While the heat persists in the southeast, there is a slight threat for severe weather on 4 July 2018. The slight severe weather threat contains central and northeast Nebraska, northwestern Iowa, southern and eastern Minnesota, the southeast corner of South Dakota and northwestern Wisconsin. Main threats for this event include damaging winds, and large hail; however, a tornado cannot be ruled out. There is a mesoscale convective system that has a history of producing hurricane-force wind gusts. The area has been under a severe thunderstorm watch for the overnight hours but as the system moved east, the watch was discontinued. As it moves eastward, the system moves into a less favorable environment. For the remainder of the day, widely scattered thunderstorms are expected to develop into the afternoon. There is risk for general thunderstorms for the central, southeast and east coast of the United States which means storms are not expected to be severe (although it cannot be ruled out).
These storms could put a damper on Independence Day celebrations especially during the evening hours. People who gather outdoors to watch fireworks and parades need to stay weather alert. In the event a thunderstorm threatens your area, seek shelter immediately. Remember, “when thunder roars, go indoors.”
You can read the entire synopsis from the NOAA Storm Prediction Center below:
A long-lived MCS that produced hurricane-force measured gusts around MBG overnight continues to weaken gradually as it moves into somewhat less-favorable environment across northern MN. Still, a severe gust or two remains possible with near-leading-edge convection forced by the cold pool. Widely scattered to scattered thunderstorms, in discontinuous nodes or clusters, are expected to develop through this afternoon near the front and prefrontal/outflow boundaries, from the Upper MS Valley to central/southwestern NE and northeastern CO. Damaging gusts and sporadic large hail are expected from the most intense activity. In addition to afternoon development, this scenario may include regeneration of thunderstorms later this morning over portions of MN along the outflow boundary from ongoing activity, as it impinges on a destabilizing boundary layer. Regardless, rich low-level moisture from central NE northeastward will combine with diabatic surface heating and steep midlevel lapse rates to boost pre-convective/warm-sector MLCAPE into the 3500-4500 J/kg range. Although large-scale ascent aloft should become more displaced from the region through the day, given the track of the aforementioned shortwave trough, that heating along with lift along the boundaries will support pockets of convective development and fairly rapid intensification in that large-buoyancy setting. Initial multicell and messy supercell modes are possible, with upscale clustering anticipated late afternoon into evening. Given the geometry of the mid/upper-level pattern and related northern-stream height gradient, flow aloft and deep shear should decrease with southward extent. Veering wind profiles with height are expected to aid in convective organization, even over southern parts of the outlook area where absolute flow in midlevels will be modest in closer proximity to the axis of the anticyclone. Additionally, an MCV -- now evident in radar composites over northeastern NE -- also may augment deep-layer lift on the mesobeta scale over part of the upper MS Valley region this afternoon.
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ⓒ 2018 Meteorologist Brandie Cantrell
DISCUSSION: Throughout the Spring and Summer-time months, many people around the world who live across many inland areas are often increasingly more concerned about the relatively consistent threat which is imposed by strong to severe thunderstorm activity. As always, when it comes to strong to severe thunderstorm threats, there are many corresponding sub-threats that come along with the storms themselves. First and foremost, you generally will tend to have stronger winds courtesy of powerful downdrafts within more intense storms and then you will also find particularly heavier rainfall as well. However, in addition to both of those severe storm components, you can also sometimes run across hail (and some destructive hail) depending on the specific situation.
Although many people around the world have experienced a hail event of some kind at some point during their lifetime, many people are uncertain or misled for how and why hail stones form in severe storms in the first place. There is a somewhat common misconception that chunks of ice “simply cannot ever occur during the Summer since the ice would melt before reaching the surface of the Earth.” However, this is a sincere error in judgement, since that cannot be farther from the truth. In fact, hail forms within severe thunderstorms via very strong updrafts within a given thunderstorm suspending ice molecules within the higher parts of the thunderstorm. During this process, a decent percentage of said ice molecules will collide and begin to “stick” to one another which increases the overall size of these individual ice molecules into smaller “pea-sized” ice chunks. Depending on the strength of the main updraft within a given thunderstorm, the relatively small ice chunks may simply fall out of the cloud, but if the updraft remains strong enough, they will continue to remain suspended within the thunderstorm.
As they remain suspended, the smaller ice chunks will continue to undergo the process of aggregation and accretion which collectively act to further increase the average size of the smaller “ice chunks” into what atmospheric scientists more commonly refer to as hail stones. Hail stones can be as small as “pea-sized” ice chunks as noted above or as large as softball and/or grapefruit-sized hail stones. Thus, the destructive potential for larger hail stones is tremendous to say the very least. Hence, the next time you or someone you know is projected to be in the path of a nasty thunderstorm with a history of producing large hail, be sure to make the person aware of the incoming and potentially life-threatening situation so they can take proper shelter.
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© 2018 Meteorologist Jordan Rabinowitz
DISCUSSION: When it comes to forecasting and predicting severe weather events, there is no doubt that one of the critical factors in anticipating when and how fast updrafts within a given thunderstorm cell will develop and grow the course of a certain period. A thunderstorm’s updraft is best defined as the core rising column (or metaphorical tube) of air which transports much warmer (and typically ground-based air parcels) higher up into a developing thunderstorm cell. This is shown in the idealized graphic attached above courtesy of Australia's Bureau of Meteorology. Whether an updraft grows quickly or if an updraft happens to develop more slowly will often determine the sort of threats which a given updraft can bring to a given town or city which it is developing over. One thing to understand is that the atmosphere is uniquely a dynamically changing gaseous fluid which means that by its very nature it is nearly always changing on a minute-to-minute and even a second-to-second basis.
For this reason, it is also imperative to understand that such real-time changes in a given dynamic and/or thermodynamic set-up over a given region at a certain time can greatly influence how an updraft develop. For example, in situations where a thunderstorm’s updraft develops and grows more rapidly, this can often facilitate the development of a situation wherein an updraft can quickly begin to generate an increasingly larger threat for very heavy rainfall, large/destructive hail, and damaging wind potential. Thus, if a severe storm is developing with rather vigorous updraft speeds being measured along the way, this would be a situation to concern yourself with if you happen to be in the given storm’s projected path.
On the flip-side, if you are in the path of a given thunderstorm cell which is having a tougher time getting its act together, then there is often much less to worry about. This is because when a thunderstorm’s updraft is having a challenging time growing and intensifying, this consequently greatly lessens the storm’s potential to acquire any in-storm characteristics which are remotely close to those noted above for more severe thunderstorm activity. Hence, when evaluating the given threat level for a given thunderstorm event, one must ask oneself if there is a strong updraft developing within a given storm which can almost always be found out from your local weather broadcaster online, on your local television news station, or on the radio in a given severe weather situation as they are covering it. So, always be prepared and always be paying attention when severe weather threats bear down on your hometown.
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© 2018 Meteorologist Jordan Rabinowitz
Image: NWS WFO Denver/Boulder Science and Operations Officer Paul Schlatter updating the warning polygon using radar reflectivity on the Gibson Ridge Software program
Discussion: On June 19, 2018, I had the privilege of observing an afternoon of severe weather from inside the National Weather Service (NWS) Weather Forecast Office (WFO) Denver/Boulder in Boulder, CO. What is fascinating about being on the inside of a NWS WFO during thunderstorms is watching the process of weather forecasters issuing watches and warnings for the storms. On this day, nearly 10 severe thunderstorm and tornado warnings were issued for the Denver/Boulder County Warning Area (CWA) and there were three confirmed tornadoes.
To understand the forecasting process, here is a brief overview. To begin, view the current conditions using surface observations, radar and satellite imagery, and most effectively, look out of the window. You have to know where you are starting to understand where you’re going. From there, forecasters look forward into the next several hours using tools such as weather models, maps of atmospheric thermodynamic and dynamic conditions, and analyze air mass movement. Much more detail goes into this process, but these general steps are repeated throughout the day to update a forecast.
Once it has been determined that severe thunderstorms are on the horizon, it’s time to ensure the office is adequately staffed for the occasion. In the case of afternoon thunderstorms, as recently experienced, the forecasters on duty extended their shifts until the late evening and even midnight shifts began. This was primarily to keep forecast continuity and efficiency throughout the event as opposed to taking precious warning time to brief the new forecasters on what’s happening in the area. Now that storms are popping up on radar and satellite, it’s time to evaluate which, if any, storms need warned.
All watches and warnings from NWS are issued using Advanced Weather Interactive Processing System (AWIPS), a weather forecasting package that allows you to display and analyze data. In this case, numerous storms were intensifying such that the WFO assigned two forecasters to keep an eye on separate storms in the CWA. These forecasters mastered the art of multitasking as they not only were forecasting and warning storms, but, answering phone calls to collect weather reports as well. The following description is just a broad overview of the warning process.
Each forecaster used five computer screens to warn the storms. The first screen was dedicated to creating watch and warning statements using the WarnGen feature. Verbiage for these statements was formed by selecting a series of pre-determined phrases that accurately described the current hazards. Then, the statement was automatically generated and disseminated on the web. The next three screens displayed radar and satellite data. On these screens, the forecasters were constantly monitoring the storm development and evolution. They also used the interactive WarnGenfeature to create and edit the warning polygon based on the storm track. After one warning had been issued, the polygon was manually edited and updated as needed so that once the previous warning expired, the succeeding area was ready to be warned. In this situation, it’s important not to jump the gun and warn over a large area at once as a storm track can rapidly change direction and intensity. The fifth screen displayed the Boulder social media pages and NWSChat page of forecasters at different WFOs. NWSChat is a forum for forecasters from different WFOs to communicate in real-time with emergency managers and media, which, as you can imagine, is important during severe weather.
Severe weather days equate to all-hands-on-deck for the WFO. Everyone works together during hazardous weather events to ensure safety of people and their property by answering phone calls from the general public and emergency officials, collecting storm reports from the SKYWARN volunteer severe weather spotters, and frequently update social media on storm conditions while concurrently improving models through verified model conditions. Not only does this benefit the public, it also helps the forecasters verify actual weather conditions. So, the next time you’re under a watch or warning, remember the detailed process of which the NWS forecasters underwent to alert you of incoming hazardous weather!
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© 2018 Meteorologist Amber Ligget
DISCUSSION: During a typical severe weather season, there are a large variety of different forms of severe weather threats which evolve during a given situation based on the given atmospheric dynamics in place. Having said that, in many cases, severe thunderstorm development nearly always involves some sort of dynamic interaction between updrafts and downdrafts. In many cases wherein the convective storm development becomes what is referred to as predominantly “outflow dominant,” these types of convective scenarios consistently involve a storm exhibiting very impressive low-level features. When a convective storm is outflow dominant, this implies that the storm has a strong low-level air stream impinging on the back-end of the storm and forces stronger winds near the front of and/or just out ahead of the storm’s region of peak intensity.
One such feature which is somewhat consistently observed with many outflow dominant severe weather events is known as a shelf cloud. Shelf clouds form as a result of rain-chilled air within a strong downdraft of a strong to severe thunderstorm descending out of the base of the leading edge of the thunderstorm and then forcing relatively warmer and moister ahead out ahead of the approaching storm to be lifted. This lifting of the relatively warmer air is directly due to the fact that this warmer air out ahead of a such a storm is warmer and moister which also means that such a storm has a greater degree of vertical buoyancy.
Hence, as the colder (storm-generated outflow) air descends both down and away from a given storm, this allows for the warmer and moister air to be lifted more easily and then often condense as well as it rises through the lowest levels of the atmosphere. During this process of moisture condensation, there are many occasions during which this moister air condenses and is visualized by way of the development of a shelf cloud. A great example of this is captured in the image attached above (courtesy of Marty Hendickson via Meteorologist James Spann) in association with a severe storm which occurred on the afternoon of June 1st over the coastline of Palm Beach, Florida.
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© 2018 Meteorologist Jordan Rabinowitz
DISCUSSION: As of later yesterday evening and the later night-time hours of Sunday (3 June 2018), there were two distinct convective thunderstorm complexes occurring across portions of both central and eastern Texas. During the course of the evolution of the respective severe thunderstorm complexes which evolved into bowing thunderstorm complexes most often referred to as being mesoscale convective system’s (or MCS’s) these two bowing thunderstorm complexes were on such a trajectory which took them closer and closer to one another as the night progressed. In fact, as time went on, it became increasingly clear that the respective MCS’s were going to collide into one another. Although that reality was fairly certain, one of the primary questions was how this thunderstorm complex collision was going to affect and ultimately influence the intensity and duration of the respective areas of convective storms.
In light of the ongoing progress of the GOES-16 or the GOES–East satellite imager products, there is an even more cutting-edge level of insight which has been made possible now. This newer level of scientific insight has been made possible by GOES-East’s Geostationary Lightning Mapper (GLM) imager. The GLM is a product which observes and archives data pertaining to lightning strikes both from a vertical and a horizontal perspective. The GLM gives a state-of-the-art on the evolution of severe weather it since it allows to gain a better understanding for how particular storms or storm complexes evolve with time during their lifetime.
In addition, this also substantiates how atmospheric scientists and operational forecasters can analyze how a given storm’s severe weather threats evolve during their existence. In the fairly recent example attached above, note how the lightning density count increased notable as the respective thunderstorm storm complexes approached each other and even more so as they merged. However, what you cannot clearly see is that once the respective MCS’s merged, the lightning substantially dropped off in frequency since the interacting updraft cores interacted and likely affected the angle at which the respective updrafts were positioned. More specifically, as the respective MCS’s collided, this collision most likely affected the ability of the updrafts and downdrafts to continue maintaining their most recent intensity prior to the thunderstorm segment collision.
Thus, it just goes to prove that through using modern satellite remote sensing technology, atmospheric scientists have the increased ability to improve the ways by which we study severe thunderstorms of varying types and intensities. The most incredible part is that we are likely only just beginning to tap the ongoing potential of atmospheric science in studying severe weather as we move further into the 21st century.
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© 2018 Meteorologist Jordan Rabinowitz
On Sunday, May 27th, Ellicott City, Maryland experienced a flash flood caused by a line of thunderstorms that created much devastation in the city. CBS news reported that this flood was so severe that cars floated down Main Street in Ellicott City, Md. There was also a report on Sunday that someone had been missing since being washed away by the flood on Main Street after assisting with water rescues. Unfortunately, on Tuesday the 29th, he was found deceased. This shows how devastating, dangerous, and life-threatening floods can be.
The water receded the day after the flood. Overall it is estimated that there were about 15 inches of rain in Catonsville (a town next to Ellicott City). Although the water had receded, The Weather Channel stated that on Tuesday the 29th authorities issued a “precautionary health alert” after a sewer spewed about 500,000 gallons of raw sewage about 2 miles from downtown Ellicott City.
The geography of Ellicott City makes it flood-prone. The Washington Post explained that the area is located downhill next to the Patapsco River. Several streams flow downhill towards Ellicott City and Patapsco River, which makes the city susceptible to floods.
This is the second time within two years that Ellicott City had a major flood. They had just recovered from a flood in 2016. Hopefully, with much support, the city can make a quick recovery.
(credit: The Weather Channel, CBS News, The Washington Post)
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© 2018 Forecaster Brittany Connelly
This past Tuesday marked the 7th anniversary of when the city of Joplin, Missouri was impacted by the deadliest and most damaging tornado since records began in 1950. At its peak, this EF-5 tornado was nearly a mile wide, with winds of 200+ miles per hour. From start to finish, the tornado tracked a path stretching 22.1 miles, resulting in 158 deaths and over 1000 reported injuries.
On May 22nd, 2011 at 5:34 p.m, a supercell dropped a tornado just east of the Missouri-Kansas border. This tornado tracked due east near 32nd street where storm chasers and eyewitnesses had reported seeing multiple vortices around the main circulation, a typical sign that the tornado is rapidly strengthening and getting larger in size, and right before the tornado became rain-wrapped.
Sirens sounded 20 minutes before the tornado struck Joplin as tornado warnings were issued by the NWS office in Springfield, MO. The tornado intensified into an EF-1 as it started to plow through rural areas. From there, the tornado continued to track east as it made its way along 32nd street, where evidence of EF-2 damage was surveyed. At this point in the tornadoes’ lifespan, it was near a ¼ mile wide. This was only just the beginning.
Once it crossed 32nd street, the tornado strengthened from an EF-3 to an EF-4 from surveyed damage. At this point the storm was showing a textbook tornadic supercell signature on radar. The radar picture below depicts what a thunderstorm looks like if it is about to or has produced a tornado. If you take a closer look at the radar scan, you can see a purple circle at the end of the hook. In meteorology, this is classified as a debris ball, a sign that the tornado is strong enough to pick up debris off the surface and fling it into the air.
The tornado continued to move east toward McClelland Boulevard at 20 to 25 miles per hour where it was approximately ¾ to a mile wide. Once it passed this area, St. John’s hospital was heavily damaged, and the tornado leveled homes which were swept off their foundations.
Two schools in Joplin, East Middle School and Joplin High School both suffered major damage from the tornado. The newest part of the high school, the Franklin Technical Center, was destroyed. More EF-4 damage and even low-end EF-5 damage was surveyed along the intersection of South Rangeline Road and 20th street as the tornado continued to destroy well structured establishments.
As the tornado passed the city of Joplin, it began to weaken substantially. The tornado finally lifted roughly 5 miles northeast of Granby and east of Diamond, MO around 6:12 p.m. Along the tornado’s path, approximately 6,950 structures were destroyed, and resulting in a staggering number of injuries and lives lost. The costliest tornado in American history, the Joplin Tornado totaled up to $2.8 billion in damage. According the American Red Cross, about 25% of the city was destroyed as of a result of this tornado.
Weather Channel’s Mike Bettes appeared on the air to report live from the scene. Struggling to keep his composure, he emotionally reported the destruction that occurred in the city of Joplin. During his broadcast he becomes speechless and starts to tear up. After a moment, he regains himself, chokes back his emotions, and continues his report. The scar this tornado left on the city of Joplin may never be forgotten. Fast forward to 2018, it is amazing to see how this city has grown since this tragedy. Neighborhoods have been rebuilt, and a few memorials have been built around Joplin to remember all of the lives that were lost.
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©2018 Meteorologist Joseph Marino
A thunderstorm viewed from north Douglas Island, looking east towards Juneau on June 17, 2013.
While the Great Plain states are gearing up for prime storm chasing season, Juneau skies remain quiet. While thunderstorms aren’t completely unheard of in southeast Alaska, they aren’t a common occurrence either. A case study on thunderstorm climatology performed by the National Weather Service office in Juneau found that between 1970 and 2011, Juneau observed 16 thunderstorms (or averaging about one thunderstorm every two years).
In order to get thunderstorms, you need three key ingredients: a source of moisture, lift, and instability. Juneau is a maritime climate kept cool during the summer by the Gulf of Alaska waters and largely lacking the instability to create large updrafts that would build cumulonimbus. One important attribute of this reason is latitude. At 58 degrees north, the air is thinner than near the equator. Thunderstorms in the tropics can easily surpass 50,000 feet, but thunderstorms at 15,000-20,000 feet simply cannot be supported. In addition, the town is located next to the Juneau Icefield- the 5th largest glacier field in the world that acts as a “refrigerator” to cap thunderstorm development.
When Juneau does get thunderstorms, however, it is mainly the result of strong daytime heating during the summer months. By the summer solstice, Juneau peaks at just under 18 ½ hours of daylight. Combined with moist air from Canada, this could be enough convection to lead to the formation of thunderstorms. Otherwise, thunderstorms may develop inland over British Columbia and the Yukon with cloud bases high enough to clear the Coast Mountain range.
Though thunderstorms are rare in Juneau, they are much more common along the outer coast of Southeast Alaska and the Interior, north of the Alaska Range. Late autumn and winter is a typical time of year for thunderstorms in the Gulf, with the warm ocean as the main heat source interacting with the cooler land onshore. Regardless, thunderstorm wind gusts and lightning are still capable of causing hazards with regard to marine vessels, power outages, as well as the potential risk of forest fires.
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©2018 Meteorologist Sharon Sullivan
DISCUSSION: As the Central United States woke up to the 1st of May here in 2018, many millions of people woke up to the developing threat for widespread severe weather across portions of the Central Plains today. Based on the fact that there was an approaching low-pressure system from the west during the course of the day, this facilitated an effective surge of warm-air to the east of the cold front (i.e., within the warm sector of the strengthening low-pressure system). This surge of warm, moist air in the warm sector of this low-pressure system allowed for robust convective storms to develop during the course of the afternoon hours. In addition, there was also a substantial amount of vertical wind shear which facilitate a more conducive low/mid-level atmospheric environment for rotating updrafts within these developing convective storms.
As the deep convective storms fired up by around 2:00 to 4:00 PM CDT on 1 May 2018, there was also a fairly persistent presence of deeper vertical wind shear across a substantial portion of Nebraska. This more persistent deep vertical wind shear allowed for more persistent supercell thunderstorm activity to persist through the mid- to late-evening hours as is reflected by the tweet attached above (courtesy of WeatherNation Meteorologist Dakota Smith). It is also worth noting that such persistent late-night supercell thunderstorm activity is a MAJOR threat to both life and property since nocturnal convective storms can often bring prolific natural hazards which can "sneak up" on unsuspecting people in the path of such storms. Therefore, if you are ever in the path of nocturnal convective storms, always be sure to remain aware of the current severe weather situation in your "neck of the woods." This way, whenever you are under a severe weather threat, always stay closely tuned to the local forecast as it evolves and always keep a severe weather plan in place.
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© 2018 Meteorologist Jordan Rabinowitz