‘Most extreme rain’ in 100-plus years: ‘Office Hours’ with Daniel Swain

From Southeastern flooding to Southwestern fire weather, there's lots to discuss on the climate change front. Join UCLA climate scientist Daniel Swain Tuesday, Oct. 1, at 3 p.m. PT for more climate context about the widespread catastrophic flooding from Hurricane Helene, and anticipated record highs from another major heat wave this week in the broader Southwest.

YouTube 'Office Hours' with Daniel Swain

Tuesday, Oct. 1
3 p.m. PT / 6 p.m. ET

Join live to submit questions in the chat or watch the recording anytime. Get an advance look at Swain's thoughts on Southern Appalachian flooding from his recent thread on social media (BlueSky/Twitter), calling it the "most extreme rain" in more than 100 years of record-keeping, and comparing the risks to a severe flood scenario projected in California. You can also read his Monday blog post about both the flooding and fire weather. Excerpts:

On the Southwest:

• "I would expect fire activity to continue to increase through this week as temperatures stay sustainedly high, even closer to the coast, and then also begin to pick up across the interior West again by this weekend as persistently very hot temperatures continue. As earlier noted: I suspect that places in the West that don't usually see major wildfire activity in October or even November may do so this year (i.e., not just coastal CA, where such activity is not that unusual even later into fall given the typical seasonal lag in temperature there)."
• "Another major heat wave has already arrived, but won't peak until Tue/Wed (along the NorCal coast) and then later this week (further inland across CA and the interior West). There are some indications that weak offshore flow could push temperatures around 100 degrees Fahrenheit all the way to the coast even in places like SF, which could make Oct. 1 or 2 the hottest day of the year in these places (always a bit of uncertainty with these patterns)."
• "The Line Fire, which had been pretty inactive in recent days since it started during the record heat wave in SoCal during early September, roared back to life yesterday from within containment lines and various evacuation orders and warnings have been reissued. As of this writing, additional new fires are popping up in NorCal amid hot, dry and breezy conditions. I would expect fire activity to continue to increase through this week."
• "Phoenix will continue to experience an extraordinary and record-shattering string of midsummer-like temperatures that continues right on into October."

On the Appalachians:

• "Helene's remnant circulation made a beeline for the Southern Appalachian Mountains, bringing a round of record-breaking torrential tropical rainfall. This rain event came immediately on the heels of another record-breaking rain event just one day prior, though this one too was indirectly associated with Helene (in the form of a "predecessor rain event," or PRE). The next result is the worst regional flood catastrophe the United States has seen in some years (and likely the worst this region has experienced in recorded history). 20-35 inches of rain fell in less than three days in steep and mountainous terrain, causing rivers, creeks, and streams to not only spill their banks but literally carve new paths through mountain valleys - regardless of what was in the path."
• "California faces a real risk of similarly catastrophic flooding."

Via BlueSky and Twitter: "This was, by far, the most extreme rain event in observed record across much/most of the region, where reliable records date back over 100 years. For my West Coast audience, I wanted to reflect on this event in the context of ARkStorm 2.0 - a hypothetical but plausible catastrophic flood scenario we've developed for California, with the intent of improving preparedness and planning for such an event. The Sept. 2024 event in Southern Appalachians has had "ARkStorm-level" impacts in eastern Tennessee and western North Carolina. Widespread, catastrophic flooding has resulted; many lives have been lost; transport, electric, telecomm infrastructure is devastated; some towns are completely isolated.

"These are the type and magnitude of impacts we would likely see during an ARkStorm-like event in California. It's possible such effects could be even more widespread, and affect more people, than this Southern Appalachian disaster. As always, other factors are also at play: Expanding populations into known and extant floodplains as well as artificial modification of river channels; old and crumbling infrastructure built decades ago; differential societal exposure via economic inequity, and etc."