Daniel Swain Office Hours Notes 8/21/23

Link to the video.

My rough notes

As usual, these are my very rough notes so treat them accordingly (don’t quote me!).

• Focused on Hilary impacts

• Still some after effects of moisture and instability in central CA

  • Pair of sever thunderstorms over I-5, south of Newman, one has tornado warning attached to it

• Talked about track of HIlary might wobble

  • This is what happened, center of storm wobbled

  • Initially made landfall in Baja, but less clear is second landfall because storm took slightly western track, so instead of mountains east of SD, it mostly went over SD, went between there and Orange County and went over LA

  • Did this storm be the first as a CA landfall?

  • Hard to tell because it was so close

  • “Postseason” analysis of this storm might tell us, sort of an academic distinction, these areas more rain than expected because storm went on west side of uncertainty envelope

  • Some people claiming just some street flooding, but there were some debris flows, took out bridges, trees, etc.

  • One report of people high in the mountains climbing trees to avoid flooding

  • Many highways shut down, almost all of east-west routes across desert, north south routes in NE California east of sierra highway 395 is closed in many miles

  • Some places there is no road

  • Some places saw severe flooding, mount Charleston area of Nevada had debris flows

  • Some areas in SE CA escaped worse case scenarion

• Why wasn’t flooding even worse in some places

  • Despite some places saw wettest august day or set new records for wettest day in august, some set record for wettest day in summer, that’s not nothing

  • Points to extremity of precipitation event

  • Records 100-150 years old broken

  • Latent potential energy/instability of the atmosphere in southeast sector of storm wasn’t realized

  • It was possible, setup could have 3-4 inches per hour in areas that only see ~3 inches in a year

  • Some clouds in these areas that blocked sun so less instability to lower rain rates

  • Atmospheric instability, not as many convective bands as might have been the case, so same amount of water fell overall it didn’t fall as quickly

  • Flood impacts not at potentially catastrophic as could be

  • Was forecast bad? Nope not really, potential was there, don’t have that level of granularity/sophistication

  • Storm really did produce record breaking rainfall across most of the region

  • Some stories still untold, waiting for updates/images to come in

  • Hardest hit areas are often most inaccessible so don’t hear or see anything from them as early

  • Curious to see what happens in Death Valley, seems like they broken all time record

• Medium term implications

  • Remnants are not making widespread beneficial rainfall where there are fires

  • northwestern half of state approximately fire season not impacted

  • southern/south-eastern part of state got some help with fire season

  • Lucky overall so far in CA, spring floods not so bad, spring cooler than average, fire season not too bad except for a bit in north part of state, this flood event with Hilary not as bad as could have been

  • Finally kind of getting a break

• Questions

  • Why don’t hurricanes cross from Caribbean passed equator

    • Don’t see hurricanes mover from Caribbean to pacific, but you do see storms generally do this, Dora for example

  • What does this storm and other events in CA tell us in terms of early warnings

    • Warmer climate + El Niño, people talk about new normal with all these extremes, push back on this phrasing though because it suggest we’ve reached a stable spot which we haven’t. In the future, this summer might be a mild one overall (cooler in CA this year but generally very warm)

    • Warming is exponential, like compound interest

  • Was the storm over-hyped?

    • Some people intentionally create hype videos so…

    • Two misconceptions

      • Widespread notion this would be historically destructive storm for the urban corridor around LA and SD which was just not true

      • Think the NWS language was justified

      • If there’d been more sun or if the storm was in a different location, flooding would have been worse

      • Possibly overhyped for the coast but hard to not have that with some newspaper headlines

      • Twitter was useless during this storm BTW