Record glacial outburst flood near Juneau for 3rd year in a row
Federal science key to helping understand, forecast and mitigate the impacts
Starting off this morning with some breaking news on the glacial outburst flood event in Juneau that I posted about yesterday afternoon. Earlier this morning as forecast by the National Weather Service (NWS), the US Geological Survey (USGS) streamflow gage on the Mendenhall River near Juneau passed its record level of 16’, and just crested at 16.65’ and per NWS Juneau has started to fall.
Glacial outburst floods have become an annual occurrence in the Juneau area since the first Suicide Basin outburst flood in 2011. These types of floods — known as a jokulhlaup in Iceland where these events are more common — occurs by a process where a glacier — in this case Mendenhall Glacier — form a natural dam for glacial meltwater. That meltwater continues to build up and then due to melting and other processes the dam naturally erodes and releases the built up water downstream.
This is now the third consecutive year that a record stage has been recorded at the Mendenhall River gauge near Juneau due to the glacial outburst flood. Last year’s flood damaged hundreds of homes, and since then officials have built temporary levees to try to reduce the damage should this year’s flood reach record levels again, which of course it . State and local officials have urged all people living in areas subject to flooding at up to a 17’ stream gauge level to evacuate, although initial reports indicate that the barriers are mostly holding.
Given the current threats to federal science agencies, I think it is really important to highlight how this situation shows the tremendous scientific services that these agencies provide to our country. I had someone who was a park ranger at the Mendenhall Glacier Visitor Center during the first 2011 Suicide Basin flood comment about how they did not have any real understanding then of what was happening and when the waters would stop rising on the river. The federal science agencies — including the USGS, NWS, and US Army Corps of Engineers (USACE) — clearly recognized this data gap and worked together with state and local partners to fill it.
After the 2011 flood, the US Geological Survey (USGS) in collaboration with the USACE began installing monitoring equipment including cameras and equipment to monitor water levels and temperatures in Suicide Basin, as well as additional streamflow gauges along the Mendenhall River downstream of the basin.
This graph shows the plot from the USGS water level gauge in the Suicide Basin, dramatically showing how the water level is plunging as the water drains out of the glacial lake into the Mendenhall River. This data was absolutely crucial for the NWS —the agency responsible for river flood warnings and forecasts — to know when the glacial outburst started yesterday and have an estimate of how much water could potentially flow into the river, necessary data if one has any hope of making a reasonably accurate river forecast.
It is obvious that strong partnerships have been built between the federal science agencies and state and local entities to ensure that the public has the best information possible about these flood events and can develop effective mitigation strategies like the levees. The entities shown above have worked together to build an excellent webpage that provides a comprehensive one-stop shop for people to understand the threat and have real-time data and forecasts. The local National Public Radio (NPR) station KTOO is providing excellent YouTube live camera feeds and coverage of the event. USACE played a key role in the construction of the temporary levees helping to protect residences.
Obviously as I have documented in many earlier posts, both the NWS and USGS are dealing with both real and threatened staffing and budget cuts, and Alaskan public radio stations are at particular risk from recent Congressional cuts to public broadcasting. Real world public safety partnerships like the ones helping to keep people safe during this Suicide Basin glacial flood are what are at risk from federal cuts to science and other programs, and why I will continue to try to bring attention to their work and importance.
Speaking of flooding, another metro area had to deal with impactful flash flooding yesterday. Chattanooga, TN officially reported 6.42” at the airport on Tuesday, a daily record and the second highest daily rainfall total on record. Much of this rain fell in just a few hours as can be seen on the 3-hourly rainfall map from 8 pm ET last night and resulted in major flash flooding.
Interstates in the region were flooded as shown above (picture from NBC News) and people were trapped in homes, resulting in emergency officials having to make numerous water rescues. Unfortunately, one person was swept away by floodwaters and is missing, and 3 others were killed in the area when a tree fell on their car.
Additional thunderstorms with heavy rainfall are expected in the Tennessee Valley region again today, and flood watches are in place. More heat is expected in the West today, and fire danger will become a serious concern again as winds increase and high based thunderstorms with lightning and gusty winds are anticipated. Red flag warnings are in effect for much of the interior Northwest and Intermountain West.
Turning now to Tropical Storm Erin, while morning satellite imagery shows a slightly healthier looking system than yesterday, Erin is still clearly struggling with dry air and likely some easterly wind shear as most of the thunderstorm activity is west of the center of circulation. NHC continues to analyze it as a low end tropical storm with maximum sustained winds of 45 mph. Erin is starting to move into the area more favorable for development with increasing moisture and sea surface temperatures, and by Thursday should be in a position to start intensifying more steadily.
As of now the models (Google AI ensemble shown above) continue to show Erin passing just northeast of the Puerto Rico and the Leeward Islands and then between the east coast of the United States and Bermuda. At a minimum, the track of Erin could certainly be close enough to cause some rain and wind impacts to the northeast Caribbean islands, and people with interests there should be monitoring forecasts closely. Farther downstream, while the models show any direct impacts to the US beyond rip currents are unlikely at this point, we are still several days away from the anticipated turn to the north so forecast changes are still possible. Bermuda of course should be monitoring Erin closely.
Elsewhere in the tropics, the system I mentioned in the northwest Caribbean yesterday is now being tagged by NHC with a low probability of development once it reaches the western Gulf. As of now the models show nothing more than a weak system, but we will continue to monitor it.