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Key paragraph: """ To put it simply, this will likely be one of the most impactful systems on a widespread scale that this meteorologist has seen in a long whi

Key paragraph: """ To put it simply, this will likely be one of the most impactful systems on a widespread scale that this meteorologist has seen in a long while. The impacts will include widespread flooding, roads washing out, hillside collapsing, trees down (potentially full groves), widespread power outages, immediate disruption to commerce, and the worst of all, likely loss of human life. This is truly a brutal system that we are looking at and needs to be taken seriously. """

throwaway2037 4y ago
I saw that. Then I read: The most recent forecast package calls for the following rainfall totals late Tuesday night through early Friday: Around the SF Bay (including East & South Bay): 1.5 to 3" I assume that is up to 3 inches of rain over a few days. What part do I misunderstand?
- pertymcpert 4y ago
  Are you saying that it’s not much rain?
- alar44 4y ago
  Probably the timeframe. If you get 3 inches of rain in 12 hours, that's 6in/day. If that's all the rain you got in 3 days, you got 1in/day.
- nostrademons 4y ago
  That's about what the South Bay saw on the NYE storm. Peninsula & SF got about 5", mountains up to 12". Seems to be roughly comparable in raw precipitation. The concern over this next storm is that the ground is already saturated and the creeks are already overflowing. In a normal rainstorm like the one we just had, the first inch or so is absorbed into the ground, then the rivers start rising and mudslides start happening. This time, we're going to start seeing those effects from the very start of the rain (which is already happening - it's raining now).
- cjsplat 4y ago
  It is a stretch of over 200 miles of coastline getting a whole lot of rain. Over the coastal peaks, 6 to 8 inches. And the land is pretty saturated already. But "what part do I misunderstand" kind of requires me guessing what you understand and concluded.
- topkai22 4y ago
  To put that in context, snow/water ratios are normal about 10:1, so if what was snowing you’d expect close to a 1.5 feet to 3 feet of snow- that’s a lot, as my snow shoveling back is telling me. If my quick internet search is correct, SF will be getting well over 10% of its average annual rainfall in just a day or two. Another way of saying a lot. Also, the water doesn’t just stay there, it flows, and it makes soil looser and heavier. 3” in the hills can mean many feet of extra water in valleys/flood plains and can cause mud slides. In others words, again, that’s a lot of rain.
- cjensen 4y ago
  It will be 3 inches of rain on fully saturated soils. This will lead to 3 inches of pure runoff on a landscape that rarely experiences such runoff. So hillsides, channels, creeks, rivers, and so forth will all be experiencing record run-off levels. This is why the forecast calls for significant hillside failures: it will be more water on a hillside than many of those hillsides can bear. It will flood beyond the normal flooding limits. It might... be historic. Maybe. Huge if. But super-dangerous if it happens. 3 inches in the Olympic Peninsula would be less of a big deal because that's routine. All the hillsides that can fail with that already have. So you're right that 3 inches is not a big deal in most places. But on landscape where that doesn't ever receive that much, it suddenly is a big deal. The fear I have with these recent atmospheric rivers is that we have a lot of snow in the Sierras now. If we get an atmospheric river which is too warm, bad things could happen[1]. Fortunately as we get deeper into Winter it's probably too late for that disaster to be possible. [1] https://en.wikipedia.org/wiki/ARkStorm https://en.wikipedia.org/wiki/ARkStorm
  - sbierwagen 4y ago
    >it will be more water on a hillside than many of those hillsides can bear A good example was the Oso mudslide. Nearby Darrington gets 80 inches a year. (Twice as much as Seattle!) March 2014, a storm drops 3 to 5 inches on soil saturated by six months of rain, and a hill lets go. Killed 43 people: https://en.wikipedia.org/wiki/2014_Oso_mudslide https://en.wikipedia.org/wiki/2014_Oso_mudslide
    - pseudobry 4y ago
      I've driven past Oso many times in the last few years—it's a solemn drive. It's also a tiny reminder of the planet's ability to shrug its shoulders and wipe out civilizations.
  - dendrite9 4y ago
    I thought about the ARkStorm prediction when I saw the forecast. https://weatherwest.com/archives/16626 https://weatherwest.com/archives/16626
- DoreenMichele 4y ago
  My recollection is the SFBA gets around 20 inches of rain annually. Three inches in a few days time is 15 percent of the rain it is supposed to get all year. It's a lot. The landscape won't cope well, especially if it's already seen rain prior. We saw 2 inches of rain one day in The High Desert, an area that gets 6 inches annually. The flood waters took weeks to recede and brine shrimp hatched out.
- s1artibartfast 4y ago
  Looks like it will be over about 12 hours, maybe as few as 6 hours, which is generally the challenge.

throwaway2037 4y ago

I saw that. Then I read: The most recent forecast package calls for the following rainfall totals late Tuesday night through early Friday: Around the SF Bay (including East & South Bay): 1.5 to 3" I assume that is up to 3 inches of rain over a few days. What part do I misunderstand?

pertymcpert 4y ago
Are you saying that it’s not much rain?
alar44 4y ago
Probably the timeframe. If you get 3 inches of rain in 12 hours, that's 6in/day. If that's all the rain you got in 3 days, you got 1in/day.
nostrademons 4y ago
That's about what the South Bay saw on the NYE storm. Peninsula & SF got about 5", mountains up to 12". Seems to be roughly comparable in raw precipitation. The concern over this next storm is that the ground is already saturated and the creeks are already overflowing. In a normal rainstorm like the one we just had, the first inch or so is absorbed into the ground, then the rivers start rising and mudslides start happening. This time, we're going to start seeing those effects from the very start of the rain (which is already happening - it's raining now).
cjsplat 4y ago
It is a stretch of over 200 miles of coastline getting a whole lot of rain. Over the coastal peaks, 6 to 8 inches. And the land is pretty saturated already. But "what part do I misunderstand" kind of requires me guessing what you understand and concluded.
topkai22 4y ago
To put that in context, snow/water ratios are normal about 10:1, so if what was snowing you’d expect close to a 1.5 feet to 3 feet of snow- that’s a lot, as my snow shoveling back is telling me. If my quick internet search is correct, SF will be getting well over 10% of its average annual rainfall in just a day or two. Another way of saying a lot. Also, the water doesn’t just stay there, it flows, and it makes soil looser and heavier. 3” in the hills can mean many feet of extra water in valleys/flood plains and can cause mud slides. In others words, again, that’s a lot of rain.
cjensen 4y ago
It will be 3 inches of rain on fully saturated soils. This will lead to 3 inches of pure runoff on a landscape that rarely experiences such runoff. So hillsides, channels, creeks, rivers, and so forth will all be experiencing record run-off levels. This is why the forecast calls for significant hillside failures: it will be more water on a hillside than many of those hillsides can bear. It will flood beyond the normal flooding limits. It might... be historic. Maybe. Huge if. But super-dangerous if it happens. 3 inches in the Olympic Peninsula would be less of a big deal because that's routine. All the hillsides that can fail with that already have. So you're right that 3 inches is not a big deal in most places. But on landscape where that doesn't ever receive that much, it suddenly is a big deal. The fear I have with these recent atmospheric rivers is that we have a lot of snow in the Sierras now. If we get an atmospheric river which is too warm, bad things could happen[1]. Fortunately as we get deeper into Winter it's probably too late for that disaster to be possible. [1] https://en.wikipedia.org/wiki/ARkStorm https://en.wikipedia.org/wiki/ARkStorm
- sbierwagen 4y ago
  >it will be more water on a hillside than many of those hillsides can bear A good example was the Oso mudslide. Nearby Darrington gets 80 inches a year. (Twice as much as Seattle!) March 2014, a storm drops 3 to 5 inches on soil saturated by six months of rain, and a hill lets go. Killed 43 people: https://en.wikipedia.org/wiki/2014_Oso_mudslide https://en.wikipedia.org/wiki/2014_Oso_mudslide
  - pseudobry 4y ago
    I've driven past Oso many times in the last few years—it's a solemn drive. It's also a tiny reminder of the planet's ability to shrug its shoulders and wipe out civilizations.
- dendrite9 4y ago
  I thought about the ARkStorm prediction when I saw the forecast. https://weatherwest.com/archives/16626 https://weatherwest.com/archives/16626
DoreenMichele 4y ago
My recollection is the SFBA gets around 20 inches of rain annually. Three inches in a few days time is 15 percent of the rain it is supposed to get all year. It's a lot. The landscape won't cope well, especially if it's already seen rain prior. We saw 2 inches of rain one day in The High Desert, an area that gets 6 inches annually. The flood waters took weeks to recede and brine shrimp hatched out.
s1artibartfast 4y ago
Looks like it will be over about 12 hours, maybe as few as 6 hours, which is generally the challenge.