 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) To learn more about severe weather, please click here! © 2018 Forecaster Brittany Connelly
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 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. To learn more about severe storms, please click here! ©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. To learn more about severe storms, please click here! ©2018 Meteorologist Sharon Sullivan Impressive GOES-16 View of Training Supercell Thunderstorms (credit: NOAA GOES-16 Satellite)5/1/2018 
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. To learn more about other high-impact severe weather events from around the world, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz  Discussion: Thunderstorms are a powerful yet beautiful display of nature and can bring needed rainfall or devastating wind and hail. While they are most common in the afternoon during spring and summer, they can occur at any time of day, and in any season of the year. While thunderstorm formation is a complicated subject, meteorologists have become increasingly skillful in forecasting thunderstorm activity days in advance. When you think of a thunderstorm, you typically think of a warm and humid day. There is reasons behind this is chiefly due to three necessary ingredients for thunderstorm formation; instability, moisture, and a lifting mechanism.
The environment that thunderstorms thrive in consists of high moisture content especially closer to the surface of the Earth. It probably makes sense why this is the case. Without moisture, you cannot condense moisture into clouds and therefore no thunderstorms can be produced under such conditions. Typically, meteorologists use moisture variables such as the dew point temperature (the temperature at which air becomes saturated with respect to water vapor) to forecast if the atmosphere contains enough moisture. The next ingredient is instability, and to think of instability, we must imagine a parcel of air. Meteorologists use the concept of a parcel because it is easier to visualize the intricate processes of the atmosphere. Now imagine you were standing on the ground and you released this parcel into the atmosphere. What happens to that parcel at this point can tell us if we have a stable or unstable atmosphere. A stable atmosphere is one in which a parcel will want to sink back down to the surface and resists vertical accelerations. This is typically what you see underneath the influence of high pressure systems. An unstable air mass on the other hand is one in which a parcel will want to keep rising because the temperature of that parcel is warmer than the air around it. Back to our parcel visualization, if we release this parcel and it keeps rising, then we know we have an unstable air mass. Meteorologists utilize a variety of tools to diagnose the stability of the atmosphere and even have equations to help us identify instability. One such that you may have heard of is Convective Available Potential Energy or CAPE. CAPE combines the moisture content of the atmosphere along with the stability to give us a proxy for environments conducive to thunderstorm formation. These values have a wide range that is dependent on season, and synoptic (or larger-scale) environment. Now, we have a moist atmosphere, and we have a situation where air parcels will want to rise freely on their own. However, usually the atmosphere is not that simple. In fact, there can be a layer of stable air close to the surface underneath the more unstable air. We must find a way to push those air parcels above this layer into the unstable air. This is why thunderstorms usually form out ahead of a cold front. The cold front gives those air parcels the initial push they need to overcome the stable layer and rise freely on their own. There are other lifting mechanisms other than the cold front such as warm fronts, sea-breeze fronts, and even the cold-dense outflow produced from another thunderstorm. Thus the formation and sustenance of convection is simple from a standpoint of forecast operations. To learn more about other interesting and high-impact topics in severe weather from around the world, be sure to click here! ©2018 Meteorologist Allan Diegan  DISCUSSION: Although it is one day after the anniversary of the Super Outbreak of 2011, this event still has me in disbelief, and in awe, that such an event transpired. This article will feature some details and explanations on this incredibly memorable weather event focused on Mississippi and Alabama and nearby locations as shown above to have been impacted by dozens of tornadoes. This article will focus on the four main features needed for severe weather: moisture, a lifting mechanism, instability, and wind shear. Let’s first assess the wind shear present in the atmosphere on the 27th of April, 2011.  When analyzing severe weather, wind shear is a common variable assessed to determine the type of convection that may develop in the atmosphere. The 0 – 6 km bulk shear is the most typical quantity with values greater than 40 knots indicating most of the convection likely to be supercellular. Above is the analyzed 0 – 6 km wind shear during the mid-afternoon (21Z) on April 27th 2011 overlaid with the tornado tracks and intensities developing at around the same time. Values where most of the tornadic activity is developing ranges anywhere from 50 – 80 knots of 0 – 6 km wind shear, easily eclipsing the threshold leading to essentially solely supercell storms at this time.  Next, let’s assess the instability. The same time that is analyzed in the previous section shows substantial instability present across Mississippi and Alabama where most of the violent tornadoes are developing during this time. 2000 – 3500 J/kg of surface based convective available potential energy (CAPE) shows plenty of potential for strong rising air and predominantly supercell convection, as we concluded in the previous section. However, just because there is a lot of CAPE does not necessarily mean severe weather, there needs to be a lifting mechanism to get the ball rolling, to allow for this air to rise on its own.  Shown above is the surface analysis for the 27th at 21Z which shows a sub 1000 mb low pressure system along the Tennessee and Arkansas border with the surface winds out of the south in head of one of the lifting mechanisms, being the cold front. At this time the front is situated somewhere in Mississippi indicated by the shift in the surface winds. This strong cold front is providing a lifting mechanism for these storms to fire across Mississippi and soon after Alabama, throughout the overnight, and on the 28th across much of the rest of the Southeast and Mid-Atlantic. A surface trough out in head of the cold front was analyzed by the WPC at this time increasing the convergence across the area of interest providing another source of lift and initiating storms. The strong surface winds play another role is this setup, which is advecting that warm and moist Gulf of Mexico air into the Southeast enhancing the lift out in head of the cold front and destabilizing the atmosphere around the surface trough. The moisture is the last ingredient needed for severe weather and will be discussed below.  And here we have the surface dewpoint temperatures in degrees F. Dewpoints in the upper 60s to lower 70s throughout the region, especially across Mississippi and Alabama, is a strong indicator of severe convection with tornadoes possible. It should be noted that 850 mb dewpoint temperatures were also quite impressive in the upper 50s and even a few lower 60s which is indicative of an incredibly moist lower troposphere which enhanced the potential for a widespread severe weather outbreak.  Taking a quick look at a sounding from Birmingham, Alabama at 00Z on the 28th, 3 hours after the analysis from above, shows everything that has been pointed out thus far. The large amounts of instability in the form of CAPE, wind shear numbers off the charts, the moisture at the surface and at 850 mb, as well as a good indicator of the overall spin in the atmosphere. This can be assessed by looking at the hodograph which shows a nice “fish hook” meaning lots of storm relative helicity present. All of these ingredients developed in a spectacular, yet deadly fashion. Take a look below at this incredible radar loop of the storms developing. The amount of rotation in the atmosphere is quite notable just by looking at the reflectivity and noticing all the hook echo’s across the region (northern Alabama and Mississippi). An incredible meteorological event, but also incredibly deadly. Every so often mother nature reminds us that “she” can produce in a spectacular way when just the right condition are in place.
Stay tuned to GWCC, and if you want to read more severe analyses, click here! ©2018 Meteorologist Joe DeLizio 
During the month of April, the frequency of tornadoes in the United States tends to increase especially in the Midwest or the region known as “Tornado Alley”. This is all thanks to a gradual lift in the jet stream, which allows the warm moist air from the Gulf of Mexico to lift into the Midwest. This warm moist air then clashes with the cool air sinking down from Canada, creating a prime tornadic environment for thunderstorms in the Midwest. The story this year has been the complete opposite as old man winter has held a firm grasp over much of the United States. As the jet stream has stayed put in its late winter position, letting the cool air from Canada spread across most of the continental U.S well into late April. This leaves the warm moist air from the Gulf of Mexico suppressed to areas across the deep south. Hence why we have had more severe weather events occurring down in the south instead of the Midwest. In a sense, the Ohio and Mississippi Valley's have become the "new" tornado alley in 2018. As of a result of this, both Oklahoma and Kansas have yet to record a tornado in 2018. In comparison, California averages about 10 tornadoes per year, and so far, has recorded 5 tornadoes in 2018. On April 22nd, 2018, a few waterspouts came ashore near Fort Walton Beach in the Florida panhandle causing a few tornado reports to emerge. In fact, 19 other states have recorded a tornado this year as shown by the graphic above with neither being Oklahoma or Kansas. Each red dot is a tornado report confirmed by a survey team from the National Weather Service. You can see that Oklahoma and Kansas have had a few close encounters will a tornadic thunderstorm, but never has it touched down in those two states. The latest first tornado on record in the state of Oklahoma is April 26th. As for Kansas, the latest first tornado report is May 28th, 1980 per the National Weather Service office in Topeka. Although the record for Kansas will not be broken, the record for Oklahoma has already been broken as it seems to stay quiet severe weather wise during the final week of April. The next tornado that is confirmed in Oklahoma will set a new mark for the latest first tornado in Oklahoma since records began in 1950. To close, there were 651 tornado reports spanning from January to the end of April last year. This year, the Storm Prediction Center has documented only 268 tornado reports, a 41 percent drop from last year. To learn more about other interesting and high-impact topics in severe weather from around the world, be sure to click here! © 2017 Meteorologist Joey Marino  DISCUSSION: As April ends, tornado season approaches its peak. However, this year so far, there has been fewer tornadoes than in the past 3 years. This pattern is expected to continue as the Storm Prediction Center’s (SPC) latest outlook has only slight chance for severe thunderstorms for the upcoming week which includes the beginning of May. April has generally been thought as the main start of the tornado season in the United States with May being the main peak. This April has been below average as the SPC has only reported a preliminary total of 47 tornadoes for the month alone which is far from the 3-year average of 174 tornadoes. One of the biggest reasons there has been a low number of tornadoes so far in April has been a combination of upper-level and low-level winds. The southern plains have been receiving dry warm winds from the southwest which with help from multiple low pressure systems from Canada become westerly. In addition, there has been a dominant cold dry northwesterly flow across the northern plains. This lack of a moist southerly flow especially in the upper levels of the atmosphere removes one of the crucial ingredients of a tornado since tornadoes are typically formed because of a collision of the dry cold northerly winds and a warm moist southerly from the Gulf of Mexico. The combination of these two dry winds especially at the surface makes the surface a bit drier which increases the dewpoint depression. The dewpoint depression is important in severe weather as it is used to determine the level of condensation (LCL). The LCL is the level of the atmosphere where if you take a parcel of air from the surface that has the moisture condensing until the moisture in the parcel is fully condensed. After you take a parcel of air from the surface to the LCL, the parcel follows the moist adiabat, which is the temperature change of a parcel full of condensation, all the way up the atmosphere to about 53,000 feet (100 mb). If the parcel crosses the temperature of the surrounding environment, there is Convective Available Potential Energy (CAPE). CAPE is the measure of buoyancy in the upper atmosphere and is related to the vertical velocity. However, an increase in dewpoint depression leads to a higher LCL and a lower moist adiabat which decreases CAPE. Also, a temperature inversion creates difficulties for CAPE due to the increase in temperature. The combination of the temperature inversion and the higher dewpoint depression is one of the reasons that there is not such a large number of tornadoes. Another major reason there has been few tornadoes is a result of little directional shear in the winds as they reach higher in the atmosphere across much of the Central U.S. Directional shear is necessary to jumpstart rotation in order to form a tornado. To sum it up, the lack of tornadoes this year so far is due to the directional multi-level winds. To learn more about other interesting and high-impact topics in severe weather from around the world, be sure to click here! © 2017 Meteorologist JP Kalb  A tornado northeast of Cheyenne, Wyoming on June 12, 2017. As spring is spinning up, tornado season is already at an active start. Despite deadly winter outbreaks earlier this year, the U.S. is running behind on the number of tornadoes this year- 58 through February 28th (compared to the average of 107). A strong blocking pattern over the western Atlantic (North Atlantic Oscillation) has allowed cold fronts to drop into the South, limiting the flow of warm, moist air from the Gulf and keeping instability low.
PDO (Pacific Decadal Oscillation) remained somewhat positive throughout the winter, helping California, the Southwest, and even the Great Plains to be drier than normal (negative PDO regimes allow storms to dig southward to bring moisture across the central and eastern U.S.). Drought conditions can lead to greater dew point depressions at the surface (having been warmer and drier than normal) and higher cloud bases. The higher the cloud base, the harder it is for a circulation to reach the ground to become a tornado. In addition, a moderate La Niña can favor increased tornadic activity, as the jet stream shifts farther north and drags up moist air from the Gulf. This pattern of a positive PDO, borderline moderate La Niña, and positive NAO leans towards a below to near normal tornado season and favoring an active start of tornado season across the Southeast and Mississippi Valley. A quieter than normal May is not out of the question for prime chasing territory across the Great Plains due to the weighting of a below normal season so far. But, what would tornadogenesis look like in the future? Climate change may affect the frequency and intensity of tornadic events, as a warmer atmosphere can hold more water vapor and changing the amount of energy available in these storms. Above normal winter temperatures can also be an indication of events to come. Since climate change influences the onset of seasons, tornado season may shift earlier in the year and continue longer than normal. A strong tornado outbreak in late January of this year producing 81 tornadoes across the southeastern U.S. was the second largest January tornado outbreak and the third largest winter tornado outbreak since 1950. Climate change could be the only plausible explanation as to why extreme events, such as widespread tornado outbreaks, are happening with increasing frequency, but a single event cannot necessarily be attributed as a direct result of these changes. This discussion is only meant to be a best-guess outlook and should not be used as a basis for interpretation without checking your local short-term forecast first. To learn more about severe storms (and their climatology), please click here! ©2018 Meteorologist Sharon Sullivan The Difference between Mesocyclone and Mesovorticie Tornadoes (Credit: Meteorologist Joey Marino)3/31/2018   Photo Credit: Severe Warning Systems, Joey Marino, Radarscope According to the National Weather Service, supercells are the least common type of thunderstorm. However, they are the most dangerous type of thunderstorm because they tend to produce all types of severe weather such as damaging winds, very large hail, and of course, tornadoes. A thunderstorm needs to have an organized and strong updraft to produce damaging winds and large hail, but a mesocyclone must be present for tornadogenesis to occur. A mesocyclone is a cyclonically rotating vortex of air in a thunderstorm. The mesocyclone is often found near the updraft on the backside of a storm. For a mesocyclone to form, there needs to be a few things happening in the atmosphere. There needs to be both a change in wind direction and an increase in wind speed as you increase with height. This will create a horizontal spin in the lower atmosphere (stage 1). Even in an environment where there is no thunderstorm activity, a mesocyclone has now formed. Now that the mesocyclone has formed, the air within the updraft tilts the rotating column of air from horizontal to vertical (Stage 2). Once the rotation is tilted vertically, a locally lowered cloud base known as the wall cloud, typically forms at the base of the updraft (Stage 3). It is in this region of the supercell where a tornado will form. The first graphic sbove provides a great representation of the formation and maturing stages of a mesocyclone. Tornadoes associated with supercells can range from weak EF-0’s to violent EF-5 tornadoes. A great example of a supercellular tornado is the EF-4 Solomon-Chapman, Kansas tornado that occurred on May 25th, 2016. An isolated supercell thunderstorm had formed over Ottawa county in north central Kansas. This supercell had produced 4 tornadoes during its lifespan. One of the tornadoes was a long-lived wedge tornado that was on the ground for 90 minutes and had a path length of 26 miles. That is astonishing since the average tornado is only on the ground for approximately 10 minutes. In the picture above, you can see the stunning structure of the massive rotating wall cloud as well as the wedge tornado as it heads in the east direction. However, supercells are not the only type of thunderstorm that can form a tornado. Quasi-linear convective systems (QLCS), squall lines and bow echos are known to have the capability of producing tornadoes as well as other types of severe weather. These types of thunderstorms generally are a line of thunderstorms that can travel for hundreds of miles and can sustain themselves for hours. Unlike supercells, tornadoes with these types of storms are produced by the formation of mesovorticies. Mesovorticies are compact couplets of spinning air with very high vertical spin that form on the leading edge of a line of thunderstorms. These do tend to produce strong damaging winds but can also produce weak and brief tornadoes. They also are low level storm features and typically happen at least 1 km above the surface. Meanwhile, the mesocyclone of a supercell is more common in the mid-levels. In order for a tornado to have a chance at forming, the mesocyclone has to work its way down into the low-levels and form low-level rotation. A prime example of this occurred just recently on March 29th, 2018. A line of severe storms was moving through parts of southern Texas late Tuesday night into Wednesday morning. As these storms were moving through Corpus Christi and Woodsboro, TX, a few mesovorticies had formed along the leading edge of the line of storms. Multiple tornado warnings were issued as radar had detected the rotation associated with this mesovorticies. Below is a screenshot of the velocity scan from the NWS office in Corpus Christi as the line of storms was moving through. A velocity scan is a type of radar image used by meteorologists to observe the strength of winds and rotation associated with a thunderstorm. You can see that the mesovorticies are circled in blue and the rotation is shown by using light red and green colors. During that morning, many damage reports were being sent to the NWS office in Corpus Christi. And so, a survey team was sent out to survey the damage. Windows were blown out and roofs were damaged in Woodsboro, TX and several mobile homes were flipped over in Seadrift, TX. The survey had presented enough evidence to conclude that a few weak EF-0 tornadoes and EF-1 tornadoes had formed briefly as the line of storms was moving through the area. To learn more about other interesting and high-impact topics in severe weather from around the world, be sure to click here!  |
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