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  1. Mick West

    Mick West Administrator Staff Member

    This discussion is split from the main Oroville discussion thread, and should be focussed only on weather forecasts, hydrologic forecasts, and lake level forecasts

    Some things to note:
    • The weather forecast, especially just loca rain forecast, don't tell you the picture. You need the hydrologic forecast - i.e. how much water is gong to reach the lake
    • The watershed (catchment area that drains into the lake) is about 3,600 square miles.
    • It's the average rainfall over the whole watershed that's important. 2" in one small spot is not as important as 1" over the whole area.
    • The snow level is very important, as the more that falls a snow, the less goes directly into the lake. But later higher snow level can melt the low lying snow
    • It takes some time for rainfall to get into the lake.


    DWR-CDEC Oroville Dam real time sensors:

    NOAA 6-Day precipitation accumulation

    Bucks Creek Powerhouse (BUP) sensor which gives daily rainfall totals.

    For a nice wide view of the incoming water vapor, try the GFS / Pacific Sector / Precipitable Water loop at
    Nam, Nam4k, and others, will have higher resolution maps of P.W., 6 hour, and total precip. is also good. Their map even has Lake Oroville on it.

    First rains have arrived in the area:

    Should not be a problem in terms of rising lake levels for at least a day - and probably not at all if 100K CFS is maintained. Just might cause some operational difficulties - and less opportunities for good photos.
    Last edited: Feb 18, 2017
  2. Mick West

    Mick West Administrator Staff Member

    Another way of looking at the potential inflows.

    Oroville watershed, based on original reservoir plans, and tweaked for ridges in Google Earth.

    GE tells me this is 3672 square miles. Oroville Lake is 25 square miles. So the watershed is very roughly 150x the lake area.

    Very simplistically that would mean if you get 1" of rain, then that's maximum 150" of lake rise (12.5 feet)

    Looking at a weather station in the watershed, Berry Creek, that's six inches over the next 8 days, realtively evenly spread.,+CA


    That would translate (and again, a very simplistic figure) to 100 feet rise over those 8 days at 12.5 feet per day.

    Current 100K CFS is dropping the lake at 0.6 feet per hour, or 15 feet per day, 120 feet over 8 days.

    So the level of the lake should continue to fall overall, with only some minor pauses to rise. It's at 877 now. After the storm is over, worst case it will be at 857 feet.

    And I think this a very conservative estimate. For one thing not all the precipitation will fall as rain (some will be snow, which just stays on the hill for now), and some is lost to groundwater aquifers, and the actual streams and rivers take some time to get to the lake. So almost certainly the level of the lake will be well under 850 feet in 8 days.
    • Like Like x 3
  3. Vicki W

    Vicki W New Member

    This is what I was looking for yesterday. This storm is also supposed to be colder from what I understand, meaning more water stays in place as snow.
    Last edited by a moderator: Feb 16, 2017
  4. Mick West

    Mick West Administrator Staff Member

    I saw a tweet say the waterflow intake was 3,222 sq miles, a bit lower than my measurement from GE. However he also said that this means an inch is 171,840 acre-feet flowing in, and this exceeds the 150K acre-feet flowing out.

    However, at 100,000 cubic feet per second, that's 100000*60*60*24 cubic feet per 24 hours, which is actually 198K acre feet, according to google.*60*60*24+cubic+feet+in+acre+feet

    I suspect he was simply mistaking the 150K cfs standard release for 150K acre/feet. But perhaps this misconception is based on something else. Have there been acre-feet figures given for the releases?
  5. alec

    alec Member

    from here on out (full season) storm temperature (can also be read as given storms snowfall elevation) matters. First case rain flows quickly to res, snow slowly (weeks, months), second case, rain on snowpack increases flow beyond rainfall amount.
    Precip quantity also matters, high snow load eventually melts, flows downhill, later season gradual melting = better
  6. yellowsubmarine

    yellowsubmarine New Member

    press conference now--they feel they can hold reservoir level as is with the first round of storms (i.e. it won't go back up); don't be surprised if they reduce the 100k cfs outflow when they can. Makes sense given they have to manage the downstream impacts too. of course, this is assuming their input models are correct and storms don't bring in more (Croyle said they expect 45k cfs coming in, which they can easily deal with)
  7. Ethan O'Connor

    Ethan O'Connor New Member

    Strong agreement with the points in your entire post.
    In addition to differential erosion following bedding planes, there are known vertically dipping shear zones in both abutting ridges that strike perpendicular to the plane of the dam and exhibit chemical weathering to 100':

    The identified zones are "mid-height" on the abutments, but it's fairly clear that the geologic survey work in the zone below the emergency spillway was nowhere near as thorough as that in the immediate abutment zones of the embankment and there may be additional sheared/schistose zones at all scales in alignments consistent with the deep, rapid erosion we saw into bedrock in the new ravines directly below the weir.

    Meanwhile, the 2000Z 7-day QPF actually looks worse than the setup at the start of precipitation on Feb. 5th. Here's now - the 10-15" zone lies right over the Lake Oroville drainage:


    and here's at the start of the precipitation event that led to the weir overflow:


    Compared to the 5th, inflows are nearly the same but there's now less than half as much storage below 901'.

    Lower snow levels will help, of course, but this is not a bullet-dodged scenario yet.
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  8. Mick West

    Mick West Administrator Staff Member

    Croyle was saying it would be a much smaller storm.

    Here's a more local forecast with the watershed outlined

    Looks like it will average under 1" per day over the whole area, which is manageable.
  9. Scott Gates

    Scott Gates Active Member

    I posted a tweet earlier that said the 15" rain last time translated to appx 50' total increase in lake levels ...

    You have to keep in mind that what falls as snow doesn't get released to the lake immediately ... and I'd heard they stirms may be colder than the prior ones
    • Like Like x 1
  10. yellowsubmarine

    yellowsubmarine New Member

    On Jan 8, the lake level was at 805.5, 2254644 acre-feet. On Jan 9, 820.67, 2433696. So you could estimate the AF at the 813.6 level using those. When the lake level was 900.11, 3539318 AF. So it looks like that top between where spillway can empty, up to spilling over the emergency spillway, is roughly 1.2 million acre feet of water.
  11. Mick West

    Mick West Administrator Staff Member

    Or about 7 inches of rain over the entire watershed, (none it falling as snow)
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  12. Gregory

    Gregory New Member

    I see that almost a foot of rain is coming according to the story in this link:


    It is a warm storm so I'm wondering if some of the snow in the watershed will be melted - creating a "perfect storm"...

    Further, the levies are designed to handle a Feather River flow of 300,000 cfs.

    Any comments welcome.
  13. yellowsubmarine

    yellowsubmarine New Member

    Last edited by a moderator: Feb 16, 2017
  14. Mick West

    Mick West Administrator Staff Member

    Here's a more local forecast with the watershed outlined

    Looks like it will average under 1" per day over the whole area, which is manageable.[/QUOTE]
    The forecast has got somewhat worse.


    Black line is the watershed. Given that more than half the area is 6" or above, then average over the area is probably over 1". Just a simplistic visual estimate with the range going from 3" to 12" put it at 7.5" over 6 days.
    Last edited: Feb 16, 2017
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  15. Mick West

    Mick West Administrator Staff Member

    Forecasts vary though.
    Here I'm using the 7 day NOAA QPF in Google Earth


    This is national scale forecast, so might be less accurate. But shows range of 3" to 7" over the watershed.

    I've attached the Google Earth file for the watershed.

    Attached Files:

  16. FishOutofWater

    FishOutofWater New Member

    First post here. Retired PhD geochemist / geologist who appreciates the informative technical discussion here. My professional experience is with nuclear waste disposal safety research and regulation.

    The weather forecast for Monday and Tuesday just got worse, as Mick noted in the other thread. Basically there's going to be a warm atmospheric river event with a high snow level starting on Monday. Precipitation forecast amounts just went up. Because snow levels will apparently be over 5000 feet snow that fell at lower elevations in the cooler storms over the week end could melt so there could be a pretty good inflow starting late Monday. This storm swings in a moisture fetch from north of Hawaii so it's going to be warm and wet early on. By Tuesday colder air will be moving in and the snow level will drop.

    After this storm, forecasting gets difficult because the models have trouble handing blocking patterns. However, it looks like a colder drier pattern will set in so there's potentially good news after Tuesday.

  17. Mick West

    Mick West Administrator Staff Member

    This article is from yesterday, so opinions might have changed a little.
    But I think a very important thing here is the snow level of the storm. Current NWS storm warning for the area (Pluma County covers most of it) has the snow level at 6,000 storm watch
    • Agree Agree x 1
  18. SR1419

    SR1419 Senior Member

    this might be useful

  19. Mick West

    Mick West Administrator Staff Member

    No it's not. As mentioned above it miscalculates the acre feet from of the outflow

    • Agree Agree x 1
  20. SR1419

    SR1419 Senior Member

    sorry- didnt notice which tweet it was. Good point. Perhaps someone can ask him or point it out. I notice he (Jan Null) didnt really comment on his miscalculation.
    Last edited: Feb 16, 2017
  21. Dale R

    Dale R New Member

    • Like Like x 3
  22. whoosh

    whoosh Member

    That site's no good. Atmospheric River is not observed in the 250mb jet stream. Better to use Precipitable Water (PWAT) from the models, and/or this site from UCSD
    • Like Like x 1
  23. whoosh

    whoosh Member

    You can tweak around on this NWS site for recent and forecast weather, river stages, etc.
    As noted earlier, since the watershed isn't overlaid, focus on the whole of Plumas County, back toward the reservoir.
  24. CRM114

    CRM114 Member

    There's a very good USGS report on this basin. A couple of notes:

    About 40% of precip leaves the basin as evapotranspiration in an average water year. However in a wet year that % would go down. Just a very rough guess, maybe 2 inches would evapotranspirate this month and never reort as inflow.

    Also, they report the basin as 3600 sq mi reporting to the reservoir, I believe.
  25. Mick West

    Mick West Administrator Staff Member

    I'd think that while it's actually raining there's pretty much zero percentage loss from evaporation, as relative humidity is very high.
    • Agree Agree x 1
  26. JustCurious

    JustCurious New Member

    Last edited by a moderator: Feb 16, 2017
  27. CRM114

    CRM114 Member

    Yes, but plants are uptaking water, which seems to be the main mechanism in this basin, at least in the rainy season. They later lose this water.
  28. JustCurious

    JustCurious New Member

    With the current storm snowfall elevation is lower 4-5000 with the next system snow levels projected to be 6000' and above. This in mind anyway to determine the added run-off and water inflows as the air warms and snow melt begins?
    Last edited by a moderator: Feb 16, 2017
  29. whoosh

    whoosh Member

    You may have been referring to this document, which looks fascinating and I'm starting to peruse. Thanks!
  30. CRM114

    CRM114 Member

    Thats the one, enjoy!
  31. David T

    David T New Member

    I would think that after all the earlier rain, the ground is already fairly saturated and the plants have already taken up what they want/need. So I would suggest most of the rain precipitation will make it into the lake. Key will be how much falls as snow and stays in the mountains.
    • Agree Agree x 2
  32. CRM114

    CRM114 Member

    It's complicated and there are all sorts of processes involved. Don't assume 100% immediate runoff from this storm. It's probably safe to assume 》60% of the precip from this storm will eventually flow to the reservoir. The more precip it gets, the greater the runoff %.
  33. Mick West

    Mick West Administrator Staff Member

    Agreed, and we can do a different ballpark calculation, with 3600 square miles of catchment, what the CFS for 1" over 24 hours? It's 3600*5280*5280/12/24/60/60 = 96K cfs.
    (3600 square miles which are 5280x5280, then /12 for on inch, /24 for hour /60 for minutes /60 for seconds)

    So that's a real simple figure that give an upper bound. If it were raining 1" per day for weeks, and all the water went into the lake, and we ignore the effects of snow, then you've got 96K inflow all day.
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  34. Mick West

    Mick West Administrator Staff Member

    LA Times is reporting the NWS says that Sunday/Monday is going to be a warm wet storm.
  35. CRM114

    CRM114 Member

    Yes. 1 inch of water a day and reservoir level is static at 95 k cfs release (though that ignores evaptranspiration). Technically, its say 1.2 inches. So if next 7 days averages over 8.4 inches, reservoir goes up not down like they claim.

    Snow is a big factor. Stations I have looked at are 30+ inches water equivalent. So that could be 25 days of 95 k cfs outflow alone, but I cannot find what basin average snowpack is. This will spread over several months but bulk is in next month or two I believe. Between this storm and snow, there could be a month of outflows already in the pipeline. This surely is not the last storm.
  36. Mick West

    Mick West Administrator Staff Member

    While the average rain over the watershed is going to determine the average runoff, it's probably significant that the rain is strong loaded over the area directly adjacent to the lake:
    That pink and white region next to the dam is about 1000 square miles, about 10" over six days.

    700*5280*5280/12/24/60/60*10/6 = 45K cfs just from that region
  37. JustCurious

    JustCurious New Member

    CRM 114 this what your looking for?

    Snow pack vs water content for Feather Valley Region

    Station Name ID Elev. Date/Time Value
    BUCKS LAKE BKL 5750' 02/16/2017 11:00 37.44"
    FOUR TREES FOR 5150' 02/16/2017 11:00 21.48"
    GOLD LAKE GOL 6750' 02/16/2017 11:00 42.84"
    GRIZZLY RIDGE GRZ 6900' 02/16/2017 11:00 31.08"
    HARKNESS FLAT HRK 6200' 02/16/2017 11:00 27.76"
    HUMBUG HMB 6500' 02/16/2017 11:00 35.28"
    KETTLE ROCK KTL 7300' 02/16/2017 11:00 34.20"
    PILOT PEAK (DWR) PLP 6800' 02/16/2017 11:00 48.39"

  38. whoosh

    whoosh Member

    Updated at press conference to be 5,000cfs increments at 2hr intervals until 80,000cfs target hold.
  39. whoosh

    whoosh Member

    Absolutely. Not only does it show that the majority of the watershed is below the 5500ft. snow line (my visual est.), but it reveals the presence of Nine!! upstream (N. fork Feather River) powerhouses (with reservoirs). Boy, I didn't see *that* coming.

    That said, the document reveals an extensive network monitoring and modelling capacity for the Oroville reservoir inflow, which I trust is calibrated and functional.
  40. whoosh

    whoosh Member Merrimac, CA (upstream, below the snow line)


    Attached Files:

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