Atmospheric River Event on Its Way, The Biggest Since 1/9

[Shasta Guy]

The NOAA issued a "Hydrologic Outlook" and that's usually not good news due to the flooding it brings.  Up in Northern California, Hydrologic Outlooks usually mean heavy rain on snow packs leading to higher water levels than rain alone.  

This event likely will trigger debris flows, and my guess is that 101 is at risk of shutting down again.  Use the weather links to your advantage to keep you safe.  Hopefully people will actually evacuate this time.  SB County has been so cautious (rightly so) that there's a risk "crying wolf" syndrome has developed and people will ignore the potential danger of this situation.  

Edhat is likely to get bogged down, so I'm glad John put this site together.  Everyone has 48hrs to get their acts together.

[Shasta Guy]

Here's the atmospheric river coming our way.  If you watch the 8km animated version you can see how the system in the central pacific keeps spinning the water vapor our way.  I don't like the way this looks.  I think people are going to be surprised by how damage this may cause after Tuesday night.  If we get severe enough orographic conditions, mudslides may shut down 101 north of Goleta and south of Santa Barbara.  

[Shasta Guy]

Report on the 1995 flooding.   We seem to have weather conditions that may repeat the 1995 flooding.  If the atmospheric river keeps dumping rain for 48 hours like in did in 1995 then we are in a heap of trouble.  Checkout the photo section at the end.  Every creek between Carpinteria and Goleta spilled over its banks, and we didn't have any burn areas then.

https://www.countyofsb.org/uploadedFiles/pwd/Content/Water/1995FloodsRpt.pdf

On Sunday, March 18, 2018 at 5:39:31 PM UTC-7, Shasta Guy wrote:

[SBitz]

As darkness fell tonight I took a look at the satellite view of the "river" heading our way over the Pacific, and thought others might be interested.  So here are animated MP4 files of hourly views up to 6:45pm in InfraRed, Visible light, and Water Vapor. On my computer (Mac running Firefox browser), I can just click "View" in the list of attachments. You might need to download to view, since I couldn't put drag them into this post the way images do. If anyone requests it, I can put them on uTube and then they'd probably play within a post. Most people will probably just use the great links put together here on SBitZ.NET by Shasta Guy.

[Shasta Guy]

Here's the 16km animated water vapor map showing the Atmospheric River.  Below it is a post of the current image because the animated version will eventually refresh.

http://www.ssd.noaa.gov/goes/west/nepac/h5-loop-wv.html

Still Image

http://www.ssd.noaa.gov/goes/west/nepac/wv-l.jpg

The width goes from the Bay Area to Northern Baja.  It looks like there are a lot of storms lined up for today.  This is going to affect a lot of people.  It was an event like this last year that filled and overtopped the emergency spillway at Lake Oroville.  I just hope we stay under 10" in the next 36hrs.

On Sunday, March 18, 2018 at 5:39:31 PM UTC-7, Shasta Guy wrote:

[Section Make8R]

heres a great discussion of what may unfold this evening.

AR discussion from NWS climate prediction   

  So far 2+ inches here at San Ysidro, creeks "seem" to be channeling water off as fast as it comes down.  Havnt heard of any troubles yet.

[Shasta Guy]

Thanks for the link from something I've never seen before.  It looks like we made it through the day, and we just need to get through the night.  I had abut 3"-4" in my unofficial rain gauge near the Mission.  It seems that much of the rain was giving us a glancing blow just slightly north.  

On Sunday, March 18, 2018 at 5:39:31 PM UTC-7, Shasta Guy wrote:

[Shasta Guy]

Thanks for the movie files.  I had to download them before I could launch them.  I expanded the window and I was able to see a lot of detail not visible in the ready-to-view things I post.  It will be a good record of the weather events of this week.  

On Sunday, March 18, 2018 at 5:39:31 PM UTC-7, Shasta Guy wrote:

[SBitz]

I've been curious before about the differences between terrestrial radar and satellite water vapor (WV). Often things look really scary on WV but radar shows nothing and it's dry outside. So in the hope someone here knows more, I made an animated GIF of two screencaps and circled areas of interest.
EDIT: I couldn't get the animation to play, and have posted it to YouTube and attached it to this Post.
The direct link is https://youtu.be/lxLL6bV5fro

The first (larger) image is the WV satellite from about 5pm. Then circled in orange on that image are two big scary looking areas, and in purple the "dry" looking area NE of Point Conception. Last is the radar image from about 5pm showing some moderate rain in that purple circled area.

So in pondering why there might be such a difference in that area I came up with a few theories:
1. The times depicted don't match due to differences in processing delay between WV and radar before they're published online.
2. WV is measured from space and may look "dry" for rain near the surface where radar sees it.
3. WV may not be precipitating to the surface below a given "wet" area of the clouds.

Whatever the reason(s), I've noticed in many storms that WV often doesn't seem to match radar or on-scene rain.  If this is the case, is there a way to accurately predict rain from WV or should we take WV as only one variable in estimating where rainfall is more likely?

Regardless of answers (if there are any), there are some areas of solid correlation between WV and radar in this storm. Anyone have ideas, details or comments?

---

180321 5PM WVradarAnimX3

[SBitz]

Well, getting that little movie online was rather a nightmare. I'd naively imagined that Google would have no trouble with animated GIFs, then thought they'd at least handle small .MOV or MP4 files. Not so.

Anyway, if anyone wants to see the WV/radar animation it's probably easiest to just click this uTube link:
https://youtu.be/lxLL6bV5fro

Unless you'd like to wander off into cyberia's cat videos or whatever, I suggest you turn off "AutoPlay" in the upper-right corner of the uTube screen before you play my little manic masterpiece. :)

[SBitz]

By way of another perspective on this rain event, here are the 8pm rainfall totals for the past 24 and 48 hours. Plenty of rain in our hills, so hopefully any really heavy rain overnight won't last long enough or be intense enough to get the mountains moving again.
24 hours:


48 hours:

[Shasta Guy]

I was tracking the rain fall totals throughout the day.  The Thomas burn gauges above Montecito have the highest accumulation approaching 3" last time I checked.  

On Sunday, March 18, 2018 at 5:39:31 PM UTC-7, Shasta Guy wrote:

[SBitz]

OK, I spelunked around on Wikipedia and have the impression that "water vapor" satellite views are probably some sort of composite combining microwave "sounding" of the atmosphere with InfraRed imaging at specific wavelengths. But I didn't find an exact description of the WV sat images we've been using. The best description I found is here: https://en.wikipedia.org/wiki/Water_vapor#Radar_and_satellite_imaging

The SBA aviation forecast is calling for rain and possible thunderstorms starting at midnight (it's starting to rain intermittently at 101@154 now at 12:30pm as I type this, but no thunder so far). From 5am-noon it calls for heavy rain & thunderstorms, then rain/thunderstorms until 4pm and tapering off to light rain showers after that. The heavy rain part is less than five hours away now, and the short-range aviation forecasts like that are usually pretty accurate though somewhat tending toward "conservative" in the sense of calling for more and harder rain.

There's a 2:37am EDT update on this MetWatch link Shasta posted:
http://www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=68&yr=2018
Here's the most relevant part of the image they include with it, showing rainfall rates of .5-1" per hour and up to 4" in our Tommy toasted coastal range.

Here's their summary, converted from SCREAMING CAPS to human-friendly sentence case:
Rainfall rates of 0.5 to 1.0 in/hr are expected at times into the Sierra Nevada mountains and along the coastal ranges of cntrl/srn California through 18z. 12 hr rainfall totals of 2-4 inches along the coastal ranges and 3-6 inches along the Sierra Nevada upslope can be expected along with possible flash flooding over burn scar regions.

I found a NOAA 11pm depiction of "precipitation potential" at this link: http://www.ssd.noaa.gov/PS/PCPN/DATA/RT/NA/GSPW/20.jpg

I pasted in the "inches" scale at the bottom and guess those small red areas headed our way from bottom-left in the atmospheric river are about 1.25 inches (per hour maybe?). Since they wouldn't be here for many hours yet, it seems they'll be rained out or will miss our area. Maybe ours are the few shown out over the Pacific to the West of the U.S. border. Guess we'll all know a lot more by tomorrow night. Be safe.

[Shasta Guy]

Thanks for the deep dive on remote sensing.  

I feel as an area we survived a game of Russian roulette.  It looks like I'll have had only 5" of accumulation in my backyard.  It seems that the main energy of this atmospheric river event was focus just 30-40 north west of us, sparing Santa Barbara and Montecito from 48hrs of orographic accumulation on the ridge behind us.  

On Sunday, March 18, 2018 at 5:39:31 PM UTC-7, Shasta Guy wrote:

[Section Make8R]

Not much going on down here.. cept for leaking roof uggg Hazard Pay....haha

....seems like we have to wait out the last slice of the cold front as it passes,  as it intersects with the AR   as thats

what can cause the most trouble.  Otherwises, slow and steady thus far at San Ysidro/101    2.50 inch

heres some interesting reading, not sure if I got it here or not!!!  (too many lnks)

Not much going on down here..yay.....seems like we have to wait out the last slice of the cold front as it passes, that what can cause the most trouble.  Otherwises, slow and steady thus far at San Ysidro/101    2.50 inch total so far

This first site is great, I havnt even started to delve into it.  (I cant currently find the piece on the 1/9 slides, but its in there somewhere...sorry)

edit to add the sites address:   http://cw3e.ucsd.edu

http://cw3e.ucsd.edu/wp-content/uploads/2017/04/YoungSkellyCordeira2017GRL.pdf

https://journals.ametsoc.org/doi/full/10.1175/1520-0493(2004)132%3C0242%3AMOFAPB%3E2.0.CO%3B2