Atmospheric river headed our way 4/5-4/7/2018

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Atmospheric river headed our way 4/5-4/7/2018

Post by maiathebee »

This heavy rain with a snow level of 11,000 ft might melt out the smallish snowpack quickly. Anybody have details about that time Yosemite Valley flooded in the late 90s for comparison? Think this could be similar?
Snow levels in the Sierra will be unusually high for a storm this potent. Rain may fall at altitudes as high as 11,000 feet at the height of the storm, with snow levels dropping closer to 5000 feet as the storm ramps down. This means that intermediate elevations now buried under several feet of snow could experience several inches of rain.

During midwinter, a deep, cold snowpack can absorb a fair amount of rainfall. In this case, though, a large part of the Sierra’s snow has been “ripened,” meaning the temperature throughout the snowpack is close to freezing (see Figure 2). As a result, runoff from heavy rain, especially at elevations below 7000-8000 feet, may be accompanied by rapid snowmelt. A flood watch is already in effect from Friday afternoon into Saturday through the Sierra Nevada and the adjacent foothills. Some flash flooding could develop at the height of the storm, especially where rainfall intensities are highest.
https://www.wunderground.com/cat6/near- ... ierra-snow
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Re: Atmospheric river headed our way 4/5-4/7/2018

Post by Wandering Daisy »

Yesterday's CDEC river projections are for a peak of 17 feet on the Merced, about 9 feet being flood, late Saturday or Sundaym, similar to the flood stage of 1965, but short lived- only a day before it quickly receeds. Way lower than the big winter floods of 1997-8. I suspect roads in Yosemite will be closed for a few days and it could do some road damage. I am actually surprised that there is no mention of this on the Yosemite web sites.
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Flood Watch 5/6-5/8

Post by maverick »

NWS:
Flood Watch is now in effect for Friday evening until Sunday morning for the Sierra Nevada and adjacent foothills in Fresno County and locations to the north. This includes the Sierra Nevada from Yosemite to Kings Canyon National Park, as well as the Sierra Nevada foothills in Mariposa, Madera, and Fresno Counties. Expect around 2 to 4 inches of rain in these areas, mainly during Friday night into much of Saturday. In addition, rivers and streams are expected to rapidly rise during Friday night into Saturday.
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Re: Atmospheric river headed our way 4/5-4/7/2018

Post by Wandering Daisy »

Here is the new projection for the Merced at Pohono Bridge. Looks like they have dropped the peak a few feet.

https://www.cnrfc.noaa.gov/graphicalRVF.php?id=POHC1
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Re: Atmospheric river headed our way 4/5-4/7/2018

Post by psykokid »

That storm that hit two weeks ago did quite a bit of damage in the area and downstream of the Detwiler Fire. I was going to head up to my dad's place near Groveland on Friday and had to postpone a week as 132, 49, and 120 were all closed and I didn't have time to take the round about route through the park. When I went up last weekend 49 was still closed, and there was a detour on 132 near Granite Springs. La Grange road was closed due to a washed out bridge so I ended up taking Merced Falls Road up to 132.
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Re: Atmospheric river headed our way 4/5-4/7/2018

Post by maiathebee »

Wandering Daisy wrote:Yesterday's CDEC river projections are for a peak of 17 feet on the Merced, about 9 feet being flood, late Saturday or Sundaym, similar to the flood stage of 1965, but short lived- only a day before it quickly receeds. Way lower than the big winter floods of 1997-8. I suspect roads in Yosemite will be closed for a few days and it could do some road damage. I am actually surprised that there is no mention of this on the Yosemite web sites.
Glad to hear it's not going to be as bad. I didn't remember the details of the 97-98 flood because I was a teen. Looked it up after posting this and wow!!
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Re: Atmospheric river headed our way 4/5-4/7/2018

Post by gary c. »

"On this proud and beautiful mountain we have lived hours of fraternal, warm and exalting nobility. Here for a few days we have ceased to be slaves and have really been men. It is hard to return to servitude."
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Re: Atmospheric river headed our way 4/5-4/7/2018

Post by markskor »

‎Chris Falkenstein‎ to Yosemite Incident Feed

We are still under a Flood Warning and currently experiencing heavy rain in Yosemite Valley. Yosemite Valley residents, please take the time to carefully read the safety reminders below.

Safety Reminders
The river is rising quickly and will continue to rise even after the rain has stopped, as water works its way from the high country to the lower elevations. If you are in the park, you may be tempted to go for a walk to see the high water, but please stay home (unless scheduled to work).

Southside Drive is now two-way from Pohono Bridge to Sentinel Bridge. Do not drive unless it’s absolutely necessary. Do not drive through standing or running water over the road. Turn around, don’t drown: two feet of flowing water is enough to sweep your vehicle away (this did apparently occur in Mariposa County during the last storm).

Be extremely cautious while walking anywhere near flowing water. Just six inches of running water is enough to sweep you away.

Large trees have already started to fall in the Valley. Watch for falling trees, looking for cracks in the soil around a tree, a tree beginning to lean, or separation between joined tree trunks.

If there is a power outage, do not use portable stoves or grills indoors.

River and Weather Conditions
As of 8 am, the Merced River at Pohono Bridge is at 10 feet (and 7 feet at Happy Isles). The current river forecast calls for a peak of 14.7 feet at Pohono Bridge at 5 pm on Saturday, with flows above 10 feet (flood stage) until Sunday at 5 am.

Yosemite Valley has received about 2.25 inches of rain since Friday morning.

Tuolumne Meadows has received just over 1.5 inches of rain since Friday morning.

South Fork Merced River, which was at about 4.5 feet earlier this week, is now approaching 8 feet.

Tuolumne River above Hetch Hetchy, which about 10 to 11 feet earlier this week, is now approaching 17 feet.

Tuolumne River at Tuolumne Meadows, which a little over 3 feet earlier this week, is now approaching six feet.

Weather forecast for Yosemite Valley calls for another inch of rain this morning, with decreasing chances of rain this afternoon and tonight.

Yosemite Valley Closure
Yosemite Valley is closed to visitors. Residents may not enter or leave Yosemite Valley.

Information for Valley Residents
For safety reasons, residents who are not working should remain at their homes through Saturday afternoon, when rainfall rates and river level are highest. Avoid driving unless absolutely necessary. (Southside Drive is currently two-way traffic from Pohono Bridge to Sentinel Bridge; Northside Drive is flooded in multiple locations.)

Please use as little water as possible (avoid doing laundry, taking showers, etc.) to reduce strain on the sewer system.

Prepare for the possibility of an evacuation if utility systems fail. The earliest this is likely to occur is on Sunday, although we are hopeful this will not be necessary.

Half Dome Village Pavilion open 8 am–10 am and 6 pm–8 pm today.

Village Store open 10 am–6 pm today.

Employees Scheduled to Work on Sunday
If you are scheduled to work in Yosemite Valley on Sunday, be prepared to work, but you will probably be on administrative leave (if not attached to the incident). Check the employee hotline on Sunday morning and remain in touch with your supervisor.
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Re: Atmospheric river headed our way 4/5-4/7/2018

Post by maiathebee »

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