for November. I'd argue that it is normal for November. The ingredients are all there and on average there are about 50 tornadoes per year in the month of November. If the total count of tornadoes is verified to be around 80 than it may be in the top 5 of November outbreaks from data from 1950-2010 (SPC).

U.S. Average Tornadoes by Month (Source: NCDC).

This system must continue its eastward trek and with it comes the possibility for severe weather for our area. Long Island and the Tri-State area may face some damaging wind gusts before the cold frontal passage and during it. Out ahead of the front there is a strong low-level jet, or a core of strong winds, that can actually be mixed down to the surface through the development of turbulent eddies. Think of waves crashing on the shore-- the air crashes with the ground which can send some air spiraling upwards (like waves splashing upwards) and consequently air must come downwards to fill the void and if that air exhibits a higher wind speed then that is brought to the surface as a wind gust. Another term for this is mechanical turbulence. Air with higher wind speeds can also be literally dragged down to the surface by heavy precipitation and the cold, dense air rapidly rushing downward because it is negatively buoyant (think of a failing hot air balloon!). The turbulent eddies caused by the temperature difference of air near the surface versus the faster-moving air above the surface is known is thermal turbulence.

The cold frontal passage is forecast to be somewhere between 4-7 AM EST. Our department's own operational model has it passing through starting at 3 AM and finally moving east of Montauk at 7 AM. Expect heavy rains and those gusty winds that were previously discussed.

Simulated Radar Imagery from the SBU-WRF for 5 AM on November 18th.

For more information about thunderstorms please visit this NWS Jetstream Page.

Weekly Weather Discussion: September 6th, 2013

The weekly weather discussion at Stony Brook University reviewed the interesting weather over the past week and discussed the increased activity in the Tropics.

On Tuesday, September 3, 2013 there was a cold frontal passage that coincided with some severe thunderstorms over Eastern Long Island. There was a report of severe hail (greater than 1.00 inch in diameter) in Hampton Bays. The storms were caused by a moist and unstable air mass that was set up over Long Island. However, the unstable air needed a lifting mechanism to tap into that instability and cause the air to rapidly rise and for storms to form and that mechanism was a cold front.

A tropical storm (Gabrielle) had formed in the Atlantic but didn't last long because it moved over the mountainous island of Hispaniola which was too harsh to keep the storm going. Recall that tropical cyclones get their energy from warm, ocean waters and need to maintain their stiff vertical structure which mountains would disrupt.

If a hurricane (not just a tropical storm, of which there have been 7) does not form by September 11th, then the previous record set for latest first hurricane formation in the Atlantic will be broken. There are a couple of areas of tropical convection that may organize into a tropical storm and subsequently a hurricane with time. Of special interest is a fresh wave of convection coming off the coast of Africa. The National Hurricane Center is paying strict attention to it because the environment in which the disturbance is moving is favorable for its development. Low shear (wind speed or direction changing with height that would disrupt the storm's vertical stiffness of its center), high moisture (food for clouds) and high heat content from the warm ocean waters (drives the winds and strengthening of intensity of the storms) are all important and expected to be present in the coming week for this wave. Stay tuned!

Weekly Weather Discussion: August 30th, 2013

          The faculty and students of the Institute for Planetary Atmospheres (ITPA) at Stony Brook University hosts a weekly weather discussion where they lead a scientific discussion of the recent past, current, and future weather. This week's discussion was led by Dr. Brian Colle and was titled, "Why has the Atlantic hurricane season been so quiet and how long will it continue?"
          Dr. Colle began his discussion by providing some statistics to put the current Atlantic hurricane season into perspective. He showed the National Oceanic and Atmospheric Administration's (NOAA) official forecast from this past May for 13-20 named storms with 11 hurricanes and 3-6 major storms. Their latest updated forecast changed a bit and called for 18 named storms with 8 hurricanes and 3 major storms. Despite the relatively “slow start” to the season they are still calling for a lot of activity. The average historical peak for tropical cyclone (TC) genesis in the North Atlantic is about the week of September 10th (NOAA/NHC), so it’s not like we already missed the expected peak period of activity. Dr. Colle discussed the quantity called accumulated cyclone energy (ACE) which measures the relative intensity of each storm by estimating the energy used by each storm (more info here). ACE can be used to compare relative intensities of storms or the relative intensity of an entire season. On a per-month basis, ACE also peaks in September in the Atlantic (from Dr. Ryan Maue’s page). Given this information, perhaps this Atlantic hurricane season shouldn’t yet be written off just yet but it looks like the date of the first hurricane formation may break records (McNoldy, CWG) for being later than previously observed. ACE on a globally integrated scale has been decreasing since 2005 (Maue 2011) but that may be a result of there being less intense storms during the later period from 2005-2012 (Maue’s page).
        What was the deal with the start of this Atlantic hurricane season? To date there have been 6 named storms, none of which reached hurricane strength. Tropical cyclones gain their energy at the surface, unlike strong winter storms that predominately gain their energy from winds at upper-levels of the atmosphere. Tropical cyclones typically start as clusters of disorganized convection (thunderstorms) that blow towards the west off of the coast of Africa. However, they can form from many other locations but those that form from African easterly waves, or the organized storms off of Africa, are the focus of this discussion. Tropical cyclones feed their energy off of warm ocean waters and there are several factors that can hurt their formation and development. They need warm ocean waters, moist air and weak vertical wind shear or strong winds from the west at upper levels when there are strong winds from the east at lower levels.
          Usually, the El Nino-Southern Oscillation (ENSO) when it is in its El Nino phase tends to contribute to a less active Atlantic hurricane season because of increased wind shear over the Atlantic. However, ENSO isn’t a major player this season because it is in its neutral phase, so Dr. Colle showed some plots to explain why the activity had been low starting on July 1st. The first point that he made was that there was anomalously dry air in the atmosphere (-12% RH anomaly) stretching westward from Africa all the way across the Atlantic into the Caribbean especially during the period  August 1st-15th. The Saharan Air Layer (SAL) which is dry, dusty air originating from the Saharan Desert provided a harsh environment for TC development and growth. In analyzing vertical stability or the resistance of the air to rise on its own, the Tropics are more stable this year compared to average conditions (McNoldy, CWG) so that would act to discourage convection. Sea surface temperature (SST) anomaly maps didn’t show too much of an explanation for why activity has been weak because the Tropical Atlantic waters are quite warm. Maps of upper-level shear anomalies did show that during the period August 1st-15th there was a 2-3 m/s westerly shear anomaly in the tropical Atlantic basin. Therefore, the weak activity was shown to be likely tied to the dry air and westerly shear that created an unfavorable environment for TC development.
          How long will this stifled activity last? Likely not long, Dr. Colle explained. Climatological shear values are back in place and the dry anomalies are starting to weaken and the atmosphere is becoming more moist. At the time of the discussion, there was an area of thunderstorms or an National Hurricane Center (NHC) invest area with a 40% probability for the chance of development that should move westward into an area with weaker shear but still some residual dry air. If it makes it past the subtropical high, according to the GFS model, it may encounter a trough that may recurve it and keep it away from the Caribbean and East Coast. We’ll see what happens. Looking beyond this one system and to the rest of the Atlantic hurricane season as a whole, most students at the discussion agreed that they were not ready to give up on the season yet. Assuming that the environment becomes more favorable for tropical cyclone development in the North Atlantic Ocean then this season's forecast for the number of storms may pan out.

For more information about tropical cyclone statistics visit the NOAA/NHC website: http://www.nhc.noaa.gov/climo/
For frequently asked questions about tropical cyclones visit the NOAA/NHC website:
http://www.nhc.noaa.gov/faq.shtml

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