Earlier this week, South-Central Montana – and Yellowstone National Park in particular – experienced extreme flooding as an atmospheric river dumped several inches of rain onto a rapidly-melting, well-above-average snowpack, pushing the Yellowstone, Stillwater, and Clarks Fork rivers to record levels.
The flooding forced the evacuation of 10,000 citizens and the National Guard rescued 87 citizens who were stranded by floodwaters, and it has washed out numerous roads, bridges, and structures across the park. The Yellowstone National Park Service has an excellent Flickr page with photos and videos that show the extent of the damage here; I’ve embedded just a few of them below.
The entire park is closed now, and the northern portion of the park, which experienced the heaviest damage, will almost certainly be closed for the remainder of the season. The southern portion of the park experienced less damage to roads and other infrastructure and, according to Park Superintendent Cam Sholly, may be able to open as early as this upcoming Monday, but an official opening date has not been set.
The Cause of the Flooding
The extreme flooding was caused by heavy rain falling over a rapidly-melting yet very robust late-season snowpack from Saturday 6/10 to Monday 6/13. This rain was due to the same “atmospheric river” that gave us the very wet weather between last Thursday 6/8 and Sunday 6/11. Take a look at the snowpack chart as of June 16… snowpack is still over 200% of normal for most of the Pacific NW, and is closer to 250-500% of normal for the Northern Rockies due to the abnormally cool and wet spring that has plagued the Pacific Northwest.
Per the National Weather Service, Yellowstone saw around 2.5 inches of rain from Sat-Mon (6/11-13), with up to 4 inches falling in the Beartooth Mountains to the northeast of the park. This is a lot of rain for Yellowstone but by no means historic – the flooding was due to this rain and the combination of a well-above-average but rapidly-melting snowpack.
Retrieved from slideplayer.com, uploaded by Shana Griffith
It’s also worth noting that the type of snowpack you see later in the season, with thicker “corn snow” granules instead of finer crystals, is much easier to melt than a colder, early-season snowpack with fresh accumulation. Late-season snowpacks are generally near or above-freezing, already have stored meltwater in them, and are gradually releasing this water, while early season snowpacks are below-freezing and, if thick and fresh enough, can actually reduce flooding risk by absorbing excess water before it can drain into rivers.
Pacific Northwest Impacts
Although the atmospheric river that brought record flooding to Yellowstone National Park didn’t cause any flooding over Western Washington/Oregon rivers, it shattered numerous daily precipitation records and caused very sharp rises on most area rivers and streams. The western slopes of the Oregon Cascades saw the heaviest rain from this series of systems with up to 4-5 inches falling in spots between 12am Thursday and noon Monday.
Credit: NWS
It was also quite a treat to look at on satellite. This is not the type of imagery you’d expect to see two weeks from the summer solstice!
Credit: University of Washington
Forecast
Wednesday and today have been some of the nicest days in a while. I’ve spent the past two days in Portland and both days have been in the low 70s – a heat wave by June 2022 standards! During the Heat Dome of June 2021, Portland hit 108, 112, and 116 degrees on June 26, 27, and 28, respectively.
Credit: WeatherTogether
Cooler and cloudier weather will return tomorrow and persist through Father’s Day with showers at times, and we should warm up/dry out slightly early next week. However, the long range forecast shows no signs of true “summertime” weather on the horizon – models instead show us staying slightly cooler and wetter-than-average.
The map below is a familiar refrain for the Pacific Northwest. Additionally, note the extreme heat by the Gulf Coast… from Father’s Day through much of next week, Houston should experience highs near or exceeding 100 degrees with dewpoints in the low/mid 70s. Oppressive heat, but they are a tough breed down there.
Going back to the Pacific NW, the good news is that this type of cool/cloudy pattern with occasional rain becomes much rarer during July and August as the jet stream weakens and shifts to the north, so I’m not yet ready to call summer a complete dud. It’s just a little late to the party.
Charlie
2 Comments
It’s hard to imagine that happening in Yellowstone. It’s a shame that it couldn’t have moved south to New Mexico and S. California where they really need it.
Agreed Cathie! The rest of the West really needs the rain – at this point, we can just hope for a good monsoon season over the Desert SW.