Identifying Warm, Moist Flow for the Ongoing Severe Weather Threat. (credit: UW-Madison CIMSS MIMIC)
DISCUSSION: As the Central United States continues to be under a larger-scale severe weather threat overnight tonight and into the day on Wednesday and Thursday, there is also a substantial threat for flooding and even potential flash flooding. The reason for this is due to the fact that the moisture track which is ending up northward into the southern and central Mississippi River Valley is tracking out of the Gulf of Mexico. This can be seen in the CIMSS-MIMIC Total Precipitable Water imagery courtesy of the University of Wisconsin animated imagery attached above. Whenever there are situations characterized by warm, moist flow emerging out of the Gulf of Mexico, this greatly favors heavier rainfall events due to the fact there is also substantial persistence to these moisture plumes.
The core of this particular moisture plume can be identified via the yellow to orange shaded colors emerging from the Gulf of Mexico. This yellow to orange coloring represents the core of the deepest moisture within this particular Gulf of Mexico moisture plume which was coming ashore during the overnight hours from Monday night (04/30/2018) to Tuesday morning (05/01/2018). Thus, per the track of this moisture plume via the animated CIMSS-MIMIC imagery attached above, the core of this moisture plume was ideally oriented for heavy rainfall across the southern to central Mississippi River valley. Hence, it is always critical to respect the potential for heavy rainfall events coincident with severe weather events during the Spring to Summer time-frame across the Central United States.
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DISCUSSION: Portions of the mid-west and mid-Atlantic experienced massive flooding during the latter part of this past February. Residents in the Mid-Ohio Valley were urged to evacuate as well as prep their homes and businesses for the Ohio River’s impending invasion. Residents along the Monongahela River in West Virginia were also urged to prepare for flash flooding and possible property damage.
Flooding is among our planet’s most common – and most destructive – natural disaster. While certain areas are more prone to flooding, wherever rain falls is vulnerable. The most common flooding occurs when water inundates land that’s normally dry, usually due to river or stream beds overflowing their banks. Ice jams, excessive rain, or failed levees/dams can also irritate a river, causing it to spill out over the adjacent land (floodplain). Coastal flooding can occur due to a large storm system off the coast or even a tsunami, both of which causes sea water to rush inland.
Most floods typically take hours, sometimes days, to develop which gives residents and city management teams plenty of time to prep or evacuate. Others occur rapidly, with little to no warning. These are called “flash floods” and can be exceptionally dangerous, instantly transforming a calm creek into a massive wall of water, taking everything it its path downstream.
Experts classify floods according to their likelihood of occurring in a certain time frame. For example, “a hundred-year flood” is a large, destructive flood that in theory should be expected once every century. In all reality, this classification simply means there is a 1% chance that a flood to that magnitude could occur in any given year. Throughout the recent decades, these massive “hundred-year floods” have been occurring worldwide with unprecedented regularity.
Water, especially when moving, has awesomely destructive power. When a river spills water over its banks or the sea moves inland, poorly equipped structures cannot withstand the strength of the rushing water. Homes, bridges, cars, and other debris can be picked up and carried off. Moving water also has an erosive force, able to drag dirt from under a building’s foundation, ultimately causing it collapse.
In the United States, where severe weather prediction is advanced, floods cause upwards of $6 billion in damage and kill 140 a year. A 2007 report filed by the Organization for Economic Cooperation and Development discovered that coastal flooding alone causes nearly $3 trillion in damage worldwide.
When the floodwaters recede, it’s often that affected areas are covered in silt and mud. Occasionally the water and newly transformed landscape can be contaminated with hazardous materials such as pesticides, fuel, raw sewage, and other debris. Another potential danger is mold blooms quickly overtaking water-soaked structures. Residents of flooded areas can be left without basic necessities such as power and clean drinking water, possibly leading to outbreaks of waterborne diseases.
Flooding, especially in river floodplains, is natural and has been occurring for millions of years. Fertile floodplains like the Mississippi Valley in the Midwest, the Nile in Egypt, and the Tigris in the Middle East have been a life source for millions of years thanks to annual flooding leaving behind a plethora of nutrient-rich silt deposits behind.
Most of the destruction that comes from flooding can be attributed to society’s desire to live near coastlines and river valleys. It’s a common practice for city governments to mandate residents in flood-prone areas to purchase flood insurance and build flood-resistant structures. Massive efforts to manipulate and redirect inevitable floods have resulted in brilliant engineering efforts, including the extensive levee system in New Orleans as well as effective dikes and dams in Holland.
Scientists, meteorologists, and engineering are constantly working towards bettering our forecasting and infrastructure. Highly advanced computer modeling now allows disaster authorities and forecasters to predict with high accuracy as to where floods will occur and just how severe they could be.
To learn more about other interesting global flooding stories and/or topics, be sure to click on the following link: www.globalweatherclimatecenter.com/flooding.
© 2018 Meteorologist Ash Bray
DISCUSSION: There is little to no argument across the global scientific community that the Earth has for quite some time been and still is continuing to experience net planetary warming. One of the premiere concerns in the presence of an increasingly warmer planet are the prospects of heavier rainfall events occurring with a greater frequency and intensity both across the contiguous United States and all over the world for that matter. This a direct result of the fact that as the Earth continues to experience a net global heating trend, this consequentially increases the average global concentration of atmospheric water vapor. As this gradual average increase in atmospheric water vapor content occurs, this increases the propensity of heavy rainfall event potential by way of there being more atmospheric water vapor available in the lower to middle parts of the atmosphere for developing storm systems (i.e., whether they be in the form of thunderstorms or much larger-scale extra-tropical cyclones).
Hence, in the presence of a warming planet, the threat for a greater frequency of heavy rainfall events has many regional, national, and international scientists (and specifically hydrologists) rather concerned. This is because an occurrence of heavy rainfall events with a greater average frequency also adds the possibility of their being a greater propensity for river and stream flooding events which consistently have the potential to inundate towns and cities both near and far from the given waterway. To better understand the reason for the major concerns tied to the percentage increase in heavier precipitation events over the 55 + years, there are direct excerpts from the actual article written by the Climate Central team.
"A warmer world supercharges the water cycle, leading to heavier precipitation. To start, a warmer atmosphere creates more evaporation — for every 1°F of warming, the saturation level is increased by about four percent. With more water evaporating into the atmosphere, there is more available to condense into precipitation, and it’s coming down in bigger downpours...............Even in the absence of urban development where there is more rain runoff, heavy rain will lead to more flooding. This means extreme flooding will become more common, resulting in more property damage. Over time, flood maps may have to be redrawn, which will have an impact on property values and insurance rates. Damage from the 2016 Louisiana floods was $10.4 billion and totaled $125 billion from Harvey."
To read more about this particular story, click on the following link.
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© 2018 Meteorologist Jordan Rabinowitz
Atmospheric river event brings flooding, landslides to Southern California (Photo Credit: Matt Roberts)
DISCUSSION: On January 8-9, California received a massive amount of rain across much of the state. However, the rain did not bring all good news as the National Weather Service had issued flood warnings as well as flash flood warnings across much of the Los Angeles and Santa Barbara areas. In addition, the National Weather Service had advised that there would be a slight chance of weak waterspouts in the Pacific Ocean near Los Angeles. Northern California was not hit as bad as the storm brought weaker than expected winds to the San Francisco Bay Area. Flooding was minimal in the San Francisco Bay Area as it was mainly minor road flooding with a small closure on California Highway 121 due to a risk of landslides.
It was a different story in Southern California on the morning of January 9th, as a flash flood was observed on the Ventura River near where the Thomas fire was occurring. In addition, mudslides have been reported across Southern California resulting in multiple deaths as well as having portions of U.S. Highway 101 closed. Much of the mudslides have been reported in the Santa Barbara area especially in the higher elevations due to a large amount of rain.
The heavy rain across the state especially in Santa Barbara was due to an atmospheric river event. An atmospheric river event is when moisture was drawn from the warmer portions of the Pacific Ocean near Hawaii and is transported to the coast of California. This atmospheric river event had very high moisture content in the atmosphere up to about 13,000 feet. In addition, the heavy rain in the mountains are also due to the rain shadow effect as moisture condenses as it climbs over mountains and precipitates as the atmosphere cannot hold as much water as the temperature decreases. Forecast models had indicated a very strong upward velocity at both 700 and 850 millibar pressure levels (9500 ft and 5000 ft respectively) in the Santa Barbara mountains during the time of the heaviest rain.
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©2018 Meteorologist JP Kalb
DISCUSSION: A major storm is expected to hit overnight tonight through Thursday night across the San Francisco Bay Area. The storm is expected to bring heavy rains in mountainous regions especially across the North Bay as well as the Santa Cruz Mountains. Flood concerns are very high in the North Bay due to the amount of precipitation being forecasted. In addition, the South Bay’s Coyote Creek will also be monitored due to the creek flooding in February which caused heavy damage in parts of San Jose.
The North Bay is expected to receive between 2 and 3 inches of rain overnight from the storm. The event is bringing flood concerns along the Napa and Russian Rivers especially in cities such as Napa, Santa Rosa, Petaluma, and Rohnert Park. These floods along the rivers are a common occurrence during heavy rain events in the Bay Area. In addition to concern of river flooding, flooding is also a concern especially in the areas that were devastated by the multiple wildfires that were burning almost a month ago. These areas are suspect to flooding due to soil conditions as well as a lack of plant life to take some of the water. The National Weather Service office in Monterey has issued a Flash Flood watch for much of the North Bay due to the concerns especially in the burnt areas.
In addition, the South Bay’s Coyote Creek will be monitored during the situation especially in San Jose. However, the South Bay is not expected to receive as much rain in the flooding area where forecast rainfall is expected to between 1 and 2 inches in the Hamilton Range mountains and an inch or less forecasted in the valleys. However, those living along Coyote Creek are bracing for a possible flood such as placing sandbags just in case more rain occurs than expected.
The storm is expected to bring heavy rain due to an Atmospheric River. An Atmospheric River is an event where moisture is drawn in from the warmer parts of the Pacific especially near Hawaii and makes its way to California when there is a deep trough in the Pacific Northwest. In addition, vertical velocity with respect to pressure are forecasted to be at about 0.1 Pa/s (pascals per second) or higher in an upward motion. This upward motion makes the atmosphere more saturated at a higher level to the point of complete saturation. At which point, the atmosphere is unable to hold any more water which is then released as rain.
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©2017 Meteorologist JP Kalb
Atmospheric River brings Historic Flooding to Juneau, AK (Photo Credit: Aaron Jacobs/National Weather Service)
A man stands outside his property near Jordan Creek on October 27, 2017
During the week of October 23rd, hints of a strong atmospheric river (a narrow band of concentrated moisture in the atmosphere) were present in the extended forecast for southeast Alaska, as moisture from super typhoon Lan was expected to push through. Typhoon Lan formed in the northwest Pacific on October 14th, affecting the Philippines, Japan, and South Korea and causing several deaths along its track. By October 23rd, Lan was showing signs of dissipation. The remnant moisture fueled the atmospheric river, bringing heavy flooding to Alaska.
On Wednesday, October 25th, an areal flood watch had been issued for the northern half of southeast Alaska due to projected small stream rises. As rain began on Thursday, a flood advisory was in effect, where rivers reached bankfull and high freezing levels (>6000 ft) increased the threat for runoff and higher elevation snowmelt. Early Friday morning, heavy rains and strong winds near 40 mph continued to impact the Skagway and downtown Juneau areas. The 48-hour rainfall totals for Thursday and Friday ranged from 3.78” at Yakutat Airport, 4” at the Glacier Bay Fuel Dock in Gustavus and at the National Weather Service office in Juneau, 4.5” for downtown Juneau, 6” at Sawmill Creek in Sitka, and 8” in Pelican.
By 10 a.m. on Friday, October 27th, a flood warning was issued for Juneau Creek near Juneau. Jordan Creek usually reaches action stage at 9.2 ft, flood stage at 9.7 ft, and moderate flood stage at 10.5 ft. It reached a record crest of 11.0 ft by 2:30 p.m. local time on Friday. The last historic crest of Jordan Creek occurred on September 9, 2016 at 10.18 ft. As a result, several residential homes, office buildings, and roads near Jordan Creek (and also Salmon Creek in Gustavus) were inundated by a foot of water. A mudslide occurred near the Mt. Roberts Tramway system in Juneau, closing roads and delaying traffic.
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© 2017 Meteorologist Sharon Sullivan
DISCUSSION: In light of the 2017 Atlantic hurricane season being a very high-impact year with respect to widespread flooding occurring from a combination of both storm surge and heavy rainfall, there are messages to be learned from such events. First off, in light of major flooding events which occurred in association with tropical cyclones such as Hurricane Harvey and Hurricane Irma, many people are always wondering whether they would ever find themselves within a major flood evacuation zone for a future winter and/or tropical storm. Having said that, it is useful and important to know that there are in fact ways to find out such information. By going to websites such as the following link, you can take a virtual tour of places around the world to see the relative sensitivity of the location to annual flooding potential. Moreover, being cognizant of potential flooding threats (regardless of the given season) is particularly important since this allows someone to be able to better prepare and protect themselves from future flooding events. Whether it is through taking precautionary measures to protect life and property while holding one's ground or taking as much as possible and getting out of town, there are always way to both prepare for and/or respond to flooding event situations.
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©2017 Meteorologist Jordan Rabinowitz
DISCUSSION: Over the past 24 to 36 hours, a small (but potent) piece of mid-level energy propagated across portions of west-central Europe and moved across areas which included (but were certainly not limited to) far western Austria, eastern Switzerland, and far southern sections of Germany. Across many cities/towns located in these parts of those respective countries there was a clear focal point for strong convection which fired up during the day on Saturday. Having said that, there was also a consistent explanation for the particularly focused nature of this regional European flooding (and in some cases the flash flooding) event which unfolded during the day on Saturday. This explanation can be best characterized by the areas of elevated terrain helping to facilitate the greater likelihood of heavier rainfall on a more localized scale. This is due to the fact that the more elevated terrain across these parts of those respective countries forces air parcels to more abruptly move up and over such topographic barriers (e.g., hills, plateaus, mountain ridges, etc.).
During such orographic-enhancement of precipitating-clouds, there is even more liquid water "squeezed" out of developing convection via increased instability due to the air parcels rising and being forced to expand more and more with increasing height. Thus, this favorable convective combination allowed for notably heavier rainfall to unfold in cities such as Tux, Austria as captured in the raw footage above. Events such as the major flash flooding event captured above just yesterday afternoon (local time in western Austria), reinforce the importance of always remaining weather-ready at all times regardless of your location, plans, or individual circumstances prior to or during the occurrence of the flooding.
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©2017 Meteorologist Jordan Rabinowitz
On Saturday, July 31, 1976, several hundred tourists and locals were enjoying a beautiful summer afternoon in the resort town of Estes Park in northern Colorado. A stationary front (when warm and cold air masses meet and neither is strong enough to move the other) had settled in an east-west fashion across Colorado, Kansas, and Missouri. Warm, moist air was forced up the Front Range and the unstable air continued rising as the water vapor condensed, becoming conditionally unstable (where the air is unstable if saturated but stable if saturated).
Light rain began falling over the Colorado Rockies during the late afternoon. By 7:35 p.m., the National Weather Service had issued a severe thunderstorm warning. Around 9:00 p.m., the National Weather Service issued an urgent warning to expect flooding in the Big Thompson Canyon, but the warning came too late for most. At this point, 12 inches of rain had fallen within the last four hours and sent a 20-foot wall of water down the narrow canyon, causing flood waters to speed up as they squeezed through. (According to the Bernoulli principle fluids speed up as they are forced through a tight space due to an increase in pressure). Weaker winds aloft made the thunderstorm nearly stationary near the upper section of the canyon.
Rex Sheets of Loveland, Colorado was driving with his friend up towards Lake Estes to go fishing on July 31st. A state patrolman began driving up the canyon during the early evening hours to warn others of the storm. The frame of his car was later found with the steering wheel attached and his keys still in the ignition. The patrolman’s body was never recovered.
The amount of rain that fell in that short amount of time made it so that the rain wasn’t able to soak into the canyon sidewalls. Boulders the size of cars were carried down the river by the floodwaters and houses were transported on top of bridges. The flood caused $35 million in damage, destroyed 418 homes, and claimed the lives of 143 people.
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© 2017 Meteorologist Sharon Sullivan
DISCUSSION: Over the past 24 hours, a storm similar to a Nor’easter dropped an immense amount of rain in the Mid-Atlantic region. Highly unusual for this time of year, this coastal storm (with a track that is typical of a winter Nor’easter) carried lots of tropical moisture which allowed it to drop nearly 6-7 inches of rain near Washington, DC. Rain gauges in parts of southwestern Delaware measured more than 10 inches of precipitation! While the rain is still continuing, a map detailing 24-hour precipitation totals for the region showcases the effects of this coastal storm (see above, courtesy of NWS WPC).
Early this morning the NWS Weather Prediction Center released a Mesoscale Precipitation Discussion (MPD #:0592) warning the Delmarva area of the threat of flash flooding from this coastal storm. The graphic they released for the MPD (below, courtesy of NWS WPC) shows the conditions that were set up for the storm. A low pressure center with counterclockwise winds around it was riding along the coast. This allowed for warm, moist air from the south to mix into the stationary front, providing it a source to draw more energy from, and cooler air from the northeast to drive strong winds into the area. The storm had a history of heavy rains, and with convection that continued to pop up along and in front of the stationary front, the storm had another source to draw energy and moisture from that permitted it to slow down and downpour.
In addition, the coastal storm had the help of the unusually sharp contrast of sea surface temperatures in the Atlantic for this time of year, (see below, courtesy of NWS Eastern Region HQ) which is typically a driving force for Nor’easters. This contrast also shows the Gulf Stream pushing further north than we usually see it. With the combination of all of these conditions, rain poured at large rates over a long duration, allowing for incredible amounts of precipitation for the area.
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©2017 Meteorologist Katie McCracken