Incoming potentially catastrophic storm for SF area
forecast.weather.gov
forecast.weather.gov
My favorite part of the forecasts is that they tell you unequivocally when they are confident in something and when they are not sure. They are not afraid to say a qualified “we don’t know”. This is is a stark contrast to almost every other forecast falsely projecting complete confidence trying to vie for viewership to attract advertising dollars.
The weather app is an app that reports data from a weather station, it is not a thermometer. If you're camping in a valley or a mountain that's 20 miles away from the nearest weather station, the temperature that your app says is almost certainly wrong.
So hard to break that habit of relying on the phone when it's not correct with some of the younger folks.
For those, I prefer wunderground.org or purpleair.com (both of which rely on both government as well as crowd-sourced data from valid sensors).
Free, no ads, using NWS and NOAA APIs. Includes the awesome forecast discussion.
This gives you a distribution of predictions, which you can use to produce an average, as well as uncertainty, confidence bands, etc.
The quality of these predictions and ensembles is empirically validated using proper scoring rules (https://en.wikipedia.org/wiki/Scoring_rule), which is a robust way to measure the quality of a probabilistic forecast. Negative-log-likelihood, a ubiquitous loss function in machine learning, is an example of a proper scoring rule (with a minus in front of it).
The science behind forecasting has gotten pretty sophisticated, it's an interesting field.
Then someone else told me that was bogus, and I suspected as much.
It may depend on the source of the forecast
Chance of rain = (chance you will be somewhere in the forecast area where it is raining) x (chance it will rain at all) [1]
The two are independent variables, the overall probability of two independent events both occurring is the product of either event occurring. The chance of rain is the product of two independent events.
So, 50% could mean a 50% chance it will rain everywhere, or a 100% chance it will rain in 50% of the forecast area, or it could be anything in between. (Eg, a 1 mile square cloud that is dropping rain travelling through a 10 square mile area, or a 10% chance that a rain forming cloud will develop over an entire area, or anything in between is a 10% chance of rain. The first case can often be observed with radar and visually, an hourly forecast can be very accurate to know that one cloud will still be raining in an hour. Hence the size of rain area and size of forecast area are variables that come into play)
As a few counterpoints:
- Multiple models do not mean each model is equally likely. Nor do multiple models mean we cover the set of all possibilities. For chance of rain to be the fraction of models predicting rain, those two statements would have to be true
- models themselves each give a chance of rain. These different values are not combined in any way, forecasters pick a model
Some implications and interesting points about forecast area: - if a forecast area is "zoomed" out, should that alter the chance of rain? [Yes, this implies that chance of rain has forecast area as a dependent variable]. Hence, if you "zoom in" on a forecast area far enough, the chance of rain developing becomes the dominant variable for chance of rain.
One interesting thing is a forecast assumes equal probability that you will be at any given location within that forecast area. Which means the percent area forecasted to receive rain is the same probability that you will be at any given location within a forecast area receiving rain
They pick a point and base it on the chance of rain there.
https://forecast.weather.gov/MapClick.php?lat=40.6924&lon=-8...
(the narrative forecasts are more compact than the hourly forecast, but it seems like they would at least have overlapping methodology)
Suppose the hourly forecast has 50% chance of precipitation each hour for two hours. In addition to the points you raise about how to interpret 50% at any moment in time, how are we supposed to know if this means either of the following (or something else):
1. A big storm is passing near a point for those 2 hours, and the only question is whether it passes over it or to the side. I.e., both hours have rain or both don't.
2. A small storm is definitely passing over that point, and the only question is when it will arrive. You either have rain in the first hour or the second but not both or neither.
But the moment one chimp stands up and says no no I can, and a large enough group is persuaded(even if its false), the game changes. Forcaster will start behaving differently. They aren't machines. They are chimps.
""" 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. """
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?
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.
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
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).
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.
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.
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.
Meanwhile Devil's Slide is in an area suited for low speeds, careful acceleration, and reliable braking.
With witnesses are describing this:
> "As I’m driving by, I’m like, ‘Wow, he's driving extremely fast to take that exit. You're not even supposed to be going up that way,” she said. "And I can see in my rear-view mirror this car that just go over the edge and straight down."
It's hard to imagine it was anything but driver error.
Guy is a bit nuts, haha.
Oddly enough, no one was killed even though the car fell a long way.
Not sure how to avoid freeways in California, though... Should I be looking at a trip to Nevada to avoid this?
If you are planning to Vegas, you gonna have problems on SR-152/I-580 to I-5. Also, expect problems on SR-58 between Bakersfield and Barstow on I-15. Even if you want to go to Sacramento, expect long delays on all routes.
Whichever freeway you pick, you will have problems: bad visibility, very slow traffic, partial closures due to puddles, complete closures due to floods (like the north of SFO airport last time).
That's why CHP, Caltrans, NWS advise people to postpone their travel unless extremely necessary. No storm tourism either.
I suspect 80 will be closed maybe overnight because way too many people think driving in snow is just like a dry road - spin outs and crashes (even semis). In general CalTrans does a good job keeping it mostly open.
For context - I live north of Truckee and deal with 80 regularly.
Storm tourism —- another name for skiing!
Also, a lot of the small mountain roads between 1 and 280/101 washed out in the New Years Eve storm, so if you are stuck on the coast there's no guarantee you'll be able to get inland.
I would not try to travel.
> Forecast there is only 1.5".
The Centrall Valley forecast for the storm is 2-3”, actually, per NWS Sacramento.
until you get to the Grapevine. Then cross your fingers.
How about hitting the road before that to be ahead of the mess?
Monterey and Big Sur are great, but just getting home seems like a better idea.
Even if you can't leave Tuesday, you did say you had planned for Monterey on Wed. So leave early Wed, cruise down I-5 and you'll be at the grapevine with time to spare.
If "I-15" is shorthand for "395 to I-15", I would recommend against it. Cold snow after wet snow is a manor avalanche condition. It would be unlikely to hit you of course, but the roads may become impassable in ways that are far worse than I-5.
Stay safe. Leave early.
If so, it's a phenomenally scenic route. It might lead to nowhere this week though...
The biggest risks I encountered were partial flooding in low lying sections that bank inland, and various sized rocks. No signs of new erosion along the edges of any sections I encountered.
Edit: to be clear though, I wouldn't say this is a time to take a joyride in the area. I'm more speaking to the fact it's a bad idea for a fun vacation right now, not a death sentence
Good luck bay area folks, definitely take it seriously. If you're a home owner and have been putting off cleaning out gutters, drains, etc. absolutely get on it right now while you have some time. These unusual rain events will easily back up semi-clogged or poor flowing drainage systems.
To this day I have ptsd when it rains hard, particularly around Christmas. Now I live on the top of a very big hill…
The essence of this design is that a single event, affecting either the ground (floods) or electricity (a grid), would not be able to single-handedly kill all AZs in an AWS region.
Source: I used to share this stuff a lot, in public, representing AWS.
Maybe they could talk to Arizona, which apparently does recognize water infrastructure is important: https://waterbank.az.gov/water-storage
The infrastructure you have to worry about is the stuff that everybody's forgotten about, eg. the levee and dam systems in the Delta.
Oriville dam is infrastructure that was forgotten about. We only know about it in any immediate sense now because it collapsed due to the failure to maintain it. Which was my point.
Seriously, any “cost cutting” measures that “defer” maintenance of infrastructure should be required to put aside funds to rebuild that infrastructure.
Both the emergency and main spillways were fully repaired in 2018, and the repairs have held up nicely in subsequent rainstorms. You probably didn't hear about the repairs because the media never reports on stuff that goes as planned. There are several case studies about it on civil engineering blogs & channels though:
https://practical.engineering/blog/2021/12/20/rebuilding-the...
The reduction of flood plains, and the removal of natural dams (beavers!) means that what you mostly get is high speed run off that is high in sediment and low in oxygen.
The goal is not to prevent a heavy storm. It’s to try to retain more of the water when the state does actually get some.
and now round 2.
1. https://www.hoover.org/research/despite-spending-11-billion-...
2. https://nypost.com/2021/06/26/san-francisco-run-homeless-enc...
Saratoga ended up having the only family friendly creeks that I could find.
I don’t understand why anyone would downvote your comment, except for denial of the reality that has become the Bay Area.
https://sanjosespotlight.com/storm-displaces-san-jose-homele...
reap what you sow I guess
It's really not a good sign when factual government projections start getting jazzed up with personal history.
All things considered, this storm is well within the design considerations for any road or building in California, so it shouldn't be considered, in advance, as catastrophic.
Is there no where to avoid relentless self-absorbed posturing?
I've wondered for a while how NOAA reports are allowed to be so good when you'd think the march of bureaucracy and bureaucracy-fans and liability/anti-responsibility pants-wetters taking the humanity and personality (except wholly fake and brand-conscious "personality") out of everything would have gotten to them by now. Please don't encourage that :-(
“People unironically expressing their anger that other people don’t write like robotic zen monks” is one of my favorite genres of posts.
God forbid someone breaks the monotony on reporting the fuckin weather. I’d rather watch paint dry
Or maybe https://www.wpc.ncep.noaa.gov/pqpf/conus_hpc_pqpf.php
Maybe one of those links has sufficiently less self-abosrbed posturing for your uses?