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Another Yosemite Fatality

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Re: Another Yosemite Fataility

Postby fedak » Wed Aug 03, 2011 7:07 pm

The weather conditions – all over the central and southern were NOT sudden and unexpected. Severe thunderstorms had, in fact, been forecasted (quite accurately as it turned out) by the NWS early in the week for Friday through Monday, with emphasis on Saturday and Sunday.


I didn't look at the forecast as far south as Yosemite- but the forecast for Tahoe that I looked at Sunday morning before heading out was only showing 20% chance of isolated storms.
At least for the Northern Sierra, the bulk of that system came through on Friday/Saturday. (And apparently Sunday's storms didn't reach as far north as Carson Pass)

And I had a pretty good vantage point at 11k at ~10am and there was barely a cloud in the sky on the Sierra Crest.
The cell that formed over the Sweetwaters formed organically over the peak.

I think you are correct that this wasn't a system that came completely out of the blue- but it also wasn't necessarily the case that the climbers ascended HD during active storm conditions.
Conditions were marginal, unfortunately the hiker gambled and lost.
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Re: Another Yosemite Fataility

Postby asmrz » Wed Aug 03, 2011 8:48 pm

As early as Wednesday (before the weekend in question, maybe even sooner) most forecasters were calling for Monsoon flow affecting California mountains. For those who don't know what that means, I will translate: It never rains in the High Sierra in summer, except for localized thunderstorm activity which is typical of 14,000' coastal mountain range. The only exception is, when monsunal moisture travels up from Baja California north to Arizona and Nevada and gets carried in westerly direction into Sierra Nevada. When that happens, like last week, you can expect rain anytime, morning, afternoon, middle of the night, combined with severe thunderstorms, lightning and heavy torrential rains. An old climber told me twenty years ago, if you hear the word "Monsoon flow" in a forecast, stay at home, you are not climbing anything and if you go anyway, you only put yourself in danger. The Sierra East Side forecast called for this flow as early as Wednesday. Please don't say this weather event was unexpected, far from it...
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Re: Another Yosemite Fataility

Postby simonov » Wed Aug 03, 2011 11:40 pm

mrchad9 wrote:I feel the same way about terrorism. 3000 people were killed on 9/11, and the country went up in arms and started two wars, drove America's economy straight into the toilet. Nevermind the number of people that die every year from car accidents, cancer, or even the flu.

Yep. Plus the fact that if you want to live in a free society, terrorism is something you simply cannot prevent.
Nunc est bibendum.
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Re: Another Yosemite Fataility

Postby granjero » Thu Aug 04, 2011 2:25 am

asmrz wrote:As early as Wednesday ... Please don't say this weather event was unexpected, far from it...


Here's the midday run from the Utah WRF on Wednesday 27 at 18Z (11am PST):
This is the 54 hour forecast! And boy did it verify in the Southern Sierra.

Image

All the ingredients are there, bullzeye!!!!

CAPE over the elevated terrain.
Southerly flow at low-mid levels.
Strong vertical motions.
Midlevel shear.
Note the major plume of precipitable water over the core monsoon region (Gulf of California, Sierra Madre Occidental)
It is even resolving the saturation above the southern Sierra.
You can also see why the NWS was freaking out initially about major thunderstorms hitting Lake Tahoe. The moisture/dynamics did not make it beyond central Reno/South Lake Tahoe. Too much SWerly flow. I had wave clouds at my house, for big time summer precip, you want SE'ly flow.

The runs from days prior had the monsoon signal as well. Such a large scale signal is not hard to capture with the models, thus we are not surprised by monsoon activities at the larger scales. It is much more difficult to pinpoint precise locations of convective plumes, thus the NWS chooses to go with 30%. But you can be positive that to avoid being caught out you should avoid elevated terrain.

Only takes 12 hours for major changes in atmospheric composition. Column RH/PW skyrockets at Reno (simplest explanation the smaller the area between the black lines (L is Tdewpoint R is Tair, as Tdew-->Tair we have increase in saturation of air parcels), the more moisture is present):
afternoon of the 28th:

Image

Image

Check out how the convection moves northward on the 28-29th and explodes over the Sierra on the 30th:

Image

Image

Image
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Re: Another Yosemite Fataility

Postby fedak » Thu Aug 04, 2011 3:12 am

Here's the midday run from the Utah WRF on Wednesday 27 at 18Z (11am PST):


Can you check the forecast from Sunday morning?
There was obviously the major weather on Friday/Sat- but when I checked Sunday morning I could have sworn it was just predicting 20% of isolated T-storms.

I based my decision to head out Sunday on that prediction and I'm wondering if I need to find a different forecasting service.
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Re: Another Yosemite Fataility

Postby granjero » Thu Aug 04, 2011 3:18 am

Just change the BOLD values in the url to match the dates you are interested in:
(You can also play with models/initialization times)

http://weather.utah.edu/index.php?runcode=2011072718&t=nam212&r=WE&d=CN

The format is YYYYMMDD. The 18 I think refers to the domain size (18km grid), but the model is actually the 12Z run of WRF (not 18 like I said above).

Its a bit of a wierd interface they use, but if you scoll along the left side you will start with the previous 48hour analysis (A-48) which decreases to A-06 then starts forecasted hours at F000 and goes out to F084 (84 hour forecast). Post what you find and I'll help you interpret. Or, you can take my Mountain Meteorology course at LTCC next fall and learn how to find the summer sun and the winter pow! :)

But like I mentioned before, creating probabilities of TStorms are hard to do. Excuse my simplicity, but if you imagine a model domain with 20 cells, and you allot 20% chances for each one, you only need 4 cells to have precip and your forecast verifies. Where those cells are and the degree at which they are autocorrelated do not matter as far as verification. It really is all about watching the sky and gut feelings. Of course, knowing more and more about the state of the local atmosphere helps, but convection is especially fickle and threshold dependent.
Last edited by granjero on Thu Aug 04, 2011 3:30 am, edited 1 time in total.
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Re: Another Yosemite Fataility

Postby fedak » Thu Aug 04, 2011 3:27 am

Ok, here's 6am Sunday morning (I think)
http://weather.utah.edu/index.php?runco ... &r=WE&d=CN

What the heck am I looking at?
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Re: Another Yosemite Fataility

Postby granjero » Thu Aug 04, 2011 3:39 am

Ah, another tricky part of weather. Zulu time/GMT. Ugh.
Just subtract 7 hours.
00Z for PST = 5pm local the PREVIOUS day than listed
12Z = 5am local the SAME day listed.

If DST is in effect, subtract 8 hours. 00Z = 4pm

So 06Z on July 31 is actually 11pm on the 30th!

You are looking at key weather indices. Moisture, momentum, and stability. In fine-ish print at the bottom of each panel you will see the variables displayed.
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Re: Another Yosemite Fataility

Postby Marmaduke » Fri Aug 17, 2012 12:55 am

Jeez this sad. No real details. Sounds like their family was there, how horrific. My prayers to all those affected by this terrible event.
http://www.sfgate.com/bayarea/article/Family-tragedy-on-Yosemite-s-Merced-River-3793391.php
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Re: Another Yosemite Fataility

Postby lcarreau » Fri Aug 17, 2012 1:49 pm

asmrz wrote: An old climber told me twenty years ago, if you hear the word "Monsoon flow" in a forecast, stay at home, you are not climbing anything and if you go anyway, you only put yourself in danger ...


It's the "flash flooding and swelling of waterways" that can really catch a person off-guard. Condolences to those who have perished.
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Re: Another Yosemite Fataility

Postby TimB » Fri Aug 17, 2012 3:42 pm

Tonka wrote:
Palisades79 wrote:I think that the National Park has to re-engineer the cables because the present setup is clearly is inadequate and dangerous. The path should be widen,every person should wear a harness ,and should be clipped into an ascent cable on one side while going up and a descent cable on the other side while going down . No one should be allowed to ascend in bad weather and the costs of the system should be included in their permit.
The present situation is going to result in new rules and regulations that will have unintended impacts on peak baggers and technical climbers .


I disagree. Accidents happen and one big problem we have in society today is implementing new rules, laws and regulations everytime something goes awry. Shit happens.


This. Part of the allure of the mountains is the element of risk. Doesn't mean that we should disregard the 'warning signs',as it seems happened in this particular case.
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